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Risk for colorectal cancer (CRC) is increased in adults with poor diet quality, low socioeconomic status, and increased body mass index (BMI). Cooked meats contain high contents of mutagenic compounds related to CRC risk. To explore differences in meat-based carcinogen exposure, a 99-item Qualtrics survey was issued to 1648 US adults. Average monthly serving size, degree of doneness, and cooking methods of meat products were obtained. The National Cancer Institute CHARRED database was used to quantify exposure to HCAs, PAHs, and Ames Predicted and Estimated mutagenicity. Questions from validated instruments assessed food security status (FSS) and demographic variables, while height and weight were self-reported to calculate BMI. Sex, FSS and obesity status (BMI > 30 kg/m2) were compared using two-sample t-tests and multivariate regression models to determine differences in meat intake and carcinogen exposure. Statistical significance was set at P

The effect of chemical pretreatments on the color and carotenoid content of yellow discolored channel catfish fillets was studied. The color and carotenoid content of the fillets were analyzed by the L*a*b* color system and high-performance liquid chromatography, respectively. Untreated fillets turned more yellow and darker after 12-d storage. Sodium bicarbonate had a beneficial effect on reducing the degree of yellowness, but the fillets still turned darker after storage. Sodium bisulfite gave the best results with fillets becoming less yellow and brighter after storage. Ascorbic acid, butylated hydroxyanisole, citric acid, and sodium metabisulfite were not successful at reducing the discoloration. The sum of carotenoid contents of untreated fillets decreased significantly (P 0.05) different from the fresh or untreated fillets. The appearance of catfish fillets may be improved during storage by pretreating with sodium bisulfite.

Summary Rebaudioside A is a noncaloric high-intensity sweetener extracted from Stevia rebaudiana. For it to be used in foods, rebaudioside A needs to be stable during processing and storage. This study evaluated the kinetics of rebaudioside A degradation in 0.02 and 0.1 m citrate and phosphate buffer solutions at pH 3, 5 and 7 stored at 20, 30 and 40 °C for 9 months. At pH 3 and temperatures less than 30 °C, degradation was slow (i.e. less than 6% loss in 6 months) and not affected by buffer type or buffer concentration. At pH 7, the degradation of rebaudioside A increased dramatically in phosphate buffer (losses of up to 25% in 6 months at 30 °C), while remaining relatively slow in citrate buffer (less than 5% loss). The degradation rates at pH 7 increased 2.6 times as the concentration of phosphate buffer increased. For optimum stability of beverages containing rebaudioside A, formulations with lower concentrations of citrate buffer stored at lower temperatures are recommended.

Yellow pigment deposition is a quality defect associated with channel catfish fillets. This study evaluated the relationship between fillet color and carotenoid contents as well as the effect of refrigerated storage on the color and carotenoid content of discolored catfish fillets. The color and carotenoid content of the yellow fillets were analyzed using the L, a, b-color system and high performance liquid chromatography analysis, respectively. A strong linear relationship between visual yellowness (i.e., the b-values) of fresh catfish fillets and the sum of three major carotenoid contents was observed. Yellow discolored catfish fillets became darker and more yellow during 12 d of refrigerated storage. However, the total carotenoid content of yellow fillets decreased or remained unchanged during storage. Results suggest that while the yellow discoloration of fresh catfish fillets is related to carotenoid contents, the intensification of the discoloration during storage appears to be related to another chemical phenomenon.

Rebaudioside A is a natural noncaloric high-potency sweetener extracted from the leaves of Stevia rebaudiana. With rebaudioside A use increasing in foods, understanding the factors affecting its stability is necessary. This project evaluated the degradation rate constants of rebaudioside A in water, 0.1 M phosphate buffer, and 0.1 M citrate buffer at pH 3 and 7 as a function of ultraviolet (UV) light intensity (365 nm, 0 μW/cm

Tagatose, a monosaccharide similar to fructose, has been shown to behave as a prebiotic. To deliver this prebiotic benefit, tagatose must not degrade during the processing of foods and beverages. The objective of this study was to evaluate the thermal stability of tagatose in solutions. Tagatose solutions were prepared in 0.02 and 0.1 M phosphate and citrate buffers at pHs 3 and 7, which were then held at 60, 70, and 80 degrees C. Pseudo-1st-order rate constants for tagatose degradation were determined. In citrate and phosphate buffers at pH 3, minimal tagatose was lost and slight browning was observed. At pH 7, tagatose degradation rates were enhanced. Degradation was faster in phosphate buffer than citrate buffer. Higher buffer concentrations also increased the degradation rate constants. Enhanced browning accompanied tagatose degradation in all buffer solutions at pH 7. Using the activation energies for tagatose degradation, less than 0.5% and 0.02% tagatose would be lost under basic vat and HTST pasteurization conditions, respectively. Although tagatose does breakdown at elevated temperatures, the amount of tagatose lost during typical thermal processing conditions would be virtually negligible. Practical Application: Tagatose degradation occurs minimally during pasteurization, which may allow for its incorporation into beverages as a prebiotic.

Tagatose is a minimally absorbed monosaccharide that has prebiotic properties. For this prebiotic effect to be achieved, tagatose should remain stable and not degrade during food processing and storage. This study evaluated the storage stability of tagatose in solutions as affected by buffer type, buffer concentration, pH, and temperature. Tagatose does degrade during storage. Minimal tagatose loss and browning were observed in 0.02 M phosphate and citrate buffers at pH 3. In 0.1 M buffers at pH 3 and 40 °C, approximately 5% tagatose was lost over 6 months and slight browning occurred. Tagatose degradation was enhanced at pH 7, especially in phosphate buffer, where it occurred faster than in citrate buffer. Higher buffer concentrations also enhanced tagatose loss. In phosphate buffers at pH 7, browning accompanied the tagatose degradation, increasing to a maximum and then decreasing. To deliver the prebiotic effect from tagatose, shelf-stable beverages should be formulated to the lowest buffer concentration and pH possible to optimize tagatose’s stability.

This study evaluated whether incorporating tagatose, a monosaccharide with prebiotic properties, into bakery products affected their flavours. Cinnamon muffins, lemon cookies, and chocolate cakes were prepared; 1 or 2% tagatose was added to the experimental products while an equal amount of sucrose was added to the control products. Using triangle tests, untrained consumer panels (n=65-81) were unable to distinguish between the flavour of products with and without tagatose. In addition, the flavours of bakery products containing and not containing tagatose were liked similarly. Based on this data, bakery products may be formulated containing low levels of tagatose for its health benefits without altering the product's flavour.

The objective of this study was to investigate the suitability of tagatose, a minimally absorbed prebiotic monosaccharide, as a replacement for sucrose in cookies. A sucrose-containing cookie recipe was prepared as the control. Sucrose was replaced with tagatose at various levels ranging from 25% to 100%. Cookies containing fructose were also prepared for comparison due to the structural similarities between tagatose and fructose. The rheological properties of the dough were measured using texture profile analysis. The baked cookies were evaluated for spread, color, and hardness. For tagatose-containing cookies, the extent of likeness was evaluated by 53 untrained panelists using a 9-point hedonic scale. When sucrose was replaced by tagatose, doughs with similar rheological properties to the control resulted. The tagatose-containing cookies were harder and darker with a lower spread than the control. Sensory data indicated that panelists liked the brown color of the 100% tagatose cookies better than the control, but disliked their sweetness. Overall likeness scores of the control and cookies made by replacing half of the sucrose with tagatose were the same. Tagatose appears to be suitable as a partial replacer for sucrose in cookies based on similar dough properties, cookie properties, and likeness scores. Using tagatose to replace sucrose in foods would reduce the amount of metabolizeable sugars in the diet as well as provide the desirable prebiotic effect.

Tagatose is a monosaccharide that contributes prebiotic characteristics to foods and beverages. Tagatose has the propensity to degrade depending upon product composition and storage environment. Intramolecular rearrangement and cleavage reactions are enhanced at higher pH levels. Citrate and phosphate buffers catalyze tagatose degradation, with the small dibasic phosphate anion being especially catalytic. Amino acids can react with tagatose via the Maillard reaction to cause browning. Degradation is accelerated by increases in temperature. The time/temperature requirements necessary for pasteurization result in tagatose losses of less than 1%. Refrigeration helps maintain at least 98% of the original tagatose concentration in beverages stored 6 mo. Stability concerns arise for shelf stable beverages containing phosphate buffer at high pH levels. Tagatose retention in beverages is improved by formulating with citrate buffer instead of phosphate buffer, reducing the buffer concentration, lowering the pH, and decreasing the storage temperature.

The effects of water activity and the glass transition on the rate constants for glycine loss and brown pigment formation due to the Maillard reaction were evaluated in a model food system. Equimolar glucose and glycine were incorporated into amorphous polyvinylpyrrolidones of various molecular weights and moisture contents. Glycine loss and brown pigment formation were quantified during storage at 25°C. At constant water activity, rate constants were higher in systems with lower glass transition temperatures. Glycine rate constants decreased upon matrix collapse, but browning rate constants were not affected by collapse. Changes associated with the glass transition influence bimolecular reactions and should be considered during product formulation and shelf-life testing.

This project reports on a model for preparing food chemistry and food analysis laboratory manuals that provide a closer link between lecture material and laboratory exercises. Teaching effectiveness was also improved by evaluating the composition and eliminating duplication between these complementary courses. Utilizing the combination of personal experience and the scientific literature, laboratory exercises were developed and modified to fit with the lecture material. Labs were initially performed and critiqued by a graduate student. After making appropriate revisions, undergraduate students tested the labs under the graduate student's supervision and completed a questionnaire about their experiences. Based on the undergraduate feed-back, final revisions were made and custom laboratory manuals were printed. This project demonstrates one effective way for developing custom food science labs to parallel with lecture material.

Many properties of foods and beverages depend upon being formulated to the proper pH. Should this pH shift unexpectedly, the stability and quality of the product could be affected. Although a pH-lowering effect of sucrose added to phosphate buffer has been observed, an explanation for the phenomenon has not been provided. The purpose of this study was to determine why the addition of non-ionic polyols changed buffer pH. Titration curves of citrate and phosphate buffers, with and without added sucrose or glycerol were constructed. Apparent p K a values were determined from titration curves and by measuring the pH values of equimolar buffer solutions. Sucrose appeared to lower the apparent p K a of phosphate buffer, but not citrate buffer. Glycerol appeared to have no effect on the apparent p K a value of phosphate buffer while causing a slight increase in the values for citrate buffer. These results parallel the effects of the polyols on buffer pH; the largest change was a pH decrease from adding sucrose to phosphate buffer. A p K a change appears responsible for this pH-lowering effect, possibly due to differences in solute–water interactions and changes to the hydration sphere around the buffer anions. Potential pH changes from food additives should be recognized during product development in order to optimize product quality and shelf life.

Thiamin is being incorporated into a variety of nutritionally enhanced beverages. Although thiamin degradation during thermal processing has been extensively studied, minimal data exist regarding its stability in solution during ambient storage. This study collected kinetic data for thiamin degradation in solutions as a function of pH, buffer type, and buffer concentration at 25 °C. Thiamin was incorporated into sodium phosphate and citrate buffer solutions, each prepared at 0.02 and 0.1 M and pH 4, 5, 6, and 7. Experimental solutions were stored in an incubator at 25 °C. Thiamin concentrations were analyzed at 9 time points over a 42-wk period. Thiamin degradation data were modeled using pseudo-1st-order kinetics. Thiamin stability generally decreased as pH and buffer concentration increased in both phosphate and citrate buffers. In 0.1 M phosphate buffer, the time for a 10% loss of thiamin decreased from 79 wk at pH 4 to 3 wk at pH 7. At pH 6 and 7, thiamin stability was greater in citrate buffer than in phosphate buffer. However, at pH 4 and 5, thiamin stability was greater in phosphate buffer than citrate buffer. To optimize thiamin stability in low pH beverages, phosphate buffer would be more appropriate to use than citrate buffer, whereas citrate buffer should be used for better thiamin stability in high pH beverages.

The thermal unfolding or denaturation of solid-state proteins during processing can affect their functionality. This project explored the relation between the glass transition temperature (T g ) and thermal unfolding temperature (T m ) using gelatin as a model system. Freeze-dried gelatin was prepared containing various polyol types at several concentrations. Using differential scanning calorimetry, T m and T g were determined. Moisture and polyols (that is, glycerol, xylitol, sorbitol, sucrose, and trehalose) promoted a lowering of both T and T m , the extent of which depended upon the plasticizer type and concentration. For all the data, T m > T g , and a pfot of T m against T g indicated a linear relationship (R 2 = 0.95). These results suggest that formulations must be in the rubbery state to have the necessary mobility for hydrogen bond disruption that leads to protein unfolding. Glass transition data should be considered when developing processing parameters for proteinaceous systems.

Although chemical reactivity in solid food systems has been studied as a function of water activity and glass transition, the possible effects of water mobility on chemical reactions have not been investigated. The effect of the glass transition on water mobility at constant temperature and water content was determined. The relationship between the experimentally determined water mobility in polyvinylpyrrolidone (PVP) systems and chemical reactivity data from the same PVP systems was evaluated. Water mobility, as determined via 17O-NMR, was not affected by the glass transition; PVP systems at constant water activities and water contents, but different physical states (glassy and rubbery), had the same water mobility. An evaluation of four chemical reactions showed no relation between water mobility and kinetic data. The effect of water on chemical reactions is multidimensional and cannot be reduced to a single physicochemical parameter.

The amount of methylxanthines (i.e. caffeine, theobromine) in food products continues to be of interest to the public. To provide such data, an improved analytical method for their determination in cocoa-based food products was developed. An aqueous extraction followed by analysis using the method of known additions was found to give a higher degree of accuracy and precision in comparison with the method accepted by the Association of Official Analytical Chemists International. This improved analytical method will allow for the collection of reliable methylxanthine concentration data that can be used to update food composition databases as well as by consumers and health care professionals.

The stability of thiamin was evaluated in solid polyvinylpyrrolidone model systems as a function of water activity (a(w)) and the glass transition. In the glassy state, thiamin degradation rate constants correlated with the glass transition temperature (T(g)), decreasing as T(g) increased. Above a(w) 0.4, rate constants correlated better with a(w) rather than T(g). However, rate constants decreased in the rubbery state above a(w) 0.4, which could be attributed to glass transition-induced structural collapse. Glass transition effects (mobility considerations, collapse) have a larger effect on thiamin stability than a(w), which should be recognized during the development of fortified food products.

The effects of porosity and collapse on the kinetics of glucose loss and brown pigment formation via the Maillard reaction were analyzed in solid low-moisture model food systems. Equimolar glucose and glycine were incorporated into amorphous polyvinylpyrrolidones having different porosities, ranging from high porosity to totally collapsed. Samples were equilibrated and stored in desiccators at water activity 0.33 or 0.44 and 25 °C. Glucose loss and brown pigment development were monitored for 3 months. Glucose loss rate constants were lower in collapsed systems compared to non-collapsed systems. The extent of porosity did not affect glucose loss rate constants. Collapse and porosity had minimal effects on the browning rate constants. Porosity and collapse affect chemical reactivity in low-moisture solids and should be considered during product development and shelf-life testing.

The effects of water activity (aW) and the state of the system as dictated by the glass transition temperature (Tg) on tyrosinase storage stability were evaluated in a model food system. Tyrosinase was incorporated into low and high molecular weight polyvinylpyrrolidone (PVP-LMW and PVP-K30, respectively). Samples were equilibrated and stored in desiccators from aW 0.33 to 0.77 at 20°C. Tyrosinase activity was monitored for a week, and pseudo-first order rate constants for activity loss were calculated. Residual activity after equilibration correlated with Tg rather than aW. An apparent rate constant increase slightly above Tg was observed and rate constants were the same at constant Tg, suggesting that molecular mobility as dictated by Tg was influencing tyrosinase storage stability.

Encapsulated aspartame (APM), developed to protect the APM molecule during baking, has not been evaluated for stability during baking and subsequent product storage. Thus, the objectives of this project were to determine the APM recovery in various cake formulations after baking and to evaluate APM degradation kinetics during product storage. The recovery of encapsulated APM after baking was 33–34% while that of non-encapsulated APM was 22%. The addition of the acidulant glucono-delta lactone (GDL) to the formulation increased the recovery of encapsulated APM to 58%. The rate constants of APM degradation in the cakes with and without GDL at 22 °C were 0.0085 and 0.035 day−1, respectively. By using 2.5% encapsulated APM in cupcake mixes for home preparation, enough APM should remain to provide adequate sweetness during typical product shelf life.

This study's objectives were to investigate the effects of buffer type and concentration on the kinetics of the Maillard reaction in low-moisture solids. Glucose loss and brown pigment formation were evaluated in low-moisture glassy systems obtained by lyophilizing solutions containing various concentrations of phosphate or citrate buffer at pH 7 and 25°C. Rate constants for glucose loss decreased as buffer concentration increased, suggesting that a change in the system pH had occurred. Rate constants for browning increased with increasing phosphate buffer concentration and decreased with increasing citrate concentration. Phosphate buffer appeared to catalyze later pathways of the Maillard reaction.

A discussion of the factors influencing peptide stability illustrates the challenges of formulation and shelf-life prediction which face biotechnologists. The activation energies of peptide degradation vary with pH and moisture content. Peptide degradation rates are influenced by both buffer type and concentration. Lyophilization results in an increase in buffer concentration which also enhances peptide degradation in low-moisture solids. Small peptides have degradation rates that depend upon water activity rather than upon mobility limitations associated with the state of the system. The pH−rate profiles for peptide degradation in solution and solids are quite different. Dehydration and partial rehydration change the pH of reduced-moisture solids, which change both the rates and mechanisms of degradation. The properties of the peptide and the system as well as potential interactions between the two need to be identified to maximize peptide stability. In addition, solution data cannot be used to predict the shelf life of reduced-moisture solids.

Encapsulated aspartame (APM), developed to protect APM during baking, has not been previously evaluated with respect to sensory acceptability. This project evaluated the sensory properties of cakes formulated with encapsulated APM. A no-sugar-added cupcake was formulated with encapsulated APM. An experienced sensory panel indicated that the sweetness level was similar in the no-sugar-added cakes after three days as compared to a full-sugar cake overall. The no-sugar-added and full-sugar cakes received consumer acceptability ratings which were not significantly different (p>0.05). The results from this project indicate that encapsulated APM can be successfully used to formulate no-sugar-added cupcake mixes for home preparation.

Buffering agents are added to many diverse foods to control the pH of the system. Limited data exist on the effects these buffers have on the Maillard reaction. The objective of this study was to investigate the effects of buffer type and concentration on the Maillard reaction. The loss of glycine and the formation of brown pigment were evaluated in phosphate and citrate buffer solutions of various concentrations at pH 7 and 25 °C. No glycine loss nor brown pigment formation was observed in the citrate buffer solutions. However, citrate did not appear to be functioning as an inhibitor of the reaction. The rates of glycine loss and browning increased with increasing phosphate buffer concentration. The bifunctional catalytic ability of the phosphate anion was proposed as an explanation for the differing effects of the buffers.

The effect of chemical pretreatments on the color and carotenoid content of yellow discolored channel catfish fillets was studied. The color and carotenoid content of the fillets were analyzed by the L*a*b* color system and high-performance liquid chromatography, respectively. Untreated fillets turned more yellow and darker after 12-d storage. Sodium bicarbonate had a beneficial effect on reducing the degree of yellowness, but the fillets still turned darker after storage. Sodium bisulfite gave the best results with fillets becoming less yellow and brighter after storage. Ascorbic acid, butylated hydroxyanisole, citric acid, and sodium metabisulfite were not successful at reducing the discoloration. The sum of carotenoid contents of untreated fillets decreased significantly (P0.05) during storage as compared to the fresh fillets. However, the sum of the carotenoid contents of fillets treated by various chemicals was not significantly (P0.05) different from the fresh or untreated fillets. The appearance of catfish fillets may be improved during storage by pretreating with sodium bisulfite.

The caffeine content of coffee as influenced by various coffee preparation methods was investigated. The variables studied included the coffee solids to water volume ratio, the volume of coffee prepared, home versus store grinding, and drip/filtered versus boiling. Caffeine contents per 177 ml (6 oz) of coffee ranged from 50 to 143 mg, depending upon the mode of preparation. As expected, more coffee solids and larger extents of grinding led to significantly higher caffeine contents in filtered coffee. Larger volumes of coffee prepared at a constant coffee solids to water ratio also yielded significantly higher caffeine contents. Homegrinding yielded caffeine contents similar to that of store-ground coffee. Boiled coffee had caffeine contents equal to or greater than filtered coffee, depending upon the length of boiling time. The variable caffeine contents in coffee resulting from the mode of preparation should be recognized and addressed by both food composition data bases and epidemiologists.

Glass transition temperatures, T g , of polystyrene, polyvinylpyrrolidone, polydextrose, gelatin, corn flakes, pasta, and aqueous glucose/glycine solutions were determined using a differential scanning calorimeter which cycled the temperature while the net temperature increased at a constant rate. Operating conditions of the modulated differential scanning calorimeter TM (MDSC TM ) for optimizing the endothermic baseline shift associated with the glass transition were a scan rate of 5°C/min with an amplitude of ± 1°C over a modulation period of 60 or 100 sec. The MDSC successfully separated the glass transition from other irreversible thermal changes in simple food ingredients. While the MDSC did not distinctly determine T g of complex food systems at low moisture contents, glass transitions were observed for solutions and food systems at higher moisture contents. T g values from MDSC were reproducible and similar to those from standard DSC.

The amount of tea or coffee estimated from the number of cups consumed is frequently used as an indication of caffeine consumption in epidemiologic studies. However, this alone may be an inadequate indication of intake since drinking practices of tea varies. In this study, methylxanthine (caffeine, theobromine, and theophylline) contents in three brews of four types of tea (black, oolong, green, and herbal) in both bags and loose leaf forms were investigated to determine the actual amount of methylxanthines present in tea as a function of different brewing methods. On a dry leaf weight basis, total caffeine after three brews was highest in black (32.8 mg/g) and green (36.6 mg/g) tea leaves and lowest in Formosa oolong tea 2 (23.8 mg/g). Total theobromine was highest in black teas (1.64 and 1.69 mg/g) and least in oolong teas (0.65 and 0.71 mg/g). Caffeine and theobromine were not detected in either herbal tea samples, and theophylline was not detected in any tea tested. The overall average caffeine released in the first through third brews were 69%, 23%, and 8%, respectively. Three cups of tea brewed using three tea bags (Western culture) have approximately twice the amount of methylxanthines as the same volume prepared by three successive brews of loose tea leaves (Asian culture). These differences should be accounted for by the epidemiologic studies evaluating the effect of methylxanthines on health.

Dehydrated proteins are frequently subjected to thermal stress in the presence of other components. The effect such substances may have upon protein structure, and therefore function, has not been fully investigated. Thus, the effect of added polyhydroxy components on the denaturation of lyophilized β-lactoglobulin, ovalbumin, and ribonuclease, as determined by differential scanning calorimetry, was evaluated. The denaturation temperature, T m , of the globular proteins decreased in the dry state after the addition of sucrose, sorbitol, or glycerol. The thermal stability (based on T m ) of the dehydrated proteins appeared to correlate with the glass transition temperature (T g ) of the polyhydroxy component, which was assumed to be related to the T g of the mixture. The lower the T g of the component, the greater was the degree of protein destabilization. Thus, glass transition data may be used to predict the effect that a component would have on denaturation of dehydrated proteins at elevated temperatures.

Aspartame (APM) is a high-intensity sweetening agent incorporated into a variety of diet beverages along with some type of buffer to control the beverage pH. However, data on the effects of individual buffer types and their concentrations on APM degradation rates do not exist. This project evaluated the rate of aspartame degradation in phosphate and citrate buffer solutions at pH 3 and 7 over a concentration range of 0.01-1.0 M ; experiments were performed at 25 °C. APM degradation rate constants were less at pH 3 than at pH 7 as reported previously. The reaction rates increased significantly as buffer concentration increased in both phosphate and citrate buffers. The degradation rate in phosphate buffer was significantly faster than in citrate buffer at pH 7. However, at pH 3, the difference between the rates in citrate and phosphate buffers was diminished. These results suggest that using citrate buffer rather than phosphate buffer would reduce the loss of APM in diet beverages, especially in higher pH beverages. Thus, diet beverages formulated with citrate buffer would have longer shelf lives than those formulated with phosphate buffer. In addition, this study provides general insight as to the mechanisms by which buffers may destabilize food ingredients.

The physical stability of a human growth hormone (hGH) formulation upon exposure to air/water interfaces (with vortex mixing) and to nonisothermal stress [determined by differential scanning calorimetry (DSC)] was investigated. The effect of these stresses on the formation of soluble and insoluble aggregates was studied. The aggregates were characterized and quantified by size exclusion-HPLC and UV spectrophotometry. Vortex mixing of hGH solutions (0.5 mg/mL) in phosphate buffer, pH 7.4, for just 1 min caused 67% of the drug to precipitate as insoluble aggregates. These aggregates were noncovalent in nature. Non-ionic surfactants prevented the interfacially induced aggregation at their critical micelle concentration (cmc) for Pluronic F-68 (polyoxyethylene polyoxypropylene block polymer) and Brij 35 (polyoxyethylene alkyl ether) and above the cmc for Tween 80 (polyoxyethylene sorbitan monooleate). However, the same surfactants failed to stabilize hGH against thermal stress in DSC studies. Higher concentrations of surfactants actually destabilized hGH as evidenced by the decrease in the onset temperature for the denaturation endotherm.

The endothermic thermal transitions (i.e., denaturation) of lyophilized recombinant bovine somatotropin (rbSt) and lysozyme as seen via differential scanning calorimetry were evaluated with respect to moisture and excipients. The denaturation temperature, Tm, of rbSt and lysozyme decreased with increasing moisture irrespective of the excipient. However, the magnitude of the decrease elicited by moisture was dependent on the type of excipient. Furthermore, the effect of the excipient was dependent on the moisture content; excipients decreased Tm in low moisture solids (i.e., 15% moisture). In the dry state (< 1% moisture), the addition of 50% sucrose, sorbitol, or glycerol lowered the Tm of rbSt from 161 °C to 136, 120, and 83 °C, respectively, indicating a destabilizing mechanism. Likewise, the Tm of lysozyme decreased from 156 °C to 142, 128, and 97 °C due to the addition of sucrose, sorbitol, and glycerol, respectively. At higher moisture contents, the excipients promoted a higher transition temperature at a given moisture content than the pure protein systems, indicating a stabilizing mechanism. An increase in the enthalpy of unfolding for dehydrated lysozyme was noted with increasing levels of moisture and/or excipient, despite the observed decrease in Tm. The thermal stability, or Tm, of the dehydrated proteins appeared to be correlated to the glass transition temperature (Tg) of the excipient, which in turn should be related to the Tg of the system. The lower the Tg of the excipient, the greater was the degree of destabilization. This result suggests different modes of conformational stabilization by excipients may exist for proteins in the solid state depending on the moisture content.

Recent debates have energed on whether water activity (a n ) or the state of the system as dictated by the glass transition temperature (T g ) controls the rates of chemical reactions in reduced-moisture solid systems. Previously, model systems in which the effects of water activity and glass transition on chemical reactions could be evaluated independently did not exist. The use of polyvinylpyrrolidone (PVP) of different molecular weights allows the water activity and moisture content of the systems to be kept virtually constant while the glass transition temperature varies. At a given water activity and temperature, the equilibrium moisture content for any molecular weight of PVP differed by only 1-2%, while the T g values differed by 20-30C. Using PVP of different molecular weights as a model system will allow the effects of water activity and glass transition on chemical reactions to be studied independently and at a constant temperature

The nonisothermal transitions of lyophilized recombinant bovine somatotropin (rbSt) as seen via differential scanning calorimetry were evaluated with respect to moisture content. The transition peak temperature of rbSt decreased with increasing moisture from 161°C in the dry state to a plateau of 65°C at 28% moisture, which is similar to that of rbSt in solution. Using high performance liquid chromatography, this irreversible endothermic transition consisted primarily of unfolding, hydrophobic aggregation, and some covalent modifications. In the dry state, covalent modifications, including polymerization into compounds of higher molecular weight, were more prominent, while in the presence of moisture, hydrophobic aggregation was most prominent. The irreversibility and scan rate dependence of the endothermic phenomena supports the kinetic nature of the transition rather than a simple equilibrium between globular and unfolded states. The apparent activation energy, for the net transition (i.e., unfolding, hydrophobic aggregation, and covalent modifications) was 57 kcal/mol for rbSt at 9.9% moisture. The observed enthalpy of the transition increased, decreased, then approximately leveled off as a function of increasing moisture content. This can be explained by the increasingly significant contribution of the exothermic aggregation at higher moisture contents. © 1995 John Wiley & Sons, Inc.

Moisture sorption isotherm and glass transition temperature (Tg data on polyvinylpyrrolidone (PVP) of molecular weights less than or equal to 40,000 as well as PVP containing added plasticizers were collected to examine the possibility of extracting T, values from moisture sorption data. Moisture sorption isotherms generated for PVP of various molecular weights were similar to those previously reported. The moisture sorption isotherm for PVP-K15 containing added vinylpyrrolidone (VP) and methylpyrrolidone (MP) were predicted reasonably well by simple addition of their respective isotherms with that of PVP-K15. The Tg values for PVP as a function of moisture was similar to that found previously. Decreasing polymer molecular weight or the addition of plasticizers (VP or MP) reduced the Tg of the polymer system, displacing the Tg to lower temperatures. When the moisture content to give a Tg of 25°C (Wg) was indicated on the isotherm, Wg shifted downward with decreasing molecular weight or increasing ...

Tagatose is a reduced-calorie monosaccharide that displays prebiotic properties. Water can interact with powdered tagatose to varying extents, depending upon the storage environment. Adsorbed water can impact the stability of tagatose, altering its functionality and usability as an ingredient. The objective of this study was to evaluate the physical and chemical stability of bulk tagatose powder as a function of relative humidity (RH) and temperature. Powdered tagatose was stored in desiccators at 20, 30, and 40 °C and 33% to 85% RH. Moisture contents (MC), physical characteristics, tagatose degradation profiles, and browning kinetics were monitored for 12 mo. The critical RH associated with deliquescence (RH0) was approximately 85% at 20 °C. MC values below RH0 were all less than 2% (wb). The MC at 85% RH ranged from 55% to 80% (wb), increasing as temperature decreased. At 33% RH and 20 °C tagatose remained a free flowing powder. As either temperature or RH increased, varying degrees of physical caking occurred. At 85% RH, tagatose deliquesced at all temperatures. Browning occurred in all samples at 40 °C. Despite physical caking and browning, measurable tagatose degradation was only observed in the deliquesced sample at 85% RH and 40 °C, where 20% loss occurred in 6 mo. Although extreme RHs and temperatures are required for tagatose degradation to occur, intermediate RHs and temperatures promote physical caking and deliquescence, which create handling problems during product formulation. The exposure of tagatose to elevated relative humidities and temperatures should be avoided to maintain its physical and chemical quality.

The monosaccharide tagatose has been shown to behave physiologically as a prebiotic. To provide its healthful prebiotic effect to consumers, tagatose must not break down during food processing and storage. The objective of this study was to evaluate the storage and thermal stabilities of tagatose in milk and lemonade. Tagatose (0.9% to 1.5%) was added to commercially available shelf stable milk and diet lemonade. Samples were stored at 20, 40, 61, and 81 °C. Tagatose loss was monitored chromatographically. Pseudo-first-order rate constants for tagatose degradation were determined along with the reaction's activation energy. No tagatose degradation was observed in lemonade at temperatures equal to or less than 61 °C. Degradation occurred faster in milk because of its higher pH in comparison to lemonade and its dairy proteins enabling the Maillard reaction. The activation energy for tagatose degradation in milk was 24.6 kcal/mol. Using this activation energy, it was estimated that less than 0.1% tagatose would be lost during pasteurization and less than 4% would be lost during storage at 25 °C for 6 mo. Although tagatose degradation occurs in beverages, the extent of its loss during pasteurization and storage would be very low. Tagatose can be formulated into beverages with minimal concern about its degradation and the subsequent loss of prebiotic activity. Practical Application: Tagatose can be incorporated into beverages as a prebiotic to improve the healthful characteristics of the product without significant degradation.

Recent debates have emerged on whether it is water activity (a 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

The kinetics of aspartame degradation as pH-rate profiles and patterns of degradation product formation in a semi-solid gel made with high and low moisture contents indicated that the actual pH of the aqueous phase in reduced-moisture solid systems was significantly different from the initial ‘wet’ pH. It is the pH of the dehydrated system rather than the pH before moisture removal that indicates the true activity of hydronium and hydroxyl ions that govern acid/base catalyzed reactions. As an example, the mechanisms of aspartame and ampicillin degradation changed as the lower moisture content changed the pH. In all cases, the pH decreased as the water activity (aw) was lowered. Enthalpy-entropy compensation predicts that the rate constants for most aqueous phase reactions decrease with decreasing aw. It has been observed that the rates and pseudo-order rate constants for many reactions have a maximum between aws of 0·6 and 0·8. In evaluating the rate constants, the concentration of hydronium or hydroxyl ions is either ignored or incorporated as an unknown constant into the pseudo-order rate constant, even when the reaction is studied at several pH values and aws. Conditions are observed where reaction rates decrease or increase as a function of initial pH at constant aw. No explanation has been provided for this. The actual hydronium or hydroxyl ion concentration in the limited moisture phase over the aw range may possibly explain the observed effect on rates. To obtain a complete picture of the influence of aw on reaction kinetics, both the rate constant and reaction rate should be evaluated as a function of aw, taking into account the actual reactant concentrations that include hydronium or hydroxyl ions.

The objective of this research was to evaluate the stability of aspartame in commercially sterilized skim milk beverages that contained different buffer salts, buffer concentrations, and flavor. The effects of pH and temperature on aspartame stability in these dairy beverages were also studied. The pH and storage temperature appeared to be the two most important factors for a successful dairy beverage sweetened with aspartame. The half-lives were 1 to 4 d at 30 degrees C and 24 to 58 d at 4 degrees C. Decreasing the pH from 6.7 to 6.4 doubled the stability of aspartame. The type and concentration of buffer had only a minor influence on the aspartame stability. The addition of vanilla did not enhance the degradation of aspartame in dairy beverages.

A discussion of the factors influencing peptide stability illustrates the challenges of formulation and shelf-life prediction which face biotechnologists. The activation energies of peptide degradation vary with pH and moisture content. Peptide degradation rates are influenced by both buffer type and concentration. Lyophilization results in an increase in buffer concentration which also enhances peptide degradation in low-moisture solids. Small peptides have degradation rates that depend upon water activity rather than upon mobility limitations associated with the state of the system. The pH−rate profiles for peptide degradation in solution and solids are quite different. Dehydration and partial rehydration change the pH of reduced-moisture solids, which change both the rates and mechanisms of degradation. The properties of the peptide and the system as well as potential interactions between the two need to be identified to maximize peptide stability. In addition, solution data cannot be used to predict the shelf life of reduced-moisture solids.

It is desirable to quickly and accurately determine the pH of reduced-moisture solid food systems. Several techniques of pH determination were evaluated on such systems. Methods involving the addition of water yielded pH values higher than actually existed based on pH-dependent chemical reactions. the Ultra M® micro electrode had problems with reproducibility and stability in the reduced-moisture systems as well as the buffer solutions used for calibration. the Horiba Cardy pH meter and the surface pH electrode used directly on the surface of the reduced-moisture solid system yielded pH values similar to those determined using pH-dependent chemical reaction markers. the ability to measure the actual pH of reduced-moisture solid systems would enable better understanding of potential modifications in product formulation needed to retard microbial growth and limit chemical reactions responsible for loss of shelf-life.

The importance of pH on food stability and food processing characteristics has been well documented. Chemical reactions and microbial proliferation depend on the pH of a dehydrated food, which may differ from the pH of the initial hydrated state. In many cases, the pH in the aqueous microenvironment of low-moisture systems is significantly lower than that of the initially hydrated system. Surface glass electrodes used without the addition of water appear to give a better indication of the actual pH of low-moisture systems than do measurements of the pH of the highly hydrated reconstituted system