Rhamnolipids Characteristics, Production, Applications, and Analysis - Biosurfactants: Research Trends and Applications - page 75

On the other hand, Cha et al. (2008) reported that the maximum production rate of
rhamnolipids by strain P. aeruginosa EMS1 was achieved by using acidified soybean
oil as the carbon source.
Similarly, Lotfabad et al. (2010) stated that P. aeruginosa MR01 grown on soy-
bean oil as a carbon source demonstrated an excellent performance on the produc-
tion of rhamnolipids. Moreover, Lotfabad et al. (2010) reported that a high rate of
the production of rhamnolipids was obtained by using lipid sources such as soybean
oil as the medium for P. aeruginosa MR01. They also suggested that the cost of the
production could be decreased by using frying oil wastes.
Wittgens et al. (2011) stated that for the production of rhamnolipid by P. putida ,
a variety of carbon sources can be used, but when a hydrophobic substrate is used,
the process of recovery and purification would be much more difficult than when
glucose is used as the carbon source. Choi et al. (2011) described inducing muta-
tion in P. aeruginosa PA14, in order to stop the growth after the biomass reached
the optimal concentration for rhamnolipid production. By applying this strategy,
the provided substrate is used efficiently and mostly for synthesizing rhamnolipids.
Many researchers have shown that the type of substrate could affect the rate of the
rhamnolipid production, and this applies to other types of biosurfactants (Mulligan
and Gibbs, 2004).
de Sousa et al. (2011) have done some experiments on the production of rhamno-
lipids by P. aeruginosa MSIC02, using a variety of carbon sources. The highest level
of the production, 1269.79 mg/L, occurred when they used hydrolyzed glycerin as
the carbon source. They noted that by altering the concentration and composition of
substrate and environmental conditions, the maximum production rate was achieved.
The optimal medium consisted of 18 g/L of glycerol, 4.0 g/L of sodium nitrate, and
62 mM of mono potassium phosphate. The pH and the temperature of the optimal pro-
duction were 7.0 and 37°C respectively. Further analysis showed that the purified prod-
uct was a mixture of RL1 (l-rhamnosyl-beta-hydroxydecanoyl-beta-hydroxydecanoate)
and RL2 (l-rhamnosyl l-rhamnosyl-beta-hydroxydecanoyl-beta-hydroxydecanoate), and
the product demonstrated very good emulsifying properties (65%).
Wittgens et al. (2011) noted that by minimizing the cell growth, a higher rate of
rhamnolipid production is achieved, and there wouldn't be any need for cell growth
monitoring. The structure of the produced rhamnolipids depends on the substrate
being used. Their experiments showed that the best result was achieved by using
sucrose or glycerol as the substrate. Wittgens et al. (2011) pointed out that the path
for using a substrate depends on the type of substrate. For example, for transporting
glucose, the ABC transporter needs a molecule of ATP for each glucose molecule,
but on the other hand, glycerol could be easily conveyed by diffusion through an ion
channel (Wittgens et al., 2011).
The type of substrate not only affects the rate of the production, but can also
determine the structure and the efficiency of the produced rhamnolipids. Costa
et al. (2006) showed that by using locally produced substrates, they could reach
the desirable results. They conducted some experiments on rhamnolipid production
by P. aeruginosa LBI, using some Brazilian native oils, such as oils from buriti,
cupuacu, passion fruit, andiroba, Brazilian nut, and babassu, as the substrates.