Carbohydrate Moieties Contribute Significantly to the Physicochemical Properties of French Bean 7S Globulin Phaseolin

We have previously reported that the solubility of French bean 7S globulin (phaseolin) at low ionic strength and its emulsifying stability are remarkably high compared with those of 7S globulins prepared from other plant species, including soybean (Kimura et al. J. Agric. Food Chem. 2008, 56, 10273-10279). In this study, we examined the role of carbohydrate moieties in the properties of phaseolin. Three preparations of phaseolin were analyzed: (i) N7S, prepared from defatted seed meal and having intact carbohydrate moieties: (ii) R7S, expressed in E coli and lacking N-linked glycans; and (iii) EN7S, having partial N-linked glycans after treatment with Endo H. The solubilities of N7S and EN7S were much higher than that of R7S at a low ionic strength (mu = 0.08). N7S exhibited good emulsifying ability under the conditions examined, but R7S did not. In terms of emulsion stability, an emulsion of R7S separated into two phases after 1 h at mu = 0.01, 0.08, and 0.5, whereas the emulsion of N7S was stable for 5 days at mu = 0.01 and for at least 10 days at mu = 0.08 and 0.5. The emulsion stability of EN7S was comparable to that of N7S under most conditions examined. These results indicate the carbohydrate modifications are necessary for the good solubility, emulsifying ability, and emulsion stability of phaseolin. Further, a structural analysis of the carbohydrate moieties indicates that truncated carbohydrate moieties are sufficient for conferring these physicochemical properties to phaseolin.