Nonenzymic browning reactions in boiled grape juice and its models during storage

Reaction orders, rate constants and activation energies were evaluated for 5-hydroxymethyl furfural (HMF) accumulation and brown pigment formation (BP F) in pekmez and its model systems stored at 55, 65 and 75 degrees C over 1 0 days at pH 4.0. The model systems and their compositions were decided by considering the major pekmez components. Accumulation of HMF and BPF were t he highest in pekmez and they were the smallest in model 1. ANOVA showed th at the effects of temperature on both accumulation of HMF and BPF were sign ificant (p < 0.05). Results obtained from non-linear regression analysis in dicated that reaction order was 0.5 for 5-HMF accumulation and was zero for brown pigment formation in the model systems. Reaction orders were zero fo r both HMF accumulation and BPF in pekmez. Calculated activation energies f or HMF and brown pigment formation were in the range of 49.7-103 kJ mol(-1) and 116-132 kJ mol(-1) respectively. (C) 1998 Elsevier Science Ltd. All ri ghts reserved.