Greener degumming production of layered sericin peptides from a silkworm cocoon and their physicochemical characteristics and bioactivities in vitro

The greener degumming method not only affects evidently the mechanical properties and uses of silk fibroin fiber, but also involves in some interesting issues including the recovery and utilization of sericin in a large number of alkaline degumming waste solutions. To this day, it remains one of the key issues deeply trouble us for the silk processing industry. Here, we systematically reported that three kinds of greener degumming methods could extract the outer-layered (OLS), inner-layered (ILS) and whole (WS) sericin peptides, respectively. Among them, the degumming method by using calcium hydroxide (CH) had an obvious advantage that the whole sericin (WS) could be fully recycled by neutralizing with sulfuric or phosphoric acid. The results show that the degumming ratios of OLS, ILS and WS were 11.4%, 16.65% and 28.61%, respectively. Three sericin peptides had evident differences from physicochemical properties and bioactivities in vitro. OLS obtained from boiling water had the highest in molecular weight (≥30 kDa), and both its antioxidation and antibacterial activities were higher than those of ILS extracted under 120 °C water for 2 h. ILS contains more β-sheet structures and its thermal decomposition temperature is approximately 14 °C higher than that of OLS. Almost the same as or higher than glycerin, the hygroscopic capacity of OLS in 160 h and the moisturizing properties of WS in 100 h reach about 32% and 50%, respectively. Furthermore, the WS had the lowest in molecular weight and stronger tyrosinase inhibitory activity and all samples had α-glucosidase inhibitory activity. Therefore, these cleaner production methods for silk degumming can result in three sericin peptides, of which OLS and ILS have potential applications and developmental value in the fields of medical biomaterials, and WS is preferable to biopharmaceuticals, cosmetics, and advanced health foods.