Ultrasound improves the digestibility of oxidized silver carp (Hypophthalmichthys molitrix) myofibrillar protein: Changes from structure to peptide release

The objective of this study was to investigate the effect of ultrasound on the digestibility of oxidized silver carp myofibrillar protein (MP). The MP solutions were oxidized with a hydroxyl radical generating system, and subsequently subjected to 100 W, 150 W, 200 W ultrasound treatment, respectively. The results showed that ultrasound effectively recovered the reduction in the digestibility of oxidized MP, especially the 150 W ultrasound achieved the best effect. The 150 W ultrasound reduced the particle size and turbidity of oxidized MP by 26.71 % and 35.49 %, respectively. The analysis of sulfhydryl, disulfide bonds, intrinsic fluorescence, and surface hydrophobicity suggested that ultrasound caused the breakage of disulfide bonds, which promoted the depolymerization oxidized MP. The morphology observed by atomic force microscope further evidenced that ultrasound reduced the degree of oxidized MP aggregation. The results of peptidomics showed that ultrasound treatment largely increased the peptide release of oxidized MP during the gastrointestinal digestion, especially the peptide containing lysine and arginine. Take together, ultrasound promoted the break of disulfide bond, which led to the depolymerization of oxidized MP and thus improved the digestibility of oxidized MP.