Comparison of Water Sorption and Crystallization Behaviors of Freeze-Dried Lactose, Lactitol, Maltose, and Maltitol

摘要

Molecular structures of sugars and sugar alcohols are quite similar, but their properties and behavior under various processing and storage conditions may vary. In this study, water sorption and crystallization behaviors of various freeze-dried sugars and sugar alcohols were compared. The water-sorption properties of samples were determined gravimetrically when stored at different relative vapor pressures (RVPs) ranging from 11% to 86% at 25°C. Crystallization was observed as the gradual loss of sorbed water during storage. The glass transition temperature (Tg_) of samples at various water contents was determined by using differential scanning calorimetry (DSC). The solid state of samples, which were freeze-dried after water-sorption study, was analyzed by using X-ray diffraction. The water-sorption isotherms of lactose, maltose, and lactitol were quite similar, and their water sorption was slightly higher than that of maltitol. The T_g values of anhydrous sugars were about 50°C higher than those of correspond-ing anhydrous sugar alcohols. Sugar alcohols with lower Tg values crystallized at lower RVP than did sugars. The lowest RVP at which both lactitol and maltitol were observed to crystallize was 44%, whereas the lowest RVP was 54% and 66% for lactose and maltose crystallization observed, respectively, in the time frame of the experiment. When these sugars and sugar alcohols are used as encapsulating matrices in low-moisture food or pharmaceutical products, crystallization during storage may result in the loss of protection ability, affecting the quality of encapsulated compounds.