Sericin modified by gamma irradiation in solution and optimized for bioactivity

Previously, a high-molecular weight sericin was developed using gamma irradiation to change its molecular structure. Although the physiological activity of sericin was enhanced by gamma irradiation, its molecular weight was too high, having increased by about 400 kDa. In this study, we tried to improve the commercial applicability of sericin by optimizing the gamma irradiation dose. A sericin solution (100 mg/ml) was prepared with a pH of 5.0, 6.0, 7.0, 8.0, and 9.0, and gamma-irradiated at the absorbed doses of 2.5, 5.0, 7.5, and 10 kGy. Non-irradiated solution was used as a control. The samples were analyzed for their solubility and DPPH radical scavenging activity. In the solubility analysis, significant differences in molecular weight were not seen according to irradiation dose, whereas their solubility and antioxidant activity were changed. Sericin irradiated with 5 kGy gamma rays at 10 mg/ml exhibited macrophage polarization to the M2 phenotype in cells; this outcome was associated with a reduction of NF-κB activation as a defense against inflammatory reactions. These findings suggest that gamma irradiation of less than 10 kGy is an effective method for the practical use of sericin. This study has important implications for the use of highly functional biotechnology products, as anti-inflammatory activity was increased without changing molecular weight. •The optimal sericin concentration and optimal absorbed dose condition were established.•Exposure of sericin to gamma irradiation was accompanied by an increase in its solubility.•Gamma-irradiated sericin negatively regulates LPS-stimulated inflammation through NF-κB deactivation.•The anti-inflammatory effect of gamma-irradiated sericin may be mediated by M2 macrophage polarization.