Upcycling agri-food side-streams via Tenebrio molitor rearing : growth performance, nutritional composition, and frass quality of larvae

Abstract

Insect bioconversion can transform agri-food side-streams into insect biomass while returning nutrients in the form of frass. This study evaluated Tenebrio molitor reared on wheat bran and on substrates in which bran was partially replaced with agri-food side-streams produced in Kosovo, including brewer’s spent grain, brewer’s spent yeast, apple and grape pomace, and surplus vegetables. Growth performance, larval composition, and frass nutrient composition were assessed across seven treatments. Larvae reared on wheat bran combined with brewer’s spent grain and melon as wet feed achieved the highest larval weight. Substrates containing wheat bran, apple pomace, and brewer spent yeast also supported high larval weights, but with a higher feed conversion ratio. In contrast, larvae reared on wheat bran, grape pomace, and brewer’s spent yeast showed the lowest larval weights. The use of potatoes as wet feed was associated with a longer development period. Larval proximate composition remained similar across treatments, with crude protein contents of 52–56% DM and only limited variation in fat and ash content. Overall, several tested side-streams supported larval growth comparable to wheat bran while generating nutrient-containing frass.