Effects of Ultrasound-Assisted Extraction of Biofractions from Yellow Mealworm Larvae Fed a Probiotic-Enriched Diet

The increasing demand for sustainable protein sources has stimulated interest in edible insects such as Tenebrio molitor (yellow mealworm) larvae. While probiotics supplementation has been explored to improve insect growth performance, its impact on protein quality and downstream processing remains poorly understood. This study investigated the combined effects of probiotic-enriched diet supplementation during larval rearing and post-harvest ultrasound-assisted extraction (UST) on the protein and lipid fractions of yellow mealworm larvae. Three probiotic strains, namely, Pediococcus pentosaceus (PP), Bacillus velezensis (BV), and Bacillus coagulans (BC), were incorporated into larval diets and compared with a standard diet (without probiotics). Protein extraction was performed by both alkaline solubilization-isoelectric precipitation, which served as a control, and ultrasound application for 5, 15, and 25 min. The results from the trial found effects of both probiotics and UST, as well as their interaction, on the protein yield, although an improvement in yield was not obtained with increased sonication, and the BV group produced the highest yield among the probiotic treatment groups. In addition to this, the study did not find any effects associated with ultrasound pretreatment or probiotics on proximate composition and color, except fat % and increased lipid co-extraction, especially at longer durations. Probiotics, on the other hand, showed an influence on the fatty and amino acid profile, while they interacted with UST to affect the extracts' content. This study did not find any effects on particle size, but the zeta potential was affected by probiotic diet enrichment. Similarly, the free SH content was influenced by sonication, while both probiotics and UST played a role in hydrophobicity. Regarding the solubility, it was found to be pH-dependent and ranged from 0 to ≈90%. Importantly, this study found that probiotics did not have any effect on protein solubility; however, UST had an effect at pH 2 and 7 but not at pH 11. In terms of hydrophobicity, both factors and their interactions were found to have an effect. Moreover, this study could not determine any effects on the inherent fluorescence absorbance of protein molecules. Apart from this, FTIR analysis revealed β-sheet-dominated secondary structures (≈41-47%), with treatment-dependent shifts in α-helix and β-turn contributions. The heat enthalpies associated with denaturation and melting temperature were influenced by sonication, where probiotics could not confer an effect. Overall, this study might demonstrate the strain-specific improvement in protein yield and modulation of the physicochemical functionality, as well as the nutritive value of the protein. Both biological factors and ultrasound-assisted extraction processes can act together to tailor the physicochemical and functional properties of biofractions, but more studies are needed for process optimization.