Optimization of Liquid Fermentation Process for Preparation of Silkworm Pupa Peptide by Bacillus natto and Its Anti-inflammatory Activity

In order to improve the utilization rate of silkworm pupa resources and the added value of products, silkworm pupa peptides were prepared from silkworm pupa proteins by liquid fermentation of natto. The optimum fermentation conditions were determined by single-factor experiment and response surface methodology. The inflammatory model of RAW264.7 macrophages was established by lipopolysaccharide, and the anti-inflammatory activity of silkworm pupa peptides were studied in vitro. The results showed that the optimum fermentation conditions of silkworm pupa peptide were inoculation amount 5.0 mL, silkworm pupa protein addition amount 2.6 g, initial pH7.0, fermentation temperature 37 ℃ and fermentation time 35.4 h. Under these conditions, the yield of silkworm pupa peptide was 14.58%. Silkworm pupa peptides were nontoxic to RAW264.7 macrophages and had significant proliferation effect on cells (P<0.05). Silkworm pupa peptides could significantly inhibit the secretion of NO, IL-1β and IL-6 in the supernatant of RAW264.7 cells induced by LPS in a dose-dependent manner (P<0.05). This study provides a theoretical basis for the high value utilization of silkworm pupa and the research and development of food-derived anti-inflammatory peptides.