The Pulsed Electric Field Treatment Effect on Drying Kinetics and Chosen Quality Aspects of Freeze-Dried Black Soldier Fly (Hermetia illucens) and Yellow Mealworm (Tenebrio molitor) Larvae

Abstract

Freeze drying is employed as one of the most effective preservation techniques, allowing dried material to be obtained characterized by high-quality properties. However, it also stands out as being one of the most energy-intensive methods and, consequently, expensive processes. Therefore, the objective of this study was to examine how the application of pulsed electric field (PEF) at 5 and 20 kJ/kg impacts the drying kinetics and the final quality of freeze-dried insects, including chemical composition, physical properties, and microbiological quality. For PEF-treated samples, a comparable content of protein (35.7–37.4 for H. illucens, 45.4–48.0 for T. molitor) to the untreated sample (35.8 for H. illucens and 48.0 for T. molitor) was noted. There were no significant distinctions found in the rehydration and hygroscopic characteristics across most tested samples. However, microtomography of freeze-dried H. illucens and T. molitor larvae unveils notable alterations in their internal structures influenced by both their species and the pre-treatment applied. The PEF-treated and freeze-dried H. illucens larvae exhibited a notably darker color (34.7–34.9) compared to the untreated sample (42.1), while a relatively consistent lightness for T. molitor larvae was observed. The performed study outlines that PEF treatment did not enhance the freeze-drying process of insect biomass and did not exhibit suitable microbiological quality for food purposes. Only fungi exhibited greater susceptibility to the effects of PEF treatment in comparison to bacteria, resulting in a reduction of 1.9 to 2.6 log cycles. Furthermore, PEF treatment did not negatively affect valuable compounds such as protein or fat.