Physical and mechanical properties of lactose/WPI mixtures: Effect of pre-crystallisation

This study investigated the physical and mechanical properties of spray-dried lactose/whey protein isolate (WPI) (4:1) mixtures with different contents of α-lactose monohydrate (1.0%, 11.2%, 29.2%, and 46.8%, w/w). Particle size of samples with 11.2%, 29.2%, and 46.8% crystallinity was significantly (P < 0.05) larger compared with the sample with 1.0% crystallinity. The presence of less than 46.8% crystalline lactose in lactose/WPI mixtures had only a minor effect on water sorption behaviour at aw 0.11–0.44, whereas samples with higher crystallinity had higher stable water content after showing lactose crystallisation. Moreover, samples with lower crystallinity showed higher initial sorption rates. Increasing the amount of crystalline lactose had no significant influence on the glass transition temperature and the initial crystallisation temperatures at aw 0.11–0.44. Furthermore, dairy powders with higher crystallinity had higher stiffness and water plasticisation showed a stronger effect on the structural relaxation of dairy powders with lower crystallinity.