A STUDY OF ACID-CATALYZED SUCROSE HYDROLYSIS IN AN AMORPHOUS POLYMERIC MATRIX AT REDUCED MOISTURE CONTENTS

The changes in viscosity and mobility which take place in the proximity of the glass transition affect the physical stability of amorphous foods and could also affect the rate of chemical reactions. The effect of glass transition on the rate of acid-catalyzed sucrose hydrolysis was investigated in an amorphous polymeric matrix of polyvinylpyrrolidone (PVP). Aqueous solutions of PVP-sucrose in a citrate buffer were freeze-dried in order to obtain the amorphous matrix. Samples were then equilibrated to several relative humidities and stored at several temperatures. The difference between the glass transition temperature (T-g) and the storage temperature (T), T-T-g, was not a key factor determining the rate of sucrose hydrolysis, which was controlled by the water content of the system. The major effect on the rate of hydrolysis was related to changes in pH which occur when the system is dehydrated. Knowledge of the actual pH of a system, and the possible changes that may occur during concentration/drying are necessary for a better understanding of chemical changes in low and intermediate moisture foods.