Effect of succinylation on the functional and physicochemical properties of alpha-globulin, the major protein fraction from Sesamum indicum L.

alpha-Globulin the major protein fraction from Sesamum indicum was succinylated to different levels and the effect of the chemical modification was evaluated both on the functional and physicochemical properties. The results suggest that the pH of minimum solubility shifted to the more acidic side (pH approximately 4.5-5.5) for the succinylated alpha-globulin whereas for control alpha-globulin the pH of minimum solubility was 6.5. Succinylation also increased emulsion activity and emulsion stability of the protein. The emulsion stability increased from a control value of 53 +/- 3 s to a value of 122 +/- 5 s. Bulk density, water absorption capacity, oil absorption capacity, foam capacity and foam stability were evaluated in phosphate buffer (pH 7.0) containing 0.5 M sodium chloride and all these properties showed increased values as a result of succinylation. Ultracentrifugation studies showed that the % composition of 7S component increases with concomitant decrease in that of 11S fraction with the increase in percentage of succinylation. Further increase in succinylation resulted in only 2S component which is a dissociated form of 11S and/or 7S protein fractions. The fluorescence emission studies showed a decrease in the fluorescence emission intensity of alpha-globulin as a result of succinylation. The thermal stability of the protein molecule decreased due to progressive succinylation as indicated by decrease in the apparent thermal denaturation temperature from a control value of 84 to 62 degrees C at a succinylation level of 40%. These results suggest that succinylation improves the functional characteristics of alpha-globulin. Such changes in the functional properties have been attributed partly to the dissociation of the protein molecule at higher levels of succinylation and the increase in the net negative charge on the protein.