Front Matter

zymes hesperidinase (EC 3.2.1.40) at pH 5.7 (yield 80 % w/w) and naringinase

(Sigma N1385) at pH 9 were able to release specifically one glucose unit from

the disaccharide lipid (Figure 9). The product of this treatment was isolated quanti-

tatively and identified as a novel acidic glucolipid (17-L-(b-D-glucopyranosyl)-oxy-

octadec-9-cis-enoic acid) by FAB-MS and NMR. The interfacial and surface tension

of this glucolipid resembles those of the deacetylated acidic-SL used as feedstock for

the enzymatic conversion (Table 9).

17.5 Surfactant properties of enzymatically synthesized

and modified glycolipids, surfactant properties

17.5.1 Surfactant properties of enzymatically derived glycolipids

As for the sugar monoesters (see Section 1.1), the following results can be presented.

Monosaccharide-based products containing fatty acids of the chain length C 10 to C 14

lower the surface tension of water from 72 mN m–1to 30–27 mN m–1(critical

micellar concentration¼ 10 –5to 10–3mol L–1at 37 8 C) and increase the stability

of oil-in-water emulsions (Scheckermann et al., 1995; Ducret et al., 1996; Lang et al.,

1997). The sugar esters based on C18 : 0or C18 : 1, are forming stabilized monolayers in

Langmuir film balance experiments. With film pressure values of more than 40 mN

m–1at a collapse point of 28 and 32 A ̊^2 /molecule, respectively, there are very good

conditions for wetting purposes (Lang et al., 1996). These long-chain products are

also suitable to stabilize water-in-oil emulsions (Ducret et al., 1996). As for aryla-

liphatic glucose esters, critical micellar concentrations between 2 and 95 mmol and

minimal surface tensions around 35 to 45 mN m-1were determined (Otto et al.,

1998a). Ethylglucoside esters of C9:0to C12 : 0 are able to remove cutting oil

from the surface of iron grains (Andresen and Kirk, 1995).

The surface-active properties of heptyl-b-D-xyloside were investigated by Shi-

noyama et al. (1991a). The critical micellar concentration was determined to be

30 mM at approximately 28 mN m–1. The corresponding molecular area at satura-

tion adsorption, the micellar weight and the aggregation number were 43 A ̊, 20.7 and

78, respectively. This surfactant was found to have a surface activity similar to that of

commercially availablen-octyl-b-D-glucoside.

17.5.2 Surfactant properties of native and modified sophorolipids

Table 9 summarizes surface tensions of native and modified sophorolipids taken

from literature. The SL and derivatives reduced the surface tension of water

from 72 mN m–1to 30 mN m–1(2-tetradecyl sophoroside) at minimum. In case

of then-decyl SL amide the surface tension was only lowered to 63 mN m–1. Un-

polar SL (derived from Rf-values of thin layer chromatography) and acetylated SL

possess a higher surface activity compared to polar and deacetylated SL. A short-

386 17 Enzymatic Synthesis and Modification of Glycolipids