Dynamic water sorption for the study of amorphous content of vacuum-dried honey powder

Abstract

Amorphous components in food powders are important as they often provide a solid structure. They also affect powder properties such as physical and storage stability. Quantification of amorphous components of food powders may be challenging. We developed a dynamic water sorption by dynamic dew point isotherm (DDI) method, which records the change of water activity and weight change (or water content) of a sample continuously. The research was aimed to study the amorphous content of vacuum-dried honey powder produced from different drying temperatures. The DDI method was calibrated using known amorphous contents of amorphous sucrose and mixtures of amorphous sucrose and maltodextrin. Amorphous materials often exhibit higher sorption of water than crystalline materials. In the new approach, water sorption data were differentiated numerically and plotted against water activity. The water sorbed by the sample during recrystallization was measured by integrating the area of the new derived water sorption curve against water activity. The water sorbed was correlated with the amorphous content of the system. The honey powder also exhibited recrystallization of its amorphous sugar during water sorption. The result showed that the higher the drying temperature, the higher the amorphous content of vacuum-dried honey powder.