Structure and Chemical Composition of Silk Proteins in Relation to Silkworm Diet

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Abstract
We investigate the structure and chemical composition of silk proteins produced by silkworms reared entirely on an artificial (A) diet, and compared those with worms entirely on a mulberry leaf ( M ) diet. The artificial diet has tofu-cake as its main component. Two types of cocoons (A and M) are used as sample materials. The dissolution behavior of the A sericin in hot water is different from that of M sericin; the amount of A sericin dissolved (28%) is higher than that of M (24%), and the dissolution rate of A sericin is also higher. Both sericins are separated into four fractions according to dissolution rate in hot water, and the amino acid composition (AAC) of each fraction is determined. Although the AAC of unfractionated A sericin is almost the same as that of M sericin, the AACs of the fractionated sericin from the A sample are distinguished from those from the M sample. AACs of the A and M fibroins are also evaluated and found to be almost identical within experimental error. The x-ray diffraction pattern of the A fibroin is also nearly the same as that of M fibroin. The artificial diet used in this study affects the dissolution behavior and chemical com position of sericin proteins, but does not affect structure and chemical composition of fibroin proteins.