THERMAL KINETIC STUDY OF COLOR CHANGES AND 5-HYDROXYMETHYL FURFURAL FORMATION IN LITCHI JUICE

Abstract

Effect of different thermal treatments on formation of 5-hydroxymethyl furfural (5-HMF) and its relation with nonenzymatic browning of litchi juice (cv. Huaizhi) were studied. The results showed that the rate of change in browning index (A 420 ) and formation of 5-HMF followed a first-order kinetic pattern when heated under 60, 70, 80, 90 and 98°C for a prolonged period of 5h. The activation energy for the browning and the formation of 5-HMF was 51.19 and 143.64 kJ/mol, respectively. As the prolongation of heating time, the rate of 5-HMF formation increased as the temperature rose. The amount of 5-HMF formed under 98°C was approximately 40 times of that under 60°C after 5h of heating, i.e., 66.98 and 1.69 mg/kg respectively. The formation of 5-HMF, and A 420 , total color difference (TCD*) of litchi juice during heating exhibited a significant positive correlation. This study indicated the browning problems related to litchi juice after thermal processing was caused by the formation of 5-HMF, a Maillard Reaction intermediate product, and therefore the color of litchi juice is vulnerable to high temperature treatment and prolonged heating time.