Growth performances, chemical composition, and microbiological loads of mealworm reared with brewery spent grains and bread leftovers

Tenebrio molitor (mealworm) larvae are one of the most intriguing edible insects, and they may be raised on a variety of substrates, including by-products, side-stream products, and former foodstuff. The substrates could affect drastically the productive performances as well as the chemical-nutritional value of the larvae. In this study we tested two main substrate ingredients, brewery spent grains (SG) and bread leftovers (B), without adding any other dry ingredients. In order to correlate the chemical composition of the substrates to the larvae characteristics, five different diets were tested as 100% of a single ingredient (SG100 and B100), 75–25% mixes (SG75B25 and SG25B75) and 50–50% mixes (SG50B50). The effects of the substrate were tested on the development rates, chemical composition, and microbial loads of mealworm larvae. The effects of fasting, washing, and cooking were also tested on the microbiological determinations. Results indicate that all the parameters were affected by the chemical compositions of the substrates. The larvae fed the higher contents of SG showed the best growth performances along with higher nutritional values. The diet with only bread (B100) showed the worst parameters, both on the growth performances and on the nutritive values. Microbial loads were also affected by the diets, with minor effects in relation to the washing and fasting procedures, while cooking drastically reduced all the microbial loads. Taking into account that the two employed ingredients were former foodstuff or by-products it is important to highlight the capacity of mealworms to positively convert side-stream materials into rich nutritional animal products.Highlights Mealworm could be proficiently reared on brewery spent grains and bread leftovers converting them into nutritional animal products. Mealworm productive performances and nutritional value could be affected by the employed substrate. Evidence of high mealworms plasticity and potential tailor made of the final outcomes.