Ultrasound-assisted transglutaminase modification regulates the structure–interface–digestion relationship of basa fish myofibrillar protein-stabilized emulsions

This study investigated ultrasound-assisted transglutaminase (TGase) modification of basa fish myofibrillar protein (BFMP) as a structure-design strategy to regulate molecular assembly, interfacial organization, and digestion-related β-carotene transfer in protein-stabilized emulsions. Ultrasound pretreatment promoted moderate unfolding of BFMP, increasing surface hydrophobicity index (H₀) to 260.66 and free sulfhydryl content to 77.38 μmol/g, which indicated enhanced exposure of reactive and interfacially active groups. Subsequent TGase treatment decreased OPA-reactive free amino groups, promoted high-molecular-weight protein assemblies, and induced concentration-dependent conformational rearrangement of BFMP. These structural changes regulated BFMP functionality in a TGase concentration-dependent manner. Moderate TGase addition improved interfacial activity, whereas higher TGase levels enhanced interfacial film integrity and improved β-carotene retention during thermal treatment and storage. During in vitro digestion, US-0.8%-BFMP showed the highest apparent gastric retention and bioaccessibility of β-carotene, while US-0.4%-BFMP exhibited the highest apparent intestinal retention. These findings indicate that gastric protection, apparent intestinal retention, and micellar incorporation were not fully synchronized, and that maximum physical stability did not necessarily correspond to optimal digestion-related functionality. Overall, ultrasound-assisted TGase modification provides a structure–interface–digestion framework for designing BFMP-stabilized emulsions in which molecular flexibility, interfacial film strength, and digestive responsiveness are balanced.