Protein identification and in vitro digestion of fractions from Tenebrio molitor

The nutritional value of insect protein is evaluated not only in amino acid composition, but also in protein digestibility. The general amino acid composition of Tenebrio molitor has been reported before, but limited knowledge is available on its digestibility. The objective of this study was to investigate in vitro protein digestibility of whole T. molitor larvae, a water-soluble fraction (supernatant) and water-insoluble fractions (pellet and residue), and to identify which proteins were present in the fractions studied. The digestibility of the supernatant fraction (~80 %) was much higher than that of pellet (~50 %) and residue (~24 %) after in vitro gastroduodenal digestion as was determined using the o-phthaldialdehyde (OPA) method. More proteins were digested after pepsin/pancreatin digestion than after only pepsin digestion. The most abundant proteins in the supernatant were hemolymph protein (~12 kDa), alpha-amylase (~50 kDa, a putative allergen), and muscle proteins (e.g. actin 30–50 kDa) in the pellet fraction as determined from LC–MS/MS and SDS-PAGE. In conclusion, the proteins in the soluble fraction that contained hemolymph proteins were more easily digestible than the insoluble, muscle protein-containing fractions.