Effect of conductive hydro-drying on physiochemical and functional properties of two pulse protein extracts: Green gram (Vigna radiata) and black gram (Vigna mungo)

In this study, the effect of two drying methods (conductive hydro-drying - CHD and freeze-drying - FD) on the physical and functional properties of green gram (GG) and black gram (BG) protein powders was investigated. CHD dried protein powder showed excellent powder characteristics with moisture contents ranging from 3 to 6%, water activity of ~0.4 and Carr index ≤10. The CHD samples were dried in 210 min; with higher drying rates, CHD samples showed no significant changes in powder characteristics, color value, and water and oil absorption indices. The solubility of both proteins were found to be lower at pH 4 to 7 and higher at pH 1, 2, 8, 9 and 10; at certain pH, the solubility of CHD protein was higher than that of the FD counterparts. No significant differences were observed in the oil absorption capacity, surface hydrophobicity, protein gel formation, pasting and thermal properties. XRD and FTIR analyses were used to explain changes in protein structure and the presence of both α-helix and β-sheet was observed, with higher β-sheet levels in both pulses dried using CHD. Results confirmed that CHD, a variant of the refractance window drying (RWD) offered protein quality in par with FD.