Microbiological quality of raw edible insects and impact of processing and preservation

Since the introduction of edible insects and insect-based products on the Belgian and European markets, specific questions regarding legislation, food safety, processing and preservation, etc. arose. This PhD project aimed to support the edible insect sector on filling these lacunas in a microbiological perspective. Hence, the goal of this dissertation was to obtain insight in the microbiota of freshly reared, raw insects for food with special attention to the occurrence of human bacterial pathogens and antimicrobial resistance genes. Next, a second objective was to elucidate the impact of processing and preservation steps on the microbiota of insects, both on laboratory and industrial scale. More specific, the research in this dissertation focussed on the post-harvest microbiological quality of four selected edible insect species for human consumption: the mealworm (Tenebrio molitor), the lesser mealworm (Alphitobius diaperinus), the house cricket (Acheta domesticus) and the tropical house cricket (Gryllodes sigillatus). Only insects that were harvested, i.e. ready for consumption, were considered. The microbiological quality of these insect species was assessed by using both culture-dependent (plate counts, pathogen detection and isolate identification) and culture-independent (next generation sequencing via Illumina MiSeq and real-time PCR) methods, in relation to a few intrinsic properties of the insects. The second part of the research focussed on processing and preservation of edible insects, using techniques currently applied in the insect sector such as blanching and oven drying. Here, specific attention was paid to the fate of bacterial endospores. In total, 33 raw insect samples from 9 different rearing companies were investigated. Generally, it was concluded that insects contain high microbial counts (7.5 to 8.5 log cfu/g on average), can contain high copy numbers of tetracycline resistance genes (up to 2.10 × 10^8 copies/g insect) and that they can harbour possible pathogenic microorganisms such as the spore-forming Bacillus cereus. Important is the high variation in microbiological quality that can occur between rearing companies, rearing batches and insect species. This demonstrates the importance of species-specific microbiological assessment and the sometimes low consistency in microbiological quality between samples. The high microbial numbers and the occurrence of pathogens should not necessarily pose a health risk. Processing by blanching could reduce the amount of vegetative microorganisms in insect samples by 3.2 to 6.4 log cfu/g. However, at least a part of the bacterial endospore population was capable of surviving the heat treatment applied, which should be considered during preservation. During storage, it was observed that chilling was only able to retain a stable microbial quality for a few days, after which for example bacterial endospores could grow. Frozen or dried preservation could, on the other hand, guarantee a shelf life of several months. The initial microbial quality as well as post-contamination were found to be important in processing and preservation. Mitigation strategies to address these factors are therefore necessary. In conclusion, the data obtained in this research can prove useful in the further development of insect legislation, sector guides, novel food dossiers, etc.status: publishe