Structure-function characterization and gelation mechanisms of mung bean albumin and globulin fractions
Cindy Lalagüe, Ugo Berthelot, G. J. Brisson, Alain Doyen
Abstract
This study aimed to evaluate the surface properties, secondary structures, solubilities, and gelling behaviors of purified mung bean globulins and albumins. The globulin fraction (88.44% protein purity) was isolated by isoelectric precipitation from a mung bean protein isolate produced by ultrafiltration-diafiltration (UF-DF), while the albumin fraction (80.72% protein purity) was purified from the soluble fraction using UF-DF. The albumin fraction maintained consistent solubility (∼50%) from pH 2.0 to pH 8.0, whereas the globulin fraction exhibited a U-shaped solubility curve, with a marked decrease near its isoelectric point and maximum solubility at pH 8.0 (91.44%). Albumins exhibited smaller particle sizes compared to globulins and were characterized by a significantly lower concentration of free sulfhydryl groups (5.79 vs 9.77 μmol/mL). The albumin fraction had a lower minimum gelation concentration (4%) compared to the globulin fraction (8%), yet albumin gels formed weaker networks, with lower water retention (73.65%) compared to globulin gels (93.59%) at 8% proteins. Rheological and microscopic analyses supported these findings, revealing a higher elastic modulus (G′) for globulin gels (8.91 Pa vs 1.08 Pa) and a denser microstructure, indicating stronger protein incorporation and more extensive intermolecular bonding. Globulin gels were formed primarily through hydrophobic interactions with no involvement of electrostatic or disulfide bonds. In contrast, albumin gels were formed mainly through electrostatic interactions, followed by hydrophobic interactions, and characterized by a high proportion of unbound proteins (25.5%). Based on these results, mechanisms were proposed to illustrate the interactions and proteins involved in the formation of albumin and globulin gels. • Mung bean albumins and globulins are efficiently separated by pH precipitation. • Albumins and globulins differ in structural and physicochemical properties. • Albumins form coarse particulate gels linked by electrostatic interactions. • Globulins form fine particulate gel linked by hydrophobic interactions. • Globulin gels show higher firmness and water retention than albumin gels.