Bioprocessing Approaches to Synthesize Bio-based Surfactants and Detergents - Food and Industrial Bioproducts and Bioprocessing - page 245

equilibrium. The three recent examples discussed encompass the current state-of-the-art.
One group reported the formation of MAG via esterification between glycerol and lauric
(12:0) acid at an 8:1 mole ratio in the absence of solvent at 45 °C, above the melting point
of lauric acid (Freitas et al ., 2010). The biocatalyst was an immobilized form of Penicillum
cambertii lipase (“Lipase G” from Amano Enzyme Inc., Nagoya, Japan), known for its
selectivity to form partial glycerides, present at 5 wt-%. The reaction was conducted at a 40
gram scale under stirred batch mode. Under these conditions, 92% of fatty acid was
consumed, yielding 60% MAG and 27% diacylglycerol (DAG) in a 6 h period. Many lipases
are regio-selective towards formation of ester bonds at the 1- and 3- glycerol positions, with
isomerization, that is, “acyl migration,” occurring non-biocatalytically to convert 1-(3-)
MAG into 2-MAG (and vice versa ) and 1,2-(2,3-)DAG into 1,3-DAG, with 1-(3-) MAG and
1,3-DAG typically predominating (Hayes, 2004).
In a second example, MAGs were produced via simultaneous glycerolyis and hydrolysis
of Camellia oil, an oleic (18:1-9 cis ) acid-rich TAG, using a 4:1 mole ratio of glycerol-to-
TAG at 50 °C in stirred batch mode on a 5-50 gram scale (Zeng et al ., 2010 ). tert -Butanol
was employed as a co-solvent, at a volume ratio of 60:40 liter of tert -butanol per liter of
substrates. The reaction was catalyzed by a commercially available immobilized thermophilic
lipase from Candida antarctica (Novozym 435, Novozymes, Inc., Franklinton, NC). Under
these conditions, >95% TAG was consumed, yielding approximately 65% MAG and 11%
DAG in 24 h. The predominant isomers were 1-MAG and 1,3-DAG, respectively, reflecting
the occurrence of acyl migration (i.e., for 2-MAG formed through hydrolysis).
In a third example, MAGs were obtained by hydrolysis of TAG in oil-in-water emulsions
at 50 °C using a 1,3-selctive lipase, which released FFA from the 1- and 3-glycerol positions
(Hwang et al ., 2009). To make the reaction irreversible, the medium was enriched in calcium
cations, to enable the formation of soaps (with the optimal pH being 10.0, further promoting
soap formation).
10.5.2 Lipase-catalyzed synthesis of saccharide-fatty
acid esters
Covalent attachment of fatty acyl groups and saccharides via ester bonds using lipases
has been reviewed (Pyo and Hayes, 2009). Use of lipases in reactions utilizing mono- or
di-saccharides (e.g., fructose, glucose, maltose, ribose, sucrose, and xylose) or sugar
alcohols (e.g., mannitol and sorbitol) as acyl acceptor substrate yields primarily mono-
or di-esters due to the regio-selectivity of lipases. Moreover, ester bonds are formed
almost exclusively from primary -OH groups, with regio-selectivity toward a particular
-OH group when multiple primary hydroxyls exist. For instance, for the lipase-catalyzed
esterification of sucrose, the 6-OH group of the latter's pyranose ring is selectively
acylated over the 1' and 6' primary hydroxyls of its furanose ring (Figure 10.3). As
described above for MAG manufacture, the key goals for the successful biotransformation
are to achieve miscibility between the acyl donor and acceptor and to remove water from
the reaction system. As reviewed, several creative attempts have been employed to
enhance miscibility, including the derivatization of saccharides with protective groups
(e.g., isopropylidene) or complexation agents (e.g., phenylboronic acid); but, in most
cases, a polar co-solvent has been employed, such as tert -butanol, DMF, or recently,
ionic liquids. However, the employment of solvent or derivitization is not desirable due
to increased cost, the incompatibility of solvents and ionic liquids with food processing
regulations, and decreased sustainability.