Enzyme debranching studies on green gram (Phaseolus aureus) starch fractions.

The molecular structural properties of green gram (mung beans; Phaseolus aureus) starch were investigated with regard to its digestibility. Green gram starch was fractionated and treated with various enzymes prior to size exclusion-HPLC analysis. The green gram starch fraction treated with concanavalin A gave highly branched amylopectin in a pure form with a yield of 61%. Hot butanol extraction was used to obtain pure sparsely branched amylose (butanol-insoluble, 29.7%) and moderately-branched intermediate fraction (butanol-soluble, 6.8%) from a crude amylose fraction present in the supernatant. Both were found to be homogenous with mol. wt. of 4.5 x 106 and 9.1 x 106 kDa, respectively. The low in vitro digestibility of green gram starch observed with glucoamylase is possibly related to its molecular structure.