Effects of diet on the biological activities and content of functional components of silkworm Bombyx mori and its faeces

Silkworm, Bombyx mori, and its faeces are notable healthy foods because of their biologically active components originating from mulberry (Morus spp.) leaves. However, in modern sericulture, silkworms are reared on artificial diet made primarily from defatted soybeans and dried mulberry leaf powder throughout the year. Neither the contents of functional components nor the biological activities of silkworms and their faeces raised on artificial diet have been investigated. Therefore, 1-deoxynojirimycin (DNJ) content, α-glucosidase inhibitory activity, Trolox equivalent antioxidant capacity (TEAC), total phenolic, total flavonoid and chlorophyll content were evaluated in silkworms and their faeces reared on mulberry leaves, artificial diet and then artificial diet switched to mulberry leaf from the fifth instar for four days. The DNJ content of silkworms depended on that in their diet and was significantly lower in silkworms fed with artificial diet than in those fed with mulberry leaves similar to the α-glucosidase inhibitory activity. On the contrary, TEAC, total phenolic content and total flavonoid content were similar in all silkworms regardless of feeding conditions. In the faeces of the artificial diet-reared group, TEAC, total phenolic content and total flavonoid content were significantly higher than those of the mulberry leaf-reared group. Chlorophyll content in faeces depended on the content of diet, whereas that in silkworms was low regardless of the diet type. The biological activities and contents of functional compounds in the artificial diet-reared group were at similar levels with those of the mulberry leaf-reared group when the diet switched to mulberry leaf from the first day of the fifth instar for four days, indicating that the biological activities and content of functional components in silkworms and its faeces are defined by diet and changeable over a short period.