Analysis On The Postharvest Softening And Pectin Degradation Of Kiwifruit

The polysaccharide degradation of cell wall was significant in postharvest kiwifruits,especially pectin,which has a great effect on the fruit texture and softening of kiwifruit.Kiwifruits of different species lead to different softening properties.Therefore,it is necessary that the research on specific kinds of kiwifruit on the pectin degradation during postharvest ripening.In this work,Actinidia deliciosa ‘Xuxiang’(XX),Actinidia chinensis‘Hongyang’ and ‘Jinli’(HY,JL),Actinidia eriantha Benth ‘White’(WT)and Actinidia arguta ‘Wanlv’(WL)were used as materials,basic physiological characteristics of kiwifruit stored at 25℃ and 4℃ were studied,and the variation rules and differences of pectin and pectinase were analyzed emphatically.The purpose of this study was to provide reference for further understanding the pectin degradation of different species of kiwifruit,which has important practical significance for postharvest storage and preservation of kiwifruit.The main findings are as follows:1.Different varieties of kiwifruits showed differences in the basic physiological properties after harvest.The fruit hardness and soluble solid content of ‘Xu Xiang’,‘Hongyang’,‘Jinli’ and ‘Wanlv’ changed considerably,the fruit texture softened significantly,and these changes of ‘White’ were small.Compared with ‘Hongyang’,‘White’ had higher calcium component contents in different forms,and its cell wall structure was relatively complete at the end of storage.2.With the softening of kiwifruit,the content of water soluble pectin increased,and the content of covalent pectin,hemicellulose and cellulose all decreased gradually.Among them,the cell wall fractions of ‘Xu Xiang’,‘Hongyang’,‘Jinli’ and ‘Wanlv’ degraded greatly,while ‘White’ degraded less,especially the pectin degradation was the least.Among the monosaccharide composition of kiwifruit pectin,arabinose,galactose and glucose were three main neutral sugars,and mannose,fucose and xylose were less abundant,and the pectin structure mainly consisted of homogalacturonan and rhamnogalacturonan-II.3.The enzyme activities of pectin methylestase(PME),β-galactosidase(β-Gal),endo-polygalacturonase(endo-PG),pectinlyase(PL)and α-L-arabinofuranosidase(α-Af)mostly showed significant or extremely significant correlations with fruit hardness and the contents of water soluble pectin,covalent pectin,hemicellulose and cellulose.For‘Hongyong’ and ‘Jinli’,the key enzymes of ripen-softening showed to be PME,β-Gal and PL,for ‘White’ and ‘Wanlv’,the key enzymes showed to be PME,PL and α-Af.4℃ low temperature treatment could restrain the activities of pectinase,delayed the degradation of cell wall of kiwifruit,and prolonged the storage period.Transcriptome sequencing results showed that PME and β-Gal-related genes may be associated with the softening of kiwifruit.