Sericin is a hot water-soluble macromolecular globular protein. It represents a family of proteins having molecular mass of 10 to 310 kDa. Sericin envelops the fibroin fibre with successive sticky layers that help in the formation of cocoon. Sericin contributes about 20-30% of the total cocoon weight. The sericin protein is made of 18 amino acids most of which have strongly polar side groups such as hydroxyl, carboxyl and amino groups 1-3.
Figure 1: Composition of Silk Filament
Silk sericin, abundantly present in the silk processing waste water, can generate revenue for silk processing industry as a natural value added material.
During last decade, sericin has emerged as a biomaterial of commercial value having diverse physiological properties such as antioxidant, UV protection, moisture adsorption, antibacterial activity etc 4. The cosmetics industry is using sericin in its moisturizing and skin care products since it inhibits the tyrosinase activity and promotes biosynthesis5. Moreover, its high hydroxyl-amino acid content has high water-binding capacity that keeps the skin moist. Masahiro et al.6 have reported that consumption of sericin enhances bioavailability of Zn, Fe, Mg and Ca in rats therefore it can be a valuable natural ingredient for food industry.
Some studies have indicated that sericin, exerts inhibitory activity on ultra-violet radiation induced acute damage, posses the biological activity of preventing cell death and promoting cellular growth after acute serum deprivation 7. Moreover, sericin has also been found to be useful as a degradable biomaterial, biomedical material and polymers for forming articles, functional membranes, fibres and fabrics 4.
Use of sericin as a finishing agent for natural or man made textiles enhances moisture absorption, antistatic properties, softness and comfort 8. Filters made of polyamide or polyester fibres coated with sericin have antioxidation and antimicrobial activity, suggesting their potential use as indoor air filters to reduce free radicals and fungi or bacteria contamination9. Sericin can be cross linked, copolymerized or blended with other polymers to produce a new range of biodegradable materials with improved properties 4.
Thus because of its varied properties, sericin can be used as an additive in food, cosmetics, textiles and pharmaceutical products as indicated in Fig. 2.
Figure 2: Application of sericin in various industries