【作者】 郭忠春；

【导师】 贾克功；

【作者基本信息】 中国农业大学 ， 果树学， 2004， 硕士

【摘要】 试验以‘桂味’荔枝(Litchi chinensis Sonn.cv.Guiwei)为试材，研究了沸水热烫时间对荔枝果皮酶活性的影响、不同温度下荔枝果实冻结规律以及5％柠檬酸+2％NaCl护色和-40℃冻结处理对荔枝果实保藏效果的影响。同时也探讨了荔枝果皮褐变的原因以及在5％柠檬酸+1％ Vc和不同温度处理条件下解冻后荔枝果实的货架寿命，结果表明： 1．新鲜‘桂味’荔枝果皮的PPO活性较低，POD活性较高。沸水热烫可以明显抑制荔枝果皮的PPO、POD活性，8s为适宜的热烫时间。经过8s的沸水热烫，荔枝果皮中的PPO和POD活性分别下降了65％和25％。 2．试验中分别采用-80、-70、-60、-50、-40、-30℃六种温度冻结荔枝果实，结果表明荔枝冻结过程3个阶段不明显，只有初阶段和中阶段。荔枝果实的冰点为-2.72℃，过冷点为-3.01℃。完成最大冰晶生成区(-2.72～-13.6℃)需要的时间分别为12、13、15、18、27、35min。冻结温度越低，冻结速度越快，解冻后荔枝果实汁液流失率也就越少。 3．-40℃温度冻结处理明显抑制荔枝果皮PPO、POD的活性，果肉细胞膜透性显著增大，而TA、Vc含量分别降低了3.24～4.22％、61.74～64.43％。 4．冻结终温为-5℃的荔枝果实在-5℃下保藏35d后，平均好果率为73.4％，TSS、TA、Vc含量分别降低了7.11％、27.1％、32.9％；冻结终温为-20℃的荔枝果实在-20℃下保藏180d后，平均好果率为81.26％，TSS、TA、Vc含量分别降低了4.96％、7.74％、11.0％。 5．速冻荔枝果实在保藏过程中，荔枝果皮花色素苷含量逐渐减少，果肉细胞膜透性缓慢升高，PPO活性呈下降趋势，而POD活性呈上升趋势。 6．8s沸水热烫+护色处理在20℃低温保藏条件下能够有效地抑制荔枝果实在保藏过程中的果皮褐变和腐烂，保持较好的果实品质。 7．5％柠檬酸+1％Vc溶液果皮涂层明显抑制速冻荔枝出库后的果皮褐变。解冻后7h，荔枝果实的好果率为70％以上，5℃缓慢解冻，降低了果实货架期的汁液流失率。更多还原

【Abstract】 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.更多还原