system from 43 to values <1 mN m
À1 (Lang 2002; Yeh et al. 2005). There has been
a broad spectrum of applications proposed for this compound including its utilization in petroleum recovery and spill mitigation (Liu et al. 2015), since surfactin
enhances bioavailability of water-insoluble substrates and regulates the attachment/
detachment of microorganisms to and from surfaces (Rosenberg and Ron 1999).
Possessing exceedingly favourable features, including low toxicity, high biodegradability and no or minimal loss of activity under harsh conditions such as extreme
temperatures, pH and salinity, as well as a high surface activity and low CMC
values, surfactin is decidedly a candidate for either ex situ biosurfactant injection or
in situ biosurfactant production that lead to an enhancement in oil recovery from
subsurface reservoirs (Banat et al. 2010; Liu et al. 2015).
Schaller et al. (2004) yielded favourable results when examining the effect of
altering salt concentration (0–10% NaCl), pH (3–10) and temperature (21–70
C) on
the performance of surfactin produced by B. subtilis ATCC 21332 cultures; high salt
concentration, high temperature and high pH describe the conditions of many oil
reservoirs and can affect compound’s activity. Al-Wahaibi et al. (2014) reported that
biosurfactants produced by B. subtilis B30 identified as a mixture of lipopeptides
similar to surfactin gave stable emulsions with a wide range of hydrocarbons
including light and heavy crude oil, and remained stable over a broad range of pH,
salinity and temperature. The crude biosurfactant preparation enhanced light oil
recovery by 17–26% and heavy oil recovery by 31%.
Similarly, lipopeptides secreted by B. subtilis HSO121 showed good dispersion
effectiveness on crude oil at low surfactant-to-oil ratios and remained active over
changes in temperature (15–25
C), pH values (5–11) and salinity (0–4% NaCl).
Lipopeptides showed excellent activity in accelerating degradation of long-chain
hydrocarbons after 2 days. The degradation rates of alkanes treated by lipopeptides
after 1 day and 2 days were 38.78% and 71.45%, respectively, which were much
higher than those of commercial dispersant-treated group (9.16% and 34.16% after
1 day and 2 days treatment) (Feng et al. 2019).
5.4.4 Saponins
Many surface-active compounds can be derived from renewable plant resources
(Xu et al. 2011). Although microbial surfactants are generally considered to have
more advantages than plant-based surfactants in terms of scale-up capacity, versatile
properties and rapid production (Randhawa and Rahman 2014), there are several
plant-based biosurfactants exhibiting excellent functional properties, among which
the best known are those belonging to the structurally diverse class of compounds
that derived their name from their ability to form soap-like foams in aqueous
solutions – saponins (Hill 2003). Saponins can be isolated from more than a hundred
plant families (Samal et al. 2017) as well as from several marine invertebrates
including Antarctic starfish of the family Asteriidae and sea cucumbers; they are
also present in some marine sponges, soft coral and small fish (De Marino et al.
1998; Xiao et al. 2019). Among the most studied plant materials that were found to
152
L. Nemček and I. Hagarová
À1 (Lang 2002; Yeh et al. 2005). There has been
a broad spectrum of applications proposed for this compound including its utilization in petroleum recovery and spill mitigation (Liu et al. 2015), since surfactin
enhances bioavailability of water-insoluble substrates and regulates the attachment/
detachment of microorganisms to and from surfaces (Rosenberg and Ron 1999).
Possessing exceedingly favourable features, including low toxicity, high biodegradability and no or minimal loss of activity under harsh conditions such as extreme
temperatures, pH and salinity, as well as a high surface activity and low CMC
values, surfactin is decidedly a candidate for either ex situ biosurfactant injection or
in situ biosurfactant production that lead to an enhancement in oil recovery from
subsurface reservoirs (Banat et al. 2010; Liu et al. 2015).
Schaller et al. (2004) yielded favourable results when examining the effect of
altering salt concentration (0–10% NaCl), pH (3–10) and temperature (21–70
C) on
the performance of surfactin produced by B. subtilis ATCC 21332 cultures; high salt
concentration, high temperature and high pH describe the conditions of many oil
reservoirs and can affect compound’s activity. Al-Wahaibi et al. (2014) reported that
biosurfactants produced by B. subtilis B30 identified as a mixture of lipopeptides
similar to surfactin gave stable emulsions with a wide range of hydrocarbons
including light and heavy crude oil, and remained stable over a broad range of pH,
salinity and temperature. The crude biosurfactant preparation enhanced light oil
recovery by 17–26% and heavy oil recovery by 31%.
Similarly, lipopeptides secreted by B. subtilis HSO121 showed good dispersion
effectiveness on crude oil at low surfactant-to-oil ratios and remained active over
changes in temperature (15–25
C), pH values (5–11) and salinity (0–4% NaCl).
Lipopeptides showed excellent activity in accelerating degradation of long-chain
hydrocarbons after 2 days. The degradation rates of alkanes treated by lipopeptides
after 1 day and 2 days were 38.78% and 71.45%, respectively, which were much
higher than those of commercial dispersant-treated group (9.16% and 34.16% after
1 day and 2 days treatment) (Feng et al. 2019).
5.4.4 Saponins
Many surface-active compounds can be derived from renewable plant resources
(Xu et al. 2011). Although microbial surfactants are generally considered to have
more advantages than plant-based surfactants in terms of scale-up capacity, versatile
properties and rapid production (Randhawa and Rahman 2014), there are several
plant-based biosurfactants exhibiting excellent functional properties, among which
the best known are those belonging to the structurally diverse class of compounds
that derived their name from their ability to form soap-like foams in aqueous
solutions – saponins (Hill 2003). Saponins can be isolated from more than a hundred
plant families (Samal et al. 2017) as well as from several marine invertebrates
including Antarctic starfish of the family Asteriidae and sea cucumbers; they are
also present in some marine sponges, soft coral and small fish (De Marino et al.
1998; Xiao et al. 2019). Among the most studied plant materials that were found to
152
L. Nemček and I. Hagarová