Leonard N. Bell

Molecular dynamics of solid-state lysozyme as affected by glycerol and water: a neutron scattering study.

Glycerol has been shown to lower the heat denaturation temperature (T(m)) of dehydrated lysozyme while elevating the T(m) of hydrated lysozyme (. J. Pharm. Sci. 84:707-712). Here, we report an in situ elastic neutron scattering study of the effect of glycerol and hydration on the internal dynamics of lysozyme powder. Anharmonic motions associated with structural relaxation processes were not detected for dehydrated lysozyme in the temperature range of 40 to 450K. Dehydrated lysozyme was found to have the highest T(m) by. Upon the addition of glycerol or water, anharmonicity was recovered above a dynamic transition temperature (T(d)), which may contribute to the reduction of T(m) values for dehydrated lysozyme in the presence of glycerol. The greatest degree of anharmonicity, as well as the lowest T(d), was observed for lysozyme solvated with water. Hydrated lysozyme was also found to have the lowest T(m) by. In the regime above T(d), larger amounts of glycerol lead to a higher rate of change in anharmonic motions as a function of temperature, rendering the material more heat labile. Below T(d), where harmonic motions dominate, the addition of glycerol resulted in a lower amplitude of motions, correlating with a stabilizing effect of glycerol on the protein.

Maillard reaction as influenced by buffer type and concentration

Abstract 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.

Kinetics of non-enzymatic browning in amorphous solid systems : distinguishing the effects of water activity and the glass transition

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.

Tea preparation and its influence on methylxanthine concentration

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.

Physical properties and consumer liking of cookies prepared by replacing sucrose with tagatose.

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.

Caffeine content in coffee as influenced by grinding and brewing techniques

Abstract 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.

Peptide Stability in Solids and Solutions

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.

Improved analysis of theobromine and caffeine in chocolate food products formulated with cocoa powder

Abstract 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.

Solid-state tyrosinase stability as affected by water activity and glass transition

Abstract 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.

Thermal stability of tagatose in solution.

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.