Black soldier fly (Hermetia illucens L.) whole and fractionated larvae: In vitro protein digestibility and effect of lipid and chitin removal

Protein quality, which can be defined by amino acid profile and protein digestibility, is of paramount importance when assessing a novel protein source. As the presence of chitin might impair insect protein digestion, and as there is little to no clarity as to how different insect fractions influence the overall protein digestibility, this study aimed at assessing the influence of lipids and chitin removal on the protein digestibility of black soldier fly larvae. The samples underwent an in vitro simulated gastro-intestinal digestion following the INFOGEST method, commonly used for humans, and both undigested matrices and digesta were characterized by means of amino acid composition, SDS-PAGE gel electrophoresis, and proteomic/peptidomic approaches. Protein solubilization, degree of hydrolysis (DH%) after digestion, and digestible indispensable amino acid (DIAA) contents were also determined. The results highlighted that the presence of chitin hindered protein digestion, as expected: in fact, the protein isolate showed the highest solubilized protein (84.0%), DH% (61.1%), and number of peptides and proteins detected by high resolution mass spectrometry (64 and 16, respectively), while the chitin-rich fraction the lowest (38.4% solubilized protein, 41.2% DH%, 37 peptides and 6 proteins detected, respectively). Additionally, the chitin-rich fraction had the lowest DIAAS. Interestingly, the preferred C-terminal cleavage sites for all samples were in line with the specificity of the enzymes used, meaning that insect proteins, compared to other matrices, do not change the enzymatic behavior in terms of their specificity.