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The kinetics of Maillard reaction in lactose-hydrolysed skim milk powder and related systems containing carbohydrate mixtures were analysed. The effect of the increase of water activity and temperature during storage of the commercial product was also evaluated. In systems with two and three carbohydrates, a marked decrease of the reaction rate was observed when monosaccharides were partially replaced by lactose, notwithstanding the fact that the former still remained in a higher proportion than lysine. The rate of available lysine loss in lactose-hydrolysed milk was mostly affected by the presence of galactose. The reaction rate constants at aw 0.52 and at 37 and 50 °C were higher than at aw 0.33. However, no significant differences were observed at 60 °C. Temperature is the most important factor to be controlled in order to minimise nutritional deterioration during storage.

The causes of darkening in honey have been attributed to Maillard reaction, fructose caramelization and reactions of polyphenols, however, no systematic studies exist on this subject. The influence of composition and initial color on the rate of darkening of several Argentine honeys submitted to storage at 37°C during 90 days was evaluated through spectrocolorimetric measurements. The most suitable color functions to evaluate darkening of honeys [lightness (Lab*), browning index (BI), metric chroma (Cab*), metric hue (Hab*) and 1/Z] increased linearly as storage time increased, after an initial induction period of very low browning development. The slope of the linear browning development zone with time was an index of browning rate, and it was analyzed in relation to the initial color and the composition of honeys (moisture content, total nitrogen, total lipids and polyunsaturated fatty acids, fructose and glucose content). Of the analyzed variables, the initial color was the parameter which better defined the rate of darkening of honeys.