Studies on the Functional Characteristics and Digestibility of Starches from Phaseolus vulgaris Biotypes

The functional properties of starches from black bean, kidney bean, navy bean, northern bean and pinto bean, all biotypes of Phaseolus vulgaris , were examined. Starch granule sizes ranged from 22 – 39 μm (length) to 19 – 28 μm (width) and shapes varied from elliptical to oval. Amylose content ranged from 30.2 – 37.3%. A highly ordered crystalline structure of granules (Ca) was suggested by restricted swelling power and solubility, resistance to α‐amylase attack, high gelatinization temperature and stable amylographic viscosities. Moreover, the existence of a crystalline structure of the highest and lowest order of stability among the Phaseolus starches was indicated for pinto bean and black bean, respectively, which were substantially different than those of kidney, northern and navy bean. The higher stability of pinto bean starch indicated a higher degree of associative bonding forces, namely, hydrogen and covalent, between oxygen and hydrogen atoms of closely packed parallel amylose chains. The wide range in amylographic viscosities was a reflection of crystalline stability, amylose exudation, granule swelling and pH of slurry. Gels exhibited a higher degree of retrogradation at +4 °C than at – 15 °C. Scanning electron microscopy showed that α‐amylase‐treated corn starch granules were degraded from the inside out by the formation of large circular holes, whereas those of kidney bean were less extensively degraded and showed only scaling and roughening of the surface as evidence of granule deterioration.