Structural properties of black soldier fly larvae protein concentrates extracted via salting-in and salting-out coupled with ultrafiltration

The black soldier fly (BSF) larvae are one of the promising edible insect species for industrial food production. The aim of this study was to investigate the effect of the salting in/out extraction techniques, coupled with ultrafiltration, on BSF larvae protein. The protein isolates were extracted using alkaline extraction and acid precipitation (AAF), salting-in (AAFSI), salting-out (AAFSO), and salting-in-out (AFFSISO) coupled with ultrafiltration. All samples exhibited significantly (p < 0.05) negative zeta potentials, ranging from -9.8 to -26.9 mV. Moreover, no significant differences (p > 0.05) were observed in the levels of exposed sulfhydryl groups between AAF and AAFSI proteins (6.8 and 6.9 mu M/g, respectively). Fourier transform infrared spectroscopy (FTIR) of protein extracts derived from AAFSO and AAFSISO revealed a significant N-H free stretching vibration in the spectral range of 3500 - 3200 cm(-1). The beta-sheet and random coil structures were transformed into alpha-helix and beta-turns by salting-out treatments, as demonstrated by circular dichroism, indicating a more compact and organized conformation. AAFSO and AAFSISO, had the highest content of ordered protein structures and showed the largest Delta H values, measured at 141.0 J/g and 137.0 J/g, respectively. This research demonstrates that the integration of salting-out extractions and ultrafiltration techniques holds significant potential for protein extraction, especially as an innovative approach to producing insect proteins with excellent nutritional quality for food-related applications.