Effect of in vitro digestion on Acheta domesticus and Tenebrio molitor nitrogenous and non-nitrogenous compounds

Acheta domesticus and Tenebrio molitor are two of the most consumed and studied edible insects worldwide. Anyway, several nutritional, chemical, and biological aspects must be further investigated. In this study, INFOGEST protocol was applied on A. domesticus and T. molitor to investigate the bioaccessibility of the released metabolites, using protein hydrolysis and bioavailability assay for amino acids, as well as NMR metabolomics for other compounds. Insect chitin content was also measured to avoid an overestimation of nitrogen determination. An optimized microwave-assisted procedure was used to quickly hydrolyse proteins, and the amino acids quantification was performed by a validated RP-HPLC-DAD method. Glutamate, alanine, cysteine, aspartate, leucine, proline, and valine were the most abundant amino acids in both insects. Differently, the amino acids composition in oral, gastric, and duodenal phases changed according to the digestion phase and insect species. In particular, alanine, serine, and phenylalanine were the main absorbed amino acids for both species, whereas threonine, glutamate, tyrosine, valine, isoleucine, and histidine were the lowest ones. Protein hydrolysis during digestion was also monitored by NMR spectroscopy, as well as other metabolites detected in the insects, such as trehalose and betaine, significantly higher in T. molitor, whereas taurine was only measured in A. domesticus.