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

Abstract

Reaction orders, rate constants and activation energies were evaluated for 5-hydroxymethyl furfural (HMF) accumulation and brown pigment formation (BPF) in pekmez and its model systems stored at 55, 65 and 75°C over 10 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 the highest in pekmez and they were the smallest in model 1. ANOVA showed that the effects of temperature on both accumulation of HMF and BPF were significant ( p<0.05). Results obtained from non-linear regression analysis indicated 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 for both HMF accumulation and BPF in pekmez. Calculated activation energies for HMF and brown pigment formation were in the range of 49.7–103 kJ mol −1 and 116–132 kJ mol −1 respectively.