In vitro impact of Tenebrio molitor insect flour on human gut microbiota

Tenebrio molitor insect flour (TMIF) is considered a nutritious food ingredient but still needs assessment of its nutritional potential in the human diet. One of the major indicators of the effect of diet on human health is the composition of the gut microbiota, especially the presence of beneficial bacterial groups, such as probiotic bacteria. In this way, two in vitro models of the gut microbiota were elaborated to evaluate the effect of TMIF on the gut microbiota. One of the models used pure cultures of Lactobacillus and Bifidobacterium strains in monocultures and co-cultures (pairs and consortium) to evaluate the effect of TMIF and the metabolic activity of these bacteria. Additionally, the direct effect of the flour on bacterial cells when they are in nutritive stress was also evaluated. Subsequently, the interaction of all groups present in the bacterial gut microbiota was evaluated from human volunteer faeces, using in this case TMIF subjects with or without pre-digestion. The evaluation of cell viability and metabolic activity was performed and compared in both models. In the first model with pure cultures, no negative effects of TMIF on the viability and growth of probiotic bacteria were observed, with an increase in the growth and production of short chain fatty acids (SCFA) and lactate. During incubation time under nutritional stress, the number of viable bacterial cells was maintained showing that the flour does not have any direct toxic effect on the cells. In the second model, the in vitro faecal model, digested and undigested TMIF have been shown to have positive effects on the growth of bacterial groups considered beneficial (e.g. Bacteroidaceae and Prevotellaceae) without promoting significant growth in groups with a negative impact on human health (e.g. Clostridium histolyticum, Desulfovibrionales and Desulfuromonales). TMIF promoted a higher production of organic acids such as acetate and propionate. In the presence of TMIF the production of ammonia was in the range of concentrations considered non-cytotoxic. Regarding the amino acid content of the TMIF samples, the undigested form presented to have higher concentration of total amino acids while the digested sample the highest concentration of free amino acids. As a conclusion, TMIF may be a potential meat substitute because of its nutritional content and the impact on the intestinal microbiota.