There are two kinds of sericin silkworms. One is the naked pupa Nd strain, which secretes silk thread at a rate of 30 mg/head, with spinning and cocooning rates of 99%. The other sericin silkworm, the Nd-s strain, which secretes only a few silk threads, with a sericin content as low as 92%, at the cocoon stage. Hence, neither of the existing strains are practical for sericin extraction.
Therefore, it was necessary to develop a silkworm variety which produces sericin protein efficiently. It secretes silk thread, at the rate of about 80 mg/head, while the spinning and cocooning rates have been improved to 99%.
The output of the cocoon layer is over four times that of the Nd strain. Sericin can be very efficiently produced, because the sericin purity is as high as 98.5% at the cocoon stage.
The sericin protein appears to be a functional material with antioxidative properties. It is expected to be of medical use in skin care and other fields.
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