Effect of High Hydrostatic Pressure on natural contaminating microorganisms and inoculated Salmonella in Hermetic illucens larvae

A microbiological characterization of black soldier fly (Hermetia illucens) larvae as well as an inactivation study of naturally contaminating microorganisms and inoculated Salmonella enteriditis varTyphimurium in these larvae by using High Hydrostatic Pressure (HHP; 300 to 350 MPa, for 1.5 to 15 min) was carried out. Larvae had a total aerobic mesophilic bacteria (AMB) load of 5.28 log cfu/g and an Enterobacteriaceae load of 4.29 log cfu/g. The presence of pathogenic microorganism varied: no Listeria spp. were found, but Salmonella spp and Escherichia (E.) coli were detected in the larvae extract at a contamination level of 4.04 log cfu/g and 3.84 log cfu/g, respectively. The total anaerobic bacteria load was 5.63 log cfu/g, but no sulfite-reducing Clostridium were encountered. The mold and yeast level was 5.19 log cfu/g. HHP was effective against naturally contaminating yeasts and molds producing reductions by around 3 log cycle at 350 MPa for 7 min of treatment, but a low reduction of AMB was achieved, even at the highest pressure level (350 MPa for 15 min).The inactivation level of Salmonella inoculated in larvae varied. At 350 MPa for 7 min, more than 3 log cycle reductions were achieved. Inactivation curves were fitted to different mathematical models. Among the three inactivation models studied, the one that best described the inactivation pattern of the cells was the biphasic model.