Biomedical Engineering Reference
In-Depth Information
OH
O
O
O
O
O
OH
O
O
OH
O
O
O
O
OH
O
O
H
Mono-rhamnolipid
O
Sophorolipid
OH
H
OH
OH
O
OH
H
OH
HO
H
OR
O
OH
O
H
H
OH
O
O
H
O
O
O
O
H
H
OH
OH
H
H
O
O
OH
OH
OH
n
Mannosylerythritol lipid
OH
R = H, or
m
H
O
Trehalose lipid
OR
m + n = 27-31
O
OH
Figure 10.7
Glycolipid-type biosurfactants.
Sophorolipids possessing lactone rings are generally more lipophilic than rhamnolipids
and are less sensitive to pH, and often have a lower surface activity per mass than
rhamnolipids. They are typically obtained from bacteria or yeasts, particularly from
Candida
sp. Fermentation is often conducted under nitrogen starvation conditions, with
abundant dissolved oxygen being present (Pinzon
et al
., 2009 ). Sophorolipids can undergo
chemical or enzymatic modification to further tune their surface-active properties (Ashby
et al
., 2009 ).
As shown in Figure 10.7, mannosylerythritol lipids (MELs), reviewed elsewhere (Rau
and Kitamoto, 2009 ; Arutchelvi
et al
., 2008), contain mannose, erythritol, and fatty acyl
groups as building blocks, with
meso
-erythritol conjugated to the reducing end of mannose,
fatty acyl groups of varying chain length esterified to hydroxyls 2
′
and 3
′
of mannose and
often acetyl groups at 4
′
and/or 6
′
hydroxyls of mannose. MELs possessing acetyl groups at
positions 4
, and the absence of acetyl groups are designated as MEL- A, B, C,
and D, respectively. They are typically produced by yeasts using a fatty acyl-enriched
carbon-energy source, such as soybean oil or biodiesel, and are recovered from the
fermentation by solvent extraction (Rau and Kitamoto, 2009). Typically a mixture of MEL-
A, B, C, and D is formed, with MEL-A being the most common.
Trehalose lipids, consisting of the disaccharide trehalose (
′
and 6
′
, 6
′
, 4
′
-D-
glucopyranoside) esterified to a branched, hydroxy fatty acid at its 6 and/or 6' hydroxyl group
(Figure 10.7), are typically produced from the
Rhodococcus
sp. bacteria. Other trehalose lipids
contain mixtures of succinoleyl and fatty acyl groups esterified to trehalose. Their fermentation,
chemistry, and applications are described elsewhere (Franzetti
et al
., 2010 ).
α
-D-glucopyranosyl-(1
→
1)-
α
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