An Assessment of the Safety of BSF Larvae Reared on Different Substrates for Use in Animal Feeds – Microbial Contaminants

The use of black soldier fly (BSF) larvae as a protein source for animal feed is gaining popularity. However, the safety of the larvae and the substrates used for rearing them has not been fully investigated, which is important for economic feasibility. This study aimed to evaluate the safety of BSF larvae and rearing substrates in Kenya by analysing microbial contaminants. To achieve this, the BSF larvae were reared on common production substrates, namely kitchen waste, fruit waste, and brewer's waste, in a Completely Randomised Design (CRD). Microbial analysis was conducted using selective culture-dependent methods to determine the total viable counts of safety indicator microbes such as Staphylococcus aureus (S. aureus), Salmonella typhi (S. typhi), Escherichia coli (E coli), and Bacillus cereus (B. Cereus) and confirmed using respective biochemical tests. The data obtained were statistically analysed using the R statistical package version 4.0.5 and compared with recommended levels by KEBS, Codex Alimentarius, and the European Union (EU) standards. The microbial analysis revealed that the larvae generally had high microbial loads compared to the substrates, except for B. Cereus, which showed a decrease in counts in BSFL from 203.3±25 CFU/g in substrate to 161.1±18 CFU/g in the larvae on average. The study found low levels of S. typhi in BSFL samples from the brewery (50±10 CFU/g) and fruit waste (60±5 CFU/g) compared to other microbes, but none was detected in larvae from kitchen waste. E. coli, B. Cereus, and S. aureus were present both in the substrates and BSF larvae, but within regulatory limits for edible insect products. Based on the results, the study recommends the use of safe substrates such as kitchen and fruit waste for BSFL rearing.