Wet Fractionation of Hard-to-Cook Bean (Phaseolus vulgaris L.) Seeds and Characterization of Protein, Starch and Fibre Fractions

Abstract

A 23 factorial design with four replicates of the central trial was used to evaluate wet-fractionation conditions for complete use of hard-to-cook (Phaseolus vulgaris L.) seeds. Tested variables were flour/water ratio (1:5, 1:7.5 and 1:10 w/v), pH (8, 9.5 and 11) and a soaking time (1, 2 and 3 h). The optimum conditions (1:10 w/v flour/water ratio; pH 8; and 1 h soaking time) were determined by the percentages of protein and starch recovery. Three fractions were obtained by the process: a protein isolate, starch fraction and fibrous residue. Isolate crude protein content was 73.03%; its in vitro digestibility was 76.7%, and its amino acids concentrations, except for methionine and cysteine, met essential amino acids requirements for preschool children and adults. Total starch content was 71.41% with an amylose content of 21.46% and an amylopectin content of 78.54%. Total dietary fibre in the fibrous residue was 42.12%, with 81.10% insoluble fibre and 18.91% soluble fibre. The protein isolate’s high protein content, the purity of the starch fraction and high proportion of insoluble fibre in the fibrous residues show wet fractionated hard-to-cook bean to be a promising source of functional ingredients with possible food industry applications.