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 proximit y of the glass transition affect the physical stability of amorphous f oods and could also affect the rate of chemical reactions. The effect of glass transition on the rate of acid-catalyzed sucrose hydrolysis w as investigated in an amorphous polymeric matrix of polyvinylpyrrolido ne (PVP). Aqueous solutions of PVP-sucrose in a citrate buffer were fr eeze-dried in order to obtain the amorphous matrix. Samples were then equilibrated to several relative humidities and stored at several temp eratures. The difference between the glass transition temperature (T-g ) and the storage temperature (T), T-T-g, was not a key factor determi ning 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. K nowledge of the actual pH of a system, and the possible changes that m ay occur during concentration/drying are necessary for a better unders tanding of chemical changes in low and intermediate moisture foods.