Lactosylation and related modifications

The interaction of lactose with milk proteins, lactosylation, is a common occurrence during processing and storage of milk and milk-derived products. It results in the formation of lactose adducts with protein-bound lysine which renders the lysine biologically unavailable. Lactosylation is the first step in a series of reactions, the Maillard reaction, which yields a multitude of products including brown pigments, melanoidins, which are an indicator of advanced Maillard reactions. The rates at which lactosylation and the subsequent Maillard reactions occur in milk depend largely on the severity of thermal processing and the temperature of duration of storage of products. For powdered milk products, water activity is an additional factor. While browning is a visible indicator, other compounds formed such as α-dicarbonyls and Advanced Glycation End-products are not readily noticed but are significant. The former are involved in protein cross-linking and the latter have been implicated in various human health issues.