Evaluation of Molecular Weight Distribution of Sericin in Solutions Concentrated via Precipitation by Ethanol and Precipitation by Freezing/Thawing

Abstract

Sericin is a globular water-soluble protein that constitutes 25 to 30 % of silk proteins weight in silkworms cocoons. This protein envelopes silk fibers gluing them and ensuring the cohesion of the cocoon. During raw silk production, sericin is separated from silk fibers and it is discarded in wastewater, leading to a high biological oxygen demand to be degraded. The sericin molecular weight ranges from 10 to 400 kDa and the structure and molecular weight depend on the method which is extracted and purified. Lower molecular weight sericin peptides are mainly used in cosmetic products, whereas higher molecular ones enable its use for many other applications, like, medical biomaterials, functional bio membranes, and others. This study evaluates the molecular weight distribution of sericin in solutions in which this protein was concentrated by precipitation by ethanol and precipitation by freezing/thawing. The solutions, which were subjected to precipitations, were filtered and the two solutions obtained (the concentrated one and the permeated one) had their molecular weight distribution analyzed. The sericin molecular weight distribution in the solutions was analyzed by size exclusion chromatography (SEC). In this analysis, the mobile phase is ultra-pure water (Milli-Q) and a standard curve was made with pullulan polysaccharide standards. The results showed that the degumming process in autoclave (1 kgf/cm 2 - 40 min) was able to extract high molecular weight sericin and both precipitation methods could concentrate sericin in solution with no significant change in the molecular weight distribution, which ranges from lower than 20 kDa and up to 400 kDa values.