Lactose/β-lactoglobulin interaction during storage of model whey powders

Abstract

The objective of this study was to evaluate the presence or absence of interaction between lactose and β-lactoglobulin during storage of model whey powders at different water activities (aw). Model whey powders were prepared by colyophilization of lactose with increasing quantities of β-lactoglobulin. These colyophilized β-lactoglobulin:lactose powders, assigned as BL powders, were stored from 0.11 to 0.95 aw. The water sorption behavior of BL powders was studied gravimetrically, and the state of lactose was investigated using differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). Before storage, BL powders were amorphous. After storage, a loss of water was observed on moisture sorption isotherms of BL powders. It was related to the formation of lactose crystals, detected by DSC and SEM analysis, and to the structural collapse of the powders. Water loss due to lactose crystallization was shifted to higher aw with increasing β-lactoglobulin content in BL powders. Moreover, kinetics of moisture sorption demonstrated that β-lactoglobulin was also responsible for a slower crystallization process in BL powders. Then, the water sorption behavior of BL powders was very different from the behavior of the 2 compounds mixed after separate lyophilization. All these results pointed out interaction between lactose and β-lactoglobulin, which appeared during lyophilization and still occurred during storage. This lactose/β-lactoglobulin interaction stabilized model whey powders against lactose crystallization.