Formation of ι-carrageenan-mediated complex: Enhancing thermal stability of α-amylase inhibitor from white kidney bean

The thermal sensitivity of α-amylase inhibitors (α-AL) from white kidney beans (WKB) poses a significant challenge in the food industry. This issue can be effectively addressed through stabilization strategies based on polysaccharides. In this study, iota-carrageenan (ι-CG) was chosen as a stabilizing agent owing to its high charge density and flexible chain structure. A chelation-based approach utilizing ι-CG was developed, and both the formation mechanism of the resulting complex and its effect on the thermal stability of α-amylase inhibitors from white kidney beans (α-AL-WKB) were thoroughly investigated. Multi-scale characterization demonstrated that the complexation at pH 6.0 and a mass ratio of α-AL-WKB to ι-CG of 2:1 effectively suppressed the thermal aggregation of α-AL-WKB, with only a minor decrease in activity from 7864.19 ± 239.90 U to 6094.88 ± 88.27 U. The compact structure of the complex was primarily stabilized through hydrogen bonding and electrostatic interactions. Surface plasmon resonance (SPR) analysis further confirmed a moderate binding affinity between the α-AL-WKB/ι-CG complex and α-amylase, with the equilibrium dissociation constants (KD) value of 4.01 × 10 −8  M before heating and 5.59 × 10 −8  M after thermal treatment. In simulated in vitro digestion assays, the complexation significantly lowered the digestibility of gelatinized corn starch, reducing rapidly digestible starch (RDS) by 27.74% ± 0.58% and increasing the resistant starch (RS) by 54.35% ± 0.27%. These findings demonstrate a promising strategy for enhancing the thermal stability of α-AL-WKB and provide a basis for developing low-glycemic-index functional foods.