Preharvest Spraying KaDoZan For Enhancing Storage Resistance Of Harvested Longan Fruit And Its Action Mechanism

Longan fruit is a famous specialty of south subtropical in China,which matures in hot season of high temperature.It is easy to suffer water loss,pericarp browning and decay after harvested;It may deteriorate after storage under room temperature(28℃)in a week.This test chooses ’Fuyan’ as material,the chief longan cultivar in Fujian Province of China,and preharvest spraying with chidosan,a natural disease resistance agent.Storage under(28±1)℃ after harvested.And study ing the effect of preharvest spraying with chidosan treatment on postharvest quality and storage property,active oxygen metabolism,membrane lipid metabolism,energy metabolism and disease-resistant material metabolism in longan fruits.The main results were as follows:1.Studying the effect of preharvest spraying with different concentration(diluting 250 times,500 times,750 times,1000 times)of chidosan treatment on postharvest Respiration rate,cell membrane permeability,soluble solid content and titratable acid content,good fruit rate,disease index,weight loss,browning index and autolysis index.The results show that preharvest spraying with diluted 750 times of chidosan in longan fruits has the best fresh-keeping effect of postharvest longan fruits.2.Preharvest spraying with diluted 750 times of chidosan in longan fruits can effectively control the rapid rise of respiration rate in the late Storage of longan fruit;better maintain the integrity of cell membrane structure;keep higher TSS content,delay the decline of total sugar content and vitamin C content;inhibite the rapid increasing of TA content during the late storagetime of longan fruit;delay the slow down of chlorophyll,carotenoid,anthocyanin and flavonoid content;control pericarp browning and autolysis of postharvest longan;reduce fruit water loss;enhance the disease resistance of longan fruit;maintain a relatively high healthy fruit percent;effectively improve the quality of longan fruit and its storability.3.Preharvest spraying with diluted 750 times of chidosan in longan fruits can effectively reduce the O2-· generation rate,reduce MDA accumulation,improve the activity of active oxygen scavenging enzyme(SOD,CAT and APX),keep higher content of active oxygen scavenger(GSH,AsA and flavonoids)of longan peel,which can improve the antioxidant capacity of longan fruit.4.Preharvest spraying with diluted 750 times of chidosan in longan fruits can maintain lower LOX and esterase activity,inhibite fast-rising of phospholipase D activity in the middle and later periods of storage,control the rise of the relative content of membrane lipid saturated fatty acids(C16:0 and C18:0),delay the decline of the relative content of membrane lipid unsaturated fatty acids(C18:1,C18:2,C18:3 and C20:1),maintain higher unsaturation index and unsaturation degree of cell membrane fatty acids of postharvest longan peel,keep better cell membrane structure completeness of longan peel.5.Preharvest spraying with diluted 750 times of chidosan in longan fruits can maintain higher ATP content and EC level,keep higher ATPase activity which can maintain an ion balance between inside and outside of longan peel cell,higher CCO activity and NADK activity,higher NADP(H)content and low NAD(H)content.6.Preharvest spraying with diluted 750 times of chidosan in longan fruits can reduce longan fruits’ disease infection in the later period of storage,and effectively restrain the decline of total phenol content of longan peel,promote the accumulation of lignin in longan peel,enhance the activity of disease resistance related enzymes:PAL,GLU and CHI,improve disease resistance of longan fruit.