The Mechanism Research Of Enzymatic Browning In Pear Flesh

With 49 pear cultivars which belonging to four species and hybrid varieties as the experimental materials, total phenol and phenolic composition contents, GSH, MDA, and Soluble protein content, PPO, SOD, CAT, PAL, and POD activities in fruits were studied. The aim is to reveal the internal mechanism of enzymatic browning. The main results are as follows:1. The enzymatic browning level exhibited larger difference among individual cultivars, and the browning of Mianli pear and Balixiang was severer while Manfeng and Hosui was less. Total phenol and Total flavonoids contents in Pyrus ussriensis Maxim fruits were Significantly higher than other species. Among the different varieties, Total phenols content and browning degrees roughly had the same trend.2. 14 different phenolic compounds were determined in fresh fruit by high performance liquid chromatography analysis. The content of phenolic compounds showed high difference among different cultivars and species. Average content of chlorogenic acid and arbutin were the highest, and followed by catechin, epicatechin, violaquereitrin and rutin in sequence. Therefore, these six phenolic compounds were major phenolic substances in pear fruit; however, average content of vanillin and cinnamic acid were the lowest. Content of arbutin, chlorogenic acid, catechin, epicatechin in fruits of Pyrus ussriensis Maxim were higher than hybrid cultivars and other species. From high to low order, the overall trends of chlorogenic acid content were Pyrus ussriensis Maxim, Pyrus bretschneideri Rehd. , Pyrus communis L. , Pyrus pyrifolia Nakai in sequence. Content of arbutin in Pyrus communis L.was the lowest.3. The role of each factor on browning in a descending order were total flavonoids >epicatechin> total phenols> POD> coumaric acid> catechin> chlorogenic acid >soluble protein> arbutin> caffeic acid> GSH> CAT>PAL> sinapic acid. Among them , total phenol, total flavonoids, chlorogenic acid, epicatechin, catechin, caffeic acid and POD, PAL, Sinapic acid, arbutin were highly significantly positive correlations with browning. CAT, GSH and soluble solids which had slight effect on enzymatic browning were significant negative correlations with browning. total flavonoids was the main factor which influenced enzymatic Browning in pear flesh, followed by epicatechin, PAL and sinapic acid were lest. Of the different polyphenols components , catechins was the most important factor of browning in pear. So the content of total flavonoids, epicatechin, and total phenols were the main factors which influenced enzymatic Browning in pear flesh.4. Enzyme activitivies and contents of non-enzyme in relation to enzymatic browning varied with different varieties, which were also similarly its relationship with enzymatic browning.Activity of PPO and enzymatic browning were no significant correlation.5. The correlation of PPO to enzymatic browning in fruits was higher than that with enzymes and non-enzymes.