How different successive elaboration methods affect Hermetia illucens meals? Macronutrients, in vitro protein digestibility, oxidative status and hygienic-sanitary quality

Abstract

Insects are an emerging protein alternative in aquaculture. To obtain an easy-to-handle feed with an improved nutritional quality, longer shelf life and better hygienic-sanitary properties, the insects must go through a multi-step process including sacrifice, drying and defatting. This work aims to evaluate the effect of the interaction of different successive methods of processing of Hermetia illucens larvae proximate composition, digestibility, and microbial loading. The examined methods were slaughtering (blanching or freezing), drying (oven drying or freeze drying) and defatting (mechanical press or supercritical CO2 extraction). Our results showed that the combination of freeze-drying and mechanical press defatting resulted in the highest residual fat content (P<0.001), that could negatively affect the relative protein content of the meals. Despite this, with respect to in vitro amino acid digestibility, the least favorable results were obtained from the samples dried by lyophilization and defatted by supercritical CO2 extraction (P<0.001), independently of the slaughter method. Regarding the oxidative status, the slaughter by freezing conserved a higher level of antioxidant defenses versus the blanching method (P<0.001), although only the freeze drying method ensured a lower level of lipid oxidation in this type of sacrificing method. The applied processes resulted in a decrease in the presence of pathogenic bacteria compared to the raw insect in all examined groups. The mesophilic aerobic microorganism content was heavily affected by the temperature applied (P<0.05), while the enterobacteria were also affected by the lyophilization, in addition to temperature. Salmonella spp was eliminated from all meals, except for the combination of freezing (sacrifice), freeze drying (drying) and supercritical CO2 extraction (defatting). Sulfite-reducing clostridia were not present in any of the prepared insect meals.