A study of solid-state epimerisation within lactose powders and implications for milk derived ingredients stored in simulated tropical environmental zones

Abstract

Isolated from milk, lactose is a food ingredient and an excipient in medicines. Its chiral forms are known to undergo epimerisation in solution but understanding whether this chemical reaction occurs in lactose powders exposed to tropical environments is of great importance for medicine stability and food quality. Thus, the aim of this study was to investigate epimerisation within lactose powders stored under specified conditions that model hot and humid climates. Powdered α-lactose monohydrate was stable under all conditions, whereas β-lactose stored at 40 °C and 75 % RH suffered epimerisation, falling to 3.9 ± 0.3 β-content after 6-months. Zero-order kinetics observed by NMR, indicated a shelf-life (5 % degradation) of 4.55-days for β-lactose containing powders. Thermal analysis revealed monohydrate formation as β-lactose epimerised, seen as tomahawk shaped α-lactose monohydrate crystals by SEM. Therefore, it is recommended β-rich lactose containing powders, e.g., infant formula or direct compression tablet formulations, are stored hermetically in tropical zones.