Molecular interactions between capsicum protein and capsanthin: enhancement of complex formation and physicochemical stability by ultrasound and microwave treatments.

To investigate the mechanisms by which ultrasound (US), microwave (MW), and ultrasound-microwave combined (UM) treatments enhance the stability of capsanthin (Cap) in chili products, this study examined the effects of US, MW, and UM on Cap stability within the capsicum protein (CP)-Cap complex system. The characteristics and molecular structure of the complex (CCAP) were also analyzed. Results indicated that all treatments improved CP-Cap binding rate and CCAP stability, enhancing the resistance of Cap to light, heat, and acid-base stress, with MW showing the strongest effect. MW induced global unfolding and reorganization of CP, promoting deeper Cap embedding and forming compact, uniform CCAP with smaller particle size, whereas US caused CP aggregation, limiting CP-Cap interactions. CCAP formation involved a static quenching exothermic reaction, and each treatment altered CP secondary structures, increasing interaction sites and reinforcing hydrogen bonding and other intermolecular forces. These structural changes resulted in more stable and ordered CCAP, particularly under MW treatment. The findings provide mechanistic insights and technical guidance for improving Cap stability in chili products.