Isoamylase debranched fractions and granule size in starches from kidney bean germplasm: Distribution and relationship with functional properties

Abstract

Fine structure, granule size distribution, thermal and rheological properties of starch separated from twenty kidney bean lines were determined. Apparent amylose content (AAC), intermediate fraction (mixture of relatively short amylose and long side chains of amylopectin), long-side chains of amylopectin (AP) and short side chains of amylopectin (AP) of starches were measured after debranching with isoamylase and fractionating using gel permeation chromatography. Starches from different lines showed unimodal, bimodal and trimodal distribution profiles for the granules size, majority of starches showed bimodal profile. The granule size ranged between 0.4 and 103μm, however, granules of 10 to 30μm were present in the highest proportion. Paste viscosities (Peak-, breakdown- and final-viscosity) had negative relation with AAC and positive with short side chains of AP. Starches with high proportion of granules of size between 1 to ≤10μm and >10 to 30μm size, respectively had lower and higher paste viscosities. Starches with higher proportion of long side chains of AP had higher gelatinization temperature (To, Tp, Tc) and enthalpy. Starches with higher proportion of granules of size >10 to 30μm had lower AAC and higher To, Tp and Tc. Gel hardness, To, Tp and Tc were lower for starches with higher proportion of granules of size >1 to ≤10μm. Viscoelasticity of cooked starch varies with AAC, short side chains of AP and granules size distribution.