Extraction of pectic substances from dehulled rapeseed

The water-insoluble residue of dehulled, defatted, and 80% ethanol-treated rapeseed was extracted following 10 different procedures, with initial extractions, comparing the effect of extracting agent [cyclohexane-trans-1,2-diamine-N,N,N′,N′-tetraacetate (CDTA) or buffer], pH (5 or 6.5), and ionic strength (0.02, 0.05 M, and in the case of buffer also 0.1 M) on yield and composition of the extracts. All 10 initial extractions were followed by two extractions with sodium carbonate at pH 10. The highest yield of pectic substances was obtained with CDTA at pH 6.5. A synergistic effect on the extracting efficiency between CDTA and pH seemed to exist. The monosaccharide composition of the polysaccharides was also different. The pectin extracted at pH 6.5 with CDTA had a higher proportion of uronic acids, suggesting a less branched variety of pectin. The sodium carbonate-extractions partly extracted a different population of pectin than CDTA. Two extracts (0.05 M CDTA/pH 6.5 and 0.02 M CDTA/pH 5) were further characterised by ion-exchange chromatography and monosaccharide analysis of the fractions. The proportion of neutral (non-retained) and acidic (gradient-eluted) polysaccharide material differed between the two extracts. The gradient-eluted material of the 0.05 M CDTA/pH 6.5 extract was retained longer on the column than the 0.02 M CDTA/pH 5 extract. Different conditions were evaluated for the extraction of pectic substances from dehulled rapeseed by chemical characterisation of the extracts.