Multiple effects of viscosity, water activity and glass transition temperature on peroxidase activity in binary and ternary carbohydrate solutions

The individual and combined effects of water activity (aw), bulk viscosity and glass transition temperature (Tg’) on the activity of horseradish peroxidase (HRP) in buffered sugars (glucose, trehalose and maltose) and maltodextrin solutions were investigated. Viscosity was the most important factor in the inhibition of HRP activity; however, when Tg’ was changed by the using solutes with different molecular weight, it became a key factor in the modulation of enzyme activity. Viscosity being equal, the sugar addition to maltodextrin solution lowered aw and lowered Tg’ causing an increase of the enzymatic activity. Nevertheless, an inhibition of the HRP activity occurred when aw values of 0.87 were reached due to the addition of glucose, which, among the tested sugars, showed the lowest molecular weight. Among disaccharides, maltose was more effective than trehalose in impairing the enzyme activity both in binary and ternary systems, and this is due to a non competitive biochemical inhibition exerted by this sugar on HRP. When compared to glucose, maltose and trehalose were more effective in reducing HRP activity only in the low viscosity range whilst in the high viscosity range (1–4 10−6 m2 s−1) glucose, despite its lower Tg’ value, was slightly more efficient than disaccharides due to its aw lowering effect.