In vitro digestibility, structural and functional properties of Moringa oleifera seed proteins

The aim of this work was to compare the structural and functional properties of Moringa oleifera seed albumin and globulin with those of the isoelectric pH-precipitated protein isolate (ISO). The 0.5 M NaCl extract of defatted Moringa flour was dialyzed against water to give water-soluble albumin (ALB) and water-insoluble globulin (GLO). The three protein products were evaluated for in vitro protein digestibility, functional properties and polypeptide composition while structural conformations were obtained using surface hydrophobicity (S_o), intrinsic fluorescence and circular dichroism (CD). Results showed that ALB had the most exposed number of hydrophobic groups with S_o of 946.6 when compared to 7.8 for GLO and 50.4 for ISO. The GLO had the highest protein digestibility while ALB and GLO had least gelation concentration of 0.8%, which is significantly (p < 0.05) lower than the 2.2% for the ISO. At pH 3.0, all the proteins showed tryptophan and tyrosine emission peaks; increases in pH led to disappearance of the tyrosine peak in some of the samples. Gel electrophoresis under reducing conditions suggest the presence of disulfide bonds in the three protein products. CD data indicate GLO as having more β-sheet conformation while the α-helix content varied depending on the pH. At 10, 20 and 40 mg/mL protein concentrations, foaming capacity was comparable in all the samples but the emulsifying properties carried out at 20, 25 and 50 mg/mL showed that ISO and ALB had significantly (p < 0.05) higher emulsifying ability than the GLO.