Optimizing wet isolation conditions and characterizing functionality of protein isolates from air-classified starch-rich pulse flours

Starch-rich pulse flours are an underutilized, low-value by-product from air classification of pulses. They contain 8 %–20 % proteins with substantial untapped potential. This research aimed to optimize the alkaline extraction/isoelectric precipitation method to produce protein isolates from air-classified starch-rich faba bean and pea flours and to examine their techno-functional characteristics in comparison with commercial pea protein isolate (CPPI). The alkaline extraction was performed over a range of pH (8.5, 9.5, 10.5, and 11.0) and temperatures (25, 30, 40, and 50 °C). Higher pH and temperature increased the yields but reduced the purity of the protein isolates. Fourier transform infrared (FTIR) spectroscopy further revealed that the milder extraction conditions better preserved β-sheet and β-turn structures and led to smaller percentages of unordered α-helices in both faba bean (FPI) and pea protein isolates (PPI). FPI and PPI extracted under yield-optimized condition (designated as FPI-Cyield and PPI-Cyield) exhibited greater denaturation, surface charge, and hydrophobicity than the counterparts from purity-optimized condition (designated as FPI-Cpurity and PPI-Cpurity). Consequently, FPI-Cyield and PPI-Cyield showed reduced water solubility, increased oil-absorption capacity (OAC), and enhanced emulsion stability and foaming capacity as compared to respective FPI-Cpurity and PPI-Cpurity samples. This study revealed that the alkaline extraction conditions influenced not only the purity and yield but also the surface and functional properties of generated protein isolates.