Mathematical modelling of thermal death kinetics to describe humane slaughter procedures via hot water immersion in black soldier fly and yellow mealworm larvae
Trillions of black soldier fly (BSFL; Hermetia illucens; Diptera: Stratiomyidae) and yellow mealworm (YML; Tenebrio molitor; Coleoptera: Tenebrionidae) larvae are slaughtered annually for feed. Slaughter standard operating procedures (SOPs) that protect welfare and product quality are essential to ethical and economical industry practice. This study defines humane (less than or equal to 1 second time-to-death) slaughter SOPs for hot water immersion of BSFL and YML. We assessed isothermal critical thermal maxima in water from 32, or 40, to 100 C in YML and BSFL, respectively. We used Weibull probability-based models to characterize survival as a function of processing time at different temperatures, describing the time-temperature conditions required for humane slaughter. We blanched larvae under: 1) a SOP resulting in a ~1 minute time-to-death for 99% of larvae; 2) a SOP resulting in less than or equal to 1 second time-to-death for 99% of larvae; and 3) 99.5-100 C. We compared ash, protein and fat, pH, water activity, lipid oxidation, and color change. Water temperatures kept above 81.3 C (BSFL <0.16 g), and 78.3 C (YML <0.12 g), are predicted to result in humane slaughter for >99% of larvae - though, further research is needed to develop SOPs for larger larvae. The humane SOPs have neutral or beneficial impacts on quality. We recommend producers adopt a 2 C buffer (BSFL: 83.3 C; YML: 80.3 C). Finally, we provide an energy balance model that producers can use to determine the larvae:water ratio and temperature that results in humane slaughter in their facility.