Extraction of a water-soluble polysaccharide fraction from lentils and its potential application in acidified protein dispersions

Abstract

The extraction conditions of a water-soluble lentil polysaccharide fraction (SLPS) from lentil fibers were examined. The effect of temperature, pH, and time of extraction was evaluated, to determine optimal conditions resulting in a high yield of high molecular mass polysaccharides. The optimal extraction temperature and time combination was 120 °C for 90 min. Under these conditions, the yield was as high as 23.3% at pH 4 and 19.6% at pH 8. Further, two different extractions were carried out, both for 90 min at 120 °C, one at pH 4 (SLPS4) and the second at pH 8 (SLPS8), and the fractions characterized for composition and molecular mass. The weight average molecular mass (Mw) of the main component in the fraction was 830 kg/mol for SLPS4 and 1130 kg/mol for SLPS8. Albeit SLPS4 and SLPS8 showed the same sugar linkages, their composition was different: SLPS4 contained, glucose 52.7%, arabinose 27.6%, and galacturonic acid 6.0%, whereas SLPS8 contained arabinose 49.8%, glucose 19.1%, and galacturonic acid 13.2%. The polysaccharides were observed by a scanning probe microscope and showed a characteristic multi-branched structure, with sugar chains extending from the center to the periphery of the molecule. Both SLPSs were used as stabilizers in an acidified milk system, containing 3% (w/w) non-fat milk solids. At a concentration of 0.4% (w/w) both SLPS4 and SLPS8 were able to maintain a mono-modal distribution of fine particles in the range of pH between 3.6–4.4 or 3.8–4.4, for SLPS4 and SLPS8, respectively. This work demonstrates the potential for the creation of a value added ingredient from lentil polysaccharide.