Green Chemistry and Biosurfactant Research - Biosurfactants: Research Trends and Applications - page 15

of microbial BSs for the cleanup of oil storage tanks. Sludge and oil deposits normally
accumulate at the bottom and on the walls of storage tanks, thus requiring periodical
cleaning operations. BSs can effectively drive the cleaning activity as demonstrated
in a field trial conducted at the Kuwait Oil Company. Two tons of rhamnolipid BS
containing culture broth were produced, sterilized, and added to an oil sludge tank
along with fresh crude oil and water and circulated continuously for 5 days at an
ambient temperature of 40°C-50°C. The oil sludge was effectively lifted and mobi-
lized from the bottom of the tank and solubilized within the emulsion formed. The
treatment recovered 91% of hydrocarbons in the sludge. The value of the recovered
crude covered the cost of the cleaning operation.
P otential f ooD a PPliCations
Although BSs can be explored for several food processing applications, in this
section, we emphasize their potential as food formulation ingredients and antiad-
hesive agents.
Food formulation ingredients : Apart from their obvious role as agents that decrease
surface and interfacial tension, thus promoting the formation and stabilization of
emulsions, surfactants can have several other functions in food, for example, to con-
trol the agglomeration of fat globules, stabilize aerated systems, improve texture
and shelf life of starch-containing products, modify rheological properties of wheat
dough, and improve consistency and texture of fat-based products (Kachholz and
Schlingmann, 1987). In bakery and ice cream formulations, BSs act controlling con-
sistency, retarding staling, and solubilizing flavor oils; they are also utilized as fat
stabilizer and antispattering agent during cooking of oil and fats (Kosaric, 2001). An
improvement of dough stability, texture, volume, and conservation of bakery prod-
ucts was obtained by the addition of rhamnolipid surfactants (Van Haesendonck and
Vanzeveren, 2004). The authors also suggested the use of rhamnolipids to improve
properties of butter cream, croissants, and frozen confectionery products. Recently,
a bioemulsifier isolated from a marine strain of Enterobactercloacae was described
as a potential viscosity enhancement agent of interest in food industry especially due
to the good viscosity observed at acidic pH allowing its use in products containing
citric or ascorbic acid (Iyer et al., 2006).
Antiadhesive agents : Bacterial biofilms present in food industry surfaces are
potential sources of contamination, which may lead to food spoilage and disease
transmission (Hood and Zottola, 1995). Due to the fact that food processors have
a zero tolerance levels for pathogens like Salmonella and also (in most countries)
for Listeria monocytogenes , a single adherent cell may be as significant as a well-
developed biofilm; thus, controlling the adherence of microorganisms to food con-
tact surfaces is an essential step in providing safe and quality products to consumers
(Hood and Zottola, 1995).
The involvement of BSs in microbial adhesion and detachment from surfaces has
been investigated. A surfactant released by Streptococcus thermophilus has been
used for fouling control of heat-exchanger plates in pasteurizers as it retards the
colonization of other thermophilic strains of Streptococcus responsible for fouling