Ultrasound-assisted extraction and in vitro simulated digestion of Porphyra haitanensis proteins exhibiting antioxidative and α-glucosidase inhibitory activity

Peptides from natural materials have been reported owning potential for regulating oxidative stress and hyperglycemia for human body. In this study, peptides from a favorite food, Porphyra haitanensis, were prepared by consecutive procedures including ultrasound-assisted extraction, in vitro simulated gastrointestinal digestion and fraction. Subsequently, their relevant bioactivities were investigated by several in vitro methods, such as 1,1-diphenyl-2-pycrylhydrazyl (DPPH) radical scavenging, ferric reducing antioxidant power (FRAP), and α-glucosidase enzyme inhibition assays. By single factor design experiment, the highest yield of crude protein was 3.42% extracted by alkaline solution for 20 min sonication at 35 °C. After digestion, peptides were mainly distributed in F2–F11 fractions by sephadex G-25, and the peak value was found in F5. The significant activities in three assays were displayed in F3–F7. As calculated by the polynomial curve fitting, a significantly positive correlation was found between the peptide contents and the DPPH radical scavenging rate, the FRAP value, and the α-glucosidase enzyme inhibitory rate (R2 = 0.8490, R2 = 0.7579, R2 = 0.9701, respectively). The results showed that these peptides possessed promising antioxidant activity and inhibitory activity on α-glucosidase. Therefore, peptides derived from P. haitanensis have potential anti-diabetic applications in pharmaceutical and functional food industries.