The Effect of Strain and Rearing Medium on the Chemical Composition, Fatty Acid Profile and Carotenoid Content in Silkworm (Bombyx mori) Pupae

SIMPLE SUMMARY: The replacement of environmental-costly resources in food and feed production is now imperative. Insects are recognized to be an effective protein source alternative to fishmeal and soy for animal husbandry. The evaluation of their nutritive properties can offer important insights to determine their potential use as feed. This study compares the pupae body composition of two different silkworm strains: a conventional polyhybrid producing white cocoons and the Nistari with golden yellow cocoons, rich in carotenoids, fed either on fresh mulberry leaves or an artificial diet. The results establish that feeding substrate composition strongly influences the fat and protein content of silkworm pupae. The feeding substrate also positively influences the pupae’ n-3/n-6 ratio while the carotenoid content is exclusively determined by the strain. ABSTRACT: The overexploitation of fishmeal and soy for the feedstuff industry has provided an opportunity to employ insects as an unconventional and more environmental friendly protein source. The evaluation of the nutritive properties of different insect species has consequently become a priority. The present study compares the pupal nutritive composition of two silkworm strains (White Cocoon Polyhybrid and Golden Yellow Cocoon Nistari) fed on two different rearing media (fresh mulberry leaves and a commercial artificial diet). Our results provide evidence that the composition of the feeding substrate strongly influences the fat and protein content of silkworm pupae. The two tested strains had higher fat and lower protein contents when fed with silkworm natural food (mulberry leaves) with respect to the commercial artificial diet. The analysis also showed that the n3/n6 ratio was affected almost exclusively by the feed substrate factor. On the contrary, the carotenoid content in pupae was specifically determined by the strain. The study identifies the interesting opportunity offered by silkworm pupae, which are usually a waste product of the silk-reeling process, to be used as alternative animal protein sources in a fully-closed circular production.