Fractionation, physicochemical, and structural characterization of winged bean seed protein fractions with reference to soybean

Abstract

ABSTRACTProteins from defatted flour winged bean seed (Psophocarpus tetragonolobus) were sequentially fractionated with reference to soybean seed (Glycine max) using distilled water, 25 g/kg sodium chloride solution, 0.1 M NaOH, and 70% alcohol and subjected to physicochemical, functional, and structural analysis. Winged bean seed had globulin (31.94%) and albumin (26.46%), with denaturation temperatures (Td) of 92.82 and 82.76°C, and surface hydrophobicities (SHs) of 214.51 and 189.32, respectively, whereas soybean seed had 34.95% globulin and 32.82% albumin, with respective Td of 81.68 and 90.63°C, and SH of 210.80 and 204.66. This indicates that winged bean albumin could perform better at water/oil interface in an oil-in-water emulsion system because of it higher hydrophobicity, although soybean albumin had higher extraction rate. Both legumes’ proteins showed comparable gelation when employed for their gelling ability to form three-dimensional network in food systems. Soybean proteins had significantly (P < 0.05) higher foaming capacities, but winged bean proteins foams were more stable and soluble over broad pH, good for manufacture of ice cream and protein beverages, respectively. Though β-sheets and β-turns were the major secondary structures of both protein fractions, soybean albumin had significantly (P < 0.05) higher β-sheets than winged bean albumin, whereas winged bean globulin and glutelin had higher content of β-sheets than corresponding soybean fractions. The low amounts of β-sheets in the winged bean albumin and soybean globulin could render them more digestible than the corresponding soybean and winged bean protein fractions.Abbreviations: WB: Winged bean; SB: soybean; Td: denaturation temperature; SH: surface hydrophobicity; SH: surface hydrophobicity; W-ALB: winged bean albumin; W-GLO: winged bean globulin; W-GLU: winged bean glutelin; W-PRO: winged bean prolamin; W-ISO: winged bean isolate; S-ALB: soy albumin; S-GLO: soy globulin; S-GLU: glutelin; S-ISO: soy glutelin and S-PRO: soy prolamin.