Structure of a galactoarabinan-rich pectic polysaccharide of native and fermented blackgram (Phaseolus mungo).

[During fermentation, the mucilaginous polysaccharides present in black gram (Phaseolus mungo) undergo compositional and rheological changes; chemistry and physical properties of a homogenous polysaccharide obtained from comparable fractions of native and fermented black gram were compared.] 2 homogeneous galactoarabinans containing approx. 15% D-galacturonic acid were isolated and characterized from native and fermented black gram [Phaseolus mungo]. Linkage analysis indicated highly branched structures consisting of a (1<right arrow>5)-linked L-arabinan backbone additionally being substituted with L-arabinofuranose, D-galactopyranose, D-galactopyranosyluronic acid and L-rhamnopyranose residues; a structure reminiscent of pectic polysaccharides. Analysis of carboxyl-reduced polysaccharides showed that the galacturonic acid residues are all essentially (1<right arrow>4)-linked. The fermented polysaccharide had a relatively higher degree of branching which was manifested in its overall higher viscosity and as a result better product making qualities. The uronic acid carboxyls were at least partly involved in maintaining the solution viscosity and functional property attributes, because the carboxyl-reduced polysaccharide was devoid of both these characteristics.