Submitted to: Journal of the Science of Food and Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/28/2004
Publication Date: 1/1/2005
Citation: Mohamed, A., Rayas-Duarte, P., Kim, S. 2005. Effect of starch on the thermal kinetics and transmittance properties of lysozyme. Journal of the Science of Food and Agriculture. 85:450-458. Interpretive Summary: Interactions between natural polymers in different systems are not addressed adequately in the literature. The key to understanding these interactions is to understand the effect of these polymers on each other. The interaction between wheat protein and starch is the determining factor that governs the use of wheat flour in different baking formulas. It is also important in designating different types of flours for the appropriate uses. Since wheat protein is difficult to solublize, model protein was used to study the interaction between wheat starch and lysozyme. Lysozyme is a well-studied protein with uses in the food industries as a natural antibacterial agent. The same study will benefit lysozyme producers in choosing the best means of delivering their product in an active and safe form. The results of this work will help wheat breeders to focus on the starch component that has more interaction with protein and thus helps in the production of wheat flours for specific uses. Some starch fractions increased the temperature of the beginning of lysozyme destruction and consequent inactivation. That means starch helps to stabilize lysozyme during the heating process. The study also showed that lysozyme is more stable in freeze-thaw conditions in the presence of starch indicating stability during product shipping across different climate conditions.
Technical Abstract: The effect of starch fractions added to lysozyme in aqueous solutions was estimated by differential scanning calorimetry (DSC). Lysozyme was unfolded and folded five times in the presence of starch fractions. The effect of starch fractions on the onset temperature (To), peak temperature (Tp), and enthalpy of gelatinization delta-H was used to estimate their interaction. Overall, a trend of higher To values during the unfolding process was observed with the 2% addition of all starch fractions except amylose. Amylopectin lowered the To of lysozyme thermal transition the greatest. The removal of the starch surface proteins enhanced the hydrophobic interactions in the core of the lysozyme molecules and helped to stabilize it. The effect of starch fractions on the water molecules orientation could be the cause of the interaction. The percentage of delta-H values decreased as a new heating and cooling cycle was performed (i.e., 74.4% of the delta-H of the first cycle was consumed in the second cycle). A lower percentage of lysozyme molecules unfolded in the presence of the starch fractions when compared to the control.