Study On The Relationship Between MHO And Apple Tiger Skin Disease And Active Oxygen Metabolism

Superficial scald is a serious physiological disorder occurred in apples during storage period,it brought huge economic losses to apple industry.The superficial scald can be inhibited significatly by 1-methylcyclopropene?1-MCP?and diphenylamine?DPA?,but 1-MCP cost high,DPA is harmful to human health.However resveratrol?Res?,a kind of natural antioxidants found in food,has been widely used in medicine and food additives.It has been found that Res has significant effect in inhibiting superficial scald in pear.In order to seek effective method to control the disease,this article use 'Starkrimson' and 'Fuji' apples as the test materials,treated with 1-MCP,DPA and Res,disease incidence is observed in different cold storage period and shelf life,as well as comparing their effect respectively.Previous studies suggest that 6-methyl-5-heptene-2-one?MHO?is the oxidation product of conjugated triene,which is a superficial scald pathogenesis.There is no report about how it induces the disease at present.In this paper,1-MCP,DPA and Res reducing the content of endogenous MHO,the relationship among endogenous MHO content,active oxygen metabolism and phenols oxidation has been researched in the process of superficial scald occurs;at the same time,this article studied the effect of exogenous MHO to superficial scald and the relationship between exogenous MHO and the active oxygen metabolism.The main results are as follows:?1?In cold storage conditions and shelf-life,the control effect of resveratrol treatment on apple superficial scald is a bit poor than 1-MCP,DPA,but still significantly effective than control group.Each treatment also have fresh-keeping effects at the same time.'Fuji' is more resistant to superficial scald than 'Starkrimson'.?2?As for 'Starkrimson' apples,incidence of superficial scald morbidity associated with H₂O₂ content within a certain range during cold storage,incidence of superficial scald increases seriously with the amount of active oxygen in fruit.The mass acumulation of reactive oxygen leading to the accumulation of malondialdehyde which is the production of membrane lipid peroxidation,and caused the proliferation of endogenous MHO content,ultimately result in superficial scald.Different varieties of apples vary in threshold of H₂O₂.It is supposed that,the content of H₂O₂ does not reach the threshold in 'Fuji' apples throughout the storage period,therefore does not show superficial scald.?3?1-MCP,DPA and Res inhibited the excessive accumulation of H₂O₂ and O₂-in peel,delaying emergence of POD and CAT,activity peak remaining highly active of POD and CAT in later period of cold storage.Thus maintaining the antioxidant ability of fruit in some degree inhibiting the accumulation rate of MHO which is the main oxidation product of leukotriene conjugate,consequently controlling superficial scald.?4?1-MCP,DPA and Res inhibited reduction of total phenolic and anthocyanin content during later storage period,allowing these antioxidants remained a relatively high level,it is supposed that for this reason slowing down the accumulation of oxidation product MHO,at last reducing the incidence of superficial scald.Tissue Browning during ripen and senescence process in fruits and vegetables is connected with enzymatic oxidation of polyphenol oxidase,and superficial scald is the result of enzymatic browning.1-MCP,DPA and Res inhibit the activity of polyphenol oxidase in later storage period,therefore reducing the enzymatic reaction speed of phenolic substances,which is conducive to maintaining phenolic antioxidants,slowing down the accumulation of MHO,consequently inhibiting superficial scald.?6?The results of treatment with 0.25 mL·L-1,0.50 mL·L-1,1.00 mL·L-1,2.00 mL·L-1 MHO on 'Starkrimson' and 'Fuji' apples in different cold storage period,indicate that the same varieties show different sensitivity to MHO in different period,the longer the refrigeration period,the more sensitive to MHO.Different varieties vary in sensitivity to MHO and 'starkrimson' apples express more sensitivity.Scald incidence and scald severity increased with the increased concentration of MHO within limits.MHO induced the occurrence of superficial scald.?7?MHO treatment decrease the activity of POD,SOD and content of total phenol,increase generation rate of H₂O₂ and O₂-,thus destroying the balance of active oxygen metabolism.Accumulation of reactive oxygen increase the malondialdehyde content,leading to the damage of membrane structure,phenolics and polyphenol oxidase reacting to form quinine,further polymerization into a black product,inducing the pathological changes of superficial scald.The pathogenesis mechanism of MHO inducing superficial scald is similar with the onset of natural,except that CAT activity drops rapidly in natural way.