Technology of litchi rind color retention during hot air drying of litchi fruit

Browning of litchi rind is a general problem during the storing and processing of litchi fruit. The characteristics of polyphenoloxidase (PPO) which causes the browning of litchi rind was investigated and then the experiments on the production procedure for color retention of dried litchi fruit were conducted. The results showed that optimum temperature of PPO was 30～70℃, optimum pH values of PPO were about pH=5.5 and pH=7.0. ascorbic acid, citric acid, phytic acid, sodium chloride and sodium bisulfite were used as color retention agents in this study. The orthogonal experiment shows that the relatively optimum composition of these five agents is as follows: 0.2 mol/L Ascorbic acid + 0.2 mol/L Citric acid +0.1 mol/L Phytic acid +0.1 mol/L Sodium chloride +0.2 mol/L Sodium bisulfite. The fresh litchi, after color retention treatment, was finally dried using hot air to produce dried litchi fruit with natural red rind.