Antioxidant activities and total polyphenolic content of mealworm growth on herb containing substrates

Mealworms (MW, Tenebrio molitor) can be reared on diets such as grain by-products or grain-based former foodstuffs, resulting in the production of high-quality biomass. These diets might also contain several herbs. The high levels of polyphenols in these herbs have the potential to negatively affect the growth of the insects given the elevated presence of polyphenolic compounds therein. Therefore, the objective of this project is to assess the impact of herb inclusion on the total polyphenolic content (TPC) and antioxidant activity in the larvae. The MWs were raised on a control diet consisting solely of wheat bran, as well as on wheat bran supplemented with four different herbs: namely, basil, oregano, rosemary, and thyme. The herbs were incorporated at two concentrations, 0.125% and 2% on a dry matter (DM) basis. All experiments were carried out in darkness at 27°C with 60% relative humidity for a period of five weeks. There were no significant differences in growth performance among the groups. However, the inclusion of herbs did have a minor detrimental effect on larval composition. The elevated TPC levels in the herbs negatively correlated with the TPC levels in larva. In contrast, the antioxidant activity of the larvae (as measured by FRAP and ABTS) was enhanced by the presence of herbs and their respective inclusion levels. Therefore, it can be concluded that the inclusion of herbs at elevated levels had an impact on the larval composition and antioxidant profile. Further research is required to investigate these effects more extensively.