in the surfactant creation. To replace synthetic surfactants by biodegradable, sustainable green energies and renewable surfactants, the development of new strategies
is a unique obstacle for humans and environmental protection agencies (Ajala et al.
2015). This predicament triggers the discovery of an equally potential and effective
but environmentally friendly alternative to synthetic surfactants: a class of surfactants derived from microorganisms, known as “biosurfactants.” They are similarly
diverse within the structure and function and are gaining priority because of their
eco-friendly and biodegradability attributes (Shekhar et al. 2015). Biosurfactants are
secondary metabolites and produced in the stationary phase of the microbial growth
curve (Yan et al. 2012). Like synthetic surfactants, biosurfactants have the ability to
lowering interfacial and surface tension. The molecular mass of the biosurfactants
ranges from 500 to 1500 daltons, and their critical micelle concentration (CMC)
differs from 1 to 200 mgL
À1
. Another crucial property of biosurfactants is the
hydrophilic-lipophilic balance (HLB) that specifies the value of hydrophobic and
hydrophilic compounds in surface-active substances and also has an effect on the
stability of an emulsion. The hydrophobic state is indicated by low HLB value with
more nonpolar groups forming water-in-oil (W/O) emulsions. In comparison, a
hydrophilic state marked by a high HLB means more polar groups and prefer for
oil-in-water (O/W) emulsion. HLB numbers are in range as follows for different
applications (Tadros 2013): 3–6 for W/O emulsifier, 7–9 for a wetting agent, 12–15
for detergent, and 15–18 for solubilizer.
Many aerophilic microbes reported for their production of biosurfactants only in
the presence of carbon sources such as fats, oil, and hydrocarbons in their media. The
most known biosurfactant producer are bacteria genera (Bacillus, Pseudomonas, and
Acinetobacter), fungi genera (Fusarium spp. and Aspergillus spp.), and yeast genera
(Pseudozyma and Candida). These surface-active compounds have benefits for
biosurfactant-producing microorganisms, such as ensure exponential biomass
increase, grow on water-immiscible substrates, exhibit antimicrobial activities
against possible predators, and make them survive harsh environmental conditions
(Silva et al. 2014).
The price of chemical or synthetic surfactants, such as sodium lauryl sulfate,
tends to fall in the range of $1–2/kg, and biosurfactants, such as amino acid-based
surfactants, were $3–4/kg. Sophorolipid is the most widely available and the
cheapest microbial biosurfactant, and the sales price has recently been published to
be at $3–4/kg. Based on a growth rate of 3.5% per year, the global biosurfactant
market is expected to reach 2.2 billion $. In addition to this, due to the increasing
demand from Africa, Latin America, and Asia, the global production is estimated to
reach 476,512 tons that account for around 21% of the total manufacture (Roelants
et al. 2018).
Before 2011, more than 200 patents were registered about the production of
biosurfactants, with 35% of them on sophorolipids, 10% on mannosylerythritol
lipids, and 50% of these patents on rhamnolipids (Vecino et al. 2017).
Biosurfactants have high potential for its applications in industrial scale; however,
the production and commercialization have not been enough (Varjani and Upasani
1 A Review on Production, Properties, and Applications of Microbial Surfactants as. . .
5
is a unique obstacle for humans and environmental protection agencies (Ajala et al.
2015). This predicament triggers the discovery of an equally potential and effective
but environmentally friendly alternative to synthetic surfactants: a class of surfactants derived from microorganisms, known as “biosurfactants.” They are similarly
diverse within the structure and function and are gaining priority because of their
eco-friendly and biodegradability attributes (Shekhar et al. 2015). Biosurfactants are
secondary metabolites and produced in the stationary phase of the microbial growth
curve (Yan et al. 2012). Like synthetic surfactants, biosurfactants have the ability to
lowering interfacial and surface tension. The molecular mass of the biosurfactants
ranges from 500 to 1500 daltons, and their critical micelle concentration (CMC)
differs from 1 to 200 mgL
À1
. Another crucial property of biosurfactants is the
hydrophilic-lipophilic balance (HLB) that specifies the value of hydrophobic and
hydrophilic compounds in surface-active substances and also has an effect on the
stability of an emulsion. The hydrophobic state is indicated by low HLB value with
more nonpolar groups forming water-in-oil (W/O) emulsions. In comparison, a
hydrophilic state marked by a high HLB means more polar groups and prefer for
oil-in-water (O/W) emulsion. HLB numbers are in range as follows for different
applications (Tadros 2013): 3–6 for W/O emulsifier, 7–9 for a wetting agent, 12–15
for detergent, and 15–18 for solubilizer.
Many aerophilic microbes reported for their production of biosurfactants only in
the presence of carbon sources such as fats, oil, and hydrocarbons in their media. The
most known biosurfactant producer are bacteria genera (Bacillus, Pseudomonas, and
Acinetobacter), fungi genera (Fusarium spp. and Aspergillus spp.), and yeast genera
(Pseudozyma and Candida). These surface-active compounds have benefits for
biosurfactant-producing microorganisms, such as ensure exponential biomass
increase, grow on water-immiscible substrates, exhibit antimicrobial activities
against possible predators, and make them survive harsh environmental conditions
(Silva et al. 2014).
The price of chemical or synthetic surfactants, such as sodium lauryl sulfate,
tends to fall in the range of $1–2/kg, and biosurfactants, such as amino acid-based
surfactants, were $3–4/kg. Sophorolipid is the most widely available and the
cheapest microbial biosurfactant, and the sales price has recently been published to
be at $3–4/kg. Based on a growth rate of 3.5% per year, the global biosurfactant
market is expected to reach 2.2 billion $. In addition to this, due to the increasing
demand from Africa, Latin America, and Asia, the global production is estimated to
reach 476,512 tons that account for around 21% of the total manufacture (Roelants
et al. 2018).
Before 2011, more than 200 patents were registered about the production of
biosurfactants, with 35% of them on sophorolipids, 10% on mannosylerythritol
lipids, and 50% of these patents on rhamnolipids (Vecino et al. 2017).
Biosurfactants have high potential for its applications in industrial scale; however,
the production and commercialization have not been enough (Varjani and Upasani
1 A Review on Production, Properties, and Applications of Microbial Surfactants as. . .
5