A series of purified polyglycerol monolaurates (PGML), such as di-, tri-, tetra-, and pentaglycerol monolaurates, were synthesized, and their surfactant properties in aqueous solutions were examined. The surfactant properties of PGML were compared with those of n-dodecyl polyoxyethylene monoethers (C 12 EO n ) to examine the function of the hydrophilic part of these compounds. The critical micelle concentration (CMC) values and the surface tension at CMC of PGML and C 12 EO n increased linearly with an increase in the number of glycerol and oxyethylene units, respectively; the slope of the increase was greater for PGML than C 12 EO n . The minimum surface area per molecule of PGML was smaller than that of C 12 EO n at the air/aqueous solution interface. The initial foam heights of the surfactants at the CMC increased with an increase in the number of glycerol or oxyethylene units, and the foam heights of PGML were consistently higher and more stable than those of C 12 EO n . Detergency depended on a reduction in interfacial tension. Triglycerol monolaurate showed the lowest interfacial tension and the highest detergency among all the surfactants tested. Overall, the PGML showed better performance in all the surfactant properties tested than C 12 EO n . It is noteworthy that the surfactant properties of PGML having few glycerol units (di-to tetraglycerol monolaurates) are on par with those of C 12 EO n having many oxyethylene units (hexa-and octaoxyethylene). These results suggest that PGML having a secondary hydroxyl group on every glycerol unit of the hydrophilic part could be more hydrophilic than C 12 EO n ; this characteristic feature guaranteed the superior surfactant properties of PGML.Paper no. S1334 in JSD 6, 331-337 (October 2003).KEY WORDS: CMC, detergency, foam, polyglycerol ester, polyglycerol monolaurate, surface activity, surfactant property.Polyglycerol esters of fatty acids (PGE), which are nonionic surfactants, are widely used in foods, cosmetics, and other industrial products (1,2). PGE consist of polymerized glycerol units and fatty acids. However, the commercial products of PGE in general are mixtures of many different components, which include different glycerol units from 1 to 10 with various degrees of esterification and with fatty acids of different chain lengths (3,4). Therefore, efforts have been made to purify the PGE to characterize valid surfactant properties of the commercial polyglycerols. A process of separating a narrow range of polyglycerols with pseudo-moving-bed chromatography and then esterifying the fatty acids has been reported (5).In addition, the molecular distillation method was found to be useful to refine diglycerol fatty acid esters (6). At present, the surfactant properties of diglycerol and triglycerol esters of PGE are known (7-9); however, their properties have not been compared with those of the well-characterized polyoxyethylene alkyl ethers, the typical nonionic surfactants used in most applications. PGE and polyoxyethylene alkyl ethers differ mainly in their hy...
