Isothermal batch crystallization of alpha-lactose: A kinetic model combining mutarotation, nucleation and growth steps

Abstract

A kinetic model combining first-order differential equations of the three consecutive steps of lactose crystallization, i.e., mutarotation, nucleation and crystal growth rate, was developed. Numerical solutions successfully fitted the variations of crystal mass growth rate as a function of lactose concentration during unseeded isothermal batch crystallization, at different initial lactose concentrations and temperatures. The model allowed the induction phase and the influence of seeding to be simulated by taking into account the dependency of crystal growth rate on total crystal surface area and, consequently, on nucleation rate. The proposed model highlights the large influence of the mutarotation step, even in unseeded crystallization kinetics. The effects of high lactose supersaturations that prevail at industrial scale during whey powder manufacturing and the effects of alkaline pH (9.5) on lactose crystallization kinetic were successfully predicted.