Ultrasound microwave-assisted enzymatic production and characterisation of antioxidant peptides from sweet potato protein

Herein, we investigated the effects of ultrasound microwave (UM)-assisted hydrolysis using Alcalase (ALC), Flavourzyme (FLA), and their combination (ALC + FLA), on the production of sweet potato protein hydrolysates (SPPH). UM-assisted enzymatic hydrolysis significantly increased the degree of hydrolysis of SPPH compared with untreated (UN) samples. Fractions with differences in molecular weight (MW) of >10, 3–10, and < 3 kDa in SPPH from UM-assisted ALC, FLA, and ALC + FLA hydrolysis displayed higher antioxidant activities than those from UN samples. MW < 3 kDa fractions of SPPH from UM-assisted ALC and ALC + FLA hydrolysis treatments presented much stronger Fe2+-chelating activity (98.48% and 98.59%), ·OH scavenging activity (67.11% and 60.06%), and higher ORAC values (110.32 and 106.32 µg TE/mL), from which diverse peptides with potential antioxidant activities were obtained by semi-preparative HPLC and LC-MS/MS. All identified peptide sequences exhibited at least three potential antioxidant amino acids. Additionally, changes in peptide conformational structure and antioxidant amino acid composition were revealed by structure–activity relationship analysis. Thus, ultrasound microwave treatment has great potential in antioxidant peptides production.