Waxworm (Galleria mellonella) protein concentrate as an innovative protein source: Extraction, fractionation, characterization and protein quality assessment

Edible insects are increasingly recognized as an alternative and sustainable protein source to meet future protein demands. Owing to its significant protein content (33.43%), the structurally-related properties of the edible insect Galleria mellonella were characterized in this study. To fully understand the protein fractions in G. mellonella, the Osborne fractionation was employed to separate protein fractions based on their preferential solubilities. Subsequently, protein extractability under various pH levels and ionic strengths was evaluated. Then the extracted proteins and their respective fractions were visualized by SDS-PAGE, and the secondary structures were characterized, including related properties such as isoelectric point (pI), molecular mass, and denaturation temperature. Additionally, the specific amino acid profile of G. mellonella was used to evaluate the quality of waxworm protein, as determined by In Vitro Protein Digestibility (IVPD) and Protein Digestibility Corrected Amino Acid Score (PDCASS). Protein fractions isolated by Osborne fractionation, prolamins displayed an α-helix conformation, while albumins, globulins, and glutelins predominantly adopted a β-sheet structure. Waxworm proteins exhibited greater stability in alkaline conditions compared to acidic environments. This sensitivity to ionic strength appears to be greater in waxworm proteins compared to other alternative protein sources, such as plant-derived proteins. The secondary structures of waxworm proteins, extracted under various conditions, appeared stable, with α-helix and β-conformation being the predominant conformation. The allergen tropomyosin was identified by SDS-PAGE (~32.5 kDa); however, it can be selectively removed by salt extraction. Concerning protein quality, amino acid profiles of the fractions were evaluated. It was observed that structural features could influence the overall quality of the protein. Regarding protein quality, globulins are recommended as the preferred protein fraction, showing the highest values in Essential Amino Acid Index (EAAI%, 924.02), PDCASS (0.84), and IVPD (76.33%).