The effects of WPI and Gum Arabic inhibition on the solid-phase crystallisation kinetics of lactose at different concentrations

Abstract

The effects of protein inhibition for WPI and Gum Arabic on both nucleation and the crystal-growth stage in solid-phase crystallisation have been investigated using the transition-state activated-rate theory. Mixtures of spray-dried proteins and lactose have been crystallised in the solid phase using water-induced crystallisation at high relative humidity conditions (75%). The additive concentration and temperature dependence of the crystallisation kinetics for lactose were analysed at different temperatures between 15°C and 40°C. The results suggested that, at low protein concentrations (2wt.%≤low<wt. 40%) of lactose/WPI and lactose/Gum Arabic mixtures, nucleation is mainly affected, as evident from the rise in the moisture content peak. This result shows that an increase in the protein concentration within this range requires a higher energy barrier to be overcome for the formation of the activated complex. At these low protein concentrations, the presence of WPI delayed nucleation to a greater extent than the presence of Gum Arabic. At medium (40wt.%≤medium<50wt.%), and high protein concentrations (50wt.%≤high<100wt.%), both the nucleation phase and crystal-growth phase of lactose were hindered in the presence of proteins. On the whole, the presence of Gum Arabic delays lactose crystallisation to a greater extent than the presence of WPI. This is due to the good emulsion properties of Gum Arabic in affecting protein–lactose interactions to a greater extent than WPI.