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

Two homogeneous galactoarabinans containing ∼15% d-galacturonic acid were isolated and characterized from native and fermented blackgram. Linkage analysis indicated highly branched structures consisting of a (1→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→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.