Reactions of lactose during heat treatment of milk : a quantitative study

Abstract

The kinetics of the chemical reactions of lactose during heat treatment of milk were studied. Skim milk and model solutions resembling milk were heated. Reaction products were determined and the influence of varying lactose, casein and fat concentration on the formation of these products was studied. It was observed that lactose isomerized into lactulose, and subsequently degraded into galactose, formic acid, deoxyribose, hydroxymethylfurfural, furfural and furfuryl alcohol; lactose also reacts with lysine-residues to form lactulosyllysine-residues (early stage of the Maillard reaction). From these results, a model describing the steps in the reaction network of the degradation reactions of lactose during heating of milk was proposed.It was tried to model the degradation of lactose by computer simulation in order to predict the quantities of the various degradation products in the course of time. The model appeared to fit the experimentally obtained results reasonably well. Altogether, the hypothesized mechanism for degradation of lactose appeared adequate to explain the observations for milk and model solutions resembling milk. Mathematical modelling thus allowed rigorous checking of a proposed complicated reaction network in foods. In the case of milk it has been found that, from a quantitative point of view, the isomerization reaction is much more important than the Maillard reaction in the degradation of lactose during heat treatment of milk