Solution viscosity and structural modification of pumpkin biopectin

Abstract

Solutions of ‘biopectin’ obtained from pumpkin pulp by digestion with the multi-enzyme culture supernatant from Bacillus polymyxa (strain 88A) were prepared in 0.10 M NaCl and characterised by rotational viscosity measurements at 20 °C. The resulting double-logarithmic plot of specific viscosity versus the product of concentration ( c) and intrinsic viscosity ([ η], from combined Huggins and Kraemer extrapolation to c=0) showed a sharp increase in slope at c[ η]≈1 in comparison with the normal value of c[ η]≈4 for disordered coils, suggesting a branched structure, possibly arising from Ca 2+-mediated association of constituent chains. Pumpkin biopectin is non-gelling, in marked contrast to the pectin obtained from the same source by conventional extraction with acid, although the yield is more than doubled. Attempts to induce gelation (with 70 wt% solids at low pH or with stoichiometric Ca 2+ at neutral pH) by removing the high content of divalent cations naturally present in the biopectin and by chemical deacetylation under acidic conditions (pH 1.2; 4 days; 40 °C) proved unsuccessful. Further research using enzymic deacetylation is suggested.