Microbial safety of black soldier fly larvae (Hermetia illucens) reared on food waste streams

Black soldier fly larvae (BSFL) can valorise different organic matter and yield a product of high nutritional value. The lack of knowledge about the microbial safety of BSFL grown on different organic waste streams influences the commercialisation of BSFL as stockfeed ingredient. This study evaluates the microbial safety of BSFL grown on five different commercial food waste streams collected from two commercial production facilities. The effect of larval instar and post-harvest treatments (blanching and drying) on the microbial quality of the larvae was also investigated. The results of this study showed that spore forming bacteria including B. cereus and C. perfringens appeared in higher concentration (1.3 log CFU/g - 6.6 log CFU/g) compared to yeast and moulds (1.3 log CFU/g - 4.4 log CFU/g) depending on the waste utilised. The microbial counts for the different pathogens that tested positive were higher for larvae reared with simpler homogenous waste streams (SW and BV diets). The results also showed that blanching reduced the counts of Y&M and C. perfringens compared to those observed in the unprocessed larvae. The thermal processing methods could ensure that BSFL met the microbial safety criteria determined for animal feeds by regulatory bodies. Overall, the results of this study revealed that BSFL reared on commercial waste streams can be safe against several pathogenic microbes including Listeria monocytogenes, Salmonella, Escherichia coli and Staphylococcus aureus. The 6th instar larvae (pre-pupae) have lower microbial counts than the 5th instar BSFL, attributed to the antimicrobial effect of some fatty acids present in the larvae. The outcomes of this study will assist in the development of guidelines for good manufacturing practices for commercial BSFL manufacturers, thereby promoting the quality and commercialisation of the product.