Effect Of Vacuum Impregnation On Quality And Polysaccharide Quantitative Evolution Of Postharvest Fruits

Fruits are rich in many nutrients which are necessary in people's daily life.Texture is one of the most important quality attributes of fruits.However,due to the physiological and biochemical activities,texture and quality of fruits began to deteriorate during postharvest.Ca2+ can improve the texture of fruits effectively,it was hypothesized that degradation of pectin polysaccharide was responsible for the decreasing of fruits quality including texture.Ca2+,pectinase,storage time could affect the composition and structure of polysaccharides.In this paper,the degradation of pectin polysaccharide of jujube and cherry in postharvest was investigated to elucidate the relationship of these factors.Meanwhile,this research will provide a theoretical basis for the study of the reasons for the changes of fruit texture.In this paper,effects of different vacuum impregnation(Ca2+,PME)on microstructure changes of jujube pectin polysaccharides degradation were investigated.The quality of jujube changed after vacuum impregnated by different impregnating solutions during storage.Compared with control group,Ca2+combine with PME impregnation showed more effective in maintain firmness of jujube fruit during storage,and effectivly delayed the decrease of firmness,Vc and total soluble solids content of fruit.Meanwhile,the degradation of pectin of jujube fruit was also delayed significantly.Pectin from jujube fruits after impregnated with Ca2+ and PME has an increase of calcium ions and pectin crosslinking between polysaccharide and pectin calcium to enhance the pectin network structure.This might maintain the initial physical and chemical in storage quality.At the end of storage(56 day),jujube impregnated with Ca2+ and PME has the best quality.AFM results indicated that pectin degradation occurred during storage.Meanwhile,larger width value of pectin chains degraded into smaller linear fragments.The research found that wide value of pectin chain is regularity and has obvious characteristics,the width of pectin molecules were composed of basic units.For example:water soluble pectin(WSP)molecules were composed of 15.7 nm,19.4 nm,23.2 nm and 31.9 nm.11.7 nm,15.7 nm and 19.4 nm for chelate soluble pectin(CSP),15.7 nm,21.3nm and 39.1 nm for sodium carbonate-soluble pectin(SSP)molecules,the other chain width value can generated from these basic units.Effect of pectinase on WSP and SSP of cherry fruits in vitro was investigated to elucidate the evolution of pectin polysaccharide during postharvest.Relative frequency of widths less than 30 nm of WSP molecular chain of cherry fruit at beginning of storage was 12.50%,and 17.40%and 33.33%for storage at 14 day and 28 day respectively;same chain wide value range of molecular chain in 1:500(pectin enzyme:WSP),1:50 and 1:5 group appeared frequency distribution for 10.25%,25.00%and 42.58%,SSP treated with pectinase showed similar result with WSP.It was found that effects of pectinase treatment were similar to those of storage time on pectin nanostructures.The results indicated that changes of pectin polysaccharide during storage was due to the reaction between pectinase and pectin polysaccharide.