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Variation in Oxalic Acid Content among Commercial Table Beet Cultivars and Related Crops
Abstract
Oxalic acid (C 2 O 42– ) is a compound of interest as a result of its relationship with kidney stone formation and antinutritive properties. Because table beet [ Beta vulgaris ssp. vulgaris (garden beet group)] is considered a high oxalate food, breeding to decrease oxalic acid levels is an area of interest. In this study, a field trial was conducted over 2 years for 24 members of the Chenopodiaceae using two different planting dates to determine if variation exists for both total and soluble oxalic acid levels in roots and leaves. Total and soluble oxalic acid was extracted from homogenized root core and leaf tissue samples and a colorimetric enzymatic assay was used to determine total and soluble oxalic acid levels. Mean values ranged from 722 to 1909 mg/100 g leaf tissue and 553 to 1679 mg/100 g leaf tissue for total and soluble oxalate levels, respectively. Beet cultivar Forono and swiss chard [ B. vulgaris ssp. vulgaris (leaf beet group)] cultivar Burpee's Fordhook Giant Chard produced the respective highest and lowest soluble and total oxalic acid leaf levels. Swiss chard cultivars produced 38% less total oxalate compared with table beet cultivars based on overall means. Root soluble oxalate values ranged from 103 to 171 mg/100 g root tissue and total values ranged from 95 to 142 mg/100 g root tissue. Significant variation for both total and soluble oxalic acid levels were detected, indicating progress could be made toward breeding for lower oxalic acid levels in table beet. However, gains in oxalic acid nutritional quality may be limited because it would take a substantial decrease in levels for table beet to be reclassified as a low oxalate food.
... Previous studies have shown that geosmin production in table beets is cultivar-specific (Freidig and Goldman 2011), and that geosmin is being produced endogenously within the beet (Maher and Goldman 2018). Geosmin has been shown to be a heritable trait that can be selected both for and against (Maher and Goldman 2017), although concentrations may be affected by genotype × year and year × location interactions (Hanson and Goldman 2019). ...
... Many food crops in the Amaranthaceae family, including beets, are classified as high-oxalate foods. High concentrations of oxalic acid can cause a burning sensation when beets are eaten raw (Freidig and Goldman 2011), and diets rich in oxalic acid may contribute to the formation of kidney stones (Noonan and Savage 1999). Additionally, oxalic acid may possess antinutritive qualities because it binds to calcium and other minerals and reduces the bioavailability of these nutrients (Wanasundera and Ravindran 1992). ...
... Understanding the mechanisms and trends by which compounds that affect flavor and eating quality change with regard to time can assist plant breeders with the development and optimization of methods of selecting for or against these compounds by allowing them to more efficiently allocate resources, personnel, and equipment, and by enabling them to make selections earlier or with greater confidence. Although the effects of early and late planting dates have been examined in the table beet oxalic acid concentration (Freidig and Goldman 2011) and TDS (Gaertner and Goldman 2005), an analysis of geosmin, oxalic acid, and TDS in tissue collected at multiple time points over the season has never been performed. Diurnal measurements of the geosmin concentration and TDS in table beet have not been reported, and the findings of these experiments may influence the degree to which researchers rely on refractometer data as a proxy for the sucrose concentration in table beet. ...
Consumers perceive flavor as a critically important attribute of vegetable crops. Gas chromatography-mass spectrometry (GC-MS), spectrophotometry, and refractometry of tissue samples collected during multiple years from table beet ( Beta vulgaris ) at various stages of maturity were performed to characterize the endogenous production of geosmin, oxalic acid, and total dissolved solids within the root. The geosmin concentration was primarily influenced by the cultivar and peaked early during the growing season, with root concentrations at 6 weeks after planting that were 312% higher, on average, than those found in harvest stage roots at 15 weeks after planting. The highest average concentration of geosmin in harvest stage roots was detected in tissue from the cultivar Bull’s Blood (16.08 μg⋅kg ⁻¹ ). The oxalic acid concentration showed a strong cultivar influence and statistically significant variability across the growing season. Hybrid beet cultivar Boro had the lowest soluble oxalic acid concentration (95.73 mg⋅100 g ⁻¹ fresh tissue) at all locations and during all years. The oxalic acid concentration peaked 12 weeks after planting, and it was lower at the postharvest sampling date 18 weeks after planting. Total dissolved solids (TDS) concentrations were strongly influenced by year and growing environment and displayed crossover interactions for environment × week. TDS measurements had a moderate negative correlation with root mass. ‘Chioggia Guardsmark’ consistently had the highest TDS during all years and at all locations at 12.01 °Brix. The TDS varied significantly according to time, and diurnal sampling revealed fluctuations as large as 4 °Brix over the course of a 12-hour period. The TDS concentrations increased throughout the growing season, although the rate at which they increased changed according to plant age. The results from this study suggest that interactions between cultivar, time, and environment are important determinants of oxalic acid and TDS concentrations, but they have less influence on geosmin. This information may influence the methods that plant breeders use to collect phenotypic data of important flavor compounds in beets.
... Geosmin has proven difficult to remove from water sources, and its removal is even more challenging in table beet due to its endogenous production within the plant (Hanson & Goldman, 2019;Maher & Goldman, 2018). Oxalic acid often causes a burning sensation and, although beneficial to plant defense (Fasset, 1973), can be harmful to humans as the main component of kidney stones and driver of decreased bioavailability of other nutrients, notably calcium (Altamirano et al., 2018;Brogren & Savage, 2003;Freidig & Goldman, 2011;Noonan & Savage, 1999). Oxalic acid can be reduced by cooking the raw material; however, challenges arise for the fresh eating market (Yadav & Sehgal, 2003). ...
Sweetness is a main component of the table beet (Beta vulgaris L.) flavor profile and a key determinant of its market success for fresh consumption. Total dissolved solids (TDS) is a proxy for sugar content in produce and are easily measured through a refractometer, making TDS valuable in breeding programs focused on increasing sweetness. A diversity panel of 238 accessions from the Beta vulgaris crop complex and wild relatives was assembled and genotyped using genotyping‐by‐sequencing, yielding 10,237 single nucleotide polymorphisms (SNPs) from 226 full panel accessions and 9,847 SNPs from table beet only accessions after filtering. The panel was phenotyped in field trials over 2 years and mean values were adjusted using best linear unbiased estimates. TDS levels varied among crop types and a broad‐sense heritability of 0.90 indicated that phenotypic differences can be attributed in large part to genetic variation. A genome‐wide association study (GWAS) uncovered four quantitative trait loci (QTLs) identified across multiple models to significantly associate with TDS. A QTL on chromosome 2 was consistently identified among GWAS models, explaining 12.1%–62.6% of the phenotypic variation in the full panel. Bevul.2G176300, a gene directly involved in the sucrose biosynthesis pathway, was located downstream the significant marker. A second QTL identified on chromosome 7 revealed QTL alleles that may differentiate between table beet accessions, explaining nearly half the phenotypic variation, and is the first QTL reported in association with TDS unique to table beet. The QTL described can be used to efficiently breed for higher TDS levels in Beta vulgaris, avoiding intercrop type crosses and linkage drag.
... This is especially so for the leaves which recorded higher amounts of oxalic acid than roots in all of the beetroot samples, as well as the leaves of Swiss chard, where amounts similar to beetroot leaves were detected. According to the literature, the soluble and insoluble oxalate contents in the leaves of beetroot and Swiss chard were considerably higher when compared with the roots [45], a finding which is consistent with the results obtained in the present work. ...
In this study, leaves and roots from three beetroot cultivars (cv. Albina Vereduna (white roots), cv. Burpee’s Golden (golden roots), and cv. Pablo F1 (red roots)), as well as Swiss chard leaves (also known as “rhubarb chard”, or Beta vulgaris subsp. cicla var. flavescens) were evaluated in terms of their chemical profile and bioactive properties. Roots were characterized by high carbohydrate content, which also contributed to greater energy values. In contrast, fibers were the predominant macronutrient in leaves, followed by carbohydrates. In both leaves and roots, the most abundant organic acids were quinic and oxalic, while the major free sugar was sucrose. The profile of fatty acid varied between the studied plant parts, with saturated fatty acids prevailing in root samples, while leaves exhibited higher levels of polyunsaturated fatty acids. Regarding phenolic composition, a total of 19 compounds were tentatively identified in leaves (including derivatives of vitexin, isorhamnetin, quercetin, and ferulic, sinapic, and p-coumaric acids), while the roots exhibited a less diverse composition, with a total of eight compounds identified (e.g., derivatives of ferulic, sinapic, p-coumaric and caffeic acids). A total of eight betalains were also identified, out of which seven were classified as betacyanins and one as betaxanthin. The leaves of Swiss chard presented compounds from both classes, while the roots and leaves of cv. Pablo F1 were characterized only by the presence of betacyanins, and those of cv. Burpee’s Golden only by betaxanthin. All samples exhibited relevant activity against Y. enterocolitica, L. monocytogenes, and S. aureus, although leaf samples demonstrated better antioxidant capacity. In conclusion, beetroot leaves outperformed their corresponding roots in terms of chemical composition, antioxidant, and antimicrobial activity, suggesting their high potential as nutrient-rich and functional ingredients in a diverse and well-balanced diet.
... It has been documented that oxalate content varies significantly in context to plant genotypes/cultivars (Freidig & Goldman, 2011;Hang et al., 2013;Kristl et al., 2021). A study performed by Cai et al. on 2 spinach varieties cultivated in China (SP14 and SP104) revealed SP14 showed higher soluble (567.0 mg/100 g FW) and total oxalate (1164.0 ...
Oxalic acid is among the most abundant organic acids found in different biospheres, including plants, as an end product of metabolism. It forms either soluble or insoluble salts with monovalent or divalent cations, respectively. Then, consumption of oxalic acid-rich foods in human diets, particularly leafy vegetables (e.g., spinach, tea, and rhubarb), affects minerals absorption such as calcium. Meanwhile, its high level in blood is associated with many diseases such as hyperoxaluria systemic oxalosis and is thus classified among potential anti-nutrients. Various factors have affected oxalic acid levels in foods, including agricultural traits and consumption practices. Hence, the current review aimed at rediscovering oxalic acid dietary sources, metabolism, and the various processes employed to reduce its content in foods, and consequently, health harmful effects. Among them are physical/cooking, chemical, fermentation, and biotechnological processing. Recent biotechnological approaches have been attempted to produce transgenic crops remodeling oxalate metabolism, particularly its degradation. The soluble form of oxalate seems to be better absorbed and more harmful than insoluble salts in foods aiding in kidney stones formation. Cooking (e.g., boiling, microwaving, and steaming) appears as a useful management strategy to reduce soluble oxalate and, therefore, lowering oxaluria. The present review provides new perspectives on different processing methods to lower oxalate in essential vegetables highlighting their advantages or any limitations to aid improve these foods nutritional value and consumption.
... According to Fig 2 (b) for carrying out the theoretical calculations, oxalic acid was deprotonated into O 2 oxygen. And in this case, oxalic acid (OXA) becomes a viable substance to be used as a coformer, due to the fact that it has good solubility in water, a relatively small chemical structure, which consists of two carboxylic moieties, and is non-toxic (Freidig et al., 2011;Oliveira et al., 2014;Zhu, 2001). ...
The thermodynamic properties of the compounds contribute to the theoretical analysis of the results of favorable energies that are subject to interaction. In this work, through the DFT study, the comparison of the functionals ωB97XD and B3LYP. Geometry optimization calculations and vibrational frequencies were performed for the individual ions and for the interactions. In all cases, all calculated vibrational frequencies are positive, confirming the optimized geometry obtained as a minimum on the potential energy surface. The calculations were carried out in solvent, considering the solvation effect in methanol using the IEFPCM (Integral Equation Formalism of the Polarizable Continuum Model) method. The present work aims to carry out a theoretical study, for in-depth investigations of structural, electronic and thermodynamic properties. In usability in the calculation of the thermodynamic properties, Rifampicin (RIF) and Oxalic Acid (OXA) and the interaction between RIF-OXA in the protonated form protonated RIF with charge +1 and deprotonated OXA with charge -1. In this context, the most favorable thermodynamic parameters in the interaction calculated RIF+-OXA- the values of ∆EZPVE+BSSE, ∆G298 and ∆H in kcal/mol more favorable are -19.62, -14.81 and -25,77.
... The Amaranthaceae family includes species, such as SC and SB, which typically have high leaf oxalate concentrations (although even within this family there is considerable variation in this), and this may explain the differences between the two subspecies tested in our experiment. However, in SC and SB plants the concentration and ratio (from 72.7% to 89.2%) of total and soluble oxalate were comparable to those reported by Freidig et al. [52] in Beta vulgaris. The higher leaf total oxalate level detected in SB was also linked to the higher dry matter content. ...
The human intake of selenium (Se), which is an essential element in animals and humans, can be increased through the consumption of vegetables that have been biofortified during cultivation. There is increasing interest in wild edible plants (WEPs) due to their positive effects on health. In fact, many WEPs are rich in microelements, vitamins, dietary fibers, and several antioxidant compounds. Among WEPs, sea beet (Beta vulgaris ssp. maritima) is the wild ancestor of Swiss chard (Beta vulgaris var. cicla). The present study investigated the potential of fortifying Swiss chard and sea beet with Se. The two subspecies were cultivated in a floating system with a nutrient solution enriched with four concentrations of Se (0, 1, 3, and 5 mg L−1), and the production and quality of the baby leaves were evaluated. The addition of Se to the nutrient solution resulted in a higher leaf concentration of this microelement in both subspecies, with a positive effect on the yield (+20%) and leaf chlorophyll concentration (+25%) at the Se concentration of 1 mg L−1. The leaf concentration of nitrates was reduced by the Se treatment in sea beet regardless of the Se concentration (−24%, on average). Selenium biofortification was more effective in sea beet plants than in Swiss chard due to the higher ability of the wild species to acquire readily available minerals from the hydroponic nutrient solution. In conclusion, both subspecies accumulated a significant amount of Se without negative effects on yield or leaf quality, thus proving them to be suitable for the production of Se-enriched baby leaves.
... 70 Species belonging to Amaranthaceae family, such as SC and SB, generally show a high leaf content of oxalate but this parameter is quite variable even among species of the same family. The content of total and soluble oxalate, and their ratio in SC and SB plants, were similar to those found in Beta vulgaris by Freidig et al. 71 The differences between SB and SC regarding the leaf content of total chlorophylls and carotenoids could be due to specific characteristics of the two subspecies. Indeed, carotenoid content in plants is determined by genetic factors. ...
BACKGROUND
About 35–45% of the global population is affected by iodine deficiency. Iodine intake can be increased through the consumption of biofortified vegetables. Given the increasing interest in wild edible species of new leafy vegetables due to their high nutritional content, this study aimed to evaluate the suitability of Swiss chard (Beta vulgaris ssp. vulgaris var. cicla) and its wild ancestor sea beet (Beta vulgaris ssp. maritima) to be fortified with iodine. Plants were cultivated hydroponically in a nutrient solution enriched with four different concentrations of iodine (0, 0.5, 1.0, and 1.5 mg L⁻¹), and the production and quality of baby leaves were determined.
RESULTS
Sea beet accumulated more iodine than Swiss chard. In both subspecies, increasing the iodine concentration in the nutrient solution improved leaf quality as a result of greater antioxidant capacity – the ferric reducing ability of plasma (FRAP) index increased by 17% and 28%, at 0.5 and 1.5 mg L⁻¹ iodine, respectively – the content of flavonoids (+31 and + 26%, at 1 and 1.5 mg L⁻¹ of iodine, respectively), and the lower content of nitrate (−38% at 1.5 mg L⁻¹ of iodine) and oxalate (−36% at 0.5 mg L⁻¹ of iodine). In sea beet, however, iodine levels in the nutrient solution higher than 0.5 mg L⁻¹ reduced crop yield significantly.
CONCLUSIONS
Both subspecies were found to be suitable for producing iodine‐enriched baby leaves. The optimal iodine levels in the nutrient solution were 1.0 in Swiss chard and 0.5 mg L⁻¹ in sea beet, as crop yield was not affected at these concentrations and leaves contained enough iodine to satisfy an adequate daily intake with a serving of 100 g. © 2023 Society of Chemical Industry.
... [9] . Para o OXAREC, foi possível observar no intervalo de temperatura analisado, um primeiro evento endotérmico referente a desidratação com TOnset em 40,84 ºC, um outro evento ocorre com TOnset em 149,39 ºC, referente a sublimação do OXA [10] . ...
... Historically, characterization of table beet flavor has revolved around its most salient flavor attributes-sweet flavor and earthy aroma-which are derived from sucrose (Bach et al. 2014) and the volatile terpenoid molecule geosmin (Murray et al. 1975), respectively. In addition, compounds with known bitter flavor-saponins (Mikołajczyk-Bator et al. 2016), flavonoids (Kujala et al. 2002), and phenols (Bavec et al. 2010)-are present in beet, as is oxalate (Freidig and Goldman 2011), which produces abrasive sensory qualities in other crops. A trained sensory panel detected 23 and 17 sensory attributes in raw and boiled beet, respectively; in boiled beet, sweet, earthy, and bitter flavors were salient, while prominent aromas included earthy, beetroot, boiled potato, and sweet (Bach et al. 2014). ...
Participatory plant breeding and rapid sensory evaluation are effective techniques for organic cultivar development. Table beet is an important crop for organic growers, and geosmin, a volatile compound which confers earthy aroma, has been suggested as the attribute around which hedonic liking of beet is organized. Open pollinated table beet populations with diverse pigmentation and low (LGC) or high (HGC) geosmin concentration served as starting materials for the first PPB effort in table beet. This project sought to develop consumer-accepted specialty beet cultivars for organic systems and to gauge consumer perception of and preference for geosmin concentration in non-laboratory conditions. LGC and HGC initial populations were significantly different in mean geosmin concentration but not mean TDS. LGC populations diverged significantly in geosmin concentration over two cycles of selection for hedonic liking, due to drift rather than selection. PPB yielded cultivars ‘Evansville Ember’, ‘Snowglobe’, ‘Blushing Not Bashful’, ‘Evansville Orbit’, and ‘Moving Target’. Cultivar novelty and market development were strengthened by chef input and association with a publicly funded seed system development group. Geosmin concentration was not the central determinant of hedonic liking or perceived earthy flavor in table beet. Earthiness was inconsistently associated with geosmin concentration and hedonic liking. Sweetness and bitterness were positively and negatively correlated with liking, respectively, although sweetness was not associated with variation in TDS. Cultivars with a broad range of geosmin concentration were well accepted by consumers, and manipulating expectation—via appearance—may be as powerful as manipulating flavor compounds in influencing liking of table beet.
... Sucrose, the major saccharide molecule in table beet root (Bach et al., 2015), contributes sweet flavor and is commonly measured as TDS. Oxalate is present in table beet (Freidig and Goldman, 2011) and has been associated with abrasive sensory properties in other plants (Korth et al., 2006;Salinas et al., 2001). Saponins, which confer bitter flavor in other crops, have also been identified in table beet (Mikołajczyk-Bator et al., 2016). ...
Earthy aroma and sweet flavor, conferred by the volatile terpenoid geosmin ( trans -1,10-dimethyl- trans -9-decalol) and sucrose, respectively, are two essential flavor components of table beet ( Beta vulgaris ssp. vulgaris ). To elucidate the influence of genotype, growing environment, and fertilizer treatment on geosmin concentration and sucrose [as total dissolved solids (TDS)] in table beet, a field-based genotype × environment study was conducted using a split-split plot design. Four site × year combinations served as whole plots; MgSO 4 ·H 2 O and CaSO 4 comprised split plot fertilizer treatments; open-pollinated cultivars Bull’s Blood and Touchstone Gold, F1 hybrid Merlin, and inbred line W357B constituted split-split plot genotype treatments. Geosmin concentration was measured via gas chromatography–mass spectrometry using headspace solid-phase microextraction, and TDS was measured via refractometry. Variation in geosmin concentration was attributable to a strong genotype effect and significant genotype × year and year × site interactions. Genotypes were observed to have characteristic geosmin concentration and variance, despite being grown in soils with widely divergent physical and chemical properties. While a significant genotype main effect was also present for TDS, it occurred in the context of significant four-way and three-way genotype × environment interactions, plus significant effects of year and year × site interaction. Neither geosmin concentration nor TDS was significantly influenced by fertilizer treatment or fertilizer × environment interactions, averaged across genotypes. Genetics determined a larger proportion of variance for geosmin concentration than TDS in the four table beet genotypes assessed, as reflected in repeatability measurements of 0.90 and 0.43, respectively. This experiment provides support for the primacy of genotype in determining table beet geosmin concentration and a comparatively moderate role of genotype in determining table beet TDS. Thus, genetic manipulation of table beet geosmin could yield cultivars with signature flavor characteristics to serve both niche and mainstream consumer groups, expanding market opportunities for breeders and growers.
Characterized by strong acidity, chelating ability, and reducing ability, oxalic acid, a low molecular weight dicarboxylic organic acid, plays important roles in the regulation of plant growth and development, the response to both biotic and abiotic stresses such as plant defense and heavy metals detoxification, and food quality. The metabolism of oxalic acid has been well-studied in microorganisms, fungi, and animals but remains less understood in plants. However, excessive accumulation of oxalic acid is detrimental to plants. Therefore, the level of oxalic acid has to be precisely controlled in plant tissues. In this review, we summarize the metabolism, function, and regulation of oxalic acid in plants, and we discuss solutions such as agricultural practices and plant biotechnology to manipulate oxalic acid metabolism to regulate plant responses to both external stimuli and internal developmental cues.
Geosmin, a degraded sesquiterpene molecule with earthy and musty odor, imbues table beet with its characteristic aroma. Geosmin is heritable and endogenously produced in table beet; its earthy aroma is sought by some consumers but deters others. Geosmin biosynthesis is catalyzed by a bifunctional geosmin synthase enzyme in diverse bacteria and fungi, but a mechanism for geosmin biosynthesis in plants has not been reported. This work employed association analysis and selective genotyping of a segregating F2:3Beta vulgarisvulgaris
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Presently there is a lack of knowledge that addresses the effect of the development stages of beetroot on its nutrients, anti-nutrients, and pigments. In the present study, the different development stages of beetroot (60, 80 and 100 days) were analyzed for nutrients, anti-nutrients, and pigments by applying the standard method of AOAC. The beetroot showed a significantly higher amount of moisture, calcium, iron, choline, folate, and pigments (betaine and betanin) at 60 days of maturity, and ash, crude fiber, total carbohydrate, phosphorus, magnesium, potassium, and anti-nutrients (oxalic acid and saponin) contents were highest at 100 days of maturity in beetroot. Although vitamin C content was increased from 60 days to 80 days of maturity (8.96 to 9.03), while at 100 days it was decreased. The study shows that all maturity stages produced satisfactory results but the amounts of anti-nutrients (oxalic acid and saponins) were increased during the stages of development.
Oxalate is considered an antinutrient that renders calcium unavailable for nutritional absorption by humans. Efforts have been made to generate and identify edible plants with decreased levels of this antinutrient. The extent to which a food can be nutritionally improved through genetic alterations in calcium oxalate content, however, has not been determined. The recent identification of near isogenic lines of the forage legume, Medicago truncatula Gaertn. (cv. Jemalong genotype A17), that differ in calcium oxalate content aids in filling this gap in our knowledge. In this study, we use an in vitro dialysis system to show that the decrease in calcium oxalate results in an enhancement in calcium availability. By comparing virtually identical plants a more direct assignment of the calcium availability to the presence or absence of oxalate was made. In addition, this study shows, for the first time, the feasibility of improving plant foods through the genetic manipulation of its oxalate content.
Oxalates occur as end products of metabolism in a number of plant tissues; some leafy plants and some root crops contain markedly high levels of soluble and insoluble oxalates. When consumed these oxalates can bind calcium and other minerals. Measurement of oxalate content in vegetables commonly consumed in New Zealand shows that cooking reduces the oxalate content of the food by leaching losses into the cooking water. Roots and brassicas grown in New Zealand appear to contain relatively low levels of oxalates. Leafy vegetables such as silverbeet and NZ spinach appear to approach and exceed levels found in rhubarb stalks, although New Zealand silverbeet stems contain lower levels.
Roots of taro (Colocasia esculenta [L.] Schott cvs Bun-long and Lehua maoli) exuded increasing concentrations of oxalate with increasing Al stress. This exudation was a specific response to excess Al and not to P deficiency. Addition of oxalate to Al-containing solutions ameliorated the toxic effect of Al.
Calcium oxalate is the most abundant insoluble mineral found in plants and its crystals have been reported in more than 200 plant families. In the barrel medic Medicago truncatula Gaertn., these crystals accumulate predominantly in a sheath surrounding secondary veins of leaves. Mutants of M. truncatula with decreased levels of calcium oxalate crystals were used to assess the defensive role of this mineral against insects. Caterpillar larvae of the beet armyworm Spodoptera exigua Hübner show a clear feeding preference for tissue from calcium oxalate-defective (cod) mutant lines cod5 and cod6 in choice test comparisons with wild-type M. truncatula. Compared to their performance on mutant lines, larvae feeding on wild-type plants with abundant calcium oxalate crystals suffer significantly reduced growth and increased mortality. Induction of wound-responsive genes appears to be normal in cod5 and cod6, indicating that these lines are not deficient in induced insect defenses. Electron micrographs of insect mouthparts indicate that the prismatic crystals in M. truncatula leaves act as physical abrasives during feeding. Food utilization measurements show that, after consumption, calcium oxalate also interferes with the conversion of plant material into insect biomass during digestion. In contrast to their detrimental effects on a chewing insect, calcium oxalate crystals do not negatively affect the performance of the pea aphid Acyrthosiphon pisum Harris, a sap-feeding insect with piercing-sucking mouthparts. The results confirm a long-held hypothesis for the defensive function of these crystals and point to the potential value of genes controlling crystal formation and localization in crop plants.
Genetic variation for oxalate content was studied in a Rheum genotype collection. Phenotypic variation of oxalate in rhubarb petioles ranged from 0. 24-2.99 %FW among 572 genotypes. The lowest level in a more thorough examination of selected low-oxalate genotypes from the collection was 0.28 %FW. A low heritability and a long interval between generations are negative factors for future breeding of low-oxalate rhubarb cultivars. Low-oxalate genotypes are, however, characterized by vigorous growth and normal levels of titratable acidity.
Reduction of nitrate and oxalate content in spinach (Spinacia oleracea L.) has become the major concern in terms of their toxicity to human health. The primary objectives of this study were 1) to determine the seasonal change in nitrate and oxalate concentrations and 2) to elucidate the relationship between growth rate and concentration of nitrate and oxalate in spinach. In a replicated field experiment in Hiratsuka, Japan, the authors grew 182 cultivars of spinach over four growing seasons (winter, spring, summer, and fall) under the nitrogen application rate of 100 kg N·ha -1. The average number of days required for harvest was the shortest in summer (32.7 days) and was longest in the winter (85.7 days). Mean nitrate concentration in spinach was significantly low in the winter (3797 mg·kg -1 fresh weight) compared with the other three seasons (4122-4328 mg·kg -1 fresh weight) in which no significant differences were found in mean nitrate levels. In contrast, oxalate concentrations showed a distinct seasonal variation, being the lowest in the fall (6149 mg·kg -1 fresh weight), followed by the summer (7525 mg·kg -1 fresh weight) and the spring (8903 mg·kg -1 fresh weight), and was the highest in the winter (10,929 mg·kg -1 fresh weight). Relative nitrate concentration showed a moderate negative correlation with relative days required for harvest (r = 0.411, P < 0.001), whereas relative oxalate concentration showed a strong positive correlation with relative days required for harvest (r = 0.566, P < 0.001). Accordingly, a moderate negative correlation (r = 0.325, P < 0.001 was detected between nitrate and oxalate concentrations. Moreover, fast-growing cultivars contained higher nitrate and lower oxalate, whereas slow-growing cultivars contained lower nitrate and higher oxalate. These results indicate that the growth rate primarily accounts for the nitrate and oxalate concentration in spinach, and nitrate and oxalate might play a counterrole to each other.
Summary Lemna minor root tips form raphide Ca oxalate crystals in both the root cap and root proper. An in vivo system was developed to examine raphide crystal bundle formation in the root of intact plants. By increasing the exogenous Ca concentration, crystal bundle formation could be induced. Entire new crystal bundles could be formed within 30 minutes of an inductive stimulus. The process was reversible with recently formed crystal bundles being dissolved over a period of about 3 hours. Older, previously existing bundles were more resistant to dissolution. The calmodulin antagonists, chlorpromazine and trifluoperazine (300 μM), prevented crystal formation and caused dissolution of some crystal bundles, even in the presence of exogenous Ca. When the antagonists were flushed out and replaced with fresh medium, crystals were formed in cells where dissolution had occurred under the influence of the antagonists. The Ca ionophore A 23187 (20 μM) caused slow dissolution of crystal bundles, even in the presence of exogenous Ca. A model describing the control of and physiological significance of Ca oxalate formation in plants is presented and discussed with respect to the results obtained in this study.
Tea plants (Camellia sinensis L.) were hydroponically cultured for 9 d in a solution containing ammonium as a sole nitrogen source (0 (control), 50, 100, or 200 mg N L ), and harvested after 0 (control), 1,3,6, and 9 d of treatments to investigate the effect of ammonium on the content and metabolism of oxalate in tea plants. Total and water-soluble oxalate contents in young leaves and roots treated with 50, 100, and 200 mg N L decreased in proportion to the amount of ammonium applied, with levels significantly lower than those without ammonium application. In old leaves, both total and water-soluble oxalate contents showed constant values during the treatment period. The content of total ascorbic acid (AsA) in young leaves increased with the amount of ammonium in the medium. The activity of oxalate oxidase (OxO) in young leaves also increased with the concentration of ammonium in the medium and with the duration of the treatment. However, in roots, total AsA content and OxO activity were not affected. These results suggest that in young tea leaves, the application of ammonium suppressed the synthesis of oxalate via AsA oxidation and stimulated the decomposition of oxalate by the increase of the OxO activity, resulting in the accumulation of AsA and a decrease in oxalate content. On the other hand, in old leaves and young roots, the responses to ammonium were different from those in young leaves, suggesting that the oxalate metabolism may be controlled by different mechanisms in different parts of the tea plants.
Oxalate is produced and accumulated in many crop plants and pasture weeds. Although oxalate can be a major constituent of plants, important aspects of its biosynthesis, accumulation, and catabolism are unresolved. A major precursor of oxalate is glyoxylate. Oxalate accumulators can also form oxalate by C2/C3 cleavage of ascorbic acid. Plant oxalate content is affected by nitrogen source, inorganic ion availability, and other environmental factors. Ontogenetic stage and genotype are also important factors. Oxalate may play a role in ion balance and osmoregulation. Oxalate oxidase and oxalate decarboxylase are present in some plants, and oxalate can be catabolized and the carbon recycled. Oxalate accumulation by crop and pasture plants affects the nutritional quality of foods and feed negatively. Consumption of plants with high oxalate content has led to poisoning and death of livestock. High-oxalate diets can increase the risk of renal calcium oxalate formation in certain groups of people and may also affect calcium absorption.
1 We determined the effects of simulated bulb herbivory by the dorcas gazelle, Gazella dorcas, on the geophyte, Pancratium sickenbergeri (Amaryllidaceae), in the Negev desert, Israel. In a population with a high level of herbivory, we removed 0%, 25%, 50% and 75% of bulb tissue from plants.2 Bulbs with an intermediate volume removed (50%) showed the highest re-growth capacity and fitness in relation to the other cutting treatments. The production of calcium oxalate defences increased in cut bulbs.3 There was a trade-off between investment in storage and defence. Trade-offs were not found between growth and defence, between growth and reproduction or between reproduction and defence.4 Control plants grew less, had lower levels of calcium oxalate, stored more energy and produced more flowers and fruits, but their current fitness was only slightly higher than in the intermediate cutting treatment (50%) because of the high abortion of fruits.5 P. sickenbergeri showed a complex resource allocation pattern as the result of combining defence and tolerance of herbivory. Plants respond to high herbivory levels with a high re-growth capacity as a tolerant mechanism to maintain fitness.
Oca ( Oxalis tuberosa Mol) originates from South America but is now also grown commercially in New Zealand. It contains moderate amounts of oxalate, which is only present in its soluble form. The skin of the oca tuber is thought to contain more oxalate than the flesh. In this study the concentration of soluble oxalate was measured in the skin and outer and inner flesh and in the whole tuber of raw, boiled, baked and steamed oca. The analysis was carried out on the traditionally pinkish‐red New Zealand cultivar and on the newly introduced cultivars ‘Mellow Yellow’ and ‘Apricot Delight’. In the raw oca tuber the oxalate concentration in the skin is significantly higher than in the flesh (mean value 7.3 g kg ⁻¹ fresh weight (FW) compared to 1.7 and 1.4 g kg ⁻¹ FW in the outer and inner flesh respectively). The highest concentration was found in the skin of the pinkish‐red cultivar (10.9 ± 1.0 g kg ⁻¹ FW). All cooking methods seemed to cause a migration of oxalate from the skin to the underlying flesh. On a fresh weight basis, baking significantly increased the oxalate concentration in the whole tuber, whereas boiling decreased the concentration and steaming had no significant effect ( p < 0.001). Boiling might therefore be a better way of cooking oca than baking when a low intake of oxalate is desired.
© 2001 Society of Chemical Industry
Table beet (Beta vulgaris subsp. vulgaris L) is a vegetable from the family Chenopodiaceae. Table beet is also known as garden beet or red beet in the U.S. scientific
literature, and as beetroot in Europe and many other countries around the world. Table beet is a member of a crop complex
from the genus Beta that includes Swiss chard, mangel, and sugarbeet. All three of these crops are derived from the same species, vulgaris, and are often represented with different subspecies designations. Table beet and Swiss chard are primarily used as vegetables,
the mangel and its derivatives are used as animal feed, and the sugarbeet is used as a source of sucrose. Table beet breeding
has been recently reviewed by Goldman and Navazio (2003) and we draw from sections of their work in this chapter.
Food oxalate analysis in foods is problematic due to the wide range of interfering substances. To prevent oxalate generation during sample preparation mild and rapid extraction methods were evaluated. Soluble oxalate was extracted with distilled water and total oxalate was extracted with 2 N hydrochloric acid. Filtrates were analysed using the HPLC enzyme reactor method. Evaluation yielded a high level of precision and recovery. Glyoxylic acid, d/l malic acid, isocitric acid, oxaloacetic acid, pyruvate, mesoxalic acid, ascorbic acid, d(+) glucose, d(−) fructose, chlorogenic acid, caffeic acid could be excluded as a source of oxalate generation during extraction with hot acids. The soluble and total oxalate content of about 150 food samples were investigated.
The entire USDA spinach (Spinacia oleracea) germplasm collection (338 accessions) and 11 commercial cultivars were screened for oxalate concentration. There were significant differences in oxalate concentration among the genotypes evaluated, ranging from 5.3% to 11.6% on a dry weight basis. The low-oxalate genotypes identified in our experiments are all S. oleracea. None of the two S. tetrandra and four S. turkestanica accessions screened had low levels of oxalate. Two accessions from Syria, PI 445782 (cultivar name Shami) and PI 445784 (cultivar name Baladi), consistently had low oxalate concentration. When expressed on a fresh weight basis, oxalate concentration may be affected by the moisture content of the plant. Oxalate concentration had little correlation with leaf types (flat or savoy) and leaf weight per plant. With the genetic variation and sources of low oxalate concentration found, breeding of spinach for a low level of oxalate seems feasible.
A specific enzymatic method was used to determine the oxalate content of some common foods. No preliminary isolation of oxalate was required and recoveries ranging from 95-110 per cent were obtained. Spinach, rhubarb, peanuts, chocolates, parsley and tea were found to contain high levels of oxalate as previously described by others. On the other hand the oxalate content of beetroot was found to be five times as high as previously reported, but coca-cola and beer were almost free from oxalate. Cereals and meat were either low or deficient in oxalate.
The amount of oxalate excreted in urine has a significant impact on calcium oxalate supersaturation and stone formation. Dietary oxalate is believed to make only a minor (10 to 20%) contribution to the amount of oxalate excreted in urine, but the validity of the experimental observations that support this conclusion can be questioned. An understanding of the actual contribution of dietary oxalate to urinary oxalate excretion is important, as it is potentially modifiable.
We varied the amount of dietary oxalate consumed by a group of adult individuals using formula diets and controlled, solid-food diets with a known oxalate content, determined by a recently developed analytical procedure. Controlled solid-food diets were consumed containing 10, 50, and 250 mg of oxalate/2500 kcal, as well as formula diets containing 0 and 180 mg oxalate/2500 kcal. Changes in the content of oxalate and other ions were assessed in 24-hour urine collections.
Urinary oxalate excretion increased as dietary oxalate intake increased. With oxalate-containing diets, the mean contribution of dietary oxalate to urinary oxalate excretion ranged from 24.4 +/- 15.5% on the 10 mg/2500 kcal/day diet to 41.5 +/- 9.1% on the 250 mg/2500 kcal/day diet, much higher than previously estimated. When the calcium content of a diet containing 250 mg of oxalate was reduced from 1002 mg to 391 mg, urinary oxalate excretion increased by a mean of 28.2 +/- 4.8%, and the mean dietary contribution increased to 52.6 +/- 8.6%.
These results suggest that dietary oxalate makes a much greater contribution to urinary oxalate excretion than previously recognized, that dietary calcium influences the bioavailability of ingested oxalate, and that the absorption of dietary oxalate may be an important factor in calcium oxalate stone formation.
Leafy vegetables such as spinach (Spinacia oleracea) are known to contain moderate amounts of soluble and insoluble oxalates. Frozen commercially available spinach in New Zealand contains 736.6+/-20.4 mg/100g wet matter (WM) soluble oxalate and 220.1+/-96.5mg/100g WM insoluble oxalate. The frozen spinach contained 90mg total calcium/100g WM, 76.7%of this calcium was unavailable as it was bound to oxalate as insoluble oxalate. The oxalate/calcium (mEq) ratio of the frozen spinach was 4.73. When frozen convenience food is grilled there is no opportunity for the soluble oxalates to be leached out into the cooking water and discarded. Soluble oxalates, when consumed, have the ability to bind to calcium in the spinach and any calcium in foods consumed with the spinach, reducing the absorption of soluble oxalate. In this experiment 10 volunteers ingested 100g grilled spinach alone or with 100g additions of cottage cheese, sour cream and sour cream with Calci-Trim milk (180 g) and finally, with 20g olive oil. The availability of oxalate in the spinach was determined by measuring the oxalate output in the urine over a 6-hour and 24-hour period after intake of the test meal. The mean bioavailability of soluble oxalate in the grilled spinach was 0.75+/-0.48% over a 6-hour period after intake and was 1.93+/-0.85% measured over a 24-hour period. Addition of sour cream and Calci-Trim milk reduced the availability of the oxalate in the spinach significantly (P<0.05) in both the 6-hour and 24-hour collection periods.
Approximately 75% of all kidney stones are composed primarily of calcium oxalate, and hyperoxaluria is a primary risk factor for this disorder. Nine types of raw and cooked vegetables were analyzed for oxalate using an enzymatic method. There was a high proportion of water-soluble oxalate in most of the tested raw vegetables. Boiling markedly reduced soluble oxalate content by 30-87% and was more effective than steaming (5-53%) and baking (used only for potatoes, no oxalate loss). An assessment of the oxalate content of cooking water used for boiling and steaming revealed an approximately 100% recovery of oxalate losses. The losses of insoluble oxalate during cooking varied greatly, ranging from 0 to 74%. Because soluble sources of oxalate appear to be better absorbed than insoluble sources, employing cooking methods that significantly reduce soluble oxalate may be an effective strategy for decreasing oxaluria in individuals predisposed to the development of kidney stones.
A high level of oxalate intake constitutes a health risk for infants and metabolically disposed adults. Spinach, acclaimed for its many health benefits, is among the vegetables richest in oxalate. Blanching reduces oxalate unsatisfactorily and unspecifically. An alternative, biological method is proposed on the basis of rye seedlings or radicles (also barley and wheat) containing an oxalate-specific oxalate oxidase by nature. Dissolved oxalate (0.25 mM) was rapidly degraded in the presence of radicles (e.g., 70% within 100 min). With commercial deep-frozen spinach, near-complete degradation of soluble oxalate was achieved at pH 3.5. The total level of oxalate was reduced by half. Similarly high rates occurred from 18 to 35 degrees C. Even at 55 degrees C appreciable rates were observed. The seedling as a whole is effective, too, and enrichment with cereal-specific healthy components would occur. Removal of oxalate from other vegetables, juices, cycled process waters, or feeds is conceivable with fresh or heat-dried cereal seedlings or radicles.
Red beet root discs aerated in potassium phosphate for 2 to 3 days and young spinach leaves actively produce oxalate. A series of labeled compounds was supplied to each of these tissues to determine the extent of conversion to oxalate. Similar results were obtained with the 2 tissues except that in the leaf tissue glyoxylate and glycolate were outstandingly good precursors. Carbon from glucose, acetate, and particularly from some acids of the tricarboxylic acid cycle was recovered in oxalate. Extracts from both tissues were found to contain an enzyme which converts oxaloacetate to oxalate and acetate. The enzyme was partially purified and some of its properties are described. A pathway of oxalate synthesis which does not include glycolate or its oxidase is therefore proposed.
l-Ascorbic acid-1-(14)C and its oxidation product, dehydro-l-ascorbic acid, produced labeled oxalic acid in oxalate-accumulating plants such as spinach seedlings (Spinacia oleracea) and the detached leaves of woodsorrel (Oxalis stricta and O. oregana), shamrock (Oxalis adenopylla), and begonia (Begonia evansiana). In O. oregana, conversion occurred equally well in the presence or absence of light. This relationship between l-ascorbic acid metabolism and oxalic acid formation must be given careful consideration in attempts to explain oxalic accumulation in plants.
l-Ascorbic acid functions as a precursor of oxalic acid in several oxalate-accumulating plants. The present study extends this observation to include Rumex crispus L. (curly dock), Amaranthus retroflexus L. (red root pigweed), Chenopodium album L. (lamb's-quarters), Beta vulgaris L. (sugar beet), Halogeton glomeratus M. Bieb. (halogeton), and Rheum rhabarbarum L. (rhubarb). Several species with low oxalate content are also examined.When l-[1-(14)C]ascorbic acid is supplied to young seedlings of R. crispus or H. glomeratus, a major portion of the (14)C is released over a 24-hour period as (14)CO(2) and only a small portion is recovered as [(14)C]oxalate, unlike cuttings from 2- or 4-month-old plants which retain a large part of the (14)C as [(14)C]oxalic acid and release very little (14)CO(2). Support for an intermediate role of oxalate in the release of (14)CO(2) from l-[1-(14)C]ascorbic acid is seen in the rapid release of (14)CO(2) by R. crispus and H. glomeratus seedlings labeled with [(14)C]oxalic acid.The common origin of oxalic acid carbon in the C1 and C2 fragment from l-ascorbic acid is demonstrated by comparison of (14)C content of oxalic acid in several oxalate-accumulators after cuttings or seedlings are supplied equal amounts of l-[1-(14)C]- or l-[UL-(14)C]ascorbic acid. Theoretically, l-[1-(14)C]ascorbic acid will produce labeled oxalic acid containing three times as much (14)C as l-[UL-(14)C]ascorbic acid when equal amounts of label are provided. Experimentally, a ratio of 2.7 +/- 0.5 is obtained in duplicate experiments with six different species.
Bioavailable calcium affects bone formation and calcification. Here we investigate how a single gene mutation altering calcium partitioning in the model forage crop Medicago truncatula affects calcium bioavailability. Previously, the cod5 M. truncatula mutant was identified which contains identical calcium concentrations to wild-type, but contains no oxalate crystals. In this study, equal number of male and female mice were randomly grouped and then fed one of four 45Ca-containing diets: M. truncatula extrinsically or intrinsically labeled, and cod5 extrinsically or intrinsically labeled. Absorption of the tracer was determined in the legs one day after consumption. The absorption was similar in the M. truncatula and cod5 extrinsically labeled diets; however, in the intrinsically labeled diets, calcium absorption was 22.87% (P < 0.001) higher in mice fed cod5. Our study presents the first genetic evidence demonstrating the nutritional impact of removing oxalate crystals from foods.
Food and nutrition professionals provide medical nutrition therapy for patients with kidney stones. If the stones contain oxalate or the patient has been diagnosed with hyperoxaluria, reduction of dietary oxalate may be appropriate. Differences in oxalate values for a single food may be due to analytical methods, and/or biological variation from several sources, including cultivar, time of harvest, and growing conditions. Bioavailability of food oxalate and, thus, urine oxalate, will also be affected by salt forms of oxalate, food processing and cooking methods, meal composition, and the presence of Oxalabacter formigenes in the patient's gut. Dietary advice for reducing urinary oxalate should include both reduction of dietary oxalate and simultaneous consumption of calcium-rich food or supplement to reduce oxalate absorption.
Activity products in urine
- Robertson,
Robertson, W.G. and B.E.C. Nordin. 1969. Activity products in urine.
Proc. Renal Stone Res. Symp. p. 221-232.
Effect of maturity on the oxalate and cation contents of six leafy vegetables
- Singh,
Singh, P.P. and S.N. Saxena. 1972. Effect of maturity on the oxalate
and cation contents of six leafy vegetables. Indian J. Nutr. Diet. 9:
269-276.