ety. The acidic-SL (Figure 6) is found as major compound in the aqueous superna-
tant. The acid group is able to form an internal ester linkage with the OH at C4“. The
resulting lactonic-SL precipitates as solid compound at the bottom of the cultivation
vessel. The percentage distribution between acidic- (20–43 % w/w) and lactonic-SL
(57–80 % w/w) varies depending on the substrate used (Davila et al., 1994; Manzke,
1999). However, all analyzed cultivations generally reveal a preferred formation of
the lactonic compound. The lactonic-SL can be easily transformed into the acidic-SL
by alkaline hydrolysis with concomitant deacetylation at C6’and C6“. The microbial
formation of one particular sophorolipid is not possible. Therefore, it is of interest to
modify SL structure chemically or enzymatically.
17.4.1 Chemically modified sophorolipids, chemically modified
The nonionic deacetylated methyl ester SL (Figure 6; R 1 ¼R 2 ¼H, R 4 ¼CH 3 )is
easy to prepare by refluxing acidic-SL with methanolic sodium methoxide (Tulloch
et al., 1968) or by the addition of methanol and a strong acid. Reacting the methyl
ester SL with a desired alcohol in the presence of alkaline agent results in ester
exchange. Using this procedure, ethyl-, propyl-, butyl-, hexyl-, octyl-, decyl-, laur-
yl-, myristyl-, palmityl-, stearyl- and oleyl-ester were synthesized (Inoue et al.,
1980). Ishigami (1994) prepared SL-alkyl and -aryl amides deriving from acidic-
SL. In this patent, two examples are represented at length by reacting acidic-SL
with benzylamine or decylamine in a methylene chloride solvent in the presence
ofN-methyl-2-chloro-pyridinium iodide and tributylamine, resulting a SL-benzyla-
mide and SL-decylamide, respectively (Figure 7). However, all SL-amides synthe-
sized showed no extraordinary reduction in surface tension (Table 9).
17.4 Chemically and enzymatically modified sophoroselipids 381
Table 8.Batch and feed-batch production of sophorolipids.
Carbon source
(g L-1)
Yield
(g L–1)YSL/S
(g g–1)^1Productivity
(g L–1day–1)ReferenceGlucose (304),
rapeseed ethyl ester (184)
320 0.65 38.4 Davila et al., 1992Glucose (100),
canola oil (105)
160 0.78 20.0 Zhou and Kosaric, 1995Glucose (160),
oleic acid (45)
180 0.87 21.6 Rau et al., 1996Single cell oil (20),
rapeseed oil (400)^2
422 1.0 24.7 Daniel et al., 1998;
Daniel, 1999Glucose (300), rapeseed (colza)
ethyl ester (240)
3103
(565)^40.57 51.8 Marchal et al., 1997Glucose (350), rapeseed oil (212) 360 0.64 51.2 Rau et al., 1998
(^1) Y
2 SL/S¼g sophorolipid formed/g substrate consumed.
First stage: Formation of single cell oil on deproteinized whey withCryptococcus curvatus; second
stage: Production of sophorolipids.
(^3) Anhydrous sophorolipid.
(^4) Crude sophorolipid, contains 45 % (w/w) water.