Wax Change Law And Its Relationship With Storability In Plum Fruit During Storage

Changes in peel wax structure and composition,fruit quality and physiological characteristics of three varieties of plums with different wax content(‘Kongxin’,‘Fengtang’ and ‘Cuihong’ plum)during storage at room temperature(25 ± 1℃)and low temperature(4 ± 1℃)was demonstrated.The differences in the waxes of three varieties of plum peel waxes at different temperatures during storage were discussed and the main waxy components that determined the storability of plum fruits were determined.Then the wax response mechanism of plum fruit during storage and its relationship with fruit storability were clarified.It is of great theoretical and practical significance to deeply reveal the softening mechanism of plum fruit,formulate corresponding preservation measures,develop effective wax products to prolong fruit storage and shelf life,and reduce the process of fruit softening.The main research results are as follows:(1)The effects of different extraction solvents(n-hexane,chloroform,chloroform / methanol = 4 / 1),temperature(30 ℃,40 ℃,50 ℃)and time(20 s,30 s,40 s)on the wax extraction of peel were compared by a three-factor and three-level experiment.Among them,the extraction effect of chloroform / methanol = 4 / 1,40 ℃,30 s was the best.(2)Plum peel is covered with a layer of white cream-like wax.The surface of three varieties of plum peel was composed of different degrees of rod-shaped wax and platelet-shaped wax.‘Kongxin’ plum contained a large amount of flaky wax,‘Fengtang’ plum had a great number of rod-shaped wax,and ‘Cuihong’ plum also contained rod-shaped wax which finally formed a large gap.Room temperature promoted the formation of oil droplet wax in ‘Kongxin’ plum,decreased platelet wax in ‘Fengtang’ plum,and increased platelet wax of ‘Cuihong’ plum and curled into folds and flakes.However,at low temperature,the platelet-like wax crystals covered on the rod-shaped wax of ‘Fengtang’ plum gradually disappeared,and the rod-shaped wax decreased and adhered together,the platelet-shaped wax crystals of the ‘Cuihong’plum gradually increased,and finally became a wrinkled sheet-like structure.(3)The wax content of the three varieties of plums decreased continuously during storage at room temperature,and the low temperature reduced the wax metabolism level,thus effectively inhibited the decrease of wax content.A total of250 compositions of 11 components,including alcohols,alkanes,fatty acids,ketones,aldehydes,esters,triterpenoids,olefins,sterols,anthraquinone and flavonoids,were analyzed in three varieties of plum peel wax.And 152,112 and 119 compositions were analyzed in ‘Kongxin’ plum,‘Fengtang’ plum and ‘Cuihong’ plum,respectively.Alcohols had the highest content and an important position in plum peel wax.The content of wax compositions changed during storage,and the content of alkanes,alcohols,aldehydes and triterpenoids changed significantly.Low temperature affected the changes of wax in plum peel to varying degrees,and slowed down the changes of extraction amount of three varieties of plum alkanes,alcohols,ketones and wax,and promoted the changes of fatty acids,esters,aldehydes and triterpenoids in ‘Kongxin’plum.The wax compositions of the three varieties plum during storage were positively correlated,but different varieties were obvious.The wax compositions of‘Kongxin’ plum changed little in the later stage of low-temperature storage,the wax compositions of ‘Fengtang’ plum changed stably during storage,and there was no correlation between the waxy compositions of ‘Fengtang’ plum and ‘Cuihong’ plum during storage.(4)No matter under room temperature or low temperature,‘Kongxin’ plum showed the worst storage resistance,and the storability of ‘Cuihong’ plum was better than that of ‘Fengtang’ plum at room temperature,and ‘Fengtang’ plum was better than ‘Cuihong’ plum at low temperature.(5)Different compositions of peel wax played different roles in the storage indexes of the three varieties plum fruits during storage.Compared with ‘Fengtang’plum,the wax compositions of ‘Kongxin’ plum and ‘Cuihong’ plum slowed down the changes of titratable acid and malondialdehyde in the fruit.The degradation of alkanes,ketones,aldehydes and other substances in ‘Cuihong’ plum delayed the respiratory senescence of the fruit,significantly kept the cell wall structure and inhibited the production of soluble pectin.The water retention of plum fruit could be enhanced by nonacosane,hentriacontane and ursolic aldehyde in plum fruit,and the components such as 1,22-docosadiol,1,40-tetradecanediol,nonacosane,hentriacontane,10-octanone and octacosaldehyde effectively alleviated the changes of cell wall and maintained the firmness of fruit.Low temperature dramatically slowed down the change of wax,and the alkanes,alcohols,fatty acids,ketones,aldehydes,esters and triterpenoids in the peel wax delayed the decrease of Vc and soluble sugar content of plum fruit,inhibited the respiratory senescence of plum fruit,and reduced the decrease of malondialdehyde content and cellulose degradation,and alkanes,alcohols,ketones,aldehydes,triterpenoids and sterols retarded the changes of pectin substances and related enzymes.