Dielectric Drying of Black Soldier Fly Larvae (Hermetia Illucens): Impact on Microbiological Product Quality, Safety and Stability

Along with the increasing scale of industrial production of insects as food and feed, the need for processing methods applicable on large scale is rising within the insect sector. One important processing technology in this context is drying, which aims at stabilising the quality of the insects.

This study investigated the impact of dielectric drying technologies, specifically microwave (μW) and radio frequency (RF) drying, on the microbiological quality, safety, and stability of black soldier fly (BSF) larvae in comparison to the traditional methods oven drying and freeze drying. Before, during and after subjecting a large batch of blanched BSF larvae to the four drying technologies, their water activity and moisture content as well as general microbial and pathogen counts were assessed. Dielectric drying effectively reduced water activity, thus enhancing product stability. Microbiological analyses revealed the efficacy of blanching in microbial reduction, with dielectric (especially RF) drying further contributing to these reductions.

The results, however, do not conclusively support nonthermal microbial inactivation through dielectric treatment. Specific analyses targeting foodborne pathogens indicated the absence of most selected bacterial pathogens, except for (presumptive) Bacillus cereus. This pathogen was detected in a few samples but remained below safety thresholds and was effectively eliminated by dielectric drying. Finally, a shelf life stability evaluation showed minimal changes in dielectrically dried BSF larvae over six months, indicating a microbiologically stable product.

In conclusion, dielectric drying technologies can retain or even improve the microbiological quality and stability of BSF larvae in the insect industry and can be considered as valuable and more efficient (time, energy consumption) alternatives to oven and freeze drying.

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