The rate of non-enzymatic browning reaction in model freeze–dried food system in the glassy state

Abstract

The effect of glass transition on the rate of the non-enzymatic browning reaction (NBR) of glucose and lysine in different glassy matrices; trehalose, maltose, polyvinylpyrrolodone (PVP)-k90, -k30 and -k13 ∼ 19, was investigated. The extent of NBR was determined by the absorbance at 280 nm/gram sample ( ABS 280), and the rate of NBR was evaluated as a pseudo zero order reaction rate from the time course of ABS 280. In each glassy matrix, the NBR progressed at temperatures much lower than the glass transition temperature ( T g). Although the T g of PVP matrix was much higher than that of trehalose or maltose, the NBR rate was much faster. These results suggest that the NBR rate in a glassy matrix cannot be understood by the T g of matrix only. We should also consider the direct molecular interaction by hydrogen bond between NBR reactants and a glassy matrix. Industrial Relevance Interestingly the authors show that the concept of glass transition cannot be applied to the non-enzymatic browning reactions in freeze-dried materials. They suggest that a matrix preventing non-enzymatic browning has to consist of a material exhibiting a high T g and superior hydrogen bond forming ability (e.g. disaccharides).