Chitin contents in different black soldier fly (Hermetia illucens) life stages

Black soldier fly (BSF, Hermetia illucens) is a promising insect species for valorising organic side streams into biomass high in protein and lipid. However, BSF also contains chitin known to possess anti-nutritional properties hampering its applications in food and feed. Quantification of chitin is often disregarded and studies that have quantified chitin have examined different life stages, known from other insect species to affect the chitin content. Additionally, these studies used different chitin quantification methods, whilst the potential effects of this on chitin quantification are unknown. To address these knowledge gaps, the current work examined the macronutrient content, including chitin, in all BSF life stages covering eggs to flies. Six different commonly applied chitin quantification methods were used including four direct methods (acid detergent fibre with/without amino acid correction, crude fibre, neutral detergent fibre) and two indirect methods (glucosamine determination by spectrophotometry (SP) and ultra-performance liquid chromatography (UPLC)). Independent of the quantification method, chitin was present in all life stages and its content generally increased throughout the life cycle. Large differences in chitin contents were, however, observed between quantification methods. Direct determinations yielded higher chitin contents than indirect determinations presumably due to the presence of other nutritional components in the residues resulting in chitin overestimations. The UPLC method appeared to be best suited for chitin determination in BSF, having higher accuracy and precision than the examined gravimetrical determinations and better chitin recovery compared to the SP method for high chitin samples. The nitrogen-to-protein conversion factor (Kp), based on the sum of anhydrous amino acids, ranged from 3.35-4.11 being lowest in larvae and highest in prepupae. In summary, the study underlines that both the quantification method and BSF life stage have a large impact on chitin determination and Kp factor, which should be taken into account when comparing studies.