Characterization of the pectic polysaccharides from pumpkin peel

The alcohol insoluble polysaccharide (AIP) was extracted from pumpkin (Cucurbita moschata Duch) peels, and they were fractionated subsequently into water soluble pectic substance (WSP), EDTA soluble pectic substance (ESP) and alkali soluble pectic substance (ASP) fractions. ASP fraction (24.78 and 46.07 g/100 g) contained the highest total sugar and uronic acid contents compared with WSP (17.78 and 4.89 g/100 g) and ESP (18.43 and 23.99 g/100 g) fractions. WSP fraction had 2 peaks with a small one close to 205 kDa and a major one close to 13 kDa, while ESP and ASP fractions had 3 peaks with higher molecular weight distributions than WSP. The sugar peaks in the ion exchange chromatography were detected in a low concentration of ammonium acetate buffer, but uronic acid peaks were detected in a high concentration of ammonium acetate buffer and 0.2 mol/l NaOH. ESP had higher glucose retardation effect than that of WSP and ASP, while WSP and ASP had higher bile acid retardation effects than that of ESP. AIP fractions activated growth in Lactobacillus brevis, Bifidobacterium bifidum and Bifidobacterium longum, whereas they inhibited growth in Escherichia coli and Clostridium perfringens in RCM medium.