Modification of porcine plasma protein structure and flavor by ultrasound-assisted enzymatic hydrolysis.

This study evaluated the effects of ultrasound-assisted enzymatic hydrolysis on the structural and flavor properties of porcine plasma protein (PPP). Five proteases, pepsin, stem bromelain, ficin, neutral protease and papain, were used to hydrolyze porcine plasma protein, and their effects on the degree of hydrolysis (DH) were compared. The neutral protease-treated group exhibited the highest DH, reaching 11.74 ± 0.04%. Ultrasonic pretreatment (500 W, 5 min) further increased the DH to 17.43 ± 0.40% and improved sweetness and umami taste, as revealed by sensory evaluation and electronic tongue/nose analyses. Free amino acid analysis showed that total free amino acids in the ultrasound-assisted group reached 3515.81 ± 12.17 μg/g, with significant increases in umami- and sweetness-associated amino acids. Structural characterization using endogenous fluorescence, surface hydrophobicity, particle size/zeta potential, and scanning electron microscopy indicated that the combined effect of ultrasound and enzymatic hydrolysis induced protein unfolding, exposed hydrophobic regions, and enhanced enzyme accessibility. These changes included increased α-helix and random coil contents, reduced β-turn content, enhanced surface hydrophobicity, reduced particle size, and a more fragmented and porous microstructure. This study provides a theoretical basis for using ultrasound-assisted enzymatic hydrolysis to improve the umami taste of porcine plasma protein.