Isolation and structural characterisation of pectin from endocarp of Citrus depressa

A polysaccharide was extracted with hot HCl from the endocarp of Citrus depressa grown in Okinawa, Japan. The yield was 4.1% on a fresh weight basis. Composition of the polysaccharide was 89.3% total carbohydrate, 79.2% uronic acid, 4.1% ash and 8.8% moisture. The degree of methoxylation was estimated to be 66.2%. The polysaccharide was composed of d-GalA, d-Gal, l-Ara and l-Rha in the ratio of 100:10.3:1.53:0.94, respectively. The molecular mass was estimated to be approximately 4.1 × 104. NMR spectra indicated that the polysaccharide was mainly composed of (1→4)-linked α-d-GalA and (1→4)-linked β-d-Gal. Methylation analysis results identified 1→2 and 1→2,4 linked Rha, 1→4, 1→3, 1→6 and 1→3,6 linked Gal. The results indicated that the polysaccharide was a pectin, which was relatively simpler than other pectins. The polysaccharide was classified as high-methoxyl pectin. The pectin turned into a gel by the generalised method.