Solid and liquid states of lactose

Abstract

Lactose in dairy systems can exist in various crystalline and non-crystalline forms. These forms affect lactose behaviour, particularly in processing and storage of low-water dairy foods. Crystalline α-lactose monohydrate and anhydrous β-lactose are well-known solid forms of lactose, which are relatively poorly soluble in water. Its occurrence in two anomeric forms, α-and β-lactose, makes its solubility a complex function of temperature. α-Lactose has low solubility in water at room temperature, but mutarotation to equilibrium quantities of the α-and β-forms increases the overall solubility of lactose which increases rapidly with increasing temperature, with a more rapid increase in the solubility of α-lactose. Liquid dairy systems contain dissolved lactose in a complex chemical environment and lactose is likely to exist in a composition-, temperature-and process-dependent α/β-ratio. On rapid removal of solvent water from dairy liquids on dehydration or freezing, lactose molecules retain their solution structure and, therefore, amorphous, non-crystalline solid forms of lactose are typical of dairy powders and frozen dairy desserts (Roos, 1995; Hartel, 2001). © 2009 Springer Science+Business Media, LLC.