title: Modification of pectin and hemicellulose polysaccharides in relation to aril breakdown of harvested longan fruit.
abstract: To investigate the modification of cell wall polysaccharides in relation to aril breakdown in harvested longan fruit, three pectin fractions (WSP, water soluble pectin; CSP, CDTA-soluble pectin; ASP, alkali soluble pectin) and one hemicellulose fraction (4 M KOH-SHC, 4 M KOH-soluble hemicellulose) were extracted, and their contents, monosaccharide compositions and molecular weights were evaluated. As aril breakdown intensified, CSP content increased while ASP and 4 M KOH-SHC contents decreased, suggesting the solubilization and conversion of cell wall components. Furthermore, the molar percentage of arabinose (Ara), as the main component of the side-chains, decreased largely in CSP and ASP while that of rhamnose (Rha), as branch point for the attachment of neutral sugar side chains, increased during aril breakdown. Analysis of (Ara+Gal)/Rha ratio showed that the depolymerization of CSP and ASP happened predominantly in side-chains formed of Ara residues. For 4 M KOH-SHC, more backbones were depolymerized during aril breakdown. Moreover, it was found that the molecular weights of CSP, ASP and 4 M KOH-SHC polysaccharides tended to decrease as aril breakdown intensified. These results suggest that both enhanced depolymerization and structural modifications of polysaccharides in the CSP, ASP and 4 M KOH-SHC fractions might be responsible for aril breakdown of harvested longan fruit.
authors.affiliation: Key Lab of Plant Resources Conservation and Sustainable Utilization, South China Botanical Garden, Chinese Academy of Sciences, Guangzhou 510650, China. xwduan@scbg.ac.cn.
authors.forename: Duoduo
authors.initials: D
authors.lastname: Wang
authors.forename: Haiyan
authors.initials: H
authors.lastname: Zhang
authors.forename: Fuwang
authors.initials: F
authors.lastname: Wu
authors.forename: Taotao
authors.initials: T
authors.lastname: Li
authors.forename: Yuxiang
authors.initials: Y
authors.lastname: Liang
authors.forename: Xuewu
authors.initials: X
authors.lastname: Duan
mesh_terms: D002473:Cell Wall / Q000737:chemistry; D002850:Chromatography, Gel; D005638:Fruit / Q000378:metabolism; D006878:Hydroxides / Q000737:chemistry; D008970:Molecular Weight; D009005:Monosaccharides / Q000032:analysis; D010368:Pectins / Q000737:chemistry* / Q000378:metabolism; D011134:Polysaccharides / Q000737:chemistry* / Q000378:metabolism; D017680:Potassium Compounds / Q000737:chemistry; D029631:Sapindaceae / Q000378:metabolism*; D014867:Water / Q000737:chemistry
chemical_list: D006878:Hydroxides; D009005:Monosaccharides; D011134:Polysaccharides; D017680:Potassium Compounds; D014867:Water; C007916:hemicellulose; D010368:Pectins; C029943:potassium hydroxide