Studies On The Storage Of Quick-frozen Lychee (Litchi Chinensis Sonn.cv.Guiwei) Fruits

Fresh lychee (Litchi chinensis Sonn. cv.Guiwei) fruits were used to study the enzymes activity of lychee pericarp blanched in boiling water and the freezing law of lychee fruit at different temperature. The quality and physiological changes of lychee fruits were studied by 0.05kg.l-1 citric acid + 0.02kg.l~ NaCl and -40℃ freezing temperature treament, meanwhile the browning mechanism of lychee pericarp and the marketable stage were discussed after 0.05kg.l-1 citric acid + 0.01kg.l-1 Vc and thawing treatment. The results were as follows:1 .The fresh lychee fruits of cv.Guiwei had lower PPO and higher POD activity which was inactivated obviously by blanching in boiling water. The 8s was optimum boiling water blanching treatment time, PPO and POD activity of lychee pericarp were respectively decreased by 65% and 25% by 8s boiling water blanching.2.When lychee fruit was respectively frozen at -80℃, -70℃, -60℃, -50℃, -40℃, -30℃, the three stages of freezing course of lychee fruit was not apparent enough,only initial stage and middle stage.The freezing point of lychee fruit was -2.72℃, and the super-cooling point of lychee fruit was -3.01℃. The time of past maximum crystallization (-2.72~-13.6℃) was 12, 13, 15, 18, 27, 35 min respectively. The freezing temperature was lower, the freezing speed was quicker and the juice leakage rates in lychee pulp after thawing were lower.3.Frozen at -40℃, PPO and POD activity of lychee pericarp was strikingly restrained , membrane permeability of lychee pulp remarkably increased, and the content of TA and Vc respectively decreased by 3.24-4.22% and 61.74-64.43%.4.Stored at -5℃ for 35days or at -20℃ for 180 days, the marketable rates of the lychee fruits were respectively 73.4% and 81.26%. The content of TSS, TA and Vc respectively decreased by 7.11%, 27.1%, 32.9% and 4.96%, 7.74%, 11.0%.5. Anthocyanin content of lychee pericarp reduced continuously, membrane permeability of lychee pulp increased slowly, PPO activity of lychee pericarp declined, while POD activity of lychee pericarp increased during storage.6.The 8s blanching and 0.05kg.l-1 citric acid + 0.02kg.l-1 NaCl treatment effectively restrained browning and rotting of lychee pericarp during -20℃ storage.7.0.05kg.l-1 citric acid +0.01kg.l-1Vc obviously restrained browning of quick-frozen lychee pericarp after thawing. The marketable fruits rates were over 70% after 7 h thawing.