Mechanism Of Heat Treatment In Changing Polyamines And Reducing Chilling Injury Of Postharvest Cucumber

Heat treatment(HT) was a harmless, nonpoisonous and non-pollution physical treating method without deposit of any chemistry on fruits and vegetables. It has been proved to inhibit chilling injury(CI) of fruits and vegetables during storage, and was taken more attention for its simplicity and free-pollution in the field of postharvest in recent years. Polyamines (PAs), which was a nitrogenous base with high biological activity coming from biological metabolism, was an important physiological regulating substance used for delaying senescence or inhibiting CI in fruits and vegetables during storage. However the metabolic mechanism of PAs after HT and the action of PAs in inhibiting CI weren't understood clearly. The incidence of CI in cucumber, storage Quality, the changing of physiological and chemistry, the constitution and content of endogenous PAs and membrane fatty, ultrastructure of cell were also not studied after the treatment of HT and exogenous PAs. This paper selected two varieties of cucumber "No.4 XINDAN" and "No.2 JINCHUN" as testing material which were all sensitive to chilling, and in order to investigate the action and mechanism of PAs in inhibiting CI in cucumber after HT.The incidence and index of CI, the content of Chlorophyll in cucumber were all declined slowly in cold storage(2*C) after HT and PAs treatment compared to CK. The TA, TSS, Vc, and firmness in cucumber were also delayed by HT and PAs treatment. The synthetic inhibitor of PAs (DCHA, D-arg) could eliminate the effect of HT and PAs in inhibiting CI.The HT Could retard the increase of membrane permeability significantly, decrease accumulation of MDA, delay dropping of soluble protein content. The HT could improve the activities of POD, SOD and CAT enzyme during storage. The PAs treatment had the similar role as HT. The synthetic inhibitor of PAs (DCHA, D-arg) could decrease the activities of POD, SOD,CAT enzyme in the peel of cucumber.The HT could maintain the high level of Put, Spd and Spm content in cucumber. The onset of the peak of Put content was at the same time as the emergence of CI in cucumber. The ration of Put/ (Spd+Spm) was higher significantly than the CKs during the late storage period, the result showed that the accumulating speed of Put had a close correlation to the chilling resistance of cucumber. The treatment of synthetic inhibitor of PAs (DCHA, D-arg) could decrease the content of Put, Spd and Spm in the peel of cucumber during storage.The HT and PAs treatment could retard the decrease of crude fat content, decrease the loss of unsaturated fatty acid content, maitain the constitution of unsaturated fatty acid. The decrease of IUFA after HT and PAs treatment were lower than that of CK . HT could retard the drop of UFA/FA slowly, although the UFA/FA after exogenous PAs treatment dropped more quickly than that of HT, The content of unsaturated fatty acid was maintained; it was proved that exogenous PAs treatment could regulate the metabolism ways of fatty acid, maitain the high content of higher unsaturated fatty acid, the result showed that metabolism of linolenic acid had a close correlation to the chilling resistance of cucumber.The result showed that HT and exogenous PAs treatment could maintain stabilities of membrane system in cell, retard the peroxidation of membrane lipid, improve the ability of resistance and adaptation of cucumber to CI. Organelles in cells which was sensitive to the low temperature were very different, hloroplast was more sensitive than Mitochondrion and organelles. HT and exogenous PAs treatment could retard the enlargement and structural changing of Chloroplast and Mitochondrion; maintain stability of membrane and vacuolus; restrain transformation of nucleus, and series changes of nucleus, nucleopore and nuclear membrane; retard the widening of Interstitial layer, the accumulation of electron dense material, and the enlargement of Interstitial cavity. The above experimental results proved that increase of PAs content was an important regulating way for HT to inhibit chi...