Effect of Acylation on the Emulsifying Properties of Soybean proteins

Studies on the Emulsifying Properties of Soybean Proteins. Part V

Abstract

The emulsifying capacity (EC) and emulsion stability (ES) of untreated soybean protein isolates decreased to a minimum level in the isoelectric region (around pH 4.5) regardless of protein concentration, while those of the acetylated proteins showed no decrease in that region and increased from acidic to alkaline region monotonously. The ES of succinylated proteins showed a behavior similar to that of untreated proteins, however, the minimum point of the ES shifted from pH 4.5 to 3.5 and exhibited high ES at around pH 7. The ES of soybean protein isolates varied in a complicated manner with the degree of acylation. Acetylation over 95% of available amino groups of proteins improved the ES at pH 7, especially succinylation of over 85% increased the ES at pH 7 as much as 2.5 times higher than that of untreated proteins. Acetylation and succinylation improved the ES at pH 4.5 by 40% and 25% respectively, Succinylation between 30 to 70% increased the ES at pH 3.5 by 40%, but the succinylation over 90% decreased the ES again toward 0. In the case of acetylated proteins, the simple correlation between protein solubility and the ES was not necessarily observed.