Effect of Extraction Ingredients on the Conformation and Stability of Silk Sericin (SS)

Abstract

Silk sericin (SS) has different physicochemical properties depending on the extraction technique. In this study, SS was isolated in the presence of ingredients, including 5 to 10% ethanol (EtOH) and 5 to 10% glycine. Furthermore, temperature conditions of 80 °C, 100 °C, and 120 °C were used for 1, 3, and 5 h to evaluate the extraction rates. The extraction, gelation, structural, and cytotoxicity properties of SS extracted under different conditions were investigated. Extraction at 100 °C and 120 °C were found to have the highest SS yield, with 80 °C being the lowest. SS isolated at 100 °C and 120 °C for 1 and 3 h in water, and EtOH gelled at 4 °C in 2 to 3 days and 37 °C in 40 min. Glycine SS extracts were obtained at 100 °C and 120 °C for 1 h, gelled at 4 °C for 20 days and 37 °C for 16 h. SS was observed at 80 °C, with no gelation occurring. Glycine SS extracts obtained for 3, and 5 h at 120 °C showed no gelation. Circular dichroism (CD) results show glycine in SS induces α-helix and random coil structure. SDS-polyacrylamide gel electrophoresis (SDS-PAGE) and fast performance liquid chromatography (FPLC) were used to quantify the molecular weight distribution at 63 and 70 kDa, respectively. The MMT assay (3-(4,5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide) revealed no cytotoxicity in macrophage RAW 264.7 cells treated with this method SS; these findings present the significance and possibility of using selected extraction ingredients in SS that allow for the application of native SS at an initial extraction viscosity.