Biomedical Engineering Reference
In-Depth Information
OH
O
O
OH
O
O
O
O
O
O
OH
OH
OH
OH
O
O
OH
OH
OH
OH
O
O
O
O
O
O
O
O
O
O
(a)
(b)
FIGURE 4.1
Diagrammatic representation of the sophorolipid: (a) acid form and (b)
lactonized form.
hydroxyl fatty acid, which are affected by following parameters: (1) chain length,
(2) number and position of unsaturated bonds, (3) distribution and count of hydroxyl
groups, and (4) location either at the terminal (
m
) or at the subterminal (
m
−1) position
(Asmer et al., 1988; Davila et al., 1993). These structural differences make sophoro-
lipids more versatile and biologically active compounds than the other surfactants.
Lactonized sophorolipids differ in biological and physicochemical properties while
comparing with acidic forms of sophorolipids (van Bogaert et al., 2007). In general,
lactonic sophorolipids have better surface activity and antimicrobial activity than
acidic sophorolipids, whereas the acidic sophorolipids display a better detergency
property than the lactonic sophorolipids (van Bogaert et al., 2011). Furthermore,
a small change makes more differences in bioactivities, for example, acetyl groups
render the molecules less water soluble, but enhance their antiviral and cytokine-
stimulating effects (Kim et al., 2002; Shah et al., 2005; Sleiman et al., 2009). The
di- or monoacetylation of lactonic sophorolipids shows better antibacterial activity
than the nonacetylated lactonic ones or acidic forms (van Bogaert et al., 2011), and
diacetylated lactonic sophorolipids possess a lower critical micelle concentration
(CMC) and surface tension as compared to nonacetylated acidic molecules (Lang
et al., 1989, 2000; Kim et al., 2002; van Bogaert et al., 2011). The exact mechanism
and constraints or determinants of the degree of lactonization remain unclear, but the
engineering of fermentation conditions can influence shifting in production of either
lactonic or acidic sophorolipids (Garcia-Ochoa and Casas, 1999; Kim et al., 2009;
Shin et al., 2010). The surface-active properties of sophorolipids were unaffected
by heat treatment even at a higher temperature it retained the activity (van Bogaert
et al., 2011; Hirata et al., 2009a,b). The structural diversity creates a range of the
physiochemical properties, and hence researchers have a freedom of opportunity
to screen sophorolipids against various bioactivities. For example, the solubility of
sophorolipids depends on pH as at pH lower than 5.0, the sophorolipid shows dis-
persion, while at pH higher than 6, it perfectly dissolves. Their solubility is better
in polar solvents, such as ethanol, methanol, ethyl acetate, acetonitrile, and DMSO.
The emulsification ability of sophorolipids is vast enough to use as a better surfactant
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