On the nitrogen content and a robust nitrogen-to-protein conversion factor of black soldier fly larvae (Hermetia illucens)

Currently, a broad discussion exists in the literature regarding insect protein analysis. At its core, main difficulties and uncertainties are the inconsistent use of analysis methods and nitrogen-to-protein conversion (kP) factors. While the Kjeldahl and Dumas methods are both used in the literature, their result represents inherently different nitrogen fractions. Thus far, no correlation between them is established for insect matrices, which is a major uncertainty. Although much effort has been made towards more accurate kP factors, calculation of these was based on merely one sample while the chemical composition varies depending on rearing conditions. Using a broad variation in black soldier fly (BSF) larvae samples in the present study, a correlation between Kjeldahl and Dumas and a robust kP factor have been established. Moreover, the nitrogen distribution of BSF samples was also assessed after accurate chitin analyses. A highly significant linear correlation existed between the results of Kjeldahl and Dumas (slope, 1.009; intercept, - 0.008; R2, 0.9997). Consequently, both methods were deemed interchangeable for BSF larvae. Using amino acid data, a practical, more accurate and robust kP factor of 4.43 was obtained. Concerning the chitin content, the average of all BSF larvae samples was 5.95 ± 0.86 g N-acetylglucosamine/100 g dry matter and no correlation with the kP factor was observed. Regarding the nitrogen distribution of the samples, it was found that the contribution of nitrogenous compounds other than protein and chitin is not only high but also prone to variation (12-30% of the total nitrogen content).