Model studies on acrylamide generation from glucose/asparagine in aqueous glycerol

Acrylamide formation from asparagine and glucose in different ratios in neutral glycerol/water mixtures was found to increase with decreasing water activity (0.33 <= a(w) <= 0.71 investigated) and increasing temperature (120 degrees C <= T <= 160 degrees C investigated). The initial rate of acrylamide formation was found to be approximately proportional to the asparagine concentration for an excess of asparagine, but less dependent on an excess of glucose. A steady-state concentration of acrylamide was established at 160 degrees C after 1 h for a(w) = 0.33 (30 mu g center dot L-1 for GLU:ASN = 10:1, 11 mu g center dot L-1 for GLU:ASN = 1:1, and 130 mu g center dot L-1 for GLU:ASN = 1:10) and for a(w) = 0.47 (15 mu g center dot L-1 for GLU:ASN = 10:1 and 80 mu g center dot L-1 for GLU:ASN = 1:10), suggesting a protection by glucose against acrylamide degradation. The energy of activation, as estimated from the temperature dependence of the initial rate, increased with decreasing a(w) despite a higher rate of formation of acrylamide at low a(w). For high a(w), water elimination from a reaction intermediate is suggested to be rate determining. For low a(w), the increase in energy of activation (and enthalpy of activation) is accordingly counteracted by a more positive entropy of activation, in agreement with decarboxylation as rate determining at low a(w).