Rhamnolipids Characteristics, Production, Applications, and Analysis - Biosurfactants: Research Trends and Applications - page 74

Rhamnolipid producers could use a variety of substrates for rhamnolipid production.
By using low-cost substrates such as carbohydrates, vegetable oils, and industrial
wastes, the cost of the production could be reduced. Fats and oil wastes from food
industries are considered environmental pollutants; using these materials as a sub-
strate for rhamnolipid production not only decreases the cost of rhamnolipid pro-
duction, but also solves another environmental problem.
Costa et al. (2008) have done some experiments on rhamnolipid production by
using a few different substrates made of soybean soapstock, chicken fat, hydroge-
nated vegetable fat, and soybean frying oil generated by food industry and restau-
rants. They reported that Pseudomonas LMI 6c and Pseudomonas LMI 7a were able
to utilize the substrates mentioned earlier and produce a decent amount of rham-
nolipids. In their experiments, soybean soapstock showed the best result, and the
bacteria by using this substrate produced 9.69 g/L of rhamnolipids that were able to
reduce the surface tension of the medium of soybean oil. Along the 18 strains being
tested, two of the strains (6c and 7a) were able to lower the surface tension of the
medium to 31 mN/m. Furthermore, Costa et al. (2009b) reported that the highest
overall production rate for rhamnolipids and PHAs that they achieved was by using
the waste frying oil as the carbon source; they reported that with this substrate, the
production rate for rhamnolipid was 660 mg/L.
Costa et al. (2010) reported that in their experiments, the rhamnolipids produced
by P. aeruginosa L2-1, by using a waste cooking oil as the substrate, were a mixture
of 16 different rhamnolipid congeners in which monorhamnolipid (Rha-C 10 -C 10 )
and dirhamnolipid (Rha-Rha-C 10 -C 10 ) were the largest portion. The L2-1 rhamno-
lipids demonstrated a similar or, even in some cases, superior surface-active prop-
erties than commercial rhamnolipids produced by P. aeruginosa (JBR599—Jeneil
Biosurfactant Co., Saukville, Wisconsin).
The experiments of Zhu et al. (2007) consisted of the comparison of rhamnolipid
production rate by using the sludge from a refinery versus the sludge from a cater-
ing as substrate. It was shown that the substrate made with the sludge from catering
resulted in the highest rate of the rhamnolipid production. In the experiments of
Nitschke et al. (2005), it was observed that P. aeruginosa was able to grow and pro-
duce rhamnolipids using various waste oils as substrates. In their experiments, they
compared the rhamnolipid production rate on the substrates composed of wastes
from soybean, cottonseed, babassu, palm, corn oil, and waste obtained from refinery.
Their experiments showed that the rate of the production was highest when the bac-
teria were cultured on the substrate made of the soybean soapstock waste. They
reported that the rhamnolipids produced on the substrate made of soybean soapstock
waste had the ability to lower the surface tension of the medium to 26.9 mN/m and
demonstrated a low CMC of 51.5 mg/L. Their analysis also showed that the produced
rhamnolipids are a mixture of 10 different homologues with monorhamnolipid (44%)
and dirhamnolipid (29%) as the chief components in the mixture.
Gunther et al. (2005) pointed out that P. aeruginosa is able to grow and produce
rhamnolipid by using a variety of different carbon sources. However, the highest
levels of rhamnolipid production were obtained when they used vegetable-based
oils such as soybean oil, olive oil, corn oil, and canola oil as the carbon sources.