Effect of water activity, temperature and pH on solid state lactosylation of β-lactoglobulin

Glycation of whey proteins leads to changes of the nutritional and functional properties of the proteins. Lactosylation of β-lactoglobulin was monitored under conditions varying with respect to temperature, water activity (aw), and pH. The rate of the overall lactosylation and the average lactosylation degree increased with temperature (50–70 °C) and aw of 0.51–0.64, but were only slightly affected by reaction mixture pH (pH 5–7) before drying. The reaction seemed to occur in two phases, the transition between which was related to a lowering of the glass transition temperature of the system. Detailed kinetic analysis of the initial step showed that the pseudo first-order rate constants for formation of mono-lactosylated β-lactoglobulin in general were higher than the rate constants for formation of di-lactosylated β-lactoglobulin. However, the temperature dependencies of the two reaction steps were similar, corresponding to an activation energy of about 100 kJ mol−1.