Chemical Composition of Silk and Its Influence on Yellowing Mechanism

点击翻译按钮获取中文摘要

We investigated the yellowing behavior and chemical compositions of cocoon filaments produced by the silkworms reared on an artificial diet, and compared with those on a mulberry leaf diet. To this end, silkworms were reared on an artificial diet (A) or on a mulberry leaf diet (M) for an entire instar. The artificial diet consisted of a Tofu-cake as its main component. Two types of cocoons (A and M) were used as sample materials. Yellowing of M-sample was remarkable after irradiation with ultraviolet light. On the other hand, it was scarcely observed for A-samples. The Amino Acid Composition and the X-ray diffraction pattern of the A fibroin was found to be almost the same as those of M fibroin. The amount of the A sericin dissolved in hot water (28%) was higher than that of M (24%), and the dissolution rate of the A sericin was higher than that of M.Hot-water-soluble fraction from A-sample contains relatively a large amount of nucleotide compounds, such as deoxycytidylic acid (dCMP) and cytidylic acid (CMP). On the other hand, M-smple contains little nucleotide compounds. This difference may cause the differences in yellowing behavior between these two samples. The artificial diet used in this study affects yellowing behavior of cocoon filaments and chemical compositions of hot-water-soluble fractions (sericin) ; on the other hand, it does not affect those of fibroin proteins.