Isolation and characterization of alkali-soluble pectic polysaccharides in peach (Prunus persica Batsch) fruit

Abstract

The alkali-soluble polysaccharides in the cell wall extracted from immature and over-ripe peach fruit (Prunus persica Batsch) were analyzed. After removing water and the chelate compound (CDTA) soluble polysaccharides from the crude cell wall in the peach fruit tissue, the residual alkali soluble polysaccharides were extracted sequentially with 50 mM Na2CO3, 1 M KOH, and 4 M KOH. Using an ion exchange chromatography (DEAE-Sepharose 2.5 cm X 30 cm), the 1 M and 4 M KOH fractions were separated into three (1 M KOH a-c) and four fractions (4 M KOH a-d), respectively, but Na2CO3 soluble polysaccharides were not fractionated by this method. The acidic polysaccharide in 1 M KOH fraction (1 M KOH-b and c) was subjected to further analysis. The major sugars in fraction 1 M KOH-b and 1 M KOH-c were xylose and arabinose, respectively. The result of gel filtration (Sepharose CL-4B 1.5 X 40 cm) showed that the average molecular weight of the fraction 1 M KOH-b was heavier than that of the fraction 1 M KOH-c; moreso in immature fruit harvested on Aug. 7 than that in over-ripe fruit harvested on Aug. 24. The results of xylanase (EC 3.2.1.8) treatment of fraction 1 M KOH-b and sugar composition analysis using GLC showed that this fraction was composed of complex polysaccharides of xylan and rhamno-galacturonan. Based on the data of acid hydrolysis and sugar composition analysis the polysaccharides in fraction 1 M KOH-c consisted of xyloglucan and rhamno-galacturonan.