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Degradation and metabolism of 14C‐labelled proanthocyanidins from carob (Ceratonia siliqua) pods in the gastrointestinal tract of the rat
Journal of The Science of Food and Agriculture
Abstract
The aim of the work was to study the binding, degradation and metabolism of dietary condensed tannins in the gastrointestinal tract of an omnivore. Young pods of carob ( Ceratonia siliqua L) were radiolabelled by in vivo feeding of ¹⁴ CO 2 , trans ‐[U‐ ¹⁴ C]cinnamate or L ‐[U‐ ¹⁴ C]phenylalanine. [ ¹⁴ C]Proanthocyanidins (condensed tannins) were extracted with acetone/water (3:1 v/v), isolated on Sephadex LH‐20 and fed to rats by gavage. After 4 and 18 h, 90–94% of the gavaged ¹⁴ C was in the gut contents and/or faeces. Much of the gavaged ¹⁴ C (57%), predominantly that originally in tannins of high degree of polymerisation (DP), became insolubilised, mainly in the form of protein–tannin complexes. Some of the [ ¹⁴ C]tannins that remained soluble decreased in DP, especially in the small intestine and caecum. A further fraction (12% of the ¹⁴ C gavaged) underwent chemical modifications in the gut to form soluble, non‐tannin compounds. Small proportions of the ¹⁴ C were found in the liver (1.0–1.5%), urine (1–2%) and ¹⁴ CO 2 (1–2%). We conclude that proanthocyanidins are not inert within the gut but undergo various modifications which may affect the nutrition of the animal.
© 2001 Society of Chemical Industry
... A large fraction of the proanthocyanidins and associated monomers consumed passes to the colon where they are subject to gut microbiotic catabolism, [6,22,23] producing phenolic acids (C6-C5, C6-C3 and C6-C1) with varying hydroxylation patterns, [6,22,23] and non-phenolic catabolites [22] (perhaps including oxaloacetate, succinate, butyrate and carbon dioxide) [10,[24][25][26] and unidentified components. The extent to which, for a given flora, the yield and profile of catabolites varies with the substrate, is uncertain. ...
... A large fraction of the proanthocyanidins and associated monomers consumed passes to the colon where they are subject to gut microbiotic catabolism, [6,22,23] producing phenolic acids (C6-C5, C6-C3 and C6-C1) with varying hydroxylation patterns, [6,22,23] and non-phenolic catabolites [22] (perhaps including oxaloacetate, succinate, butyrate and carbon dioxide) [10,[24][25][26] and unidentified components. The extent to which, for a given flora, the yield and profile of catabolites varies with the substrate, is uncertain. ...
... A large fraction of the proanthocyanidins and associated monomers consumed passes to the colon where they are subject to gut microbiotic catabolism, [6,22,23] producing phenolic acids (C6-C5, C6-C3 and C6-C1) with varying hydroxylation patterns, [6,22,23] and non-phenolic catabolites [22] (perhaps including oxaloacetate, succinate, butyrate and carbon dioxide) [10,[24][25][26] and unidentified components. The extent to which, for a given flora, the yield and profile of catabolites varies with the substrate, is uncertain. ...
The catabolism by human faecal microbiota of (-)-epicatechin (1) (2, 3-cis stereochemistry) and its dimer pure procyanidin B2 (2), has been compared using a static in vitro culture model. The catabolites were characterised by LC-MS(n), UV absorption and relative retention time, and quantified relative to standards. No more than approximately 10% of procyanidin B2 (2) was converted to epicatechin (1) by scission of the interflavan bond. Five phenolic acid catabolites (M(r)<290) were unique to 2, and ten phenolic acid catabolites (M(r)<290) were common to both substrates. The dominant catabolites (> or =24 h incubation) were 5-(3'-hydroxy phenyl) valeric acid (9), 3-(3'-hydroxyphenyl) propionic acid (10) and phenyl acetic acid (12) (maximum yields 27.4+/-4.2, 38.2+/-4.2, 22.7+/-2.9%, respectively, from 1 and 9.4+/-1.2, 52.8+/-2.1, 28.8+/-1.6%, respectively, from 2). Substrate 2 was degraded twice as rapidly as 1. Evidence is presented for the production of previously unreported catabolites of 2 that retain the flavanol A-ring and the C4-->C8 interflavan bond. It was confirmed that catabolism favoured removal of the 4'-hydroxyl rather than the 3'-hydroxyl group and that both beta-oxidation and alpha-oxidation occurred.
... This was confirmed for monomeric flavan-3-ols in vitro using cultivated microbiota [13,34]. 4H-DHPVA was also observed in vitro [35], but was only detected in traces in rat urine after an administration of (+)-catechin [21]. ...
... Since we also observed a slight decrease of DHPV formation after the intervention with PC B1, we assume that microbial degradation of higher molecular procyanidins is hampered. This is in line with studies conducted in rats: Applying 14 Clabeled proanthocyanidins from carob pods with a mean degree of polymerization of four to rats, resulted in a faecal excretion of 90 to 94% of the radioactivity [35], indicating the lack of transformation to smaller and absorbable breakdown products. The limited microbial degradation of high molecular procyanidins might be caused by a low uptake of the compounds by bacteria due to their huge molecular size. ...
ScopeFlavan-3-ols are abundant polyphenols in human nutrition and are associated with beneficial health effects. The aim of this study was to comparatively investigate the metabolic fate of (-)-epicatechin, procyanidin B1, and polymeric procyanidins in a randomized cross-over study in humans.Methods and resultsParent compounds, conjugates, and microbial metabolites were determined in plasma, urine, and faeces by HPLC-MS and GC-MS/MS. Glucuronidated, sulfated, and methylated (-)-epicatechin and 5-(3′,4′-dihydroxyphenyl)-valerolactone were the dominant metabolites in blood and urine. In addition, minor amounts of procyanidin B1 and 4-hydroxy-5-(3′,4′-dihydroxyphenyl)valeric acid and their conjugated metabolites were detected. The formation of 5-(3′,4′-dihydroxyphenyl)-valerolactone and 4-hydroxy-5-(3′,4′-dihydroxyphenyl)valeric acid varied largely between individuals as well as with the degree of polymerization of flavan-3-ols. Monomer units were not detectable in plasma or urine after procyanidin B1 and polymeric procyanidin intake. No correlation was found between the intake of flavan-3-ols and the occurrence of phenolic acids in blood and urine or the phenolic compound profiles in faeces.Conclusion
In addition to conjugated metabolites derived from the absorption of monomeric flavan-3-ols, 5-(3′,4′-dihydroxyphenyl)-valerolactone represents an important in vivo metabolite of (-)-epicatechin and procyanidin B1 produced by the gut microbiota.This article is protected by copyright. All rights reserved
... The molecular complexity of PhCs seems to be a major factor limiting their bioavailability, with monomeric phenolics being easily absorbed through the intestine, while no studies have detected the presence in plasma of PhCs with degrees of polymerization greater than dimers (Manach et al., 2005). Controversial results have been provided by in vivo studies using 14 C-labelled tannins to follow their metabolism in the gastrointestinal tract of rats and ruminants (Terrill et al., 1994;Perez-Maldonado and Norton, 1996;Abia and Fry, 2001). Ruminal microbial population can adapt to the antinutritional effects of tannins (Smith et al., 2005), but the hydrolysation of tannins in the rumen is unlikely (Makkar et al., 1995). ...
... Ruminal microbial population can adapt to the antinutritional effects of tannins (Smith et al., 2005), but the hydrolysation of tannins in the rumen is unlikely (Makkar et al., 1995). Nevertheless, intestinal microflora of both humans and rats seems to be able to carry out an active metabolism of condensed tannins leading to their depolymerization and catabolism into smaller molecules which, in turn, could be absorbed (Déprez et al., 2000;Abia and Fry, 2001;Rios et al., 2003). More recently, Gladine et al. (2007a) detected the presence of epicatechins in the blood of sheep receiving different polyphenol-rich plant extracts by direct ruminal infusion and suggested that ruminants may be able to metabolize polymeric proanthocyanidins into bioavailable compounds. ...
Worldwide policies are encouraging the use of natural rangelands and low input feeding resources for livestock farming. Most of the low input feed contain secondary compounds (PSCs) – such as phenolic compounds (PhCs), saponins, and essential oils (EO) – which play a primary role on animal digestion and performances and also on product quality. Meat and milk fatty acid composition can be manipulated by dietary tannins as these PSCs modify ruminal biohydrogenation of dietary polyunsaturated fatty acids through changes in ruminal ecology. Dietary tannins improve products’ flavour by reducing the ruminal biosynthesis of skatole and its accumulation in meat and milk. The addition of garlic or juniper EO in lamb diets reduces the off-flavours perception while thyme or rosemary EO lowered the rancid-odour perception of meat under display. It is proved that dietary PhCs ameliorate meat oxidative stability and prevent meat from discoloration thus extending product shelf life. The dose–response effect of these PSCs as well as their mechanisms of action are not fully unravelled. Nevertheless, the use of plants rich in secondary compounds or the supplementation of purified PSCs in small ruminants diet seem to be a promising strategy for improving products quality.
... Although monomeric compounds can be absorbed, no studies have detected the presence of tannins with degrees of polymerization greater than dimers in plasma (Manach & Donovan, 2004; Manach, Williamson, Morand, Scalbert, & Rémésy, 2005; Scalbert, Morand, Manach, & Rémésy, 2002 ). Controversial results have been provided by in vivo studies using 14 C-labelled tannins to follow their metabolism in the gastrointestinal tract of rats and ruminants (Abia & Fry, 2001; Perez-Maldonado & Norton, 1996; Terrill, Waghorn, Woolley, McNabb, & Barry, 1994). Ruminal microbial population can adapt to tannins, protecting the animals from their antinutritional effects (Smith, Zoetendal, & Mackie, 2005). ...
... However, Makkar, Becker, Abel, and Szegletti (1995) demonstrated that rumen microbes do not hydrolyse condensed tannins. Conversely , in vivo and in vitro studies provided evidence for the active metabolism of condensed tannins by the intestinal microflora of both humans and rats (Abia & Fry, 2001; Déprez et al., 2000; Rios et al., 2003) undergo chemical modifications in the gut leading to their depolymerization and catabolism into smaller molecules which, in turn, could be absorbed. Moreover, tannins can modify the fatty acids composition of the meat (Vasta, Pennisi et al., 2007) and this could indirectly affect its susceptibility to oxidation processes. ...
Fourteen male Comisana lambs were divided into two groups at 45 days of age: lambs fed a concentrate diet (C), or lambs fed the same concentrate with the addition of quebracho (Schinopsis lorentzii) tannins (T). Sheep were slaughtered at 105 days of age. Lipid oxidation, colour coordinates, haem pigment concentration, and metmyoglobin percentages were measured on minced semimembranosus muscle (SM) over 14 days of refrigerated storage in a high oxygen modified atmosphere. Tannin supplementation increased (P < 0.01) a∗ values and reduced (P < 0.01) b∗ values of the SM when compared to C. Lower hue angles (P < 0.001) and metmyoglobin formation (P = 0.07) were observed in lamb from T-fed compared to C-fed sheep during the 14-days storage period. Furthermore, feeding T resulted in greater (P < 0.001) haem pigment concentrations in the SM during refrigerated storage; however, diet had no (P = 0.28) effect on lipid oxidation. Therefore, including quebracho tannins in sheep diets can improve meat colour stability of fresh lamb during extended refrigerated storage.
... In this context, Gonthier et al. [56] did not observe proanthocyanidins degradation, nor the appearance of subsequent compounds, such as catechin. Abia and Fry [57] reported that the majority of the proanthocyanidins ingested by lab rats remain undigested and appear in feces, supporting the procyanidin precipitation suggested in this study. ...
Few investigations have been conducted to evaluate pressurized liquid extraction (PLE) technology as a sustainable method for the recovery of phenolic compounds of grape seed by-products. In this study, PLE combined with an experimental design was evaluated for optimizing the sustainable extraction of phenolic compounds from grape seed by-products. The solvent ethanol content (X1, 0–100%), temperature (X2, 20–100 °C) and time (X3, 1–11 min) were studied as independent experimental factors. Yield, TPC, antioxidant activity and phenolic composition were analyzed as optimized dependent variables. Two optimal extraction conditions at different temperatures (20 °C and 100 °C) were found, but thermal degradations at 100 °C allowed for selecting the optimal condition as 75% ethanol, 11 min and 20 °C. The optimal extracts showed high phenolic content (TPC = 350.80 ± 3.97 mg GAE/g extract) and antioxidant activity (ABTS, 9.31 ± 0.33 mmol Trolox/g extract), mainly composed of polymeric and mono-oligomeric flavan-3-ols. The digestion process reduced the TPC and antioxidant activity due to the low bioaccessibility of the flavan-3-ols, mainly as catechin, epicatechin and polymeric proanthocyanidin losses during the digestion process. However, increases in the antioxidant activity of the basolateral side (DDPH, 0.061 ± 0.000 mmol Trolox/g extract) were determined after in vitro transepithelial transport, which is a consequence of bioavailable catechin and epicatechin and reduced amounts of dimer B2, dimer B1, epicatechin gallate and gallic acid. Consequently, PLE combined with hydroalcoholic solvents at a low temperature resulted in a valuable methodology to obtain sustainable extracts from grape seed by-products (contributing to the circular economy), containing bioavailable phenolic compounds, which are able to increase the antioxidant status.
... The protein binding property of procyanidins was affected by the degree of polymerization, whereby an increase in the degree of polymerization was associated with enhanced protein precipitating capacity [38]. Abia and Fry [39] observed that 90-94% of the ingested carob proanthocyanidins remained undigested in the digested samples or feces in lab rats, where the compounds with a higher polymerization degree were precipitated with digestive enzymes. Gonthier et al. [40] observed neither parent compounds nor catechin derivatives in urine samples in rats fed with procyanidins, in contrast to those fed with catechin monomers, which excreted large amounts of catechin, suggesting procyanidin non-degradation during the digestion process. ...
The bioaccessibility and bioavailability of phenolics compounds of two grape stem extracts with different composition were studied. High polymeric extract (HPE) presented a higher content of total phenolics (TPC), procyanidins, hemicelluloses, proteins, and ashes, whereas low procyanidin extract (LPE) showed a higher fat, soluble sugars, and individual phenolic compounds content. Corresponding to its higher total phenolics content, HPE possesses a higher antioxidant activity (TEAC value). The digestion process reduced the antioxidant activity of the HPE up to 69%, due to the decrease of TPC (75%) with a significant loss of polymeric compounds. LPE antioxidant activity was stable, and TPC decreased by only 13% during the digestion process. Moreover, a higher antioxidant phenolic compounds bioavailability was shown in LPE in contrast to HPE. This behaviour was ascribed mainly to the negative interaction of polymeric fractions and the positive interaction of lipids with phenolic compounds. Therefore, this study highlights the convenience of carrying out previous studies to identify the better extraction conditions of individual bioavailable phenolic compounds with antioxidant activity, along with those constituents that could increase their bioaccessibility and bioavailability, such as lipids, although the role played by other components, such as hemicelluloses, cannot be ruled out.
... The degradation of CTs into compounds with a lower degree of polymerization or even to monomers throughout the GIT would allow greater availability of absorbable compounds, but the CT metabolization in the GIT is still poorly understood. Despite the conflicting results, several reports have shown that CTs are not inert during transit through the GIT, instead they are subject to extensive biotransformation processes [23,98,100,101]. Along the GIT, there are conditions like gastric acidity and microorganisms that could promote CT changes. ...
Condensed tannins (CTs) are widely distributed in plants, and due to their recognized antioxidant activity are considered as possible natural antioxidants for application in ruminant diets. A wide range of CT-rich sources has been tested in ruminant diets, and their effects on animal antioxidant status and oxidative stability of their products are reviewed in the present work. Possible mechanisms underlying the CT antioxidant effects in ruminants are also discussed, and the CT chemical structure is briefly presented. Utilization of CT-rich sources in ruminant feeding can improve the animals’ antioxidant status and oxidative stability of their products. However, the results are still inconsistent. Although poorly understood, the evidence suggests that CTs can induce an antioxidant effect in living animals and in their products through direct and indirect mechanisms, which can occur by an integrated and synergic way involving: i) absorption of CTs with low molecular weight or metabolites, despite CTs’ poor bioavailability; ii) antioxidant action on the gastrointestinal tract; and iii) interaction with other antioxidant agents. Condensed tannins are alternative dietary antioxidants for ruminants, but further studies should be carried out to elucidate the mechanism underlying the antioxidant activity of each CT source to design effective antioxidant strategies based on the use of CTs in ruminant diets.
... Neither the TOS or TAC values were affected by the treatment, which was evidenced by the absence of dietary effects on the oxidative status of the piglets. Despite the PROC treatment containing carob, an ingredient with high levels of phenolic compounds, potentially with an antioxidant effect, most of those are in the form of condensed tannins [62], a chemical form which is poorly bioavailable [63,64]. ...
This work studied the effects of the inclusion of Clostridium butyricum on feed, alone or with carob meal or citrus pulp, on the digestive and metabolic status of weaned piglets. A total of 30 male piglets (weaned at 21 days) is used. There are five dietary treatments: negative without ZnO at high doses (C−), a positive control supplemented with ZnO at 2500 ppm of Zn (C+), supplemented with Clostridium butyricum as a probiotic (PRO), and supplemented with probiotic and 5% carob meal (PROC) or 5% citrus pulp (PROP). During the experiment (27 days), the piglets were periodically weighed and sampled for a serum biochemical, fecal microbiological, intestine histological, and digestive status analysis. The body weight, apparent ileal digestibility of dry matter (DM), and fecal microbiology were not affected by the treatments (p ≥ 0.05). However, the apparent fecal digestibility of DM was lower for the C− treatment than for C+ (p < 0.05), and the total concentration of volatile fatty acids (VFAs) in feces with C+ was lower than that for the PROC treatment (p < 0.05). The treatments with the probiotic had a higher molar proportion of butyric acid in feces than C+, and it was found that C− reached an intermediate value (p < 0.01). No general effects of diet were found on the histological measures performed on the jejunum and ileum, and in the serum biochemical analysis (p ≥ 0.05), only the concentration of interleukin-8 was lower for the PROC treatment compared to the C−, C+, and PRO treatments (p < 0.05). In conclusion, the intestinal wellness of piglets could be improved with the supplementation of Clostridium butyricum by increasing butyric acid, and this effect was not altered with the inclusion of carob meal or citrus pulp. More studies under commercial conditions are needed, as the effects might be different in more challenging environmental circumstances.
... However, Makkar et al. (1995) demonstrated that rumen microorganisms do not degrade CT. Conversely, results from studies in rats and humans showed that their intestinal microflora is able to induce structural modifications in CT (Déprez et al., 2000;Abia and Fry, 2001). ...
Utilization in ruminant diets of Cistus ladanifer (a shrub native from Mediterranean region) or its condensed tannin (CT) extracts has been intensively explored in the last years, with a wide range of studies that have provided valuable information on conditions of use, benefits and action mechanisms. Although it is considered as a feed with poor nutritional value, C. ladanifer can be used as component or as a source of bioactive compounds for ruminant diets in order to modulate the rumen metabolism and oxidative stability of animal products. Cistus ladanifer has been shown to be a good approach to improve the nutritional value of ruminant products, promoting the increase of healthy fatty acids content, which appear to be mainly due to ability of their CT to modulate ruminal biohydrogenation. On the other hand, incorporation of C. ladanifer in ruminant diets can also limits the lipid oxidation of meat, even in meat more susceptible to oxidation. Application of C. ladanifer CT extracts to silage has been shown to be effective in reducing the proteolysis, improving the silage nutritional value. Moreover, the treatment of dietary protein source with C. ladanifer CT extract also reduce the protein rumen degradability, allowing reduce the protein level in ruminant diets without compromise the animal performance.
... However, a relatively poor bioavailability of grape polyphenols likely restricts their antioxidant function in the gut [9]. In rodent studies, 88-94% of administered radiolabeled anthocyanins and proanthocyanidins were recovered in the gastrointestinal tract and feces [24,25]. The present study tests the hypothesis that grape seed-derived polyphenols reduce oxidative stress, inflammation, and epithelial permeability in the LPS-induced Caco-2 colon model, and that this effect may be related to the attenuation of metabolic syndrome caused by dietary consumption of polyphenol-rich foods. ...
Grape polyphenols have previously been shown to improve gut health and attenuate the symptoms of metabolic syndrome; however, the mechanism of these beneficial effects is still debated. In this study, we investigated the protective effect of proanthocyanidin-rich grape seed extract (GSE) on bacterial lipopolysaccharide (LPS)-induced oxidative stress, inflammation, and barrier integrity of human Caco-2 colon cells. GSE significantly reduced the LPS-induced intracellular reactive oxygen species (ROS) production and mitochondrial superoxide production, and upregulated the expression of antioxidant enzyme genes. GSE also restored the LPS-damaged mitochondrial function by increasing mitochondrial membrane potential. In addition, GSE increased the expression of tight junction proteins in the LPS-treated Caco-2 cells, increased the expression of anti-inflammatory cytokines, and decreased pro-inflammatory cytokine gene expression. Our findings suggest that GSE exerts its beneficial effects on metabolic syndrome by scavenging intestinal ROS, thus reducing oxidative stress, increasing epithelial barrier integrity, and decreasing intestinal inflammation.
... Notably, antioxidant flavonoids, such as anthocyanins, monomeric flavan-3-ols, and their oligomers, B-type proanthocyanidins (PACs), which represent the majority of polyphenols in grapes [12][13][14] and other red-or blue-colored berries are poorly bioavailable [15][16][17][18]. Relatively low systemic absorption of these compounds, combined with their documented health benefits, creates a paradox in understanding the mechanism of action of berry polyphenols and leads to several hypotheses aimed at explaining their health benefits. ...
High-fat diet (HFD)-induced leaky gut syndrome combined with low-grade inflammation increase reactive oxygen species (ROS) in the intestine and may contribute to dysbiosis and metabolic syndrome (MetS). Poorly bioavailable and only partially metabolizable dietary polyphenols, such as proanthocyanidins (PACs), may exert their beneficial effects on metabolic health by scavenging intestinal ROS. To test this hypothesis, we developed and validated a novel, noninvasive, in situ method for visualizing intestinal ROS using orally administered ROS-sensitive indocyanine green (ICG) dye. C57BL/6J mice fed HFD for 10 weeks accumulated high levels of intestinal ROS compared to mice fed low-fat diet (LFD). Oral administration of poorly bioavailable grape polyphenol extract (GPE) and β-carotene decreased HFD-induced ROS in the gut to levels comparable to LFD-fed mice, while administration of more bioavailable dietary antioxidants (α-lipoic acid, vitamin C, vitamin E) did not. Forty percent of administered GPE antioxidant activity was measured in feces collected over 24 h, confirming poor bioavailability and persistence in the gut. The bloom of beneficial anaerobic gut bacteria, such as Akkermansia muciniphila, associated with improved metabolic status in rodents and humans may be directly linked to protective antioxidant activity of some dietary components. These findings suggest a possible mechanistic explanation for the beneficial effects of poorly bioavailable polyphenols on metabolic health.
... Notably, antioxidant flavonoids, such as anthocyanins, monomeric flavan-3-ols, and their 53 oligomers, B-type proanthocyanidins (PACs), which represent the majority of polyphenols in 54 grapes [12][13][14] and other red-or blue-colored berries are poorly bioavailable [15][16][17][18]. Relatively 55 low systemic absorption of these compounds, combined with their documented health benefits, 56 creates a paradox in understanding the mechanism of action of berry polyphenols and leads to 57 several hypotheses aimed at explaining their health benefits. ...
High-fat diet (HFD)-induced leaky gut syndrome combined with low-grade inflammation increase reactive oxygen species (ROS) in the intestine and may contribute to dysbiosis and metabolic syndrome (MetS). Poorly bioavailable and only partially metabolizable dietary polyphenols, such as proanthocyanidins (PACs), may exert their beneficial effects on metabolic health by scavenging intestinal ROS. To test this hypothesis, we developed and validated a novel, noninvasive, in situ method for visualizing intestinal ROS using orally administered ROS-sensitive indocyanine green (ICG) dye. C57BL/6J mice fed HFD for 10 weeks accumulated high levels of intestinal ROS compared to mice fed low-fat diet (LFD). Oral administration of poorly bioavailable grape polyphenol extract (GPE) and ?-carotene decreased HFD-induced ROS in the gut to levels comparable to LFD-fed mice, while administration of more bioavailable dietary antioxidants (α-lipoic acid, vitamin C, vitamin E) did not. Forty percent of administered GPE antioxidant activity was measured in feces collected over 24 h, confirming poor bioavailability and persistence in the gut. The bloom of beneficial anaerobic gut bacteria, such as Akkermansia muciniphila, associated with improved metabolic status in rodents and humans may be directly linked to protective antioxidant activity of some dietary components. These findings suggest a possible mechanistic explanation for the beneficial effects of poorly bioavailable polyphenols on metabolic health.
... Unabsorbed tannin polymers that enter the colon are not inert but instead, M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT they are degraded into low molecular weight aromatic acids. Moreover, it was shown that condensed tannins undergo many different chemical transformations in the gut, yielding soluble, non-tannin compounds [20,28,29]. This may explain why condensed tannins were also undetected in the colon. ...
Objective: To evaluate the stability and bioavailability of polyphenols in pili (Canarium ovatum Engl.) pomace during simulated in vitro digestion.
Methods: Freeze-dried pili pomace was subjected to in vitro digestion simulating conditions in the stomach, small intestine and colon. Total polyphenols, anthocyanins, flavonoids and condensed tannins, and its antioxidant activity – 1,1-diphenyl-2-picrylhydrazyl, 2,2′-azinobis-3-ethylbenzothiozoline-6-sulfonic acid, and ferric reducing antioxidant power were measured using standard spectrophotometric methods.
Results: In vitro digestion of pili pomace resulted in reduction of phenolic compounds. Condensed tannins and anthocyanins were released in the gastric and intestinal stages, while total polyphenols and flavonoids after fermentation simulating colonic conditions. Antioxidant values of the bioavailable fractions showed that more than 90% of activity was lost during simulated digestion.
Conclusions: Findings indicate that pili pomace is a promising functional ingredient for food and dietary supplements which can furnish potentially bioavailable phenolic antioxidants to the body.
... ACNs and PACs have also been argued to stem the development of insulin resistance by increasing insulin signaling, glycogen accumulation and adiponectin secretion in the presence of free fatty acids 93 . Intriguingly, rodent studies indicate that just 6-12% of radiolabeled polyphenols are metabolized and enter circulation during their passage through the gut 94,95 , leaving open the question of how these compounds confer their protective effects. Recent studies of polyphenol extracts isolated from grapes 20 and cranberries 96 provide support for a mechanism that acts via the gut microbiota. ...
Although the importance of human genetic polymorphisms in therapeutic outcomes is well established, the role of our 'second genome' (the microbiome) has been largely overlooked. In this Review, we highlight recent studies that have shed light on the mechanisms that link the human gut microbiome to the efficacy and toxicity of xenobiotics, including drugs, dietary compounds and environmental toxins. Continued progress in this area could enable more precise tools for predicting patient responses and for the development of a new generation of therapeutics based on, or targeted at, the gut microbiome. Indeed, the admirable goal of precision medicine may require us to first understand the microbial pharmacists within.
... However, Makkar et al. (1995) demonstrated that rumen microorganisms do not degrade CT. Conversely, results from studies in rats and humans showed that their intestinal microflora is able to induce structural modifications in CT (Déprez et al., 2000;Abia and Fry, 2001). ...
Tannins are widespread throughout the plant kingdom, occurring as hydrolysable and condensed tannins and at different levels in several animal feeding sources. Recent years have seen an increasing interest in the use of tannin-rich plants and plant extracts in ruminant diets for improving the quality of their edible products. Some results show that this strategy is effective in improving the fatty acid profile of meat and milk, increasing the level of health-beneficial fatty acids as well as enhancing the oxidative stability of the products. However, the use of tannin-rich feed in animal diets requires great care, due to its possible detrimental effects on animal performance and induction of metabolic disorders. Although promising, the results of studies on the effects of tannins on animal performance and quality of their products are still controversial, probably depending on type and chemical structure of tannins, amount ingested, composition of diet, and species of animal. In this chapter, the current knowledge regarding the effect of dietary tannins on animal performance and the quality of their products (meat and milk), particularly on the fatty acid profile, oxidative stability, and organoleptic properties, is reviewed. The tannin chemistry diversity and its occurrence in ruminant diets, as well as its beneficial and adverse effects on ruminants, will be briefly reviewed, and aspects related to oral cavity physiology, saliva production/composition, and postingestive effects will also be discussed.
... ACNs and PACs confer protection against symptoms of MetS despite their limited absorption in circulation (21)(22)(23). In rodent studies, 88-94% of the administered radiolabeled ACN or PAC compounds were recovered in the gastrointestinal tract and feces (21,24). While polyphenols are known to be biotransformed by gut microbiota into simpler phenolic compounds that may be absorbed (25), the levels and bioactivities of circulating metabolites may not be sufficient to explain the pharmacological effects of polyphenols. ...
Dietary polyphenols protect against metabolic syndrome, despite limited absorption and digestion, raising questions about their mechanism of action. We hypothesized that one mechanism may involve the gut microbiota. To test this hypothesis, C57BL/6J mice were fed a high-fat diet (HFD) containing 1% Concord grape polyphenols (GP). Relative to vehicle controls, GP attenuated several effects of HFD feeding, including weight gain, adiposity, serum inflammatory markers (tumor necrosis factor [TNF]α, interleukin [IL]-6, and lipopolysaccharide), and glucose intolerance. GP lowered intestinal expression of inflammatory markers (TNFα, IL-6, inducible nitric oxide synthase) and a gene for glucose absorption (Glut2). GP increased intestinal expression of genes involved in barrier function (occludin) and limiting triglyceride storage (fasting-induced adipocyte factor). GP also increased intestinal gene expression of proglucagon, a precursor of proteins that promote insulin production and gut barrier integrity. 16S rRNA gene sequencing and quantitative PCR of cecal and fecal samples demonstrated that GP dramatically increased the growth of Akkermansia muciniphila and decreased the proportion of Firmicutes to Bacteroidetes, consistent with prior reports that similar changes in microbial community structure can protect from diet-induced obesity and metabolic disease. These data suggest that GP act in the intestine to modify gut microbial community structure, resulting in lower intestinal and systemic inflammation and improved metabolic outcomes. The gut microbiota may thus provide the missing link in the mechanism of action of poorly absorbed dietary polyphenols.
... Carob contains high levels of phenolic compounds, most of which are potentially strong antioxidants, but are in the form of non extractable condensed tannins(Silanikove et al., 2006). Research on the possible bioavailability of condensed tannins in animal seems to suggest that these compounds are poorly degraded into the gastrointestinal tract and, therefore, not readily bioavailable in the animal organism(Abia & Fry, 2001; Lόpez-Andrés et al., 2013). ...
The effect of feeding pigs with carob pulp on meat quality was investigated. Nine pigs were finished on a conventional concentrate-based diet (control), while two groups received a diet comprising of the same ingredients with the inclusion of 8% or 15% carob pulp (Carob 8% and Carol) 15%, respectively). Feeding carob-containing diets reduced the concentration of saturated fatty acids in the muscle, increased the concentration of monoun-saturated fatty acids in meat (P < 0.01) and of n-3 polyunsaturated fatty acids (PUFAs) and reduced the n-6/n-3 PUFA ratio (P < 0.001). The meat underwent slow oxidative deterioration over 9 days of storage. However, the Carob 15% treatment increased meat susceptibility to lipid oxidation across storage (P = 0.03), while the dietary treatment did not affect meat colour stability. In conclusion, feeding pigs with carob pulp could represent a strategy, in the Mediterranean areas, to naturally improve meat nutritional value and to promote the exploitation of this local feed resource.
... Radiocontrast tracers or markers fed to animals such as barium sulfate allow for segmental transit time determination by using timed x-rays [61][62][63][64]. Carmine red and Poly R-478 dyes [53,65,66], fluorescent compounds, radiotracers [67][68][69] and charcoal [70][71][72][73][74][75][76] facilitate the determination of total GItt. Additionally, hydrogen breath testing can measure the time that an orally ingested non-absorbable carbohydrate takes to reach the site of microbial concentration through measurement of gaseous products of fermentation, and thus, allow for determination of gastrocecal transit time [53]. ...
... This finding is further corroborated by animal research that demonstrated that oral administration of oligomeric condensed tannins resulted in detectable levels of catechin-and epicatechin-derived metabolites in plasma and urine [101,102]. Since higher molecular weight condensed tannins are not absorbed intact, and are not susceptible to mammalian digestive enzymes [103], it is generally believed that these polyphenols are mainly absorbed from colon after microbial-mediated fermentation [104,105]. Gut microflora may depolymerize condensed tannins, producing bioaccessible oligomeric proanthocyanidins, or may carry out catabolic reactions such as ring fission [104,106]. ...
The plant natural products known as polyphenols are found at micronutrient levels in fruits, vegetables, and plant-based beverages such as wine, tea, coffee and cocoa. Consumption of a fruit- and vegetable-rich diet, the "Mediterranean diet", has been epidemiologically related to health benefits especially for chronic diseases including diabetes, cardiovascular disease, and Alzheimer's disease. The abundance of polyphenols in plant-rich diets, and the potent bioactivities of polyphenols, provide indirect evidence for a role for polyphenols in maintaining good health. However, molecular mechanisms for therapeutic or preventative activity have not been demonstrated in vivo. We summarize the chemical classes of natural polyphenols, their bioactivities and bioavailability and metabolism. Because many polyphenols bind protein, we focus on the potential of protein binding to mediate the health-related effects of polyphenols. We discuss interactions with plasma proteins as the first target organ past the digestive tract for these orally-ingested compounds.
... In mice, altered expression of epithelial tight junction proteins (TJPs; occludin, claudin isoforms, zona occludens [ZO]-1/2, etc) and increased permeability are observed in HF feeding and metabolic syndrome, obesity, and diabetes models, often preceding clinical disease [18,19,222324. Reduction of endotoxin production and/or uptake in the gut would represent an ideal mechanistic target for GSE because of the poor bioavailability and high concentrations of its constituent procyanidins in the gut after consumption252627282930. Recently, Song et al [31] demonstrated that GSE reduces small intestinal permeability and increases small intestinal transcription of occludin and ZO-1 genes. ...
Animal studies have demonstrated the potential of grape seed extract (GSE) to prevent metabolic syndrome, obesity, and type 2 diabetes. Recently, metabolic endotoxemia induced by bacterial endotoxins produced in the colon has emerged as a possible factor in the etiology of metabolic syndrome. Improving colonic barrier function may control endotoxemia by reducing endotoxin uptake. However, the impact of GSE on colonic barrier integrity and endotoxin uptake has not been evaluated. We performed a secondary analysis of samples collected from a chronic GSE feeding study with pharmacokinetic end points to examine potential modulation of biomarkers of colonic integrity and endotoxin uptake. We hypothesized that a secondary analysis would indicate that chronic GSE administration increases colonic expression of intestinal tight junction proteins and reduces circulating endotoxin levels, even in the absence of an obesity-promoting stimulus. Wistar Furth rats were administered drinking water containing 0.1% GSE for 21 days. Grape seed extract significantly increased the expression of gut junction protein occludin in the proximal colon and reduced fecal levels of the neutrophil protein calprotectin, compared with control. Grape seed extract did not significantly reduce serum or fecal endotoxin levels compared with control, although the variability in serum levels was widely increased by GSE. These data suggest that the improvement of gut barrier integrity and potential modulation of endotoxemia warrant investigation as a possible mechanism by which GSE prevents metabolic syndrome and associated diseases. Further investigation of this mechanism in high-fat feeding metabolic syndrome and obesity models is therefore justified.
... However, Makkar, Becker, Abel, and Szegletti (1995) demonstrated that rumen microorganisms do not hydrolyse CT. Conversely, studies in rats and humans indicated that CT are not inert within the gut, but undergo structural modifications operated by the intestinal microflora (Abia & Fry, 2001;Déprez et al., 2000). Nevertheless, the effect of dietary CT on meat oxidative stability may be indirect, through the interaction between CT with other antioxidants compounds or with pro-oxidants compounds present in meat. ...
... Concerning intestinal absorption of OPCs the following studies have been reported: Using a rat perfusion system the degradation of procyanidin B2 and B5 to epicatechin was observed, which again was identified as absorbed monomer [18]. Also [21] observed a significant decrease of degree of polymerisation of OPCs after feeding rats with 14 C-labeled proanthocyanidins. [22] identified procyanidin B2 after feeding rats (very high concentrations of 50 mg/kg body weight) with this compound after 30 min at 0.5 μM in the plasma. ...
Extracts from hawthorn leafs and flowers (Crataegus sp., Rosaceae) are widely used as a rational based phytomedicine for declining cardiac performance. According to present literature C-glycosylated flavones and oligomeric procyanidins are considered to be the active ingredients, despite the fact that no systematic data are available on systemic bioavailability of proanthocyanidins after oral intake. The present study aims to review the actual state of literature in this field and to investigate the intestinal absorption mechanisms of defined hawthorn PAs with different degrees of polymerization by validated in vitro Caco-2 monolayer permeation system. Hawthorn OPCs with DP 2 to 6 were isolated as defined clusters. Procyanidin B2 and the procyanidin clusters DP 4, 5 and 6 had very low P(app) values between 0.6 and 6×10⁻⁷ cm/s for apical to basolateral permeation. The higher the molecular weight the lower permeation coefficients were calculated. The observed low-level transport was mainly due to passive paracellular permeation. Additionally cellular uptake of OPCs by transcellular permeation was possible; on the other side procyanidins were shown to be p-glycoprotein substrates, which leads to subsequent excretion of PAs by the efflux pump to the apical side. Mixtures of the different OPCs did not have an increased permeation. Transport experiments of complex OPC mixtures together with hawthorn flavonoids did not indicate any improved permeation or synergistic effects. In principle this raises the question if systemic pharmacological activities of hawthorn extracts, can really be attributed to OPCs with very low systemic bioavailability.
... These balance studies wherein little free condensed tannins have been observed in faeces should be interpreted with caution with respect to their degradation. The condensed tannins do not get hydrolysed by rumen microbes (Makkar et al., 1995a,b), and additionally [ 14 C] condensed tannin-based studies suggested little if any condensed tannin-carbon absorbed to the blood (Terrill et al., 1994;Abia and Fry, 2001). The free condensed tannins present in the feed get bound to fibre fractions and protein in the gastrointestinal tract and are present in faeces but in the unextractable form. ...
Trees and shrub foliage and agro-industrial by-products are of importance in animal production because they do not compete with human food and can provide significant protein supplements, especially in the dry season. But, these feed resources are generally rich in antinutritional factors, particularly tannins. The amount of tannins that they contain vary widely and largely unpredictably, and their effects on animals range from beneficial to toxicity and death. With a better understanding of tannin properties, effects and fate; and with proper management they could become invaluable sources of protein for strategic supplementation. The effects and fate of tannins in the rumen, and post-absorption, and likely mechanisms of adaptation to tannins are discussed. Simple methods based on post-harvest technology, treatment with low-cost chemicals, biological treatments, and supplementation with tannin-complexing agents, to enhance the feeding value of tannin-containing feeds; and roles of rumen microbes in degradation and overcoming the detrimental effects of tannins are also presented. © 2003 Published by Elsevier Science B.V.
... This may also contribute to the lower number of metabolites and to the lower extent of metabolism of long-chain condensed catechins. In contrast, the low degree of polymerization of condensed catechins supports their degradation, especially in the caecum, resulting in an accumulation of polar phenolic compounds (Abia and Fry 2001;Levrat et al. 1993). ...
Plant foods contain substantial amounts of phenolic compounds. Dietary interventions with phenolic supplementation show that
phenolic compounds are transformed into phenolic acids or lactone structures by intestinal microbiota. The colon is the main
site of microbial fermentation. The metabolites circulate in plasma and are excreted via urine. The entero-hepatic circulation
ensures that their residence time in plasma is extended compared to that of their parent compounds. Thus these metabolites
may exert systemic effects, which however have not been studied adequately. In particular the health implications of microbial
metabolites of flavonoids, mostly phenolic acids, are unknown. This review aims to elucidate the microbial metabolism of most
of the phenolic classes: flavonoids, isoflavonoids, lignans, phenolic acids and tannins. Some examples of biological activity
studies of flavonoid and lignan metabolites are given. Biological significance of enterolactone, a mammalian plant lignan
metabolite, has been studied quite extensively, but convincing evidence of the health benefits of the diverse pool of microbial
metabolites is still scarce. Hopefully, novel tools in systems biology and the constant search for biomarkers will elucidate
the role of the phenolic metabolome in health and in the prevention of chronic diseases. In conclusion, the colon is not only
an excretion route, but also an active site of metabolism and deserves further attention from the scientific community.
... Articles dealing with fermentation of PAs mainly focus on EPAs, whereas there are very few articles dealing with NEPAs. Moreover, most studies use isolated standards or concentrated extracts of PAs as test samples [9][10][13][14][15][16], whereas it is less common to study PAs as part of the food matrix [17,18]. ...
Proanthocyanidins (PAs) or condensed tannins, a major group of dietary polyphenols, are oligomers and polymers of flavan-3-ol and flavan-3, 4-diols widely distributed in plant foods. Most literature data on PAs' metabolic fate deal with PAs that can be extracted from the food matrix by aqueous-organic solvents ( extractable proanthocyanidins). However, there are no data on colonic fermentation of non-extractable proanthocyanidins (NEPAs), which arrive almost intact to the colon, mostly associated to dietary fibre (DF). The aim of the present work was to examine colonic fermentation of NEPAs associated with DF, using a model of in vitro small intestine digestion and colonic fermentation. Two NEPA-rich materials obtained from carob pod (Ceratonia siliqua L. proanthocyanidin) and red grapes (grape antioxidant dietary fibre) were used as test samples. The colonic fermentation of these two products released hydroxyphenylacetic acid, hydroxyphenylvaleric acid and two isomers of hydroxyphenylpropionic acid, detected by HPLC-ESI-MS/MS. Differences between the two products indicate that DF may enhance the yield of metabolites. In addition, the main NEPA metabolite in human plasma was 3,4-dihydroxyphenyl acetic acid. The presence in human plasma of the same metabolites as were detected after in vitro colonic fermentation of NEPAs suggests that dietary NEPAs would undergo colonic fermentation releasing absorbable metabolites with potential healthy effects.
... Moreover, Goel et al. (2005) showed in ruminants that tannins can be degraded by certain gastrointestinal bacteria and that hydrolysable tannins like Globatan Ò are more susceptible to hydrolysis and subsequent inactivation than condensed tannins (Goel et al., 2005). In addition to this, Abia and Fry (2001) showed that the amount of tannins that reaches the gut can differ from the orally administered amount of tannins in rats. Although the functioning of the digestive system of pigs and rats, and subsequently its effect on modification and/or degradation of tannins, can differ, extrapolation of our in vivo results must be made very carefully. ...
The aim of this study was to determine whether a hydrolysable tannin extract of sweet chestnut wood (Globatan(®)) has an inhibitory effect on Salmonella Typhimurium survival both in vitro and in vivo in pigs. In a first experiment, the minimal inhibitory concentration of Globatan(®) on 57 Salmonella Typhimurium isolates was determined. For all isolates, an MIC of 160-320 μg/ml was found. The second in vitro study revealed that Salmonella growth was strongly reduced using Globatan(®) concentrations of 25-50 μg/ml and nearly completely inhibited at a concentration of 100 μg/ml Globatan(®). In an in vivo trial, two groups of six piglets, each group receiving feed with or without the addition of Globatan(®) (3 g/kg), were orally inoculated with 10(7) colony forming units of a Salmonella Typhimurium strain. Globatan(®) had no effect on faecal excretion of Salmonella, and no differences in colonization of the intestines and internal organs were demonstrated in pigs euthanized at 4 days post-inoculation. In conclusion, the hydrolysable tannin extract used in this study showed strong action against Salmonella Typhimurium in vitro but not in vivo.
... In vivo, hydrolysis of procyanidins B2 and B5 to epicatechin has been reported in isolated rat small intestine [128]. The degree of polymerisation of proanthocyanidins has also been reported to decrease in rat small intestine [129]. Nevertheless, other in vivo findings suggest that oligomeric proanthocyanidins are not depolymerised into monomeric flavan-3-ols to any extent during passage through the stomach and gastrointestinal tract in rats, although trace quantities of procyanidin B1, B2, B3 and B4 dimers and the C2 trimer have been detected in urine [124]. ...
Tannins are a unique group of phenolic metabolites with molecular weights between 500 and 30 000 Da, which are widely distributed in almost all plant foods and beverages. Proanthocyanidins and hydrolysable tannins are the two major groups of these bioactive compounds, but complex tannins containing structural elements of both groups and specific tannins in marine brown algae have also been described. Most literature data on food tannins refer only to oligomeric compounds that are extracted with aqueous-organic solvents, but a significant number of non-extractable tannins are usually not mentioned in the literature. The biological effects of tannins usually depend on their grade of polymerisation and solubility. Highly polymerised tannins exhibit low bioaccessibility in the small intestine and low fermentability by colonic microflora. This review summarises a new approach to analysis of extractable and non-extractable tannins, major food sources, and effects of storage and processing on tannin content and bioavailability. Biological properties such as antioxidant, antimicrobial and antiviral effects are also described. In addition, the role of tannins in diabetes mellitus has been discussed.
... When 14 C-labeled PAs were given by gavage to rats, only a small proportion of the label was found in liver (1-1.5%), urine (1-2%) and carbon dioxide (1-2%) [1]. Polymeric PAs were catabolised by human colonic microbiota in vitro producing several phenolic acids: 3hydroxyphenylpropionic acid, 3-phenylpropionic acid, 4-hydroxyphenylpropionic acid and 4-hydroxyphenylacetic acid as major microbial metabolites [12]. ...
Proanthocyanidins (PAs) in apples are condensed tannins comprised mostly of (-)-epicatechin units with some terminal (+)-catechins. PAs, especially those having a long chain-length, are absorbed in the upper intestine only to a small extent and are passed to the colon. In the colon they are subjected to microbial metabolism by colonic microbiota. In the present article, the ability of human microbiota to ferment apple PAs is studied. Freeze-dried fruit preparations (apple, enzymatically digested apple, isolated cell-walls, isolated PAs or ciders) from two varieties, Marie Ménard and Avrolles, containing PAs of different chain lengths, were compared. Fermentation studies were performed in an in vitro colon model using human faecal microbiota as an inoculum. The maximal extent of conversion to known microbial metabolites, was observed at late time point for Marie Ménard cider, having short PAs. In this case, the initial dose also contributed to the extent of conversion. Long-chain PAs were able to inhibit the in vitro microbial metabolism of PAs shown as low maxima at early time points. Presence of isolated PAs also suppressed SCFA formation from carbohydrates as compared with that from apple cell wall or faecal suspension without substrates. The low maximal extents at early time points suggest that there is a competition between the inhibitory effect of the PAs on microbial activity, and the ability to convert PAs by the microbiota.
... Procyanidins B 2 and B 5 were also reported to be hydrolysed to epicatechin in the isolated rat small intestine (Spencer et al. 2001). The degree of polymerization of proanthocyanidins has also been reported to decrease in the rat small intestine (Abia & Fry, 2001). Other authors also suggested that procyanidin dimers might be degraded into catechin monomers by microflora in the colon although they did not report the presence of catechin as an intermediate breakdown product in their in vitro experiments (Groenewoud & Hundt, 1986;Déprez et al. 2000). ...
Flavanols are the most abundant flavonoids in the human diet where they exist as monomers, oligomers and polymers. In the present study, catechin, the procyanidin dimer B3 and a grape-seed extract containing catechin, epicatechin and a mixture of procyanidins were fed to rats in a single meal. After the meals, catechin and epicatechin were present in conjugated forms in both plasma and urine. In contrast, no procyanidins or conjugates were detected in the plasma or urine of any rats. Procyanidins were not cleaved into bioavailable monomers and had no significant effects on the plasma levels or urinary excretion of the monomers when supplied together in the grapeseed extract. We conclude that the nutritional effects of dietary procyanidins are unlikely to be due to procyanidins themselves or monomeric metabolites with the intact flavonoid-ring structure, as they do not exist at detectable concentrations in vivo. Future research should focus on other procyanidin metabolites such as phenolic acids and on the effects of the unabsorbed oligomers and polymers on the human gastrointestinal tract.
... It has been suggested that proanthocyanidins may be hydrolyzed into bioavailable monomers by acid present in the stomach. [66] The degree of polymerization of proanthocyanidins has been reported to decrease in the rat intestine, [67] and an energy dependent cleavage of dimers was described in the rat small intestine using intestine perfusion experiments. [68] In vivo experiments have failed to support this theory. ...
Flavonoids are components of fruit and vegetables that may be beneficial in the prevention of disease such as cancer and cardiovascular diseases. Their beneficial effects will be dependent upon their uptake and disposition in tissues and cells. The metabolism and pharmacokinetics of flavonoids has been an area of active research in the last decade. To date, approximately 100 studies have reported the pharmacokinetics of individual flavonoids in healthy volunteers. The data indicate considerable differences among the different types of dietary flavonoids so that the most abundant flavonoids in the diet do not necessarily produce the highest concentration of flavonoids or their metabolites in vivo. Small intestinal absorption ranges from 0 to 60% of the dose and elimination half-lives (T1/2) range from 2 to 28h. Absorbed flavonoids undergo extensive first-pass Phase II metabolism in the small intestine epithelial cells and in the liver. Metabolites conjugated with methyl, glucuronate and sulfate groups are the predominant forms present in plasma. This review summarizes the key differences in absorption, metabolism and pharmacokinetics between the major flavonoids present in the diet. For each flavonoid, the specific metabolites that have been identified so far in vivo are indicated. These data should be considered in the design and interpretation of studies investigating the mechanisms and potential health effects of flavonoids.
... In contrast, 14 C-labeled proanthocyanidins from sorghum (31), Lotus pedunculatus (32), and Ceratonia siliqua (33) were reported not to be absorbed in chickens, sheep, and rats, respectively. The discrepancies between these results are probably due to the insufficient purity of the proanthocyanidins used in the assays because of the complexity of their chemical structures, the difficulties involved in fractionating proanthocyanidins, the sensitivity and specificity of the measurements used to detect them in plasma and urine, and differences between the animals used in the assays. ...
In this study, we investigated the absorption of apple procyanidins, namely, apple condensed tannins (ACTs), in rats using the Porter method and high-performance liquid chromatography/tandem mass spectrometry. The apple procyanidin concentrations in the rat plasma reached a maximum 2 h after administration and decreased thereafter. To investigate the limits of the absorption of apple procyanidins in the polymerization degree, we administered the procyanidin oligomer fraction, which was separated from ACT using normal-phase chromatography according to the degree of polymerization. Procyanidins from each dimer to pentamer group were detected in the plasma by the Porter method. Moreover, by the study using reconstituted procyanidins, polymeric procyanidins influenced the absorption of procyanidin oligomers. These results suggest that ACTs are absorbed and directly involved in physiological functions in the rats.
This review covers recent advances in the synthetic labelling and biolabelling of dietary polyphenols over the last 10 years. During this period, the production of labelled flavans and their proanthocyanidin oligomers, isoflavones, lignans and stilbenes such as resveratrol, has received the most attention. Radiolabelled compounds are mostly used for tissue distribution and pharmacokinetic studies in animals. In parallel, methods for the synthesis of more easily handled compounds labelled with stable isotopes have been extensively developed. The use of both types of labelled compounds in metabolic studies has significantly contributed to the identification of metabolites produced by the intestine, the liver, and/or the colonic microflora.
Animal production systems in the tropical and subtropical countries utilize a wide range of feedstuffs; the main amongst these being the crop and industrial by-products, grasses, legumes, trees and shrubs. Trees and shrubs are of importance in animal production because they can provide significant protein supplements, especially in the dry season. But, the amount of tannins that they contain vary widely and largely unpredictably, and their effects on animals range from beneficial to toxicity and death. Similarly many agro-industrial by-products contain tannins. With a better understanding of tannin properties and proper management, they could become invaluable source of protein for strategic supplementation. As the demand for food rises, these unconventional feedstuffs must play an increasingly important part in the diet of animals, in particular for ruminants in small-holder farming in developing countries. It is therefore critical that proper techniques be used to measure and manage the anti-nutritional effects they cause. The analysis of tannins remains highly problematic. Various chemical assays for hydrolysable tannins and condensed tannins are available. Most tannin-containing feedstuffs contain both hydrolysable tannins and condensed tannins, but unfortunately only condensed tannins are generally analysed, probably because of simplicity of the assays measuring these; and the feedstuffs termed as tannin-containing or tannin-free feedstuffs. Furthermore, the biological effects are ascribed to mostly the condensed tannins (or the synonym: proanthocyanidins), which might be misleading. This paper reviews the available assays for hydrolysable tannins and condensed tannins and highlights the advantages and disadvantages of each. Protein precipitation assays, both isotopic and non-isotopic, representing the operational property of both hydrolysable tannins and condensed tannins; a tannin bioassay based on an in vitro simulation of the rumen and measurement of tannin activity for both free and bound tannins in terms of rumen fermentation parameters; and 14C-polyethylene glycol binding assay are also discussed. Each type of tannin responds differently in each of these assays. This variability makes it impossible to use any single method. Use of a battery of methods, therefore, is suggested; and these assays are being used in the FAO/IAEA-sponsored projects on the utilisation of tree foliage as livestock feed. Using these assays for 37 shrub and tree leaves, highly significant correlation existed between protein precipitation capacity and extractable total phenols (r = 0.87) or tannins (r = 0.83). On the other hand, a weak correlation was observed between condensed tannins (measured by the butanol-HC1 method) and protein precipitation capacity (r = 0.41), which could be due to the variation in structural and biological activity of tannins. The correlations observed between extractable total phenols, tannins or condensed tannins and the tannin bioassay values based on the rumen simulation technique were similar to those obtained between extractable total phenols, tannins or condensed tannins and protein precipitation capacity. Highly significant correlations between extractable phenolics or tannins with protein precipitation capacity or the values obtained using the tannin bioassay suggest that extractable total phenolics and tannins values could be taken as a measure of biological activity of tannins. The condensed tannins values by the butanol-HC1-iron method do not appear to reflect the biological activity. From the relationships between chemical, protein precipitation and bioassays, it was postulated that tree and shrub leaves with extractable total phenol and tannin contents of approximately 4.5% and 2.0% respectively (as tannic acid equivalent) will not produce significant adverse effects on ruminant livestock. The hydrolysable tannins, measured by an HPLC and a spectrophotometric method (rhodanine), were present in all the 37 samples (one having ca 14%; three between 1.5 and 3.5%; six ca 0.5% and the rest below 0.5%) analysed; and the hydrolysable tannins bind proteins, affect rumen fermentation, and could cause adverse effects similar to condensed tannins. Hydrolysable tannins are also known to be toxic and can cause death of animals if consumed in large quantities. The roles of rumen microbes in degradation and overcoming the detrimental effects of tannins, and the effects and fate of tannins in ruminants are also discussed. Simple methods based on postharvest technology, treatment with low-cost chemicals, biological treatments, and supplementation with tannin-complexing agents, to enhance the feeding value of tannin-containing feeds are needed.
Proanthocyanidins (PACs) are an abundant but complex class of polyphenols found in foods and botanicals. PACs are polymeric flavanols with a variety of linkages and subunits. Connectivity and degree of polymerization (DP) determine PAC bioavailability and bioactivity. Current quantitative and qualitative methods may ignore a large percentage of dietary PACs. Subsequent correlations between intake and activity are hindered by a lack of understanding of the true PAC complexity in many foods. Additionally, estimates of dietary intakes are likely inaccurate, as nutrient databank values are largely based on standards from cocoa (monomers to decamers) and blueberries (mean DP of 36). Improved analytical methodologies are needed to increase our understanding of the biological roles of these complex compounds. Expected final online publication date for the Annual Review of Food Science and Technology Volume 7 is February 28, 2016. Please see http://www.annualreviews.org/catalog/pubdates.aspx for revised estimates.
Bioactive components present in edible plants are of particular interest for the prevention of disease. Their widespread presence in common foods and dietary supplements has the potential to impact human health on the population level. Dietary phytochemicals can be generally classified into two distinct classes based on their absorption properties: water-soluble (phenolics and polyphenols) and lipid-soluble (carotenoids, tocochromanols, and curcuminoids). The bioavailability of dietary phytochemicals is a measurement of their prevalence in body fluids and exposure to tissues, and it is often considered when assessing their potential for beneficial and/or harmful activity. The biological activities and the resultant health benefits from phytochemical-rich foods have generated great interest in the elucidation of factors that impact the bioavailability of dietary phytochemicals. The aim of such research is primarily to identify food factors (macro- and microcomposition, physical form, phytochemical concentration, etc.) and in vivo biological factors (digestion, absorption, metabolism, distribution, and excretion processes) that can limit or promote bioavailability. Such knowledge is then used to improve the bioavailability of dietary phytochemicals and, by extension, their activities at the tissue of interest. This chapter discusses the factors contributing to the bioavailability of dietary phytochemicals as well as the measurement of bioavailability and its implications on health and disease.
Metabolism of flavanols (catechins, procyanidins) by gut microbiota has been extensively characterized. Comparatively little is known about accumulation of flavanols and their metabolites in the colon tissues, particularly during chronic exposure to low doses. Mice were fed low doses of cocoa flavanols for 12 weeks. Supplementation of the control diet with flavanols did not increase colonic tissue accumulation of flavanols nor microbial metabolites vs. control. The type of cocoa flavanols did not impact colonic tissue accumulation of native flavanolss or metabolites. Total phenolic content of the diets indicated that these results are not explained by background levels of undetected phenolics in the control diet. This is the longest known chronic flavanol feeding study to examine colonic tissue accumulation. Vast differences appear to exist between acute high doses and chronic low doses where gut microbiota and epithelium adapt to exposure. Our results indicate that we do not fully understand the fate of flavanols in the colon during chronic exposure.
Procyanidins have been extensively investigated for their potential health protective activities. However, the potential bioactivities of procyanidins are limited by their poor bioavailability. The majority of the ingested dose remains unabsorbed and reaches the colon where extensive microbial metabolism occurs. Most existing analytical methods measure either native compounds (catechins and procyanidins), or their microbial metabolites. The objectives of this study were to develop a high-throughput extraction and UPLC-MS/MS method for simultaneous measurement of both native procyanidins and their metabolites, facilitating high-throughput analysis of native and metabolite profiles in various regions of the colon. The present UPLC-MS/MS method facilitates simultaneous resolution and detection of authentic standards of 14 native catechin monomers and procyanidins, as well as 24 microbial metabolites. Detection and resolution of an additional 3 procyanidin dimers and 10 metabolites for which standards were not available was achieved. Elution and adequate resolution of both native compounds and metabolites were achieved within 10 min. The intraday repeatability for native compounds was between 1.1-16.5%, and the interday repeatability for native compounds was between 2.2-25%. Intraday and interday repeatability for metabolites was between 0.6-24.1% and 1-23.9%, respectively. Observed lower limits of quantification for native compounds were ∼9-350 fmol on-column, and for the microbial metabolites were ∼0.8-12,000 fmol on-column. Observed lower limits of detection for native compounds were ∼4.5-190 fmol on-column, and for metabolites were 0.304-6020 fmol on-column. For native monomers and procyanidins, extraction recoveries ranged from 38-102%. Extraction recoveries for the 9 microbial metabolites tested ranged from 41-95%. Data from tissue analysis of rats gavaged with grape seed extract indicate fairly high accumulation of native compounds, primarily monomers and dimers, in the cecum and colon. Metabolite data indicate the progressive nature of microbial metabolism as the digesta moves through the lower GI tract. This method facilitates the high-throughput, sensitive, and simultaneous analysis of both native compounds and their microbial metabolites in biological samples and provides a more efficient means of extraction and analysis than previous methods.
Acacia angustissima is a tropical legume which originated from Central America and has potential as a protein supplement to improve ruminant nutrition if the adverse effects of anti-nutritive factors can be diminished. It has a high nitrogen content and possesses many advantageous growth characteristics such a high leaf yield, drought tolerance, adaptation to acidic infertile soils and large temperature variations. However, the widespread implementation of supplementation practices with A. angustissima is currently impeded by reports of anti-nutritive/toxic effects in feeding trials with both monogastric and ruminant animals. Although the plant contains an array of secondary metabolites in high concentrations there have been few documented reports of toxicity under conventional feeding. The intent of this paper is to review the current knowledge on the secondary plant metabolites in A. angustissima, their toxic and anti-nutritive effects and investigations of rumen microbial interactions with these compounds. Condensed tannins, simple phenolics and non-protein amino acids have been investigated experimentally for their role in the reported toxicity of A. angustissima but recent studies have not been able to establish a definitive link between these classes of compounds and toxicity. Attempts to reproduce toxicity in the ruminant animal have also proved difficult particularly when the plant comprizes less than 300g/kg of the dry matter intake. Ruminal adaptation to the plant occurs in that the major non-protein amino acids are degraded by rumen microorganisms while the condensed tannins promote populations of organisms which are tolerant to these compounds. In vitro studies indicate that condensed tannins in the plant could severely impair nitrogen digestibilility whereas digestibility trials in ruminants show favourable responses in nitrogen utilization when A. angustissima is provided as a supplement. Further research needs to focus on feeding trials in ruminants which demonstrate the nutritional benefits and toxic potential of this plant at varying inclusion rates in the diet.
McSweeney, C.S., Odenyo, A. and Krause, D.O. 2002. Rumen microbial responses to antinutritive factors in fodder trees and shrub legumes. J. Appl. Anim. Res., 21: 181–205.The major limitation to ruminant production in many tropical regions of Africa, Asia and Australia is poor nutrition. Annual growth rates of animals are restricted by the low nitrogen and high fibre content of the native grasses and crop residues that form the basis of the diets in these regions. Supplementation of tropical roughages with fodder trees and shrubs (FTS) is a promising method to alleviate nutrient deficiencies associated with these basal diets. However, FTS often contain toxins and anti-nutritional factors (ANFs) that limit their use as feedstuffs. Selection and breeding for cultivars that are low in toxins/ANFs has not been successful since the presence of these compounds is strongly associated with survival in many tropical environments. A solution to the problem may be the rumen microorganisms from adapted domestic and wild ruminants that have evolved rumen fermentation mechanisms to transform or detoxify some of these plant secondary compounds. This review examines the use in ruminant feeding systems of FTS that contain deleterious secondary compounds; our current understanding of microbial interactions with these secondary compounds, and advances in the use of rumen biotechnology to overcome these limitations.
This paper examines the nutritional and veterinary effects of tannins on ruminants and makes some comparisons with non-ruminants. Tannin chemistry per se is not covered and readers are referred to several excellent reviews instead: (a) Okuda T et al.Heterocycles 30:1195–1218 (1990); (b) Ferreira D and Slade D. Nat Prod Rep 19:517–541 (2002); (c) Yoshida T et al. In Studies in Natural Product Chemistry. Elsevier Science, Amsterdam, pp. 395–453 (2000); (d) Khanbabaee K and van Ree T. Nat Prod Rep 18:641–649 (2001); (e) Okuda et al.Phytochemistry 55:513–529 (2000). The effects of tannins on rumen micro-organisms are also not reviewed, as these have been addressed by others: (a) McSweeney CS et al.Anim Feed Sci Technol 91:83–93 (2001); (b) Smith AH and Mackie RI. Appl Environ Microbiol 70:1104–1115 (2004). This paper deals first with the nutritional effects of tannins in animal feeds, their qualitative and quantitative diversity, and the implications of tannin–protein complexation. It then summarises the known physiological and harmful effects and discusses the equivocal evidence of the bioavailability of tannins. Issues concerning tannin metabolism and systemic effects are also considered. Opportunities are presented on how to treat feeds with high tannin contents, and some lesser-known but successful feeding strategies are highlighted. Recent research has explored the use of tannins for preventing animal deaths from bloat, for reducing intestinal parasites and for lowering gaseous ammonia and methane emissions. Finally, several tannin assays and a hypothesis are discussed that merit further investigation in order to assess their suitability for predicting animal responses. The aim is to provoke discussion and spur readers into new approaches. An attempt is made to synthesise the emerging information for relating tannin structures with their activities. Although many plants with high levels of tannins produce negative effects and require treatments, others are very useful animal feeds. Our ability to predict whether tannin-containing feeds confer positive or negative effects will depend on interdisciplinary research between animal nutritionists and plant chemists. The elucidation of tannin structure–activity relationships presents exciting opportunities for future feeding strategies that will benefit ruminants and the environment within the contexts of extensive, semi-intensive and some intensive agricultural systems. Copyright © 2006 Society of Chemical Industry
The non-extractable fraction of many fruit and vegetables contains putatively bioactive polyphenolic compounds that, in most cases, have not been well characterised structurally. Non-extractable proanthocyanidins (NEPA) of a polymeric nature are part of the dietary fibre fraction of food. Using liquid chromatography coupled to a mass spectrometer equipped with an electrospray ionisation chamber and a triple quadrupole mass analyser for tandem analysis (HPLC-ESI-QqQ-MS/MS) techniques, we examine the phenolic metabolites present in urine and faeces from rats 24 h after ingestion of an NEPA-rich fraction. We show that NEPA are partially depolymerised during their transit along the intestinal tract, as evidenced by the presence of (epi)catechin (EC) monomers and dimers in faeces and phase II conjugates of EC in urine. Moreover, NEPA are further metabolised by the intestinal microbiota into smaller metabolites including phenolic acids that are present in urine as both free phenolics and conjugates with glucuronate or sulphate moieties. For the first time, we report evidence that NEPA behave in vivo as a source of phenolics that are released progressively and deliver phenolic species that come into contact with the intestinal walls and are bioavailable for at least 24 h after ingestion.
The present research proved that grape seed extract could be used as hypocholesterolemic agent. Research: GSE was subjected to a series of experiments to document its AA, safety for use as a food supplement and/or phytochemical drug. We further compared the effects of GSE on the prevention and treatment of hypercholesterolemia. Our GSE was proven to have a potent AA and more efficient than ascorbic acid (Vitamin C), in addition to its safety for use as nutritional supplement where the LD50 value was 6.3 g kg-1. On other word, GSE is not toxic. The hypolipidemic effect of GSE was investigated at two levels, the preventive level and treatment level. It was found that GSE could prevent the hypercholesterolemia on which GSE lowered serum Total Cholesterol (TC) by 32%, Low-Density Lipoprotein (LDL) by 40% and elevated the High-Density Lipoprotein (HDL) by 23%. The current research, shows for the first time that GSE could be used for the treatment of hypercholesterolemia on which GSE reduced the serum TC by about 42% and LDL-C about 56%, while had elevation effect on the serum HDL-C by 56%. Therefore, both the LDL-C/HDL-C ratio and TC/HDL-C ratio were decreased by more than half, thus determining an improvement in the atherosclerotic risk index. In conclusion, GSE showed an obvious hypocholestrolemic effect that may have important pharmaceutical applications in the prevention and treatment of cardiovascular disease and atherosclerosis.
By means of the representative scientific publications review on the tannins biochemistry, the main results related to their beneficial and antinutritional properties from chemistry-analytical, in vitro and in vivo studies were presented. The paragraphs are greater relevance and the repercussion of the knowledge acquired on these compounds is described; in the development of viable strategies of feeding. Historically, until the chemistry of natural products was not developed quantitatively, the animal nutrition studies with phenolic forages sources were insufficient. The first tests made after 1950, were directed to the phytochemical characterization of the majority tannin sources and the determination of the biological activity of the main groups, with particular emphasis in fodder leguminous like additional resource of nutrients. In one second stage the analytical techniques were implemented and validated that would be used to describe the polyphenols antifeeding effect and its interaction with the primary and secondary metabolites. The critic concentrations, in which these compounds could affect the good digestive process of ruminants and monogastric were postulated. Besides, the detrimental action of tannins hydrolysables and condensed in different conditions of feeding was compared, determining the variables of greater influence in the toxicological action. Independently to that the investigations made until the present have contributed much information as far as the characteristics of vegetal tannins, at the present time exists important subjects such as, the mechanisms related to the antihelmintic effect, the ecological function of hydrolysables tannins in non leguminous species and the interaction of polyphenols with alkaloids; among others, that have not been boarded with force; reason why integral studies need to explain these urgent questions.
To assess the safety of grape seed extract with less than 5.5% catechin monomers (IH636), 4 groups of male and female Sprague-Dawley rats were provided grape seed extract in the diet at levels of 0 (control), 0.5, 1.0, or 2.0% for a period of 90 days. All animals survived the duration of the study, and no significant changes in clinical signs, hematological parameters, organ weights, ophthalmology evaluations, or histopathological findings were observed. A significant increase in food consumption was observed in male and female rats provided the grape seed extract diets compared to that of the control rats, especially in male rats consuming 2.0% grape seed extract. This effect was not accompanied by increases in body weight gains. Grape seed extract appeared to increase the insoluble fraction of the diet. Male rats in the high-dose group exhibited decreased serum iron levels and decreased serum iron/total iron binding capacity ratio compared to those of the controls, although all values were within historical ranges for Sprague-Dawley rats. In conclusion, administration of the grape seed extract IH636 to male and female Sprague-Dawley rats in the feed at levels of 0.5, 1.0, or 2.0% for 90 days did not induce any significant toxicological effects.
Three experiments were conducted to determine the fate of condensed tannins (CT) during digestion in sheep. CT were measured as extractable, protein-bound and fibre-bound fractions using the butanol-HCI procedure. In Expt 1, purified CT were added to digesta from different parts of the digestive tract obtained from a pasture-fed sheep. Recoveries of CT after 0 and 4 h of anaerobic incubation at 39° averaged: rumen 78.9 and 57.5 %; abomasum 50.9 and 49.0 %; duodenum 64.4 and 46.0 % and ileum 43.4 and 38.8%. In Expt 2, [14C]CT was given per abomasum over a 6.5 h period at 15 min intervals to a sheep previously fed on Lotus pedunculatus (which contains CT). The sheep was killed at the end of the period and 92.4% of the label was recovered. Virtually all of the label was in the digesta, and none was detected in the blood, so that the CT-carbon appeared not to be absorbed from the small intestine. In Expt 3, rumen, abomasal and ileal digesta and faeces samples from sheep fed on Lotus pedunculatus were analysed for CT and CT flow along the digestive tract calculated from reference to indigestible markers. Values were low in all digesta samples, indicating disappearance of CT across the rumen and small intestine, and CT recovery in faeces was only about 15% of intake. However, the 14C results from Expt 2 suggested that little if any CT-carbon was absorbed and the low recoveries in Expt 1 are considered to be a consequence of either conformational changes to the CT molecule such that it is no longer detectable by colorimetric methods, an inability of the analytical method to release bound CT for the butanol–HCI assay, or interference from other digesta constituents. It is concluded that the butanol–HCI method of CT analysis is appropriate for quantifying CT in herbages but not in digesta or faeces, and that a substantial part of CT released during protein digestion in the small intestine may not be detectable by normal CT analytical methods.
The proanthocyanidins or condensed tannins, phenolic polymers which are synthesized by many plants, characteristically bind and precipitate proteins. The specificity of the interaction was investigated using a competitive binding assay to compare directly the affinities of various proteins and synthetic polymers for the tannin obtained from Sorghum bicolor (Lin.) Moench. At pH 4.9, the relative affinities range over more than 4 orders of magnitude, indicating that this proanthocyanidin interacts quite selectively with protein and protein-like polymers. The affinity for tannins is an inverse function of the size of the polymer, and peptides with less than six residues interact very weakly with tannin. Proteins are precipitated by proanthocyanidins most efficiently at pH values near their isoelectric points. Proline-rich proteins and polymers have very high affinities for tannin. Tightly coiled globular proteins have much lower affinities for tannin than conformationally loose proteins.
Three experiments were conducted to determine the fate of condensed tannins (CT) during digestion in sheep. CT were measured as extractable, protein-bound and fibre-bound fractions using the butanol-HCl procedure. In Expt 1, purified CT were added to digesta from different parts of the digestive tract obtained from a pasture-fed sheep. Recoveries of CT after 0 and 4 h of anaerobic incubation at 39 degrees averaged: rumen 78.9 and 57.5%; abomasum 50.9 and 49.0%; duodenum 64.4 and 46.0% and ileum 43.4 and 38.8%. In Expt 2, [14C]CT was given per abomasum over a 6.5 h period at 15 min intervals to a sheep previously fed on Lotus pedunculatus (which contains CT). The sheep was killed at the end of the period and 92.4% of the label was recovered. Virtually all of the label was in the digesta, and none was detected in the blood, so that the CT-carbon appeared not to be absorbed from the small intestine. In Expt 3, rumen, abomasal and ileal digesta and faeces samples from sheep fed on Lotus pedunculatus were analysed for CT and CT flow along the digestive tract calculated from reference to indigestible markers. Values were low in all digesta samples, indicating disappearance of CT across the rumen and small intestine, and CT recovery in faeces was only about 15% of intake. However, the 14C results from Expt 2 suggested that little if any CT-carbon was absorbed and the low recoveries in Expt 1 are considered to be a consequence of either conformational changes to the CT molecule such that it is no longer detectable by colorimetric methods, an inability of the analytical method to release bound CT for the butanol-HCl assay, or interference from other digesta constituents. It is concluded that the butanol-HCl method of CT analysis is appropriate for quantifying CT in herbages but not in digesta or faeces, and that a substantial part of CT released during protein digestion in the small intestine may not be detectable by normal CT analytical methods.
Dietary tannins are reported to impair the absorption of nutrients and minerals in whole animals and in semi-isolated intestinal preparations. The present studies investigated the effect of purified procyanidin from black beans (Phaseolus vulgarus) on tissue electrical parameters, isotopic Na+ and Cl- fluxes and Na+-dependent absorption of labeled glucose by isolated rat ileum. In short-circuited ileal preparations, 0.5-2 g/L procyanidin (PC) inhibited Na+ and Cl- absorption and stimulated Cl- secretion, with consequent increases in short circuit current (Isc), total tissue conductance and transepithelial voltage. The effect was not blocked by indomethacin (20 micromol/L). Also, PC significantly inhibited the glucose-dependent and phlorizin-sensitive component of Isc; a similar result was obtained for the alanine-dependent fraction of Isc. In everted ileal sacs PC inhibited Na+-dependent uptake of labeled glucose, but not passive uptake, by a noncompetitive mechanism. The effects of PC are reminiscent of those of recognized intestinal secretagogues and suggest that the antinutrient effects of condensed tannins involve stimulation of intestinal secretion at the expense of absorption. The results argue against use of black bean broth or cooking liquor in rehydration media for treatment of secretory diarrhea.
In livestock diets, tannins may diminish weight gains, apparent digestibility and feed utilization efficiency. These antinutritional effects have generally been attributed to inhibition by tannins of digestion of dietary proteins. Other effects associated with dietary tannin are systemic, requiring absorption of inhibitory material from the digestive tract into the body. We have been investigating this problem using ¹⁵N-labelled protein, ¹⁴C-labelled tannins, and drugs such as propranolol which inhibit the secretion of specialized proline-rich tannin-binding salivary proteins that otherwise diminish the antinutritional effects. Dietary tannins do somewhat inhibit the digestion of protein, but the evidence suggests that the protein affected is largely endogenous, not dietary, and that this inhibition accounts for only a small part of the antinutritional effects. Inhibition of digestion seems to be less significant than inhibition of post-digestive metabolism, a systemic effect. Low MW polyphenol components associated with tannins are more readily absorbed from chick diets than are tannins, and may account for the major antinutritional effects.
A procedure was developed for extraction of ‘free’ condensed tannins (CT) using a mixture of acetone/water/diethyl ether (4.7:2.0:3.3), followed by extraction of protein-bound and fibre-bound CT using boiling sodium dodecyl sulphate containing 2-mercaptoethanol (SDS). CT concentrations in all three fractions were determined by a modified butanol-HCI procedure. Separate standard curves using purified CT in water or SDS solution were utilised for analysis of extractable CT (water standards) and protein-bound and fibre-bound CT (SDS standards). The method accurately predicted the concentration of CT added to forage extracts. CT extractable in acetone/water/diethyl ether comprised, on average. 68% of total CT in a range of freeze dried forage legume samples, with most of the remainder being bound to protein. When total CT concentration was low (0.6-3.0% DM), a lower proportion was extractable (33-35%). In protein concentrate meals containing CT, the extractable, protein-bound and fibre-bound components comprised 15, 60 and 25% respectively of total CT. Total CT concentration in the forages Lotus corniculatus and Coronilla varia was considered appropriate for ruminant nutrition (2.1 and 3.0% DM). whilst CT concentration in the forage of Dorycnium spp (13–19% DM) was more suitable for soil conservation purposes. The substantial CT concentration in cottonseed meal (1.6% DM) may be involved in the high resistance of proteins in this product to ruminal degradation. CT concentration was indistinguishable from zero in perennial ryegrass forage, in barley and triticale grains and in soya bean meal (0.1% DM).
The macromolecules of plants are distinguished from all other constituents by their high molecular weight. This may vary from 10000 to over 1000000, whereas in other plant metabolites the molecular weight is rarely above 1000. Chemically, macromolecules consist of long chains of small structural units or ‘building blocks’, linked covalently in a number of different ways. Chemical characterization in the first instance therefore depends on identifying these smaller units. Proteins, for example, are long chains of amino acids (up to twenty different ones) joined together through peptide (—CO—NH—) links. Polysaccharides are similarly derived from the union of simple sugar units, such as glucose, joined through ether (—O—) links. The nucleic acids, by contrast, are more complex and have three types of structural unit: purine and pyrimidine bases, pentose sugars and phosphate groups. The three main classes of macromolecules found in plants are thus proteins, polysaccharides and nucleic acids. However, mixed polymers are also known. such as the glycoproteins, which contain both sugars and amino acids in covalent linkage.
Condensed tannins have been isolated from legume pasture species and purified by gel chromatography on Sephadex G-50 and LH-20 media. Molecular size di
Three O-β-glucosides of procyanidin polymers (condensed tannins) have been isolated from the ripe fruits of Cydonia oblonga (quince) and the barks of Pinus brutia and Picea abies.
A proanthocyanidin (PA) polymer, a condensed tannin, was isolated, purified and characterized from the leaves of Leptarrhena pyrolifolia. The predominant extension units in the polymer were (−)-epicatechin and (+)-gallocatechin with traces of (−)-epigallocatechin. (+)-Catechin was the predominant terminal unit. The PA polymer contained both prodelphinidin and procyanidin units in the estimated ratio of ca 1. The cis:trans ratio and the number-average Mr of the polymer were determined and are discussed.
The complexation of phenols with proteins has been quantitatively examined using a range of physical methods; a theory is put forward for the precipitation of proteins from solution by complex polyphenols and by simple phenols.
The fate of retrograded and gelatinized bean starch in the rat was followed using an in vivo radiolabel technique. [U-14C]Bean starch was obtained by incubating excised unripe pods of broad beans with 14CO2. After extraction and purification, [14C]bean starch was either retrograded or gelatinized and fed to rats by gavage. Rats were housed individually in metabolic cages and were given free access to food and water. After 3 and 18 h of gavage, rats were killed by cervical dislocation and the radioactivity was measured in gut contents, tissues, feces, urine, and CO2. The rate and extent of degradation of [14C]starch in the small intestine were lower for 14C-retrograded starch, as indicated by the high amounts of α-glucans of degree of polymerization >70 in the distal fraction of the small intestine 3 h after gavage. After 18 h of gavage, the percentage of radioactivity present in tissues, feces, and urine was higher in rats fed 14C-retrograded starch. The [14C]starch degradation products were mainly metabolized by the carcass, pelt, liver and intestinal tissues. Keywords: Retrograded starch; gelatinized starch; small intestine degradation; starch metabolism
This text is a comprehensive reference covering the chemistry, physiology, chemotaxonomy, biotechnology and food technology aspects of the anthocyanins. Topics discussed include types of anthocyanins, structural transformations, colour stabilization and intensification factors, biosynthesis and intensification factors, biosynthesis, analysis and functions of anthocyanins. An in-depth review of the literature discussing anthocyanins of fruits, cereals, legumes, roots, tubers, bulbs, cole crops, oilseeds, herbs, spices, and minor crops is included as well.
The flavonoids and condensed tannins of the heartwood of Acacia baileyana var. purpurea are described. In conformity with other Acacia species, the hydroxylation pattern of the flavonoids is of the resorcinol type but, in sharp contrast, the tannins are heterogeneous consisting of a mixture of the resorcinol and phtoroglucinol series. Dimeric proanthocyanidins of the phloroglucinol type were absent and this exception to the general observation that they invariably co-occur with the polymers may be explained by the relative nucleophilicity of the aromatic A-rings.
Effects of MW, stereochemistry of monomer units, and B-ring oxidation pattern on relative astringency were studied. Efficiency of protein precipitation is primarily a function of proanthocyanidin polymer (condensed tannin) size and whereas oligomeric proanthocyanidins have a relative astringency less than tannic acid, polymeric proanthocyanidins of sufficiently high average MW (Mn∼2500) are equally as efficient at precipitating haemoglobin.
[14C]Cinnamate was taken up very rapidly by cultured spinach cells and completely incorporated into low-MW conjugates within 20 min. The 14C-labelled products were similar whether the [14C]cinnamate was supplied continuously over a period of hours via a peristaltic pump or instantaneously. Radioactivity was slowly recruited from the low-MW pool into aromatic components of the cell-wall fraction. Saponification of the radioactive wall fraction yielded, in addition to radioactive ferulate and p-coumarate, large amounts of ethyl acetate-soluble radioactive material with the properties of oxidatively coupled phenols. The coupled material was associated with the most highly ‘Driselase’-resistant fractions of the cell wall. In contrast, ‘Driselase’ released most of the wall's ferulate and p-coumarate on disaccharide fragments. It is suggested that the oxidatively coupled phenols are formed from simpler phenols by peroxidase and that they cross-link the polysaccharides to which they are attached, making these polysaccharides relatively ‘Driselase’-resistant.
The molecular weight distribution of tannins from the wood, bark and leaves ofEucalyptus camaldulensis, E. globulus andE. rudis from two different Spanish provenances has been studied by high performance gel permeation chromatography, using the compounds' acetylated derivatives. The MW distribution profiles showed important variability depending on the type of vegetal tissue, the species and, in some cases, on the geographical provenance of the samples. Bark was the vegetal tissue that yielded tannins with the highest molecular weight, followed by wood and leaves. Tannins from wood and bark ofE. camaldulensis were of higher molecular size than those fromE. globulus andE. rudis; those in the leaves ofE. globulus andE. camaldulensis were similar in molecular size and larger than those in the leaves ofE. rudis.
Homogeneous polymeric proanthocyanidins have been isolated from 22 plant sources and all are based on a C(4)–C(8)[or C(6)] linked polyflavan-3-ol structure. 13C N.m.r, spectroscopy in 2[H6]acetone–water is used to calculate the ratio of procyanidin to prodelphinidin monomer units, the average heterocyclic ring stereochemistry of the monomers, and the ratio of monomers to chain-terminating units. The majority of polymers isolated in this study possess monomers with predominantly a 2,3-cis stereochemistry [the same configuration as (–)-epicatechin]. The number-average molecular weight, calculated from monomer to terminal unit ratios, of the polymers is 1 500–5 000. The structure of the chain-terminating group is established by thiolysis degradation and g.l.c. analysis of the products.
The isolation and determination of structure of some plant procyanidins in their free phenolic forms are described. The distribution of procyanidins in the tissues of twenty-nine plant species has been examined and the biogenetic implications of this study are briefly discussed.
The MW profiles of proanthocyanidin polymers (condensed tannins) from 32 samples representing a wide range of plant tissues of many different species have been obtained by gel permeation chromatography of the peracetate derivatives. The tannins vary widely in MW, with M̄n values for the peracetates in the range 1600–5500. The MW profiles vary greatly from those with narrow, rather smooth distributions, to those which are discontinuous.
Different derivatization methods for hydrolysable tannins were compared and assessed for calibration of gel permeation systems. Methylation of ellagitannins such as vescalagin or castalagin with either diazomethane or dimethyl sulphate yields small amounts of the expected permethylated products together with several by-products resulting from the cleavage of some ester bonds. Acetylation with acetic anhydride—pyridine mixture of the same ellagitannins gives a unique product from each compound, which is partially degraded if the excess of reagent is destroyed by addition of water or methanol. In contrast, application of the same methods to β-penta-O-galloyl-d-glucose and gallic acid gives a unique permethylated product or a relatively more stable peracetate. The best calibration graph for gel chromatography on Styragel columns with tetrahydrofuran as eluent was obtained with peracetylated derivatives.
The protein precipitating capacity of canola tannins was evaluated using the protein precipitation assay of Hagerman and Butler (J. Agric. Food Chem. 1978, 26, 809−812) and the dye-labeled bovine serum albumin (BSA) assay of Asquith and Butler (J. Chem. Ecol. 1985, 11, 1535−1543). Condensed tannins were isolated from hulls of Cyclone, Excel, and Westar canola cultivars. The tannin content in the hulls ranged from 98 to 1973 mg of catechin equivalents/100 g of hulls, as determined by the vanillin assay. The effect of pH on the affinities of dye-labeled and unlabeled BSA, fetuin, gelatin, lysozyme, and pepsin was monitored. The optimum pH for the precipitation of dye-labeled and unlabeled BSA was found to be 3.5 and 4.0, respectively. The optimum pH for the precipitation of proteins was found to be 0.3−3.1 pH units below the isoelectric points of the proteins. The crude tannin extracts contained about 20% proanthocyanidins, which were soluble in ethyl acetate as determined by the vanillin assay. Canola tannins showed definitive thresholds prior to the formation of insoluble tannin−protein complexes as determined by the protein precipitation assay. There was also a linear correlation (r2 = 0.975) between the amount of tannin−protein complex formed and the amount of tannin added to the system. Ethyl acetate soluble proanthocyanidins contributed to the protein-precipitating capacity of crude canola tannins isolated from low-tannin Cyclone canola hulls. Keywords: Condensed tannins; canola; hulls; tannin−protein interactions
Nitrogen-corrected true metabolizable energy (TMEn) and true amino acid digestibility values were determined, using cecectomized cockerels, for 20 sorghum [Sorghum bicolor (L.) Moench] cultivars that ranged in catechin equivalent (CE) percentages from 0 to 3.88. There were significant (P ≤ 0.01) overall inverse relationships between CE content and (1) the individual digestibilities of lysine, methionine, threonine, isoleucine, leucine, valine, phenylalanine, histidine, and arginine; (2) the mean digestibility of essential amino acids; (3) the mean digestibility of nonessential amino acids; and (4) TMEn values. In contrast to these overall trends, several cultivars of similar condensed tannin content had markedly different nutrient digestibilities. The dissimilarity of protein digestibilities in sorghum genotypes of similar tannin content was confirmed by subjecting samples of the ground grains to in vitro pepsin digestion with subsequent visualization of the undigested proteins by SDS−PAGE. The present work suggests that other components besides tannins are responsible for variations in the availability of nutrients in sorghum. Keywords: Sorghum; tannin; amino acid digestibilities; true metabolizable energy; TMEn; pepsin digestibility; chicken
The tannin content of crude plant exts. or of purified prepns. was detd. by adding the sample to a std. soln. of protein, isolating the insol. tannin-protein complex, dissolving it in alk. soln., and measuring the absorbance at 510 nm after adding FeCl3. Plots of absorbance as a function of the amt. of tannin are linear for 0.20-1.0 mg tannic acid and partially purified sorghum tannins. Nontannin components of crude MeOH exts. of sorghum and cowpeas do not interfere with the assay. The results of the pptn. method are qual. similar to those obtained by vanillin assay. The pptn. assay can be used to study the effects of pH and other parameters on tannin-protein interactions
To evaluate the type of binding involved, thermodynamic analysis of the temperature dependence of proanthocyanidin binding to bovine serum albumin (BSA) and bean glycoprotein G-1 (G-1) was investigated. Binding was analyzed with tritiated proanthocyanidin by ultrafiltration to separate free ligand and protein-bound ligand. Binding constants were determined from Scatchard plots. Van't Hoff plots indicated proanthocyanidin binding to BSA was spontaneous and entropy driven. Analysis with cis-parinaric acid supported the conclusion drawn from the thermodynamic analysis that the binding of proanthocyanidin to BSA was a hydrophobic interaction. Van't Hoff plots indicated proanthocyanidin binding to native G-1 protein was also spontaneous but, in contrast to BSA, enthalpy driven. Analysis with cis-parinaric acid confirmed the hydrophilic character of proanthocyanidin binding to native G-1. Evaluation of proanthocyanidin binding to heat-denatured G-1 with cis-parinaric acid indicated hydrophobic interactions.
Condensed tannins from sorghum [Sorghum bicolor (L.) Moench.] seeds are the only type of tannins found in this plant and are commonly associated with toxic effects in animals fed diets based on high-tannin sorghum grains. However, it is still not certain whether those polyphenolic polymers are absorbed from the digestive tract. Condensed tannin and other related phenolic fractions from sorghum seeds were metabolically radiolabeled with 14C and separately fed to Hubbard White Mountain chicks. Their tissues were examined to determine the absorption and distribution of the polyphenolic fractions. Immature high-tannin sorghum seeds (Dekalb BR-64) were radiolabeled with NaH14CO3 or 14CO2, and various phenolic compounds were purified according to the method of Reddy and Butler (J. Agric. Food Chem. 1989, 37, 383-384). Radiolabeled condensed tannin and non-tannin phenolic fractions were lyophilized and separately placed into starch capsules, and each capsule was placed into the crop of chicks. Eight hours later, blood samples were taken by cardiac puncture, the birds were killed by excess CO2 inhalation, tissue samples were excised, and total excreta were collected. Analyses of 14C distribution in chick tissues and excreta suggest that radiolabeled condensed tannins from sorhum grain were not absorbed from the digestive tract of chickens. However, 14C from non-tannin fractions was absorbed and distributed in various tissues. It is proposed that low molecular weight polyphenols present in these fractions may be partially responsible for the toxic effects seen in chickens fed high-tannin sorghum diets.
The effect of genetic removal of condensed tannins on the levels of other antinutritional factors in faba beans (Vicia faba L.) has been studied by comparison between partners of six near-isogenic pairs for trypsin inhibitor activities (TIA), concentrations of lectins and pyrimidine glucosides (vicine and convicine), seed weight, and the proportion of testa thereof. Each near-isogenic pair consisted of two lines which were genetically almost identical, apart from the absence [tannin-free (TF)] or presence [tannin-containing (TC)] of condensed tannins. Within these pairs no effect of tannin content was observed on cotyledon-bound TIA or lectin concentrations. Seeds of the TF lines showed higher levels of pyrimidine glucosides, lower seed weight, and lower proportion of testa as compared to the TC lines of the same near-isogenic pair. Methanolic extracts from testa of exclusively the TC lines showed significant TIA with both porcine and bovine trypsin. This TIA was completely inhibited by 1% poly(vinylpyrrolidone). These data indicate that condensed tannins are responsible for the testabound TIA. The observations are discussed in relation to the consequences of breeding faba beans, free of condensed tannins, for the agricultural characteristics and for the nutritional quality of the crop.
The composition of mesquite pods (Prosopis pallida L) (PP), a legume cultivated in the large desert areas of Peru, was studied. These fruits have at the present time very little practical or commercial use. Taking into account the morphological and compositional similarities to Mediterranean carob pods (Ceratonia siliqua L) (CS), which are widely used in the food industry, some applications of PP are considered. PP shows better nutritional properties than CS, mainly owing to its lower polyphenolic content and higher protein digestibility.
Determination of the tannins, pectins, hemicellulose, cellulose, nitrogen, mineral elements, total and reducing sugars and fat contents was carried out on carob pods from Mallorca, Spain. The results are compared with data from the literature. A survey of papers on the composition and practical applications of carob pods is included.
Feruloyl and p-coumaroyl groups in spinach cell walls (CW) were labelled using [14C]cinnamic acid and fed to rats. In the caecum and colon, ferulic acid (FA) and p-coumaric acid (PCA) were released from the CW. Few feruloyl or coumaroyl groups remained in the CW to be excreted in faeces, and thus the presence of simple phenol–sugar esters provided little protection of the polysaccharides to enzymic attack. Some oxidatively coupled phenols were also released but a portion remained in the CW. The oxidatively coupled phenols accumulated in the gut whereas the FA and PCA were absorbed by the rat. Thus enzyme-resistant fragments, containing oxidatively coupled phenols (and possibly sugar residues), may survive microbial attack by rat intestinal bacteria.
The possible degradation of non-extractable condensed tannins (NECT) within the intestinal tract and their effect on faecal weight and composition was studied. Two groups of male Wistar rats were fed either a NECT-free control diet, or a diet containing 100 g carob pod concentrate kg−1 (53 g NECT kg−1 dry matter) for 5 weeks. A slight effect of NECT on growth rate was observed in the fifth week. The NECT diet did not affect food intake. Significant increases of total faecal output as well as water, nitrogen and fat excretion were observed. NECT were not degraded in the intestinal tract, since they were quantitatively recovered in faeces (98 ± 1%). Since the usual spectrophotometric methods gave contradictory results on NECT levels in the diet and faeces, an alternative method based on Klason lignin residues was used.
Tannins isolated from ripe carob pods were subjected to thioglycolic acid degradation and mild and strong acid hydrolysis. Mild acid hydrolysis did not degrade the tannins, strong acid hydrolysis resulted in the production of delphinidin, cyanidin and pelargonidin. The ethyl acetate-soluble thioglycolic acid degradation products were identified by paper chromatography, UV and IR spectral analysis as (−) epigallocatechin, (−) epigallocatechin gallate and (−) epicatechin gallate. The minimum molecular weight of the polymers, 3200, was estimated on Sephadex columns. It is concluded that the polymeric condensed tannins from ripe carobs consist of subunits of flavan-3-ols and their gallate esters.
Methanol extracts of Larix gmelini bark yielded (−)-epiafzelechin, (+)-catechin and (−)-epicatechin, dimeric procyanidins B-1, B-2, B-3 and B-4 and oligomeric procyanidins. Chemical degradation of the oligomers using toluene-α-thiol and acetic acid showed the oligomers to have flavan-3-ol terminal units possessing either the 2,3-trans (catechin) or 2,3-cis (epicatechin) stereochemistry, with the former predominating. Likewise the extension units were shown to consist of flavan-3-ol units with 2,3-trans or 2,3-cis stereochemistry in roughly equal proportion. The average degree of oligomerization was calculated as 6–7 and the number average molecular weight as 1700–2000. The structure of the residual procyanidins remaining in the bark after methanol extraction is also briefly commented upon. Larixinol is shown to have an unusual spirobiflavonoid structure and a pathway of biogenesis is proposed.
The grain of some varieties of sorghum contains 2% or more condensed tannin; many other varieties contain no tannin at all.
Agronomic advantages, e.g., resistance to bird depredation, are associated with high-tannin sorghums, which have relatively
low nutritional value for nonruminants. The biological effects of tannin are a result of its propensity for binding proteins;
both hydrogen bonding and hydrophobic interactions are involved. Sorghum tannins can bind dietary proteins and reduce their
digestibility. Purified digestive enzymes are inhibited by tannin, but significant inhibition in vivo is unlikely. Proteins
differ greatly in their affinity for tannin. Those with highest affinity are large, have an open structure, contain no bound
carbohydrate and are rich in proline. Sorghum proteins of the alcohol-soluble prolamine fraction associate strongly with tannin,
are difficult to remove during tannin purification and are found combined with tannin in the indigestible residue after in
vitro digestion with pepsin. On germination, the seed may sacrifice a portion of these proteins to bind the tannin that might
otherwise interfere with metabolism by inhibiting seed enzymes. During seed development, tannin molecules are relatively short
and do not effectively precipitate proteins; as the seed dries, tannins undergo polymerization to an average of ca. 6 flavan-3-ol
units/molecule. The antinutritional effects of sorghum tannins can be eliminated by soaking the grain in dilute aqueous alkali,
but not by cooking. When rats are put on high-tannin sorghum diets, their parotid glands undergo hypertrophy and produce a
group of unique salivary proteins with extremely high affinity for tannin. These proteins contain over 40% proline and are
devoid of sulfur-containing and aromatic amino acids. This metabolic adaption may protect rats against tannin by binding and
inactivating it immediately when it enters the digestive tract.
Fractionation of a grape (Vitis vinifera) seed extract yielded various natural procyanidin dimers and trimers isolated and identified for the first time in grapes: procyanidin dimers B5 [epicatechin-(4β → 6)-epicatechin], B6 [catechin-(4α → 6)-catechin] and B8 [catechin-(4α → 6)-epicatechin]; four procyanidin trimers [epicatechin-(4β → 6)-epicatechin-(4β → 8)-epicatechin], [epicatechin-(4β → 8)-epicatechin-(4β → 6)-catechin], [epicatechin-(4β → 8)-epicatechin-(4β → 6)-epicatechin], [epicatechin-(4β → 6)-epicatechin-(4β → 8)-catechin] along with five galloyl procyanidins: B2 3-O-gallate, B1 3-O-gallate, B4 3′-O-gallate, B2 3,3′-di-O-gallate and [epicatechin-(4β → 8)-epicatechin 3-O-gallate-(4β → 8)-catechin]. The presence of (+)-catechin, (−)-epicatechin, (−)-epicatechin 3-O-gallate, procyanidins dimers B1, B2, B3, B4, B7, B2 3′-O-gallate and procyanidin trimers C1 and [epicatechin-(4β → 8)-epicatechin-(4β → 8)-catechin] was also confirmed. The structures of all these compounds were elucidated by enzymatic hydrolysis, complete acid hydrolysis, partial acid-catalysed degradation with phloroglucinol and phenylmethanethiol, FABMS and 1H NMR. Separation of procyanidins and of their phloroglucinol or phenylmethanethiol adducts was achieved by TLC on silica plates and HPLC.
The aim of the study was to compare the effect of a soluble fiber (citrus pectin) and prefermented condensed tannin (Quebracho) on the cecal fermentations, bile acids excretion and lipid metabolism in rats fed semi-purified diets. Analysis of the fermented tannin established than it is rich in monomers and trimers with little highly condensed polymers. Food intake and weight gain were not affected by addition of 5% citrus pectin or 1% Quebracho tannin in the diet. In the cecum, there was evidence of a depolymerization of polymers and of degradation of monomers, together with an accumulation of polar phenolic compounds. There was a significant enlargement of the cecum and of the volatile fatty acids (VFA) pool in rat fed the pectin diet; the Quebracho diet depressed the cecal VFA concentrations, compared to controls. The 1% Quebracho diet enhanced bile acids excretion, but the 5% pectin diet did not. In contrast, plasma cholesterol was depressed more effectively by pectin than by Quebracho. Both diets increased the activity of liver HMG-CoA reductase, a rate limiting enzyme of cholesterogenesis. The data show that, at a relatively low level in the diet, condensed tannins and soluble fibers may affect lipid metabolism by distinct mechanisms, which could be complementary in natural product diets.