Crystallization in amorphous lactose-maltodextrin mixtures

Solutions of maltodextrins (MD) with the dextrose equivalent (D.E.) 9-12 and D.E. 23-27 were mixed with lactose solutions at different ratios. Freeze-dried amorphous solids of lactose and lactose-MD were prepared from solutions containing 20% total solids. The ratios of lactose and MD were 90:10, 80:20, and 70:30 (w/w). Crystallization rate of amorphous lactose was followed from changes in water sorption properties. Freeze-dried amorphous materials were stored over saturated salt solutions over the range 11.4 to 76.1% relative humidity (RH) in vacuum desiccators at room temperature (20±2°C) for 25 days. Changes in weight were followed at intervals. The glass transition temperatures (Tg) of the amorphous materials were measured using differential scanning calorimetry (DSC) following storage over P2O5 and over saturated salt solutions (11.4-44.1% RH) in vacuum desiccators. At low RH (11.4-44.1% RH) all materials showed typical sorption behavior of food systems up to a RHdependent steady state water content. Lactose crystallization was affected by MD at all ratios at high RH (54.5-76.1% RH) and the rate of crystallization decreased with increasing MD concentration. The amorphous lactose-MD mixtures (70:30) inhibited crystallization up to 54.5% RH. The Tg of the amorphous mixtures increased with increasing MD concentration. The mixtures of lactose-MD D.E. 9-12 (70:30) showed the highest Tg. The lactose-MD D.E. 23-27 (90:10) showed similar Tg to amorphous lactose being the lowest Tg for the mixtures. The amorphous lactose-MD D.E. 9-12 (90:10) showed similar Tg to the amorphous lactoseMD D.E. 23-27 (70:30) but the inhibition of crystallization of lactose was different. MD D.E. 23-27 was a better inhibitor of crystallization of lactose than MD D.E. 9-12. Thus the crystallization of lactose was not dependent only on Tg but it was also affected by the molecular weight of the system.