The chemical composition of the cocoons of silkworms raised with Lusang leaves is as follows: water 1.40%, ash 1.14%, protein 97.34%, ether-soluble extract 0.26%, fiber 0.39%. Silkworm cocoons are mainly made of fibrous protein fibroin (Fibroin), wrapped with another protein sericin (Sericin) bonded together, in addition to containing a small amount of oils, pigments, inorganic substances and so on. In raw silk, silk fibroin accounts for about 70%, and sericin accounts for about 22%. Silk fibroin is a kind of keratin, which is composed of amino acids, with glycine and alanine as the most. The nitrogen of these two amino acids accounts for about 80% of the total nitrogen. 105g silk fibroin contains the following amino acids (the number after the substance is the number of moles): glycine 578, alanine 381, valine 29, leucine 7, isoleucine 9, serine 157, threonine 12. Tyrosine 67, Phenylalanine 8, Proline 5, Tryptophan 2, Lysine 4, Histidine 2, Arginine 6, Aspartic Acid 17, Glutamic Acid 13, Total 1297 moles.
Sericin is also a keratin. Its amino acids are generally similar to silk fibroin. The slight difference is that glycine, alanine, and tyrosine are less; serine, glutamic acid, and aspartic acid are more. The cocoon contains 50mg% of free hydrogen acid (calculated as glycine). Silkworm cocoons contain oily waxy substances, which are composed of primary alcohols (C28-C32), solid fatty acids (C26-C32), paraffin wax (C25-C31) and liquid fatty acids. It also contains sitosterone (glucoside) and lupeol (Lupeol).