Quantitative Evolution Of Cell Wall Polysacchairdes, Quality And Coating Effects Of Postharvest Fruits And Vegetables

Fruits and vegetables are human's important source of vitamins and minerals; however, fresh fruits and vegetables are perishable after harvest. For Chinese cherries and tomatoes, it was hypothesized that degradation of cell wall polysaccharides (CWP) might be responsible for the decreasing of quality including texture. The purposes of the research were to extend the shelf life of fruits by low temperature and coating, and to illustrate the fundamental of CWP evolution by investigating the effects of cultivar and ripening stages.In this thesis, low temperature (2°C) and coating treatment (SiOx and chitosan) were applied to extend the shelf life of Chinese cherries through decreasing the evolution of CWP. Effects of cultivar and ripening stage on the evolution of tomato CWP were also investigated.For Chinese cherry, both low temperature and coating were effective to delay the decrease of firmness, total soluble solids content, titratable acidity, weight loss of individual fruit and the degradation of CWP, and inhibit the increase of decay rate. SiOx was more effective than chitosan. It shows that there was a close relationship between polysaccharide contents, morphology and fruit quality. The dissociation and degradation of main and side chains of water-soluble and chelate-soluble pectins were significantly delayed by lowered temperature and coating. The widths of pectins and hemicellulose that determined by atomic force microscopy (AFM) show that the values were composed of basic units: 15.625, 19.531 and 23.438 nm for water-soluble pectin (WSP), 19.531, 23.438 and 31.250 nm for chelate-soluble pectin (CSP), 15.625, 23.438 and 35.156 nm for sodium carbonate-soluble pectin (SSP) molecules, and 15.625 and 23.438 nm for hemicellulose molecules. At the late stage of cold storage, CWP polymers disappeared while linear single fractions increased. Chinese cherry fruit with coating treatment showed less frequency of chains with small widths and lengths than that of control group. It indicates that coating delayed the degradation of CWP of cherry fruit.For tomatoes, cultivar and ripening stage were significantly correlated with quality, content and nanoscale morphology of CWP. Softening rate of cultivar"Geruisi"was higher than that of"Dongsheng"fruit. The widths of CSP chains were composed of basic units with 15.625, 17.578, 19.531 and 23.438 nm, the basic units were 15.625, 19.531 and 23.438 nm for SSP. Quality difference of tomatoes with among different cultivars and ripening stages were mainly attributed to the variance of contents, neutral sugar composition and morphology of CSP and SSP.It indicates that the fundamental of coating for postharvest cheery was by inhibiting the degradation of CWP. The result will help optimize the coating technology for better maintaining fresh fruits and vegetables.