Lactose: Chemistry, Processing, and Utilization

Abstract

In this review recent advances in dairy chemistry, materials science, engineering and pharmaceutical science have been integrated with established knowledge to explain how lactose is used in mainstream dairy products and chocolate, for the synthesis of derivatives including galacto-oligosaccharides and as an excipient in tablets and dry powder inhalers. Lactose exists in crystalline and amorphous forms. The crystalline forms are alpha lactose monohydrate, anhydrous alpha lactose, beta lactose and compound crystals. The consequences for dairy and pharmaceutical products of the interconversion of these forms are described. Moisture induced crystallization of amorphous lactose is a cause of physical and chemical instability in dairy and pharmaceutical products. Methods for estimating the level of amorphous lactose- and its obverse, the estimation of “lactose crystallinity”- are described. Edible and pharmaceutical grades of lactose are made by cooling batch crystallization of whey permeate supersaturated in lactose. The shape, size, purity and yield of lactose crystals are influenced by mutarotation between alpha and beta lactose, the rate of cooling and the presence of compounds including calcium phosphates, lactose phosphate and riboflavin, which are normally present in the permeate. Milling of the lactose crystals to achieve the required particle size forms small yet critical amounts of amorphous lactose. Strategies for improving the manufacture of alpha lactose monohydrate are critically discussed. The role of pre-crystallization of lactose in the manufacture of non-hygroscopic whey powder is explained.