Pre-Harvested Spraying DA-6 For Increasing Storability Of Harvested Longan Fruits And Its Action Mechanism

Longan（Dimocarpus longan Lour.）is a famous subtropical fruit in China,that has high nutritional and medicinal value.However,China’s longan ripens in summer with high temperature,therefore fruit deterioration like rot occurs rapidly after harvest,which has a serious impact on the quality and shelf life of longan fruit,restricting the development of longan industry.Fruit of longan were sprayed with 10 mg/kg diethyl aminoethyl hexanoate（DA-6）or distilled water（as control）for 3 times at 70,90 and 110 days after full bloom.Longan fruit were harvested at 120 days after full bloom,the harvested longan fruit were selected,cleaned and dried prior to packaging in 0.015 mm thick polyethylene bag（50 fruit per bag）,then stored at 28±1℃ and 85%relative humidity.The aims of this work were to study the role of DA-6treatment before harvest on quality and storability of harvested ’Fuyan’longan fruits,and their relation to metabolisms of active oxygen,membrane lipid,energy,and anti-disease substances.Results were as follows:1.The effects of pre-harvest spraying diethyl aminoethyl hexanoate（DA-6）on quality and storability of harvested longan fruit.The results exhibited that in comparison to the control longans,pre-harvest spraying DA-6 could effectively reduce fruit respiration rate,keep higher contents of pericarp pigment and retard its browning,maintain higher contents of pulp total soluble solids,total soluble sugars,sucrose and vitamin C,reduce aril breakdown and weight loss,and maintain higher percentage of healthy fruit of harvested longans during storage.From the results it could be concluded that pre-harvest spraying DA-6 could reduce fruit respiration rate,keep higher fruit quality,and display better storage behavior which might suggest a promising method for keeping quality and extending the shelf-life of harvested ’Fuyan’ longan fruit.2.The effects of pre-harvest spraying diethyl aminoethyl hexanoate（DA-6）on active oxygen metabolism in pericarp of harvested longan Fruits were studied.The results showed that,as compared with the control fruits,pre-harvest spraying DA-6 could increase reactive oxygen removal enzyme activities and delay the decline of endogenous antioxidant substances content,reduce O₂^-· production rate and MDA content.From the results it could be concluded that pre-harvest spraying were effective to delaying active oxygen metabolism and then enhancing storage quality of harvested longan fruit.3.The effects of pre-harvest spraying diethyl aminoethyl hexanoate（DA-6）on metabolism of membrane lipid in pericarp of harvested longan fruit were studied.The results showed that,as compared with the control fruits,pre-harvest spraying DA-6 could inhibite the activities of membrane lipid-degrading enzymes such as lipoxygenase（LOX）,lipase and phospolipase D（PLD）,keep higher contents of PC,PI and index of unsaturated fatty acids（IUFA）,unsaturation of fatty acids（U/S）and lower contents of PA were also found in pericarp of harvested longan fruit preharvest-sprayed with DA-6.Therefore,pre-harvest spraying DA-6 could delay the degradation of unsaturated fatty acids of cellular membrane,beneficial for maiantenance of cellular structure and improvement of quality and storability of harvested longan fruit.4.The effects of pre-harvest spraying diethyl aminoethyl hexanoate（DA-6）association with energy metabolism in pericarp of harvested longan fruit were researched.The results indicated that as compared to control fruit,pre-harvest spraying DA-6 could keep higher contents of ATP,ADP and energy charge level,increase the ATPase activities,NADK and maintain higher NADP（H）content in pericarp of harvested longanfruit.From the above results,it could be concluded that pre-harvestspraying DA-6 could supply more energy to keeping the intracellular environment and the integrity of cellular membrane structure,which enhanced the storability of harvested longan fruit5.The effects of pre-harvest spraying diethyl aminoethyl hexanoate（DA-6）on anti-disease substances metabolism in pericarp of harvested longan fruit were studied.The results showed that as compared to control fruit,pre-harvest spraying DA-6 could inhibit the activities of pericarp browning enzymes such as PPO and POD in pericarp of harvested longan fruit.Meanwhile,higher activities of disease defense-related enzymes such as PAL,GLU,CHI,and higher contents of resistance substances like lignin and total phenolsin were maintained in pericarp of harvested longan fruit preharvest-sprayed with DA-6.Therefore,pre-harvest spraying DA-6 could enhance the disease resistance and storability of harvested longan fruit.