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Role of Moisture in Maillard Browning Reaction Rate in Intermediate Moisture Foods: Comparing Solvent Phase and Matrix Properties
Abstract
In intermediate-moisture foods, a mechanism describing how moisture affects chemical reaction rate is unknown. Previously, research showed glycol addition to model systems allowed high rates of nonenzymatic browning below the monolayer moisture value and an aw of 0.2. These works were replicated, focusing on a mechanism of either plasticization or reactant dissolution. Tg curves showed plasticization increased with added glycerol and sorbitol. The maximum rate of nonenzymatic browning with glycerol occurred at an aw= 0.25 and was 1.5 times higher than the control (aw= 0.65). Sorbitol showed rates similar to the control. Plasticization and aw were poor predictors of reaction rate. Dissolution of glucose in glycerol explained the effect.
... The surface color of samples prepared with mixed sugar kept at vacuum conditions was less changed, compared to the samples kept at 75 and 33 %RH conditions. This might be due to the effect of relative vapor pressure (RVP) or a w of samples influenced by browning development by Maillard reaction [31,32]. Moisture equilibration between sample and environment during storage at different conditions affected RVP or a w of the sample ( Figure 2). ...
... The samples kept at 33 %RH showed a substantial a w decrease, in a range of 0.6 to 0.4, when the storage time increased (p < 0.05) which corresponded to the highest browning intensity. The maximum rate of Maillard reaction development was in a range of a w of 0.6 -0.8, which covered the a w range of chicken meat jerky kept in all storage conditions [31,32,39,40]. Pan and Melton [39] concluded that the fastest rates of Maillard reaction in lactose and caseinate mixture heated at 60 °C occurred at intermediate RHs (67 to 80 %RH), with a maximum rate close to 75 %RH. ...
The color characteristics of chicken meat jerky, prepared with sucrose and mixed sugar (sucrose: fructose: sorbitol 70: 15: 15), were investigated during storage at room temperature under different conditions (vacuum, 33, and 75 % relative humidity (RH) conditions). Changes in color values (L*, a*, b*) and the degree of Maillard reaction of the product were determined. The samples prepared with mixed sugar had more browning (brown color) than the samples prepared with sucrose (dark-yellow color) in all storage conditions (p < 0.05). The samples prepared with mixed sugar had a decrease in L* value and an increase in a* and b* value during storage, which corresponded to Maillard reaction development. The values of L*, a*, and b*, as well as the degree of Maillard reaction of samples prepared with the same sugar types, were not significantly different during storage in various storage conditions (p ≥ 0.05). Sensory scores of the color of chicken meat jerky kept in vacuum and 75 %RH conditions indicated preference within 30 days of storage, while samples stored in 33 %RH condition were acceptable within 15 days of storage.
... Returning to the lack of dependence of browning reaction rates on water activity when the initial concentration of reactant sugars was constant at 11.65°Bx ( Fig. 2a and b), this finding indicates the enhanced browning phenomenon in concentrated juice as compared to a diluted system; this can be mainly attributed to the higher initial concentration of sugars rather than the decreased value of water activity, reaching the region where the maximum of browning rates usually occurs. Thus, it is the mass of water rather than the a w , that should correlate with reaction rate, as reported by Shierwin and Labuza (2003). In the latter study, the non-enzymatic browning of powders varying in water activity and humectant content (glycerol, sorbitol) was studied. ...
... (1)- (5)). Previous studies of the non-enzymatic browning have revealed that this reaction fits either zero order (Bozkurt et al., 1999;Ibarz et al., 1999;Koca et al., 2003;Peterson, Tong, Ho, & Welt, 1994;Rattanathanalerk et al., 2005;Shierwin & Labuza, 2003), or first order Johnson et al., 1995;Toribio & Lozano, 1984, 1986) kinetic models, with relatively small statistical differences between the two types. A parabolic kinetic model has also been applied by Buedo et al. (2001). ...
The kinetics of non-enzymatic browning in apple juice concentrates were investigated. The effect of aw (in the range of 0.74–0.99) and/or reactant concentration on brown pigment formation was monitored under isothermal heat treatment at four temperatures (60, 70, 80 and 90 °C) in apple juice solutions having either the same or different concentrations of reactant solutes. The extent of the Maillard reaction was evaluated by spectrophotometric measurements at 420 nm (A420). The absorbance–time curves were fitted to five different kinetic models (zero and first order, weibull, logistic and the parabolic model) and estimates of browning rate constants and other model parameters were obtained. Regression analysis revealed that the logistic model was the most appropriate for describing browning in apple juice. The initial reactant concentration, but not water activity, had a significant effect on the colour change of apple juice. The processing temperature also had a strong impact on browning kinetics. Secondary models, expressing the dependence of the best fitted primary model parameters on temperature and aw, were further developed and validated by comparing the predicted model parameters with the values observed in independent isothermal experiments. Finally, the derived model was further evaluated against the observed browning responses of apple juice under dynamic heating conditions, underlining the applicability of the developed model as a practical prediction tool for the study of non-enzymatic browning.
... 23,27 Other reports have stressed the importance of specific surface area (SSA), and some studies have suggested that optimal water content may be determined by that needed for monolayer coverage of the available surface. [28][29][30] While the interactions among these factors likely play a role in stabilization, this study was designed to be an initial investigation into the effects of moisture content on the storage stability of freezedried lipoplexes. ...
... Previous studies on the stability of dried food have suggested an interplay between moisture content and surface area such that oxidation is minimized when sufficient water is available for monolayer coverage. [28][29][30] A straightforward calculation reveals that our moisture contents are at least 5-fold higher than that necessary for monolayer coverage, even in our driest samples. However, such an analysis assumes that water molecules are only present on the surface of the sample; an assumption that is clearly invalid for a glassy system. ...
The purpose of this study is to investigate the effects of moisture content on the storage stability of freeze-dried lipoplex formulations. DC-Cholesterol: DOPE (dioleoyl phosphatidylethanolamine)/plasmid DNA lipoplexes were prepared at a 3-to-2 DC-Cholesterol(+) to DNA(-) molar ratio and lyophilized prior to storing at room temperature, 40, and 60 degrees C for 3 months. Different residual moistures (1.93%, 1.10%, 1.06%, and 0.36%) were obtained by altering the secondary drying temperatures. In addition to moisture content, lipoplex formulations were evaluated after freeze-drying and/ or storage for particle size, transfection efficiency, accumulation of thiobarbituric acid reactive substances (TBARS), glass transition temperature, DNA supercoil content, and surface area. Lipoplex formulations stored at room temperature for 3 months maintain TBARS concentrations and supercoil contents. At higher storage temperatures, formulations possessing the highest moisture content (1.93%) maintained significantly lower TBARS concentrations and higher supercoil content than those with the lowest (0.36%) moisture content. Curiously, the intermediate moisture contents exhibited marked differences in stability despite virtually identical moisture contents. Subsequent measurements of surface area indicated that the lower stability corresponded to higher surface area in the dried cake, suggesting that there may be an interplay between water content and surface area that contributes to storage stability.
... However, prolonged storage can result in a decline in the flavor and texture of HPNBs, accompanied by a noticeable increase in hardness. This greatly limits their shelf life and consumer acceptance (Sherwin & Labuza, 2010). The hardening of HPNBs can be attributed to various factors, including the crystallization of sugars, migration of water, self-aggregation of proteins, phase separation, and glycosylation (Rao et al., 2013). ...
Model high-protein nutrition bars (HPNBs) were formulated by incorporating whey protein isolate (WPI) and casein (CN) at various extrusion temperatures (50, 75, 100, 125, and 150 °C) with a protein content of 45 g per 100 g. The free sulfhydryl groups, amino groups, hardness, and microstructures of HPNBs were analyzed periodically at 37 °C over a storage period of 45 days. Specifically, sulfhydryl group, amino group and surface hydrophobicity of extruded whey protein isolate (WPE) and extruded casein (CE) were significantly reduced (P
... It was found that E a increased with increase in RH, indicating that the maillard reaction took longer time to proceed, in other words, form brown pigment (Fig 3). Also, high RH might have caused reactants to be more mobile in the food matrix (due to presence of moisture), resulting in accumulation red maillard intermediate compounds, precursor of melanoidins (brown color) (Murata, M., 2020; Sherwin & Labuza, 2003). Texture: Our study revealed that the fracturability and springiness were most sensitive to moisture change ( Figure); pecans stored at high relative humidity environment started losing the fracturability as moisture accumulated in the pecan (higher fracturability value means more force required to break pecan). ...
... The glass transition temperature Tg corresponds to the change from amorphous glassy state to the rubbery state, in which the inter-chain mobility increases and makes chemical reactions possible. The increase of the powder aw and sugar content decreases the Tg (Sherwin and Labuza, 2003;. Thus, chemical reactions such as denaturation or lactosylation may occur at a lower temperature. ...
The objective of this work is to identify the conditions and mechanisms of the creation or improvement of the stability and rheology of whey proteins foams. To this aim, we studied the interfacial rheology of protein layers adsorbed at the air/water interface, the liquid films dynamics after a topological rearrangement, the stability and rheology of whey protein foams. Both a mixture of whey proteins and purified β-lactoglobulin, used as a model protein, were studied. To study the relationships with protein structure, proteins were modified by dry-heating of whey protein powders. A wide variety of structural changes was obtained by varying simultaneously multiple dry-heating parameters. Interestingly, low-extent structural modifications have a dramatic impact on interfacial rheology, liquid film dynamics, foam stability and foam rheology. The effects of dry-heating parameters on the foam properties are complex and depend on their combination and the considered foam feature. Our original multiscale approach (interface, film dynamics and foam) sheds light on the contribution of the interfacial rheology to protein foam properties. In particular, foam dynamics have been shown to play a predominant role.
... Maillard reaction and caramelization are both non-enzymatic processes conditioned by different factors such as temperature, water activity, pH, moisture content and chemical composition (Bastos et al., 2012). Maillard reaction implies the presence of protein and carbohydrates heated at around 140-165°C (Bastos et al., 2012;Eichner and Karel, 1972;Sherwin and Labuza, 2003), while caramelization takes place above sugars heated between 110 and 180°C (Corzo-Martínez et al., 2012 andVillamiel et al., 2006). On the other hand, pyrolysis implies the decomposition of organic materials in an inert atmosphere, and may occur from around 200 to 300°C (Jouhara et al., 2018). ...
Charring is the most common preservation state of plant remains retrieved at archaeological sites. Therefore, archaeobotanists have often performed charring experiments mainly aimed to produce comparative materials and to better understand the various processes affecting the morphology and composition of archaeobotanical assemblages. In this paper, and based on previous works, we develop a laboratory protocol which standardizes the charring process and proposes how to perform charring experiments with a step-by-step description of the methodology. Our observations have focused on ripe Triticum spelta, a species seldom approached by former experiments, both in its ripe and unripe and roasted form, known as Grünkern. We explore the parameters that affect the production of comparative material which preserves the features closest to the non-charred individuals both as regards overall shape and external morphology but also as regards the effects of charring on the internal morphology of the cereal grains examined with the aid of Scanning Electron Microscopy. Based on our own experience and on which information we missed when performing our experiments, we describe here the work that we carried out with the aims of exploring the effects of charring on cereal grain structure, but simultaneously of providing a protocol useful for charring experiments, needed for the standardization of similar work. This standardization is needed in order to achieve meaningful comparisons of results when producing charred material. Being applicable to other experiments and laboratories, it will enable in the future a more reliable exploration and interpretation of ancient cereal foods.
... When the temperature of dry heating, or the water content of the powder increase, an increasing polymerisation of whey proteins appears. When the content in moisture increases at low moisture contents, like in powdered proteins, water molecules act as a plasticizers, the Tg decreased, and the amorphous glassy structure tends to the rubbery state, so that diffusion and reactions can proceed at a lower temperature than with a high water content (Sherwin & Labuza, 2003;Zhou & Labuza, 2007). Moreover, some small molecules like sugars can also decrease substantially the Tg so that the product can easily become unstable at low temperatures, with consequences on the powder quality. ...
Whey protein products are of widespread use as food ingredients because of their high nutritional, biological andfunctional properties. Whey proteins are important structural components in many foods as used in their nativeform, for example for their heat-induced gelation abilities. Furthermore, they also offer reliable functionalitieswhen modified by heating processes as denatured or aggregated proteins. Heat treatment of whey proteins in aliquid state has received much attention in recent years. While dry heating of whey proteins, say heating wheyproteins in the dry state, is frequently cited in the literature as a potential and efficient means to improve thefunctional properties of proteins, it has received very little attention. We report first on the dry heating of wheyproducts as applied to promote glycation of whey proteins with a low denaturation, and second, to promote theirdenaturation and aggregation and on their consequences on the functional properties of whey proteins.
... The Maillard reaction being moisture dependent for optimum activity, it can be inhibited by reducing the moisture content through dehydrating procedures. Sherwin and Labuza [211] showed the role of moisture in the Maillard browning reaction rate in intermediate moisture foods. They found that the addition of humectants to a model formulation caused signifi cant plasticization and a lowering of the T g curve. ...
... This is due to the fact that rutin or naringenin, antioxidant compounds isolated from the Prunus mume., could maintain the meat color stability (Han et al., 2001). Sherwin and Labuza (2003) showed that discoloration of jerky products could be affected by temperature. ...
The objective of the study was to evaluate the quality characteristics of sun-dried Hanwoo beef jerky added with the extract of Citrus junos seib. or Prunus mume. Hanwoo beef shank muscles were sliced, marinated, and sun-dried at 25°C, relative humidity of 35%. The physicochemical quality and microbiological safety of the Hanwoo beef jerky aerobically packaged were analyzed during the storage of 25°C. The moisture content of beef jerky with Citrus junos seib. was the lowest among the treatments after 20 d. Citrus junos seib. and Prunus mume jerky after 10 d had significantly lower aw than those after 0 and 20 d (p<0.05). The pH values of jerky generally ranged from 5.76 to 5.84. The pH value of Prunus mume jerky was significantly higher than those of other jerky samples (p<0.05). Prunus mume jerky showed significantly lower TBARS value than the others after 20 d (p<0.05). Citrus junos seib. jerky showed a significantly lower lightness (L*), redness (a*) and yellowness (b*) than the others during the storage (p<0.05). Prunus mume samples after 10 d had significantly higher L*, a*, and b* values than the others (p<0.05). With regard to sensory properties, Citrus junos seib. and Prunus mume jerky showed significantly higher flavor and overall acceptability scores than the control (p<0.05). The extracts of Prunus mume will be used in sun-dried Hanwoo beef jerky as a natural agent to retard lipid oxidation and to improve meat color.
... Darkening as a result of reduced a w was the only effect discernible by the eye. Several researchers reported enzymatic or non-enzymatic browning in meat, due to the reactivity of fruit or glycerol with protein (Sherwin and Labuza, 2003). However, the addition of sorbitol, kiwi and pineapple did not show a significant difference in L * compared to the control. ...
This study was carried out to investigate the textural and sensory properties of pork jerky with differently added sources of tenderizer or humectant at final concentrations of 2 or 5% (v/w). Pork jerky treated with 5% glycerol, kiwi, or pineapple had lower moisture content and water activity than that of control pork jerky (p<0.05). The addition of tenderizer or humectant resulted in a lower shear force than that of control (p<0.05). The addition of 2 or 5% glycerol resulted in higher equilibrium moisture content (EMC) than other treatments, and addition of tenderizer or humectant produced a higher EMC than that of control (p<0.05). Furthermore, addition of pineapple and kiwi to the samples affected the structures of the myosin heavy chain and the actin filaments of myofibrillar protein, respectively. Trained panel sensory evaluations indicated that pineapple enhanced the flavor score, whereas tenderness score was improved by the addition of tenderizer or humectant (p<0.05).
... In this study, as the addition of RBF increased, the proportion of meat to the proportion of total weight decreased, this may be caused the percent of metmyoglobin decreased. In general, myoglobin denaturation is affected by grinding and mixing (Govindarajan et al., 1997), processing temperature (Sherwin and Labuza, 2003), the addition of salt (Huffman et al., 1981) and lipid oxidation (Faustman and Cassens, 1990). ...
This study evaluated the effects of rice bran fiber (RBF) on the quality of semi-dried pork jerky (SDPJ). SDPJ was supplemented with RBF at levels of 0 (control), 1, 2, and 3%. The addition of RBF at various levels affected the composition of SDPJ except for the fat content (p>0.05). The addition of RBF at a level higher than 2% increased the protein and ash contents of SDPJ (p<0.05). The addition of RBF at various levels also affected the physiochemical properties of SDPJ (p<0.05) except for water activity (p>0.05). Increased level of RBF increased the pH. The rancidity of SDPJ was increased (p<0.05) regardless of the RBF level, whereas the metmyoglobin content (%) of SDPJ was increased at a level higher than 2%. Increased level of RBF decreased the shear force (p<0.05) and the increased processing yield of SDPJ (p<0.05). Jerky made with 2% RBF scored highest for sensory properties, including color, tenderness, juiciness, and overall acceptability (p<0.05). These results indicate that SDPJ containing 2% RBF had the most acceptable quality characteristics, but further study is required to reduce the rancidity induced by the addition of RBF.
... Such color of meat products is commonly seen in meat product displays and is not attractive to consumers because it shows that the meat product is no longer fresh. In restructured meat products, myoglobin denaturation is affected by grinding, mixing, and multiplication of microorganisms (Govindarajan et al., 1977) and increase in temperature (Hood, 1980;Sherwin and Labuza, 2003), salt (Huffman et al., 1981;Rhee et al., 1983;Trout, 1989), and peroxide from lipid oxidation (Faustman and Cassens, 1990). The percent metmyoglobin of the semidried pork jerky samples that were prepared with various kimchi powder levels are shown in Table 2. ...
This study was carried out to investigate the effects of kimchi powder addition on the quality properties of semi-dried pork jerky. Jerky was unamended (control) or was amended with dried kimchi powder to a concentration of 1% (T1), 2% (T2) or 3% (T3). The contents of moisture and ash were the highest in the T3 treatment. The protein content was highest in the control, but there was no significant difference in the fat content. The control exhibited the highest pH value, whereas T2 exhibited the lowest metmyoglobin content. The dry yield and water activity of T2 treatment were highest. There was no significant difference in the thiobarbituric acid value. Shear force was highest in the control. Overall, T2 produced a product with the best sensory evaluation results.
... The percent metmyoglobin content of semi-dried chicken jerky significantly decreased with increasing chicken feet gelatin, and that of samples containing 2% wheat fiber was lower than of those without added wheat fiber (p<0.05). In general, sodium chloride (Huffman et al., 1981), temperature (Sherwin and Labuza, 2003), lipid oxidation (Faustman and Cassens, 1990), and manufacturing processes are known to affect discoloration. Choi et al. (2008) found that the percent metmyogolbin content of semi-dried jerky prepared with pork/beef levels gradually decreased as the beef content increased. ...
The aim of this study was to investigate the effect of chicken feet gelatin and wheat fiber levels on the quality characteristics properties of semi-dried chicken jerky. The obtained chicken feet gelatin swollen with hydrochloric solution (0.1 N HCl, pH ) was dehydrated via freeze-drying. Six formulations of chicken jerky that were prepared, based on the ratio of chicken meat, chicken feet gelatin and wheat fiber, were 100:0:0, 98:0:2, 99:1:0, 97:1:2, 98:2:0 and 96:2:2, respectively. The moisture content of semi-dried chicken jerky containing 2% wheat fiber was higher than that of jerky without the added fiber (p
... It is assumed that pigment isolated from the SH might be affected the meat color stability (Kim and Hong, 2011), which could be attributed to photochemical reaction of sun. Sherwin and Labuza (2003) showed that discoloration of jerky products could be affected by temperature. From the results, as the storage period increased, all treatments caused a significant decrease in a* values (p<0.05). ...
The objective of this study was to evaluate the quality characteristics of sun-dried Hanwoo beef jerky added with Salicornia herbacea (SH). Sliced Hanwoo beef shank were marinated and sun-dried at 28-30 degrees C, relative humidity (RH) 30-35% for 3.5 h. The physicochemical and microbiological traits of the Hanwoo beef jerky were analyzed during the aerobically packaged storage at 25 degrees C. The water activities of beef jerky with 0.5% and 1.0% SH were lower than those of the control at 0 d (p < 0.05). The pH values of beef jerky with SH were significantly higher than those of the control (p < 0.05). The beef jerky with SH and ascorbic acid showed significantly lower TBARS values than the control (p < 0.05). The beef jerky with SH showed a significantly lower redness (a*) than the control (p < 0.05). Total plate count (TPC) of beef jerky with 1.0% SH was significantly lower than that of the control during the storage of 20 d (p < 0.05). Yeast/mold was detected in the control and beef jerky with SH after storage periods of 10 and 20 d, but was not detected in jerky with ascorbic acid. With regard to the sensory properties, beef jerky with SH showed significantly greater flavor scores than the others (p < 0.05). The result shows that SH powder can be used to increase the sensory quality and microbial safety of beef jerky.
... On the other hand, the reheated patties contained 90-91% metmyoglobin regardless of NaCl/phosphate levels and reheating methods (p>0.05). In the manufacture of restructured meat products, the addition of sodium chloride (Rhee et al., 1983;Trout, 1989) and cooking condition (Hood, 1980;Sherwin and Labuza, 2003) are known to affect discoloration. But because the patties cooked at All values are means ± standard deviation. ...
The objective of this study was to determine the effect of reheating methods on the color characteristics of precooked pork patties with various NaCl and phosphate levels. NaCl/phosphate levels for each formulation were as follows; N1 (1% NaCl), N1+P (1% NaCl+0.3% phosphate), N2 (2% NaCl), and N2+P (2% NaCl+0.3% phosphate). The reheating methods used were by electric grill and microwave oven. The surface color of the patties reheated by microwave showed more brown and less-intense red, and the phosphate-treated patties reheated by microwave were more reddish and less brownish. With increased amounts of added NaCl and phosphate, the internal color of patties was more reddish, and the phosphate-treated patties reheated by microwave had more brown than those reheated by electric grill. Among all of the treatments, there were no significant differences in surface color, internal color, and overall appearance. Thus, the color changes in reheated patties were influenced by reheating methods and phosphate.
... The findings of this study agree with Park and Park (2007) noted that meat color values (L*, a* and b*) were higher in the air-blast dried beef jerky than in the hot airdried samples and the drying methods showed the great- est effect on the redness (a*). Sherwin and Labuza (2003) showed that discoloration of jerky products could be affected by temperature. It is assumed that hot air and shade-dried jerky might have a discoloration due to the high temperature in hot air-dried and drying for a long time in shade-dried. ...
To determine the effects of various drying methods on the quality characteristics of beef jerky from low-valued cuts, Hanwoo beef shank muscles were either hot air-dried, shade-dried, or sun-dried. The physicochemical quality and microbiological safety of the Hanwoo beef jerky were analyzed during a storage of 25 degrees C. Moisture content and water activity (a(w)) of the samples decreased as the time period of storage increased, regardless of the drying condition (p<0.05). Shade-dried jerky showed higher a(w) compared to others after storage of 20 d (p<0.05). The pH value of hot air-dried jerky was higher than those of others (p<0.05). For color properties, sun-dried samples showed higher redness (a*) and yellowness (b*) compared with the properties of others (p<0.05). The hot air-dried jerky showed higher shear force values than the sun-dried or the shade-dried jerky after 10 and 20 d (p<0.05). However, the total plate counts (TPCs) of naturally dried jerky (shade and sun-dried) were higher than hot-air dried jerky after storage of 10 and 20 d (p<0.05). With regard to sensory properties, naturally dried jerky showed higher tenderness, juiciness, and overall acceptability scores than the hot air-dried jerky (p<0.05). In conclusion, although natural drying appears to be more susceptible to microbiological contamination than hot air-drying, the natural drying method seems to result in superior quality than the hot air drying method.
... Both protein and glycerol contribute strongly to the moisture sorption characteristics of DDGS (Kingsly and Ileleji, 2009); the moisture sorption characteristics of CDS can reasonably be expected to be affected by these components, as well. Glycerol is a humectant food ingredient which can lower the water activity (a w ) of high-moisture foods to bring them into the category of intermediate-moisture foods (Sherwin and Labuza, 2003). Conversely, if the objective is to dry down a glycerol-containing material as much as possible, the strong water binding of the glycerol is expected to hinder this process. ...
Condensed distillers solubles (CDS) is a viscous, syrupy co-product of ethanol production from corn or other starchy grains; CDS exhibits strong recalcitrance to drying due to its chemical composition, which includes a substantial amount of glycerol. The objectives of this study were to determine the drum drying performance of CDS and to compare it to that of a physically modified CDS (MCDS) having a reduced glycerol level. Material type (CDS versus MCDS), dwell time, drum internal steam temperature, and gap width were evaluated for their effects on the final moisture content, water activity, and color of the dried product. While both CDS and MCDS could be dried to a range of endpoint moisture contents, dried CDS exhibited a narrow range of water activity compared to that of MCDS. Gap width was found to be the predominant factor affecting dried product color. This work demonstrates that drum drying can effectively reduce the moisture content of CDS, even though the water activity of the dried product cannot be reduced beyond ∼0.45. In contrast, MCDS can be readily drum-dried into a shelf-stable, flaked product with a pleasing appearance.
... The measure of water activity (a w ) is useful to describe a thermodynamic equilibrium state and for predicting reaction rate [159]. Browning rate is strongly influenced by environmental factors, such as temperature and water activity. ...
This paper is a review of the recent studies on Maillard reaction products, the formation mechanism for these compounds and melanoidin structure, the undesirable consequences in food especially in fruit juice processing, the desirable effects and the biological properties related to the beneficial health. Melanoidins are compounds generated in the late stages of the Maillard reaction from reducing sugars and proteins or amino acids during food processing and preservation. Recently, the effects of melanoidins on human health and the chemical characterization of the beneficial components have gained a lot of attention, and their implications on several levels, sensory, nutritional, toxicological and technological were investigated. Food melanoidins have been reported to be anionic, coloured compounds, and some of their key chromophores have been elucidated. The antioxidant activity and other biological effects of melanoidins from real foods and model systems have been widely studied. Despite this, very few different melanoidin structures have actually been described, and specific health effects have yet to be linked with chemically distinct melanoidins. The variety of Maillard reaction products formed during the reaction, in conjunction with the difficulty in purifying and identifying them, makes a thorough analysis of melanoidins challenging.
... reactants becomes difficult. Previous studies on molecular mechanisms, involving the role of water in governing the reaction rate in low-to intermediate-moisture foods, showed that solubilization of reactants may contribute to the observed increase of the reaction rate (Sherwin & Labuza, 2003). These results showed that lactosylated CMP can be efficiently prepared during short time storage of freeze-dried powders of CMP-lactose mixtures under appropriate pH water activity and temperature conditions. ...
Glycation of caseinmacropeptide (CMP) during storage with lactose at 40 and 50 °C and water activity 0.33–0.65 was studied by measurement of furosine. At pH 8.0 and aw0.44, maximum levels of furosine up to 1.9 mg/100 mg CMP were obtained within five days at 50 °C, while this value had not been reached at 40 °C after 13 days of storage. Increasing pH up to 11 caused considerable increase in the rate of furosine formation and maximum values were obtained after 9 h at 50 °C. The rate of furosine formation was also enhanced with increasing aw up to 0.65. These results showed that lactosylated CMP can be efficiently prepared during short time storage of CMP–lactose mixtures under appropriate pH, water activity and temperature conditions.
... La calidad, en general, se mantuvo sin variación significativa durante el almacenamiento; sin embargo, se observó pérdida de algunas características de calidad en algunos tratamientos. En el caso del puré con 30% de humedad y 10% de glicerol, se detectó un oscurecimiento que, de acuerdo con Alzamora et al. (31) y Sherwin and Labuza (40) se puede haber debido al desarrollo de pardeamiento no enzimático que se ve favorecido por el mayor contenido de humedad y la presencia de glicerol. ...
Beans consumption has been associated to reduction on chronic, non transmissible, diseases development. Generally, its consumption is less to the recommended and it is done principally as whole grain dishes. To increase the consumption, there is an especial interest in the use of new products. The main goal of this research was to design intermediate moisture bean purees (IMP) using soaked, cooked and grained Tortola bean, removing an important testa portion. In preparation of IMP two moisture levels, 25 and 30%, and two glycerol levels, 10 and 15%, were studied. Purees were preserved at ambient temperature (20 +/- 2 degrees C) for 30 days. Proximal analysis, phytate content and trypsin inhibitors were determined in the original non processed purees. IMPs were analyzed at preparation time and after 15 and 30 days of storage for moisture content, pH and water activity. Besides, microbiological analysis for total plate count on aerobic mesophile microorganisms, molds and yeast, total colifoms, fecal coliforms and Staphylococcus aureus, was carried out. Global quality and sensory acceptance was also determined. IMPs presented a(w) values between 0.800 and 0.844, a pH between 6.20 and 6.24 and the microbiological counting was negative or far below the accepted limits for more strict foods. IMPs presented good qualifications for global quality and were well accepted. Sensory parameters maintain their values during storage, except for color that in treatment with 30% moisture and 10% glycerol showed a light darkening. It is possible to elaborate intermediate moisture bean puree, with low level of antinutritional compounds, good quality and sensory acceptance and with adverse conditions for the development of food safety importance microorganisms.
... However, in most food degradation studies, the rate generally increases as a w is lowered from 0.98 reaching a maximum at around an a w of 0.8 and then decreasing to zero at a w = 0.2-0.3, even in complex reactions such a the Maillard browning reaction, a problem in some liquid drug formulations 8,9 . It has been proposed that for semisolid matrix systems prepared by drying or combining dry ingredients and then humidification to different water activities, a 'dilution effect' occurs, where above a certain a w in the range of 0.6 to 0.8 all the reactant is dissolved, and thus increasing the water content decreases the rate as the total liquidus volume increases dramatically at high a w . ...
Creatine degradation to creatinine, which has no biological activity, in combinations of glycerol and pH 4.0 buffer solutions followed first-order kinetics up to a point where degradation started to level off, generally beyond the first half-life. Practical data are reported for a wide range of water activity (a(w)) values (0.31-0.983) at 4 degrees C, 23 degrees C, and 35 degrees C. Creatine degradation did not exhibit a dilution effect, that is a decrease in rate about an a(w) of 0.7, as is found for both microbiological growth and chemical reactions in semisolid food matrix systems. The temperature dependence obeyed the Arrhenius relationship with an energy of activation of about 20 kcal/mol at a(w) >or= 0.68 increasing to 23 kcal/mole below that a(w). In addition, a semilog plot of half-life as a function of a(w) at each temperature follows a predicted straight line. The pH and assumed liquid viscosity increase through increased glycerol concentration were not able to completely explain the decrease in rate of degradation as a function of a(w). Furthermore, we confirmed that creatine stability in the crystal form is very high as long as it does not reach the deliquescence state.
... Kinetic data derived from experiments with model systems indicate that the activation energy of Maillard type reactions increase with decreasing water activity a w , in particular at a w < 0.3 (Eichner and Karel 1972;Sherwin and Labuza 2003). A more recent investigation with a potato model also showed that the activation energy of acrylamide formation increased with decreasing moisture content (Amrein and others 2006). ...
The influence of roasting conditions on the acrylamide content and on the color of roasted almonds of 3 cultivars was investigated. The temperature inside the almond kernel, the water content, the color, and the acrylamide content were determined at different roasting temperatures and times. The formation of acrylamide started only when the kernel temperature had exceeded approximately 130 degrees C. The activation energy for the acrylamide formation during the roasting of almonds was 123 kJ x mol(-1). The color as measured by the degree of brightness correlated well with the acrylamide content as acrylamide content increased with increasing darkness. Therefore, control of roasting temperature presents the critical factor for limiting the acrylamide concentration in the final product. At constant roasting conditions, almonds with higher initial moisture content contained less acrylamide after roasting, which is probably due to the influence of moisture on the development product temperature during roasting.
High-protein nutrition bars (HPNBs) contain 20–50% protein and can effectively and quickly provide the energy needed by the body for performance. They are widely used as sustenance in sports, fitness, and the military as a means of replenishing vital nutrients after physical endurance. However, the hardening of HPNBs occurs quickly during storage due to the interaction of ingredients in the bar's matrix and effects of the external environment. This will lead to deleterious changes in the qualities of the HPNBs, such as taste, and it can seriously affect their market value. This review expounds the factors affecting the hardening of HPNBs during storage, such as sugar crystallization, water migration, protein self-aggregation, phase separation, and Maillard reactions. Research advances in the current anti-hardening methods are summarized, and the characteristics, advantages, and mechanisms of various methods employed in anti-hardening strategies are also expounded. The hardening of HPNBs is a complicated process involving physical changes during the early stage and chemical reactions during the middle and late stages of the storage period. Measures such as the selection of raw materials, substitution of protein with hydrolyzed protein, protein modification, addition of polyphenols, storage conditions, and other methods have achieved promising preliminary anti-hardening results. However, the development of anti-hardening HPNB methods that enable prolonged shelf lives and maintain or enhance taste and nutritional benefits represents a crucial focus for improving the processing and storage of HPNBs.
Drying is a widely used technique in food manufacturing to preserve food stability by minimizing physical and chemical changes during storage. In dried pasta production, drying is a crucial operation for the quality of the end-product. The traditional drying methods use low temperature (less than 60 °C) and long treatment times (for up to 60 h depending on the pasta shape); but on large-scale retail trade production, the high/very high temperature (75–100 °C or ≥ 100 °C) and short-time (for 10 to 3 h) drying processes are widely employed. A lot of studies prove that drastic heat treatment promotes the Maillard reaction causing changes in the final nutritional and organoleptic properties of pasta. Furosine, an amino acid derived from the acid hydrolysis of Amadori compounds formed during the early stage of the Maillard reaction, has been extensively used as a marker of the heat damage. This review aims to carry out an in-depth investigation of the scientific literature about the role of furosine as a marker of quality. Particularly, to valorise on the market durum wheat dried pasta that has not undergone to thermal stress and also to identify potential commercial fraud. Additionally, volatile compounds, formed during the advanced and final stage of Maillard reaction and responsible for several food properties, were considered due to the possibility to use them in combination with furosine for food security and food quality purposes.
Large amounts of Chinese medicinal materials (CMMs) should be quickly dried during the harvest period because improper drying leads to a browning reaction, which deteriorates the medicinal value of CMMs. In this study, a bidirectional alternating hot air drying system was designed for thick-layered CMMs. The drying capacity could be greatly improved by increasing the thickness of the material layer. The time-weighted average temperature (TWAT) was defined to determine the appropriate reverse time of the airflow direction. The two-stage air supply could reduce the moisture content of the sample to a certain degree at a low temperature, and then realizing the rapid drying of the sample at a high temperature. When the moisture content of honeysuckle reduces to 60%, the browning reaction would be effectively inhibited. Moreover, the drying efficiency of the thick layer could be improved by reducing the frequency of changes in the direction of hot air. An equal TWAT could be obtained in each layer by adjusting the ratio of the upward to downward airflow supply duration. When the TWAT of the upper layer was equal to that of the lower layer, the drying uniformity improved. The difference between the moisture content of the middle layer of the sample and that of its upper and lower layers could serve as the standard for drying uniformity; the smaller the difference is, the better the drying uniformity will be. The bidirectional alternating hot-air drying method was applied to thick layer drying of Chinese herbal medicine and grain. On the one hand, it reduces the drying energy consumption, on the other hand, it helps to improve the uniformity of drying for Chinese herbal medicine. Additionally, this drying method can be applied for grain drying.
Palace halva is a traditional flour-containing confectionery of Turkey. Primarily, physical deterioration is observed in this halva due to its brittle-fibrous structure and low aw. In this study, effects of storage relative humidity (RH) and temperature on quality of palace halva were investigated. Halva samples were stored at different RH (22-90%) at 25-35°C until equilibrium moisture content was reached. Moisture content, aw, hardness, oxidation, color and X-ray diffraction measurements were made before and after storage. Adsorption isotherms of palace halva were determined. Fresh palace halva had aw of 0.21 and glassy structure. Glassy structure of palace halva was not preserved at RH of 54% at 25°C and 32% at 35°C and crystalline structure formed because of state change. Hardness of halva increased and then decreased as RH was increased. Color change by Maillard reaction and increase in TBARS by oxidation occurred in the product as RH and temperature were increased.
The glucose glycation of α-Lactalbumin and β-Lactoglobulin at 50 C in glycerol-based liquid system was investigated to evaluate the effect of water activity on glycation and site-specificity in glycerol matrix. Glycation extent during the reaction was determined using o-phthalaldehyde (OPA) method as well as ultra-performance liquid chromatography combined with electro-spray ionization mass spectrum (UPLC-ESI-MS). Glycation sites were identified by data-independent acquisition LC−MS (LC-MSE). The surface potential achieved by PyMOL and tertiary structure determined by circular dichroism (CD) were used to assist the analysis of the glycation site-specificity in glycerol matrix. The water activity of glycerol solutions was negatively correlated to the glycerol concentration. Results showed that the initial glycation rate in glycerol matrix was fitted to a liear equation in the first 48 h. Glycation accelerated with the increase of glycerol concentration, namely the decrease of water activity, regardless the native structure of protein. The glycation sites were identical at a similar DSP although achieved at different water activity, with 4 and 7 sites detected in α-lactalbumin and β-lactoglobulin, respectively. However, compared with the glycation sites in water based matrix, the site-specificity of glycation was affected by the glycerol matrix, depending on the native structure of proteins. Glycation was prone to occur at the reactive sites distributed on the surface of the proteins, particularly the region with positive potential.
The decolorization of actual molasses wastewater using the electro-Fenton (EF) process was investigated. The optimization of decolorization was performed by means of a Box-Behnken design (BBD), with the operating parameters studied being the applied voltage, H2O2 dosage and reaction time. The results showed that the color removal efficiency reached 88.50% under the optimal conditions, in which 2.86 V, 15.8% H2O2/wastewater ratio and 90.7 min reaction time were applied. The pulse electro-Fenton (PEF) process using the applied voltage and reaction time in the obtained optimal condition was performed afterward. The effects of pulse frequency, pulse duty cycle, electrode distance, H2O2/wastewater ratio and H2O2 stepwise addition were studied. From the results, under the optimal conditions of 2.5 kHz pulse frequency, 25% pulse duty cycle, 2 cm electrode distance and 15.8% H2O2/wastewater ratio, the color and COD removal efficiencies reached 89.59% and 40.71%, respectively. Under these conditions, the PEF process could reduce the energy consumption by at least 75% compared with the regular EF process. Additionally, compared with stepwise addition, the single step addition of H2O2 was more effective in color removal.
Maillard reaction is a nonenzymatic browning reaction that involves the reaction of carbonyl groups, primarily reducing sugars with free amino groups which cause the changes of chemical and physiological properties of proteins (Labuza and Saltmarch 1981). It results in the development of complex mixtures of colored and colorless reaction products which range from flavor volatiles (low molecular weight compounds) to melanoidins, a series of brown pigments with high molecular weights (Carabasa-Giribet and Ibarz-Ribas 2000; Martins and Van-Boekel 2005); these effects could be either desirable or undesirable. Browning and the formation of aroma are desired in baking, roasting, or frying, while it is undesirable in the foods which have a typical weak or other color of their own such as browning in the products of condensed milk, white dried soups, tomato soup, etc. and generation of off-flavors in food during storage. Besides, Maillard reaction can also have negative effects on nutritional values such as the losses of essential amino acids, as well as the formation of mutagenic compounds (Belitz et al. 2004).
In this study, the effect of Pulsed Light (PL) treatment as a cross-linking method on the properties of casein films was evaluated. Casein films were prepared from micellar casein concentrate, with 5 g/100 g glycerol added as a plasticizer. The UV-curable resins PEG (200) diacrylate and PEG (400) diacrylate were added as photo-initiators. Films were prepared by casting and equilibrated under a range of relative humidity (%RH), then treated with Pulsed Light (PL), with up to 15 pulses of light on each side, at a fluence of 1.57 J/cm2 per pulse. The microstructure, mechanical and water barrier properties, water sorption and hydrophobicity of the films were evaluated. PL treatment of casein films with up to 12 pulses increased the films' smoothness and homogeneity, while higher levels of treatment caused structural defects. Mechanical strength and elongation of some of the films, particularly those with added PEG (400) diacrylate, were significantly increased by PL, but no improvement of their water vapor permeability was observed. The incorporation of PEG (200) diacrylate resulted in highly porous film microstructures, and interesting photo-patterning effects observed at high PL doses. These results indicate the potential of PL for creating protein films with unique characteristics and functionality.
ABSTRACTA number of studies have focused on bar hardening of protein bars. The instrumental texture analyzer measurement of peak force is known to measure bar hardness or firmness. However, to understand overall bar texture, another important texture dimension, crumbliness/cohesiveness, needs to be considered. This study was based on three functionally modified dairy proteins, including one whey protein concentrate and two milk protein concentrates. A mixture design was used to study the synergistic effects of these three proteins on bar texture. Instrumental texture parameters that correlated with sensory texture were developed. Peak force (Force 1) was correlated with firmness (being opposite of softness) dimension, and maximum negative force (Force 2) was correlated with cohesiveness (being opposite of crumbliness). Mathematical models with R 2 > 90% were developed to optimize the texture over a 12‐month storage period, with storage at 20C, for bars using one or more of the three proteins. PRACTICAL APPLICATIONSProtein bar manufacturers will be able to select the type of dairy protein and the level of the proteins in a blend required to achieve desired texture in bars based on the findings of this study. The whey protein concentrate, used in this study, proved to be important to minimize firmness over time. The milk protein concentrates in this study performed differently from each other in bars due to the different modifications made during the manufacture of these ingredients. This study has also shown the importance of the crumbliness/cohesiveness texture dimension and investigated a method to quantify this using instrumental texture analysis. The mixture design approach used in this study could be applied to a bar manufacturer's specific formulation to develop a predictive model that will help them adjust key ingredient levels to manipulate the texture in bars.
Research efforts aim to enhance fundamental understanding about the role of salt in cereal products. Such knowledge may open new strategies for salt reduction in respective product categories. A model system, containing pregelatinized starch, glucose, and amino acids heated at 230°C for up to 10 min demonstrated that NaCl leads to darker products compared with the same model heated without NaCl (P > 0.05). The same trend was observed in wheat breakfast cereal flakes toasted at 230°C. The present study investigated two hypotheses how salt may influence color formation through Maillard Reaction: 1) hygroscopic behavior of salt may change the retention of water during heating and encourage Maillard reactions by improving mobility of reactants; 2) salt has a plasticizing effect and the presence of salt might keep the product in a rubbery state longer while heating, hence improving mobility and Maillard reactions of reactants. The same models (pregelatinized starch, glucose, and amino acids) mixed with several types of plasticizers (NaCl, KCl, or trehalose) and a blank without plasticizer were made and heat-treated under controlled conditions. The presence of plasticizers always led to darker products but no correlation was found between color formation, the hygroscopic behavior of the system, and its glass transition temperature as measured by phase transition analyzer.
Introduction: In today's competitive world, development of new approaches through novel technologies is in demand to utilize the food ingredients in a better way. To achieve this goal, there is a need to understand different properties of food ingredients through basic research. Texturized whey protein concentrate (WPC) is one such novel food ingredient, which is currently being investigated by various researchers. Objective: The objective of this study was to compare a few selected mechanical properties of texturized whey protein concentrate (tWPC) films with those of the traditional WPC films. Materials and Methods: To perform this comparative study, moisture content, tensile strength, percentage elongation (PE), water vapor permeability, and water contact angle were evaluated by conditioning the films specimens for 3 h at 11%, 32%, 53%, 75%, 84%, and 100% RH with the help of supersaturated salt solutions to get a water activity of 0.11, 0.32, 0.53, 0.75. 0.84, and 0.99, respectively. Results: The results showed that as the water activity and thus the moisture content increased the PE and water vapor permeability of the tWPC films decreased significantly in comparison with the WPC-based films. On the other hand, the tensile strength and water contact angle of the tWPC films were found to be superior to those of the WPC films at all water activities. Conclusion: These results provide strong evidence that the tWPC films have improved mechanical properties of utility in package design in comparison with films made with WPC films. These attributes can be commercially exploited to advantage in fabrication of new food packaging systems and in edible coating of food products.
IntroductionPhysical State Changes in Foods in StorageExamples of Use of the State Diagram and Glass Transition CurveConclusions
References
Nonenzymatic browning (NEB) in lactose, trehalose, and lactose/trehalose food model systems containing L-lysine and D-xylose (5% w/w) as reactants was studied at 4 different relative vapor pressure (RVP) (33.2%, 44.1%, 54.5%, 65.6%) environments at room temperature. Sorption isotherms of model systems were determined gravimetrically, and data were modeled using the Brunauer-Emmett-Teller (BET) and Guggenheim-Anderson-deBoer (GAB) models. Glass transition, Tg, was measured by differential scanning calorimetry (DSC). NEB was followed spectrophotometrically. Although the 3 model systems showed similar glass transition behavior, different crystallization properties were observed from loss of sorbed water. Mixtures of trehalose and lactose showed delayed crystallization of component sugars. The NEB rate was affected by sugar composition. At a low RVP (33.1%) environment, the NEB rate in trehalose system was higher than in the lactose/trehalose system, and the NEB rate in lactose system was the lowest. The NEB rate in different models seemed to be affected by component crystallization. The highest extent of browning in the trehalose matrix system seemed to be related to the formation of trehalose crystals in the system after crystallization at high RVP. The results indicated that the composition of the carbohydrate-based low-moisture real food systems should be considered in controlling NEB reaction.
In the present study, the effects of phloretin and phloridzin on the formation of Maillard reaction products in a lysine-glucose model with different reactant ratios were systematically investigated. In terms of the formation of Maillard-type volatiles, phloretin and phloridzin treatmen could significantly reduce their generation, where the effects depend on the ratio of lysine to glucose used in the model systems. Phloretin and phloridzin could also affect the colour development of Maillard reactions; especially phloretin, which could significantly promote the formation of brown products in the system with the lowest ratio of lysine to glucose. Based on the carbon module labelling (CAMOLA) technique and HPLC-DAD-ESI/MS analysis, it was found that phloretin and phloridzin could actively participate in the Maillard reaction and directly react with different reactive carbonyl species. The effect of phloretin and phloridzin treatment in both N(α)-acetyllysine-glucose (AC-glu), and N-acetyl-gly-lys methyl ester acetate salt-glucose (AG-glu) model systems, which are close to the Maillard reactions occurring in real food, where the free amino groups of lysine residues were considered as the reactive site, were further investigated. Similar impacts on the formation of Maillard-type volatiles and brown products as in the lysine-glucose models were observed which can also be explained by the capability of phloretin and phloridzin to quench sugar fragments formed in these model reactions.
The aim of this study was to investigate the effects of pork/beef levels and the casings on the quality properties of semi-dried jerky. The pork/beef levels in the four test formulations were as follows: T-1 (pork: beef=100:0), T-2 (95:5), T-3 (90:10), and T-4 (80:20). After tumbling for 30min with curing solution, the cured meats were stuffed into natural sheep casings, collagen casings, or cellulose casings, and then dried. The restructured jerky with cellulose casing had the lowest water content and the highest protein content, with no significant differences between various formulations. There were no significant differences among all formulations with regard to pH and total microbial counts, and jerky with cellulose casing had the lowest value of water activity. The processing yields of jerky made from the T-3 formulation were not significantly different with the various casings. The shear force of jerky with cellulose casing was lower than with other casings, and the metmyoglobin contents were more than 85% in all formulations. With regard to sensory properties, jerky made with the T-3 formulation and cellulose casings rated most favorable in evaluations than other treatments.
Beans consumption has been associated to reduction on chronic, non transmissible, diseases development. Generally, its consumption is less to the recommended and it is done principally as whole grain dishes. To increase the consumption, there is an especial interest in the use of new products. The main goal of this research was to design intermediate moisture bean purees (IMP) using soaked, cooked and grained Tortola bean, removing an important testa portion. In preparation of IMP two moisture levels, 25 and 30%, and two glycerol levels, 10 and 15%, were studied. Purees were preserved at ambient temperature (20 +/- 2 degrees C) for 30 days. Proximal analysis, phytate content and trypsin inhibitors were determined in the original non processed purees. IMPs were analyzed at preparation time and after 15 and 30 days of storage for moisture content, pH and water activity. Besides, microbiological analysis for total plate count on aerobic mesophile microorganisms, molds and yeast, total colifoms, fecal coliforms and Staphylococcus aureus, was carried out. Global quality and sensory acceptance was also determined. IMPs presented a(w) values between 0.800 and 0.844, a pH between 6.20 and 6.24 and the microbiological counting was negative or far below the accepted limits for more strict foods. IMPs presented good qualifications for global quality and were well accepted. Sensory parameters maintain their values during storage, except for color that in treatment with 30% moisture and 10% glycerol showed a light darkening. It is possible to elaborate intermediate moisture bean puree, with low level of antinutritional compounds, good quality and sensory acceptance and with adverse conditions for the development of food safety importance microorganisms.
Kinetic studies on carotenoid loss and changes in other quality attributes of saffron were carried out under varying conditions of water activity (aw) and temperature. The water sorption isotherms of saffron powders were also determined. Within the aw range tested (0.11-0.75), both Brunauer-Emmett-Teller (BET) and Guggenheim-Anderson-Deboer (GAB) sorption models fit the data well and gave estimates for the monolayer values between 1.8 and 5.2 g of H2O/100 g of solids, depending on temperature and the equation used. The glass transition temperature (Tg) of freeze-dried saffron carotenoid extracts, as detected by calorimetry (DSC), was very sensitive to the moisture content of the system; water plasticizes the amorphous matrix and thereby increases the mobility and reactivity of the reactants. Saffron carotenoid (mainly crocins) degradation followed first-order-like reaction kinetics, and it was strongly dependent on temperature and aw. The dependence of the rate constant (k) for decoloration on aw was different from that for other typical nonpolar carotenoids, resembling more the kinetic responses of water-soluble pigment degradation and nonenzymatic browning reactions. Carotenoid loss occurred only at temperatures above the Tg, presumably because of limited molecular diffusion in the matrix at sub-Tg temperatures. However, testing of the applicability of a Williams-Landel-Ferry (WLF)-governed dependence of k on temperature was not successful. Activation energies, calculated from Arrhenius-type plots, gave an average value of ∼20 kcal/mol, typical of other deteriorative processes in food materials. At ambient temperature, an intermediate water activity (aw ∼ 0.43-0.53) seemed to favor the development of aroma constituents (safranal) while maintaining a relatively low degradation rate for the carotenoids.
The nonenzymatic browning patterns of whole egg, egg white, and egg yolk, with and without food humectants, were examined. The browning intensity of the pure egg systems decreased in the sequence of egg white, whole egg, and egg yolk, with maxima at water activity (aw) .65 to .75, .65, and .85, respectively. Glucose incorporation reversed the order of the melanoidin development rate with drastically higher pigment concentrations in the egg yolk (aw of maximum browning = .81) and whole egg (aw of maximum browning = .86). Interestingly, although egg white in the presence of glucose increased browning with time, its intensity throughout the entire storage period was lower than that of the pure egg white system. The browning potential of the egg samples with added sucrose was not significant except for whole egg at the high aw of .95 to .97. Glycerol, propylene glycol, and sodium chloride exhibited an inhibitory effect on the Maillard reaction in the egg products at all the aw values, thus being more desirable for use in the formulation of intermediate moisture foods.
Water, the most abundant constituent of natural foods, is a ubiquitous plasticizer of most natural and fabricated food ingredients and products. Many of the new concepts and developments in modern food science and technology revolve around the role of water, and its manipulation, in food manufacturing, processing, and preservation. This article reviews the effects of water, as a near-universal solvent and plasticizer, on the behavior of polymeric (as well as oligomeric and monomeric) food materials and systems, with emphasis on the impact of water content (in terms of increasing system mobility and eventual water "availability") on food quality, safety, stability, and technological performance. This review describes a new perspective on moisture management, an old and established discipline now evolving to a theoretical basis of fundamental structure-property principles from the field of synthetic polymer science, including the innovative concepts of "water dynamics" and "glass dynamics". These integrated concepts focus on the non-equilibrium nature of all "real world" food products and processes, and stress the importance to successful moisture management of the maintenance of food systems in kinetically metastable, dynamically constrained glassy states rather than equilibrium thermodynamic phases. The understanding derived from this "food polymer science" approach to water relationships in foods has led to new insights and advances beyond the limited applicability of traditional concepts involving water activity. This article is neither a conventional nor comprehensive review of water activity, but rather a critical overview that presents and discusses current, usable information on moisture management theory, research, and practice applicable to food systems covering the broadest ranges of moisture content and processing/storage temperature conditions.
Grain protein films plasticized with glycerol were prepared from corn zein (CZ), wheat gluten (WG), and a 2.3:1 mixture of wheat gluten and soy protein isolate (WG/SPI). Moisture adsorption curves of the three types of protein films at 25°C and within an approximate water activity range of 0.11 to 0.84 were obtained using a static gravimetric method. The Smith, Oswin, Halsey, and Guggenheim-Anderson-de Boer (GAB) models were applied to collected data. For all protein films, the GAB model showed the best fit over the entire studied water activity range yielding mean deviation modulus values (P) of 4.69, 3.44, and 7.95 for WG, WG/SPI, and CZ films, respectively. The Smith and Halsey models fitted well the high water activity (0.53 to 0.84) portion of the isotherms with P values ranging between 2.55 and 6.74. Moisture adsorption behavior by the protein films at the low water activity range (0.11 to 0.58) was reasonably well described by the Oswin model (P values of 6.68, 5.25, and 5.24 for WG, WG/SPI, and CZ films, respectively).
Protein hydrolysates play an important function in many special dietary foods, e.g. for infants, those with genetic disorders, athletes and geriatrics. Because of hydrolysis these materials are more hygroscopic than the initial intact protein. In this reset the moisture sorption isotherms and the glass transition profile as a function of moisture content for fish protein hydrolysates (FPH), whey protein hydrolysates (WPH) and casein hydrolysates (CH) were determined. The properties of each hydrolysates were related to molecular weight with a lower glass transition curve at lower molecular weight, the Tg was proportional to degree of hydrolysis. These hydrolysates may be as important as sugars in lowering Tg. Fish moisture sorption was related to hydrolysis. CH was less susceptible to caking than FPH and WPH.
Debates have emerged recently on whether water activity or the state of the system as dictated by the glass transition temperature (Tg) impacts the rates of chemical reactions in reduced-moisture solid systems. The objective of this study was to evaluate the kinetics of brown pigment formation in polyvinylpyrrolidone model systems of different molecular weights so that the effects of water activity and the glass transition could be distinguished. Browning rates at different Tgs, but constant water activity, were significantly different except when all were in the glassy state. As the system changed from a glassy state to a rubbery state, the rate of browning increased 7-fold. The rate of browning also increased as water activity increased from 0.33 to 0.54, but then appeared to plateau with further increases in water activity. Thus, the rate of brown pigment formation is influenced significantly by the glass transition temperature of the system and less by the water activity. In addition, the concentration of reactants in the aqueous microenvironment had a significant impact on the rate of brown pigment formation.
One of the important characteristics by which the consumer judges the accept- ability of dry products of milk is the color of the products. Factors such as ex- cessive exposure to heat during processing, high moisture content and prolonged storage time at high temperature are generally known to promote browning. A rapid and reproducible method for estimating the extent of discoloration is desir- able from the standpoint of quality control. In their study of the factors influencing the development of color in evap- orated milk, Webb and Holm (5) employed the Munsell color system of visual examination, using permanent color standards prepared from ferric chloride and potassium dichromate. A procedure for extracting color from browned nonfat dry milk solids and dry whey solids using a concentrated solution of trisodium phosphate and sodium chloride was reported by Doob et al. (1). Experience with this method indicated that only a small fraction of the color is extracted from browned nonfat dry milk solids. A method involving the measurement of reflec- tance by means of the Beckman Spectrophotometer recently was reported by Nelson (3) for the determination of color of evaporated milk and related products. One of the factors influencing the extraction of color from dry products of milk is the rather strong adsorption of the color by casein. Kass and Palmer (2) 1 showed that the adsorption follows Freundlich's equation, _x = KC ~ where x is m the amount of material adsorbed, m is the weight of the adsorbent, C is the equi- librium concentration of the adsorbate and K and n are constants. Since the amount adsorbed depends directly on the concentration of the adsorbent, it is reasonable to believe that by breaking down some of the large casein molecules extraction of the color may be more complete. Hydrolysis of the protein mole- cules may be accomplished easily at ordinary temperatures by means of proteo- lytic enzymes with minimum danger of further color production during the hydrolysis. Consequently, when the remaining proteins, proteoses and peptones are precipitated, the filtrate should contain most, if not all, of the undesirable color in addition to the small amount of water-soluble, natural chromogenic mate- rials of milk. The following procedure was developed based upon this principle. Received for publication February 16, 1949. 1 The subject matter of this paper has been undertaken in cooperation with the Quarter- master Food and Container Institute for the Armed Forces. The opinions or conclusions con- tained in this report are those of the authors and do not necessarily reflect the views or endorsement of the Department of the Army.
A methodology for preparing biodegradable films from egg white proteins was developed in this study. Film formation was based on the partial denaturation of egg white proteins by a preheating treatment at pH 10.5, followed by enzymatic polymerization of the proteins at 50 °C, pH 8.2, using a Ca2+-independent microbial transglutaminase. SDS−PAGE confirmed the cross-linking of protein and showed that the polymerization reaction increased with increasing preheating temperature (from 60 to 80 °C) before the enzyme treatment. Films plasticized with higher glycerol content possessed higher equilibrium moisture content, indicating higher film hydrophilicity. The moisture sorption isotherms were well described by the GAB equation. Tensile properties of the films were dependent on relative humidity (RH) and glycerol content. Oxygen permeabilities of the films were low under low RH conditions but increased strongly as RH increased. Films with reduced glycerol content were better oxygen barriers but were more sensitive to RH variation. Keywords: Egg white proteins; edible films; tensile strength; oxygen permeability; transglutaminase
Effects of physical state and glass transition on nonenzymatic browning rate in water, glycerol, poly(vinylpyrrolidone) (PVP), and maltodextrin (MD) systems were studied. All systems had the same concentration of reactants, glucose and lysine, in the water phase. The systems, except water, had also comparable water activities (0.33). Sorption isotherms and glass transition temperatures (Tg) at various water contents for the freeze-dried PVP and MD systems were determined. Nonenzymatic browning rate was determined at several temperatures from optical density at 280 and 420 nm. The PVP and MD systems contained 12.9 and 8.2 g of H2O/100 g dry matter and had Tg values of 67 and 62 °C at 33% relative humidity and 24 °C, respectively. The liquids exhibited significantly higher browning rates than the concentrated systems, especially below the Tg values. The browning rate was higher in the PVP than in the MD system, suggesting that a possible phase separation may affect nonenzymatic browning in foods. Keywords: Glass transition; nonenzymatic browning; physical state; reaction rate
Recent debates have emerged on whether it is water activity (alpha(w)) or the state of the system as dictated by the glass transition temperature (T-g) that impacts the rates of chemical reactions in reduced-moisture solid systems. Previously, model systems could not evaluate the effects of water activity and glass transition independently. By using poly(vinylpyrrolidone) (PVP) of different molecular weights, the effect of water activity and glass transition on chemical reactions can be studied independently and at a constant temperature. The kinetics of aspartame degradation, via its rearrangement into diketopiperazine, was evaluated in the PVP model system. Reaction rates at constant water activity, but different T-g values, were not significantly different. However, rates at a similar distance from T-g, but different water activities, were significantly different. Thus, the rate of aspartame degradation depends upon the water activity rather than upon the state of the system.
The effect of glass transition on nonenzymatic browning of dehydrated vegetables and of model systems (composed of amino acids and sugars reacting in matrices with different physical characteristics) was studied. Glass transition temperature (T(g)) was determined by differential scanning calorimetry. The rates of nonenzymatic browning were taken from the literature for vegetables and were determined for model systems by measuring absorbance at 280 and 420 nm. Rate constants were analyzed as a function of temperature (T) and of (T - T(g)). Browning below T(g) was very slow. Changes in activation energy (which were affected by structural changes) could be detected near the glass transition. A complete predictive model must include the variables T, (T - T(g)), m, and concentration of reactants.
Liquid model systems containing varying concentrations of glucose and glycine in a 0.1 M phosphate buffer at pH 7.0 were stored at 37-degrees-C. Formation of brown pigments and fluorescent compounds as well as the loss of glucose and glycine was monitored over time. Glucose and glycine loss individually followed first-order kinetics and second order overall, as predicted mechanistically. Amino acid loss went into a no-loss period, as expected mechanistically from Bodenstein steady-state kinetics. The rate of browning and fluorescence formation followed pseudo-zero-order kinetics after an induction period and increased when either reactant concentration was increased with the other remaining constant up to a certain level.
The glass transition temperature (Tg) and structure collapse (volumetric shrinkage) of a freeze-dried fish protein hydrolyzate (HFP) were studied. An increase in the water activity from 0 to 0.64 reduced the Tg of HFP from 79.1 to −42.8 °C. The Gordon—Taylor equation was a good predictor for the plasticizing effect of water on Tg. At room temperature (19 °C), collapse was initiated at aw = 0.44 corresponding to a T — Tg value of 35.8 °C, and browning was evident above aw = 0.55. Above these critical values several structural changes occurred: shrinkage, collapse, browning, and setting into a sticky, high-viscosity brown liquid. The viscosity of the matrix at the onset of collapse was 105–107 Pa·s, as estimated using the Williams—Landel—Ferry equation.
Nonenzymatic browning rates of several vegetables, dairy products and model food systems stored at different moisture contents and temperatures were analyzed and related to their glass transition temperature (Tg). the data analyzed corresponded to a region of moisture content in which effects due to reactant diffusion could be expected. As changes in diffusion constants may in turn, be related to glass transition, the Williams-Landel-Ferry (1955) (WLF) equation was used to describe the combined effects of moisture and temperature on the nonenzymatic browning rate constants. Ferry's (1980) procedure of reduced variables utilizing a reference temperature (T0) was applied, the T0 selected within the experimental range. In this procedure, the equation coefficients are calculated for the equation using T0. Then they are recalculated by shifting the selected reference temperature to Tg to obtain the coefficients with reference to Tg. the resulting equation can be applied to relate the browning rate constants to temperature, moisture and Tg. the equation has predictive value and the method avoids extrapolations when data at Tg are not available.
Water-adsorption data and glass transition temperatures (Tg) of maltodextrins with dextrose equivalent (DE) values ranging from 4 to 38, horseradish roots, and strawberries were used to establish relationships between water activity (aw), water content (m), and Tg. Critical m values were considered as those depressing Tg to 25C. Corresponding values of critical aw were obtained from GAB isotherms that were used to model water adsorption. the use of BET isotherms was tested, but the model showed poor correlation with experimental data at high aw values, especially for low DE maltodextrins. Critical m and aw values were lowest for strawberries (1.5 g H2O/g solids; 0.07 aw). the values increased with decreasing DE, ranging from 7.2 (0.44 aw) to 11.2 g H2O/g solids (0,70 aw). Understanding of water-sorption properties and Tg is valuable in controlling processability and stability, and for determining of food-packaging requirements.
The effects of heating rate, storage temperature and water activity on surface caking (Tsc) and advanced caking (Tac) of several dairy-based infant formula powders were determined by the modified ampule and sealed glass test tube methods, respectively. The glass transition temperature, Tg, was determined by differential scanning calorimetry. Observed Tsc and Tac values were higher at faster scan rates (5 and 10°C/min) compared to a slower heating rate (1°C/3 min). In addition, because of the sample size and the difference in viscous flow time constants, Tac≥ Tsc≥ Tg. As expected, stability towards collapse and sticking decreased with Increasing amounts of low-molecular-weight carbohydrate. The predicted stable storage water activities at room temperature based on Tsc were higher than those observed during storage; however, the water activity at which Tstarage= Tg gave a good prediction of the %RH when collapse begins.
The thermal stability of enzyme invertase in reduced-moisture model systems of maltodextrin (MD), polyvynilpyrrolidone (PVP; MW 40,000) and trehalose heated at 90C was studied. Significant invertase inacti-vation was observed in heated glassy PVP and MD systems kept well below their glass transition temperature (T g), but the enzyme was fairly stable in rubbery trehalose systems. However, at moisture contents which allowed trehalose crystallization rapid thermal inactivation of invertase was observed. Invertase inactivation in heated PVP, MD and trehalose systems of reduced-moisture could not be predicted on the basis of glass transition and this was particularly true for trehalose. Conditions which would allow collapse of the systems and crystallization of trehalose were fairly well predicted based on the estimated T g of model systems.
Osmodehydrofreezing is a ‘combined’ process consisting of osmotic dehydration followed by air dehydration and then freezing. This process has been proposed to obtain intermediate moisture (aw = 0.86) apricot ingredients without sulphur dioxide, having a natural and agreable colour, which could be suitable for different applications. The influence of the syrup composition [sucrose, maltose and sorbitol syrups with the addition of 1 % () ascorbic acid and 0.1 % () sodium chloride as antioxidant]on the chemical-physical properties of osmodehydrofrozen apricot cubes (10mm) was studied. The effect of the modification of the glass transition temperature (Tg) through the osmotic pretreatment on the ascorbic acid retention and on the colour stability during storage at −20 °C was also analysed. The incorporation of different sugars into the apricot cubes modified the percentage distribution of the sugars and their low-temperature phase transitions. The sugar composition of the syrup affected the ascorbic acid retention during air-drying and the colour stability during the frozen storage, with maltose showing the highest protective effect.
The effect of water activity on chemical reactions which are important to food stability has been studied extensively. Glass transition theory considers the effect of the state of a system on reactions and is a relatively new approach for understanding the stability of foods. The role of water in chemical reaction rates is examined based on these two approaches.The Arrhenius model has traditionally been used to describe the temperature dependence of chemical reaction rates. An approach developed by Williams, Landel and Ferry may also be applicable for describing the temperature dependence of chemical reactions within some food systems. These two approaches are examined, with emphasis on the applicability and application of each approach.
The effects of water content and temperature variation on the release of flavor components into the headspace over flavors, encapsulated by an extrusion process, in low water content carbohydrate matrixes is studied. The largest amounts of release occurred when the matrix was above its glass transition temperature, whether this was due to increased water content or elevated temperature. Under these conditions up to 70% of the sucrose in the matrix crystallized over a period of 10 days, as quantified using Fourier transform Raman spectroscopy. Smaller amounts of headspace release occurred when the water content of the encapsulated flavor system was decreased from 3. 5 to 3.1% w/w. Small amounts of release occurred from the "as prepared" materials, which were associated with the presence of small amounts of unencapsulated flavor oil with direct access to the headspace. It was concluded that release due to matrix permeability was relatively slow as compared with the above mechanisms.
The mechanistic role of water in the deamidation of a model asparagine-containing hexapeptide (Val-Tyr-Pro-Asn-Gly-Ala) in lyophilized formulations containing poly(vinylpyrrolidone) (PVP) and glycerol was investigated. Glycerol was used as a plasticizer to vary formulation glass transition temperature (T(g)) without significantly changing water content or activity. Increases in moisture and glycerol contents increased the rate of peptide deamidation. This increase was strongly correlated with T(g) at constant water content and activity, suggesting that increased matrix mobility facilitates deamidation. In rubbery systems (T > T(g)), deamidation rates appeared to be independent of water content and activity in formulations with similar T(g)s. However, in glassy formulations with similar T(g)s, deamidation increased with water content, suggesting a solvent/medium effect of water on reactivity in this regime. An increase in water content also affected the degradation product distribution; less of the cyclic imide intermediate and more of the hydrolytic products, isoAsp- and Asp-hexapeptides, were observed as water content increased. Thus, residual water appears to facilitate deamidation in these solid PVP formulations both by enhancing molecular mobility and by solvent/medium effects, and also participates as a chemical reactant in the subsequent breakdown of the cyclic imide.
Whey powders have attracted attention for use in the food industry. The Maillard reaction is a major deteriorative factor in the storage of these and other dairy food products. The objective of the present work was to further study the Maillard reaction as related to the physical structure of the matrix, either porous or mechanically compressed, or to storage above the T(g) of anhydrous whey systems. Sweet whey (W), reduced minerals whey (WRM), whey protein isolate (WPI), and whey protein concentrate (WPC) were stored in ovens at selected temperatures. Colorimetric measurements were performed with a spectrocolorimeter, thermal analyses (TGA) by means of a thermobalance, and glass transition temperature studies by DSC. The browning order in the vials and in the compressed systems followed the order W > WRM> WPC > WPI. k(w2), the slope of the second linear segment of the TGA curve, was related to the loss of water due to nonenzymatic browning (NEB). Browning development was in good relationship with this loss of weight. In the glassy state, the compressed systems developed higher rates of browning and weight loss (assigned to NEB reactions) than the porous systems. Reaction rates in both (porous and compressed) systems became similar as (T - T(g)) increased.
The physical aspects with respect to water and non-enzymatic browning Nutritional, bio-chemical and chemical consequences of protein cross-linking
- Labuza
- Warren R Tp
- Warmbier
- Hc
Labuza TP, Warren R, Warmbier HC. 1977. The physical aspects with respect to water and non-enzymatic browning. In: Friedman M, editor. Nutritional, bio-chemical and chemical consequences of protein cross-linking. New York: Ple-num Press. p 379-418.
The aqueous environment for chemical change in intermediate moisture foods
- Allison Jy Duckworth Rb
- R Clapperton Haa Davies
- Birch
- Gg
- Parker
- Kj
Duckworth RB, Allison JY, Clapperton HAA. 1976. The aqueous environment for chemical change in intermediate moisture foods. In: Davies R, Birch GG, Parker KJ, editors. Intermediate moisture foods. London: Applied Science Publishers. p 89-99.
Water content and stability of low and intermediate moisture foods
- Labuza Tp
- Tannenbaum
- Sr
Labuza TP, Tannenbaum SR, Karel M. 1969. Water content and stability of low and intermediate moisture foods. Food Tech 24:35-42.
Effect of glass transition on rates of nonenzy-matic browning in food systems
- Karmas R Buera
- Mp
Karmas R, Buera MP, Karel M. 1992. Effect of glass transition on rates of nonenzy-matic browning in food systems. J Agric Food Chem 40:873-9.
Application of the WLF equation to describe the combined
- Md-P Buera
Buera MD-P. 1993. Application of the WLF equation to describe the combined Agric Food Chem 48:5263-8.
A proposed method for the determination of color of dry products of milk Caking and stickiness of dairy-based food powders as related to glass transition
- Concus Af Choi Rp
- O Cm Malley
- Fairbanks
Choi RP, Concus AF, O'Malley CM, Fairbanks BW. 1949. A proposed method for the determination of color of dry products of milk. J Dairy Sci 32:580. Chuy LE, Labuza TP. 1994. Caking and stickiness of dairy-based food powders as related to glass transition. J Food Sci 59:43-6.
Reaction kinetics of food stability: comparison of glass transition and classical models for temperature and moisture dependence
- K A Nelson
Investigations regarding the definition and meaning of pH in reduced -moisture model systems [DPhil dissertation
- Ln
- Bell