Surface activity and critical aggregation concentration of pure sugar esters with different sugar headgroups

We have studied the surface properties of a series of enzymatically synthesized sugar monoesters of xylose, galactose, sucrose, and lactose with different hydrophobic chain lengths (C12-C16) and purified, chemically synthesized sucrose esters that, unlike the enzymatically synthesized samples, contain a mixture of isomers. Data obtained have been compared with those for dodecanoic glucoside and maltoside acetals, and also a commercial sucrose myristate. Nearly all of the sugar esters studied brought about a significant reduction of the surface tension of water (to 31.0-43.0 mN m(-1)). A reduction in the critical aggregation concentration (CAC) of the surfactants with increasing carbon chain length was observed. Surfactants with more hydrophilic headgroups exhibited higher CAC, though this trend was moderated by the alkyl chain length. Comparing the chemically synthesized sucrose esters with their enzymatically synthesized equivalents revealed only minor differences in the CAC and the surfactant efficiency, indicating that the exact point of esterification might not be critical for the surfactant's properties. The presence of 0.1 M NaCl, KCl, or CaCl2 did not significantly alter the surface behavior of the chemically synthesized esters, indicating the absence of surface-active species with charged headgroups. (C) 2000 Academic Press.