2.3 Emulsification and De-emulsification
Biosurfactants have a property to stabilize (emulsify) or destabilize (de-emulsify) the
emulsion. The feature of biosurfactants as an emulsifying agent depends on the
hydrocarbon structure. Biosurfactants can emulsify many hydrocarbons, such as
kerosene, tridecane, tetradecane, hexadecane, diesel, benzene, and other hydrocarbons. Peele et al. (2016) tested the emulsifying activity of biosurfactant produced by a
marine bacterium with different hydrocarbons, such as xylene, benzene, diesel, kerosene, and petrol. Ahmad et al. (2016) used the ANN method to optimize the growth
condition of Klebsiella sp. FKOD36 to enhance lipase, and the best outcome under the
ANN model arrived at an enhanced value of biosurfactant yield 31.67% and 31.68%
emulsification index. Rocha e Silva et al. (2017) explored the use of biosurfactants
from Candida guilliermondii, Candida lipolytica, Candida sphaerica, Pseudomonas
aeruginosa, Pseudomonas cepacia, and Bacillus sp. as de-emulsifiers of petroleum
derivatives and obtained promising results for the bacterial strains where recovery was
65% higher when compared with that of yeast’s (35–40%).
2.4 Foam and Wet Property of Biosurfactants
Foams are colloidal systems with liquid or solid as the continuous phase and gas as
the dispersed phase. Foams have two different structures that may occur in foams
containing polyhedral cells and in spherical bubbles (Drenckhan and Hutzler 2015).
The presence of oils and other particles increases the instability of foam due to the
stabilization effect of surfactants (Belhaij and Al-Mahdy 2015). Jian et al. (2011)
investigated the foam facility and stability of a biosurfactant named tea saponin. Tea
saponin was able to produce foam, but its durability and foamability was accelerated
when the synthetic surfactant was added. Wetting is the process that another fluid
displaces the phase of a liquid from the surface of a solid. The wetting property of the
surfactant indicates the ability of a liquid to cover the solid surface. The balance
between cohesive and adhesive forces specified the degree of wettability of a
surfactant. Cohesive force is the force that prevents the liquid drop from making
contact with the solid surface and causing the droplet to ball up. The force between a
liquid and a solid that allows the liquid drop to spread across the surface is called
adhesive force (Lee et al. 2017; Liu et al. 2017).
3 Classification and Source of Biosurfactants
Biosurfactant, unlike chemical surfactants which are categorized based on the
polarity of the functional group, is mainly classified based on their chemical composition and the origin of the microbes (Sharma et al. 2016). The summary of its
classification is illustrated in Fig. 1.2.
1 A Review on Production, Properties, and Applications of Microbial Surfactants as. . .
7
Biosurfactants have a property to stabilize (emulsify) or destabilize (de-emulsify) the
emulsion. The feature of biosurfactants as an emulsifying agent depends on the
hydrocarbon structure. Biosurfactants can emulsify many hydrocarbons, such as
kerosene, tridecane, tetradecane, hexadecane, diesel, benzene, and other hydrocarbons. Peele et al. (2016) tested the emulsifying activity of biosurfactant produced by a
marine bacterium with different hydrocarbons, such as xylene, benzene, diesel, kerosene, and petrol. Ahmad et al. (2016) used the ANN method to optimize the growth
condition of Klebsiella sp. FKOD36 to enhance lipase, and the best outcome under the
ANN model arrived at an enhanced value of biosurfactant yield 31.67% and 31.68%
emulsification index. Rocha e Silva et al. (2017) explored the use of biosurfactants
from Candida guilliermondii, Candida lipolytica, Candida sphaerica, Pseudomonas
aeruginosa, Pseudomonas cepacia, and Bacillus sp. as de-emulsifiers of petroleum
derivatives and obtained promising results for the bacterial strains where recovery was
65% higher when compared with that of yeast’s (35–40%).
2.4 Foam and Wet Property of Biosurfactants
Foams are colloidal systems with liquid or solid as the continuous phase and gas as
the dispersed phase. Foams have two different structures that may occur in foams
containing polyhedral cells and in spherical bubbles (Drenckhan and Hutzler 2015).
The presence of oils and other particles increases the instability of foam due to the
stabilization effect of surfactants (Belhaij and Al-Mahdy 2015). Jian et al. (2011)
investigated the foam facility and stability of a biosurfactant named tea saponin. Tea
saponin was able to produce foam, but its durability and foamability was accelerated
when the synthetic surfactant was added. Wetting is the process that another fluid
displaces the phase of a liquid from the surface of a solid. The wetting property of the
surfactant indicates the ability of a liquid to cover the solid surface. The balance
between cohesive and adhesive forces specified the degree of wettability of a
surfactant. Cohesive force is the force that prevents the liquid drop from making
contact with the solid surface and causing the droplet to ball up. The force between a
liquid and a solid that allows the liquid drop to spread across the surface is called
adhesive force (Lee et al. 2017; Liu et al. 2017).
3 Classification and Source of Biosurfactants
Biosurfactant, unlike chemical surfactants which are categorized based on the
polarity of the functional group, is mainly classified based on their chemical composition and the origin of the microbes (Sharma et al. 2016). The summary of its
classification is illustrated in Fig. 1.2.
1 A Review on Production, Properties, and Applications of Microbial Surfactants as. . .
7