Characterization, Production, and Applications of Lipopeptides - Biosurfactants: Research Trends and Applications - page 155

volume and secondary inoculation of (4-6 h) 9.5% by volume were also impor-
tant for optimizing surfactin production.
Gancel et al. (2009) investigated lipopeptide production during cell immobili-
zation on iron-enriched polypropylene particles. Immobilization improved biosur-
factant production by up to 4.3 times. The amount of fengycin to surfactin varied
depending on the iron content of the pellets. Highest surfactin (390 mg/L) and fengy-
cin (680 mg/L) production was at 0.35% iron.
Guez et al. (2008) evaluated the influence of oxygen transfer rate on the produc-
tion of the lipopeptide mycolysin by B. subtilis ATCC6633. A respiratory activity
monitoring system used for the study showed that oxygen metabolism has an effect
on the homologue production and that the regulatory system is complex. Chenikher
et al. (2010) examined the ability to control the specific growth rate for the produc-
tion of surfactin and mycosubtilin. Most feeding strategies do not take into account
the loss of the biomass with the foam. This must be taken into account to enable the
maintenance of the specific growth rate and subsequently production. The growth
rate of 0.05/h was maintained.
An integrated foam collector was integrated for biosurfactant production to study
parameters for scale-up (Amani et al., 2010). The best conditions were 300 rpm and
1.5 vvm for a surfactant yield on sucrose of 0.25 g/g. K L a of 0.01/s was achievable in
shake flasks and bioreactors, and this could potentially be used for scale-up.
MEASUREMENT AND CHARACTERIZATION TECHNIQUES
Enhanced surfactin production can be determined by blood agar plate screening
due to hemolysis by surfactin (Mulligan et al., 1984). To verify that the isolates are
biosurfactant producers, then the cultures must be grown and the surfactin levels
determined. The most common technique for determining surfactant concentration
is surface tension measurement and CMC determination. HPLC is also frequently
used. An assay based on hemolysis was used for the analysis of surfactin in the
fermentation broth. It was determined that the method could be used as a quick low-
technology method of surfactin analysis.
Huang et al. (2009) compared blood plate hemolysis, surface tension, oil spread-
ing, and demulsification. Surface tension measurement followed by demulsification
tests allowed isolation of a demulsification strain Alcaligenes sp. S-Xj-1, which pro-
duced a lipopeptide that was able to break O/W and W/O emulsions.
Knoblich et al. (1995) studied surfactin micelles by ice embedding and trans-
mission electron cryomicroscopy. The micelles found were ellipsoidal with dimen-
sions of 19, and 11 nm in width and length,respectively or spherical with a 5-9 nm
in diameter, at pH 7. However, at pH 9.5, the micelles were more cylindrical with
width and length dimensions of 10-14, and 40-160, or spherical with diameters of
10-20 nm. Addition of 100 mM NaCl and 20 mM CaCl 2 at pH 9.5 formed small
spheres instead of the cylindrical micelles.
Hue et al. (2001) examined the use of a combination of LSI-MS and MS/MS for
the characterization of the mixtures of surfactin produced by B. subtilis . Amino acid
composition was determined, and the length of the acyl chain was shown to vary
from 12 to 15 carbons. Leucine and isoleucine could be differentiated.