Effects of four herbs on the composition and growth performance of Tenebrio molitor larvae

Tenebrio molitor (MWs) are able to convert grain byproducts into high-quality biomass, which can be processed into animal feed. Since several herbs are sometimes added in small quantities to some baking materials, this study examines the effects of the dietary inclusion of herbs on growth performance, nutrient composition and the antioxidant activity of MWs. The MWs were reared on a control diet consisting of wheat bran alone, as well as a wheat bran supplemented with four different herbs: basil, oregano, rosemary and thyme. The herbs were added in two concentrations, 0.125% and 2% on a dry matter basis (DM). All experiments were conducted in the dark at 27 °C with 60% relative humidity for five weeks. Growth performance parameters were recorded throughout the trial. Nutritional composition and antioxidant activity were analysed in the resulting larvae. A greater inclusion of herbs resulted in lower levels of protein content. Only the inclusion of oregano led to a lower fat content compared to the control group. Minor detrimental effects on larval chemical composition were observed, which could be attributed to the higher total polyphenolic content (TPC) of the herbs that appeared to have had a negative impact on the larval TPC. A negative correlation was observed between the TPC of the substrates and the larval TPC. In contrast, the larval antioxidant activity was enhanced by both types of herbs and their inclusion level. Concluding, dietary incorporation of herbs had no or minor effect on growth performances and nutritional profile in T. molitor.