Abstract: Objective: The effect of fermentation by Lactobacillus (L. delbrueckii subsp. bulgaricus and L. plantarum subsp. plantarum) on the nutrient components of the fermented supernatant of Porphyra haitanensis and its antioxidant activity and inhibitory activities on key enzymes of glycolipid metabolism (α-glucosidase and pancreatic lipase) were investigated in this study. Methods: The contents of total phenols and total flavonoids in the fermented supernatant were analyzed by using the Folin-Ciocalteu and sodium nitrite-aluminum nitrate methods, respectively. The primary metabolites were analyzed by 1H nuclear magnetic resonance (NMR) spectroscopy. The antioxidant activity was evaluated through 1,1-diphenyl-2-picrylhydrazyl (DPPH), 2,2’-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid radical cation (ABTS+), and hydroxyl radical scavenging assays, and the α-glucosidase and pancreatic lipase inhibitory activities were determined. Results: The contents of total phenols and total flavonoids in the fermented supernatants of P. haitanensis were significantly increased by both L. delbrueckii subsp. bulgaricus and L. plantarum subsp. plantarum, and the release of metabolites including lactic acid, arginine and proline was also promoted by Lactobacillus fermentation. Interestingly, a significant increase in the antioxidant activity and inhibitory activities against α-glucosidase and pancreatic lipase were observed in the fermented supernatants, and the most pronounced scavenging effect was recorded on hydroxyl radicals, similar to that of 700 μg/mL vitamin C (VC). Compared with unfermented P. haitanensis, the α-glucosidase inhibitory activity was increased by 2.1–2.2 times in fermented P. haitanensis and the lipase inhibitory activity was increased up to (95.3 ± 1.3)% by 95.7%. The increase in antioxidant activity and α-glucosidase and pancreatic lipase inhibitory activities may be mainly attributed to the increase in the contents of total phenols and total flavonoids in the fermentation supernatants. Conclusion: Lactobacillus fermentation can effectively improve the antioxidant activity and the inhibitory activities against α-glucosidase and pancreatic lipase of Porphyra haitanensis. Our findings suggest that the fermented supernatant of P. haitanensis with Lactobacillus has the potential to be developed into functional foods and special dietary foods for the alleviation and adjuvant treatment of chronic diseases, such as diabetes and obesity.

Key words: Lactobacillus; Porphyra haitanensis; fermentation; antioxidant activity; α-glucosidase; pancreatic lipase; inhibition