Extraction and structural characterisation of rhamnogalacturonan I-type pectic polysaccharides from potato cell wall.

Cell wall material from potato pulp by-product was used for the extraction of galactan-rich rhamnogalacturonan I (RG-I) type pectic polysaccharides using alkaline (NaOH and KOH) and enzymatic (endopolygalacturonase from Aspergillus niger) methods. The extraction yield increased as the concentration of alkaline solution was increased from 0.5 M (22-24%) to 2 M (53-56%). The yield of 38% obtained upon the enzymatic treatment was similar to those observed with 1M alkaline solutions. The results reveal the high debranching of arabinan side chains of RG I as compared to the galactan ones under harsh alkaline conditions. The molecular weight distribution shows that the enzymatic extraction led to the highest proportion of high-molecular weight polysaccharides (>500 kDa; 62.2%). According to monosaccharide pattern, the weak acidic fractions of high alkaline (1-2 M)-based polysaccharide extracts was the most enriched with galactan-rich RG I. Using milder conditions (enzyme and weak alkaline), two RG I populations with low and high linked homogalacturonan fragments were recovered in the weak and strong acidic fractions, respectively. The structure of galactan-rich RG I was confirmed by H(1) NMR spectroscopy analysis.