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.

Effect of Pulsed Electric Field Technology on the Composition and Bioactive Compounds of Black Soldier Fly Larvae Dried with Convective and Infrared–Convective Methods

“…The structural changes in the tissue due to the electroporation may have resulted in better solvent penetration into the material and improved the fat extraction yield [28,30], which was proved in a current study. A different effect of PEF application was reported by Alles et al [16], who studied convective-dried black soldier fly larvae and Bogusz et al [33] in previous study on freeze-dried black soldier fly and yellow mealworm larvae. These studies did not show any improvement in the oil extraction yield.…”

“…The protein content was determined by the Kjeldahl method using a KjelFlex K-360 (Büchi, Flawil, Switzerland) nitrogen analyzer integrated with a TitroLine 5000 automatic titrator (SIAnalytics, Weilheim, Germany). The ash and moisture content were determined by the gravimetric method [33].…”

Nutritional Value and Microbiological Aspects of Dried Yellow Mealworm (Tenebrio molitor L.) Larvae Pretreated with a Pulsed Electric Field

“…The protein content in insects after the PEF treatment was also elaborated upon in the related literature. For instance, the study performed on yellow mealworm larvae showed that the PEF application at 20 kJ/kg prior to freeze-drying significantly decreased protein content by 5.5% as compared to an untreated sample [16]. Psarianos et al [37] illustrated that the PEF-assisted extraction process of house cricket (Acheta domesticus) flour allowed the protein yield to increase, especially after PEF at 4.9 kJ/kg and an extraction time of 60 min.…”

“…In each experiment, about 350 ± 5 g of larvae were placed inside the treatment chamber, which was filled with tap water (σ = 220 µS/cm, t = 22 ± 1 • C) until the total mass of 1000 g was reached. The trials were carried out using an electric field strength of 1 kV/cm, and a specific energy intake (W spec ) at a level of 5, 20, and 40 kJ/kg was adjusted by applying electric pulses [16]. After treatment, the larvae were separated from the water, gently tapped with blotting paper, and then weighed.…”

“…Safety aspects of edible insects may be guaranteed by heat treatments such as cooking, boiling, or processing. However, non-thermal technologies such as pulsed electric fields as well as additional hygiene practices should be considered to ensure the microbiological safety of edible insects during on-farm production, processing steps, and handling [5,16].…”