Broad bean hull extract reduces in vitro starch hydrolysis via apparent starch structural organization and α-amylase inhibition.

Modulating starch digestibility with natural ingredients is of interest for improving postprandial glycemic response. Here, a soluble broad bean hull fraction (SBBH), derived from an underutilized legume-processing byproduct, was evaluated for its effects on the in vitro hydrolysis of corn, potato, rice, pea, and wheat starches. SBBH markedly suppressed both the hydrolysis rate and final hydrolysis extent of all starches, with inhibition rates of 17.34%-27.01%, and primarily reduced the rapid hydrolysis phase, as reflected by the decrease in k1 from 0.43-0.52 to 0.05-0.12 min-1. The inhibitory effect was starch-dependent and was accompanied by apparent molecular redistribution, including reduced amylopectin-associated size (R¯h,AP decreased by 8.75-21.71%), increased apparent amylose-related fractions (from 17.66-35.62% to 38.75-61.89%), and redistribution of chain-length populations toward medium-length chains. These changes were further associated with enhanced short-range and long-range structural order, increased thermal stability, and denser microstructures. In addition, SBBH directly inhibited α-amylase activity (from 0.1108 to 0.0389 mmol·min-1·mL-1). Taken together, the results suggest that SBBH reduced starch hydrolysis through concurrent changes in apparent molecular organization and α-amylase inhibition, highlighting its potential as a natural functional ingredient for glycemic modulation and legume-processing byproduct valorization.