Environmental Engineering Reference
In-Depth Information
synthetic surfactants is over 15 million tons per
year (Van-Bogaert et al.
2007
) that are employed
in different industrial sectors ranging from food
processing, pharmaceutical, cosmetics, deter-
gent production, environmental cleanup (biore-
mediation) and enhanced oil recovery. According
to Reznik et al. (
2010
), the worldwide produc-
tion of synthetic surfactants per annum was 13
million tons in 2008, increased by 2 % in 2009
resulting to annual turnover of US$ 2,433 billion.
The market was then expected to experience a
continuous growth by 28 % from 2009 to 2012
and thereafter increase approximately by 3.5-4 %.
However, biosurfactants have been reported by
many researchers to have a variety of advantages
over the petrochemical-based or synthetic sur-
factants. They display excellent surface activity
and emulsifi cation properties with very low
toxicity and higher biodegradability features.
They have also been found to be very effective at
low concentrations and over a wide range of
environmental conditions such as pH, temperature,
salinity, alkalinity and acidity. Other important
characteristics of these biomolecules include
better environmental compatibility, lower critical
micelle concentration, higher selectivity, specifi c
activity and ability to be synthesised from renew-
able low-cost resources (Desai and Banat
1997
;
Oliveira et al.
2009
; Rahman and Gakpe
2008
).
These biosurfactants due to their amphiphilic
properties have found potential application in an
extremely wide variety of industrial process
involving emulsifi cation, foaming, detergency,
wetting, dispersing or solubilisation. In addition,
biosurfactants are currently being used as anti-
bacterial, antifungal, antiviral, antioxidant, mois-
turisers and antiradical and stabilising agents in
the production of various industries, products
ranging from cosmetics, food, pharmaceutical,
agriculture and detergents. Their ability to stimu-
late dermal fi broblast metabolism and support
healthy skin physiology has also put them on the
front line as potential raw material for cosmetics
such as deodorants, facial cosmetics, lotions, eye
shadow, skin smoothing and anti-wrinkle and
anti-ageing products (Rosenberg and Ron
1999
;
Banat et al.
2000
; Rahman et al.
2002
).
The commercial viability of biosurfactants as
alternatives to the synthetic surfactants has been
greatly hindered due to limiting technical and
economic factors including high substrate cost
(Mukherjee et al.
2006
), low product yield
(Maneerat
2005
; Thavasi et al.
2011b
), product
mixtures resulting in high-cost downstream
recovery/purifi cation processes (Heyd et al.
2008
) and the type of producing strains (Reiling
et al.
1986
). Most biosurfactant-producing organ-
isms are pathogenic and diffi cult to handle in
large-scale industrial processes (Gunther et al.
2005
; Toribio et al.
2010
). In this review, after a
discussion of the pathogenicity of biosurfactant,
we focus on the state of the art of production of
biosurfactants from nonpathogenic eco-friendly
organisms and on the heterologous production by
recombinant strains.
2
Biosurfactant Production
Using Pathogenic Organisms
and Health and Safety Issues
The development of biosurfactant production in
nonpathogenic organisms is a current challenge
that is receiving increased attention in order to
avoid pathogenicity and complex metabolic regu-
lations (Dusane et al.
2010
) especially in rham-
nolipid synthesis by
Pseudomonas aeruginosa
and to screen for novel product spectra (Müller
et al.
2012
). Application of crude biosurfactants
from pathogens in industrial and environmental
applications is largely unacceptable especially in
the cosmetics, health and food sectors due to
the potential presence of toxins and pigments
(Nicas and Iglewski
1985
).
2.1
Rhamnolipids
Rhamnolipids are widely studied glycolipid
biosurfactants synthesised in large quantities
by different strains of
P. aeruginosa
. As biosurfac-
tants, rhamnolipids play an important role for
the producing organism, displaying useful
physico-chemical, physiological (Zhong et al.
2007
)
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