Rhamnolipids Characteristics, Production, Applications, and Analysis - Biosurfactants: Research Trends and Applications - page 88

subjects of their study. There are many methods and devices that can be used for
quantitative and qualitative detection and analysis of rhamnolipids. A few of the
commonly used methods will be briefly discussed.
m easurinG CmC
One of the methods that have been used commonly for the quantitative measurement
of the rhamnolipid is by measuring its surface tension. A tensiometer measures the
force needed to pull up a thin metal ring (platinum ring) out of the surface of the
solution. To determine the concentration of the rhamnolipid in solution, the solu-
tion is sequentially diluted. At each step of dilution, the surface tension is mea-
sured until the CMC (the concentration at which surface tension starts to increase)
is found. Then the data from the surface tension at each concentration are plotted.
The CMC of rhamnolipid is the intercept of two straight lines from the concentra-
tion-dependent and concentration-independent sections of the curve. From the value
of CMC, the quantity of the rhamnolipid in the original solution can be calculated
(Ballot, 2009; Mulligan and Gibbs, 2004). Although this method is one of the easiest
methods of measuring the quantity of the rhamnolipids, it should be noted that the
presence of other tensioactive components in the solution can cause errors in the
results (Abdel-Mawgoud et al., 2010).
r hamnoliPiD h yDrolysis
Abdel-Mawgoud et al. (2011) described rhamnolipid hydrolysis test as a useful method
for measuring the quantity of the produced rhamnolipid. In these tests, the solution
contains rhamnolipids mixed with sulfuric acid and either orcinol (1,3-dihydroxy-5-
methylbenzene) or anthrone (9,10-dihydro-9-oxoanthracene), and then heated until
a greenish blue color appears. This change in color is the result of hydrolysis of the
rhamnose groups in rhamnolipids. Then the measurement is done by using a spec-
trophotometer and result is compared with a standard curve that had been prepared
by standard rhamnolipid mixtures.
s PeCtrosCoPiC m ethoDs
During recent decades, there have been many advances in the field of spectroscopy
and many devices have been developed. By studying the interaction of energy radi-
ated from a source with the matter, the structures and bonds could be identified. The
energy used depends on the application and could be visible light, gamma, ultra-
violet, infrared (IR), or x-ray. Describing all the methods of spectroscopy is more
than the scope of this chapter. Therefore, this is a summary of some of the common
spectrometry methods that have been used for measuring rhamnolipids.
Spectrophotometer
A spectrophotometer is a device for measuring the quantity of the chemicals in
the solution by measuring the reflection or transmission properties of the chemical
depending on the wavelength of radiated light; either in the ultraviolet, visible, or