Studies on Structural and Functional Properties of Sericin Recovered from Silk Degumming Liquor by Membrane Technology

This article describes the recovery of silk sericin from three different degumming liquors, that is, high temperature high pressure (HTHP), alkaline, and soap plus alkali (SPA), using membrane filtration technology. The recovery of sericin by membrane technology results in the reduction of about 78-85% chemical oxygen demand as well as biological oxygen demand values in the final discharge liquor. The sericin powders produced from the purified degumming liquors have been characterized in terms of color, nitrogen content, protein content, ash content, and thermogravimetric analysis and compared. It has been found that the sericin recovered from HTHP degumming liquor has about 98% protein content as compared to that recovered from alkaline (92%) and SPA (67%) degumming liquors. The molecular weight distribution and secondary structure of the recovered sericin powders have been determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and circular dichroism (CD) spectroscopy, respectively. The molecular weight range of sericin recovered from HTHP, alkaline, and SPA degumming liquor was 20->205 kDa, 20-97 kDa, and 20-43 kDa, respectively. The secondary structure of sericin recovered from HTHP degumming showed random coil conformation with some sheet structure. The sericin recovered from alkaline and SPA degumming liquors showed denaturation with some random coil, 0 sheet, and a helix conformation. The functional properties of the three different recovered sericin powder samples in terms of moisture content and ultra protection factor (UPF) have also been evaluated and compared. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 113: 2796-2804, 2009