Résumé
The effect of water activity on anthocyanin degradation and non-enzymatic browning (NEB) indices was determined in a blackberry juice system heated to high temperature. Blackberry juice samples mixed with quartz sand at three different water activities (a(w) of 0.34, 0.76 and 0.95) and having the same concentration of anthocyanins (51 +/- 4 mg 100g(-1) WB) were heated in a hermetically sealed reactor under non-isothermal conditions (100 to 140 degrees C). Reaction kinetics were well-represented by first-order reaction models. A non-isothermal method was used for the identification of kinetic parameters, and the confidence interval for each parameter was determined via Monte-Carlo simulations. The estimated parameters revealed an increase in the anthocyanin degradation reaction rate constant (k(ref)) from 0.9 to 3.5 x 10(-3) s(-1) as the water activity decreased from 0.99 to 0.34. The corresponding activation energies (Ea) for anthocyanins and NEB index were modified to a lesser extent by variations in water activity. Hence, the reduction of water activity had a negative effect on anthocyanin stability at high temperatures. (C) 2012 Elsevier Ltd. All rights reserved.