Effect of silkworm variety on the structural transition of silkworm cocoons by wet and thermal compression treatments

Abstract

Silk has attracted considerable attention in the biomedical and cosmetic fields due to its excellent biocompatibility and cytocompatibility. Silk is derived from silkworm cocoons, and the structure and properties of its two main protein components, fibroin and sericin, have been reported to vary depending on the silkworm variety. In the present study, the effect of silkworm variety on the structural transitions of cocoons subjected to wet and hot press treatments was investigated. Regardless of silkworm variety, the raw sericin in all cocoons underwent crystallization following wet treatment, resulting in an increased crystallinity index. However, the extent of this increase varied by variety: cocoons from varieties 9671 (6.7%) and N74 (5.9%) exhibited greater increases in crystallinity, whereas those from varieties 126 (1.5%) and Korea Sammyeon (1.6%) showed relatively smaller increases. Hot press treatment led to a decrease in crystallinity and an increase in yellowness index in all samples. Nevertheless, the degree of these changes differed significantly among the varieties. Specifically, N74 (0.5%) and Dodamnue (1.2%) exhibited the smallest reductions in crystallinity after hot pressing. Among the white-colored cocoons, variety 126 demonstrated the smallest increase in yellowness index (32.8), indicating the highest resistance to yellowing. The diameter of silk filaments also varied depending on silkworm variety. In most cocoons, silk filaments adhered to each other after hot pressing, while those in N74 and Korea Sammyeon remained unchanged.