2. Materials and methods
2.1. Materials
Silk industry wastewater material containing sericin produced by exploding cocoon shells with high temperature and pressure degumming technique, was obtained from Si-Juan Silk Ltd. (Jiang Su Province, China).
All other chemicals were reagent-grade products obtained commercially.
2.2. Preparation of sericin powder
The degumming wastewater was concentrated at about 40 °C by vaporizing water under steam heating, and recycling the condensate three times. The concentrate was spray-dried as flours. Next, the flours were dissolved in distilled water at the ratio of 1:10 (w/v), and the solution obtained was chilled close to 4 °C. Pure ethanol chilled to −18 °C previously was slowly added to sericin solution with constant stirring to obtain a final ethanol concentration of 75% (v/v). The obtained mixture was then kept at −18 °C overnight. Sericin powder was obtained by centrifuging the sericin solution at 3500 rpm for 20 min, followed by alcohol evaporation under reduced pressure (reached 0.1 MPa) at 40 °C and lyophilized by freeze drying. Sericin extraction yield was calculated by weight method, as shown in the following formula