Physicochemical Properties of Alcohol Insoluble Polysaccharides Fractions from Watermelon and Oriental Melon Peels and Their Effects on Growth of Intestinal Bacteria

Alcohol insoluble polysaccharides (AIP) extracted from watermelon and oriental melon peels were fractionated to obtain three pectic substance fractions [water soluble pectic substances (WSP), EDTA soluble pectic substances (ESP), and alkali soluble pectic substances (ASP)], and their physicochemical properties and effects on the growth of intestinal bacteria were investigated. The AIP from the watermelon peel showed higher yield and water holding capacity than those from the oriental melon peel. The total sugar and uronic acid contents were 641.90 and 805.21 mg/g, respectively, for the pectic substances of watermelon peel AIP, whereas they were 648.79 and 877.26 mg/g for those of oriental melon peel AIP. The WSP fractions of both watermelon and oriental melon peels generated two peaks. The ESP fraction from watermelon peel generated peak between 513 and 2,000 kDa, while the oriental melon peel ESP had a broad chromatography. The ASP fraction of watermelon peel generated peak between 43 and 513 kDa, while the oriental melon peel ASP had a broad chromatography. The WSP fractions of watermelon and oriental melon peels contained galactose and arabinose as predominant sugars, followed by glucose, xylose, and mannose. The watermelon peel ESP was composed of arabinose and galactose, while the oriental melon peel ESP contained arabinose, galactose, glucose, and rhamnose. The watermelon peel ASP contained arabinose, galactose, and rhamnose, whereas oriental melon peel ASP contained arabinose, galactose, rhamnose, glucose, and xylose. The watermelon peel ASP and oriental melon peel ESP showed a relatively high glucose retardation effect at 4 h dialysis time. Growth-inhibiting activity against Escherichia coli was observed for watermelon peel ASP and oriental melon peel ESP. The watermelon peel WSP had the highest growth-promoting activities against Lactobacillus brevis, Bifidobacterium bifidum, and Bifidobacterium longum, while oriental melon peel ASP had the highest growth-promoting activities against L. brevis, B. bifidum, and B. longum.