X-ray diffraction analysis of lactose crystallization in freeze-dried lactose-whey protein systems

Water sorption, time-dependent crystallization and XRD patterns of lactose and lactose-WPI mixtures were studied with glass transition data. The results indicated that the sorbed water of lactose-WPI mixtures was fractional and water content of individual amorphous components in lactose-WPI mixtures at each aw from 25 °C to 45 °C could be calculated. Crystallization occurred in pure lactose whereas partial crystallization was typical of lactose-WPI mixtures (protein content ≤ 50%) at intermediate and high aw (> 0.44 aw) from 25 °C to 45 °C. The extents of crystallization were significantly delayed by WPI. The Tg values of lactose-WPI systems showed the composition-dependent property in systems and might indicate the occurrence of phase separation phenomena during 240 h storage. XRD showed no anhydrous β-lactose and mixed α-/β-lactose with molar ratios of 4:1 crystals in crystallized lactose-WPI systems (70:30 and 50:50 solids ratios). Reduced crystallization in the presence of WPI was more pronounced possibly because of reduced nucleation and diffusion during crystal-growth. The present study showed that WPI could present an important role in preventing sugar crystallization.