Structure of faba bean, black bean and pinto bean starches at different levels of granule organization and their physicochemical properties

The structure and physicochemical properties of pulse starches isolated from different cultivars of faba bean (FB), black bean (BB) and pinto bean (PB) were examined. FB starches exhibited numerous cracked granules, whereas the surface of PB and BB starches showed no evidence of cracks or indentations. Apparent amylose, phosphorus and bound lipid contents ranged from 25.8 to 33.6%, 0.004 to 0.009% and 0.13 to 0.15%, respectively. Variations in the above parameters among cultivars of FB and BB were marginal, but significant (P<0.05) among cultivars of PB. All starches exhibited a 'C' type X-ray pattern. The amount of B-type unit cells ranged from 20.6 to 25.0% (FB), 15.4 to 17.7% (BB) and 7.9 to 17.3% (PB). Relative crystallinity ranged from 20.3 to 21.9% (FR), 20.4 to 21.3% (BB) and 21.3 to 23.1% (PB). Molecular order near the granule surface followed the order: BB similar to PB > FB. Variations in molecular order among cultivars of FR, BB and PB were marginal. Differences in amylopectin chain length distribution among FR, BB and PB starches and among cultivars were marginal. The extent of interaction of amylopectin double helical associations within the crystalline lamella followed the order: BB similar to PB>FB. Amylose leaching (AML) in the temperature range 60-90 degrees C, gelatinization temperatures and enthalpy of gelatinization followed the order: F B> BB similar to PB, FB>PB>BB, BB similar to PB>FB and BB similar to PB>FB, respectively. Variations in AML among cultivars were marginal in FB, but significant (P<0.05) in BB and PB starches. Swelling factor (SF) in the temperature range 60 to 85 degrees C and at 90 degrees C followed the order: FB>BB similar to PB and BB similar to PB>FB, respectively. Differences in SF among cultivars of FB and BB starches were more significant (P<0.05) at temperatures below 80 degrees C, whereas, in PB starches, differences among cultivars were more significant (P<0.05) at temperatures above 80 degrees C. Variations in peak viscosity, viscosity breakdown and set-back were marginal among FB cultivars, but were significant (P<0.05) among BB and PB (PB>BB) cultivars. FR starches were hydrolyzed by 2.2 N HCl at a faster rate than BB and PB starches (BB>PB). The amounts of rapidly digestible starch (RDS), slowly digestible starch (SDS), resistant starch (RS), hydrolysis index (HI) and expected glycemic index (eGI) followed the order: FB>BB similar to PB, FB>BB similar to PB, BB similar to PB>FB, FB>BB>PB and FB>BB>PB, respectively. Variations in RDS, SDS. RS, HI and eGI among cultivars followed the order: PB>BB>FB. The in vitro digestibility studies showed that PB and BB starches may be more effective than FB starches in controlling blood glucose levels. (C) 2011 Elsevier Ltd. All rights reserved.