Bioprocessing Approaches to Synthesize Bio-based Surfactants and Detergents - Food and Industrial Bioproducts and Bioprocessing - page 247

10.5.3 Lipase-catalyzed synthesis of polyglycerol
polyricinoleate
Polyglycerol polyricinoleate, or PGPR, is an important emulsifier in foods, for improved
texture and enhanced volume of bakery products, in salad dressings, and in chocolate to
decrease the occurrence of fat bloom (Bodalo et al ., 2009 ). It is conventionally formed
via a chemical process: polycondensation of ricinoleic acid at high temperature, followed
by covalent attachment to polyglycerol in the presence of alkali. This approach yields
undesired by-products and requires large energy expenditures, hence leads to production
of carbon dioxide (Bodalo et al ., 2009). In contrast, the enzymatic approach involves
relatively low temperatures (75 °C or less), and does not produce by-products. In one
approach, polyricinoleate, produced previously by bulk oligomerization of ricinoleic
acid catalyzed by lipases, was reacted with polyglycerol of average degree of
polymerization 3.0 at a 5:1 mass ratio with immobilized Rhizopus arrhizus lipase in a
stirred tank reactor operated at 40 °C (solvent-free conditions) (Bodalo et al ., 2009 ).
Acid value (AV), a measure of the free COOH groups present in the reaction, was
employed to monitor the reaction. Under these conditions, a final AV of 8.7 mg of KOH
per g of reaction mixture was achieved, which does not quite reach the maximum
allowable AV for PGPR as specified by the European Union (EU), 6 mg KOH per g
(Bodalo et al ., 2009). However, this requirement was met if vacuum pressure was
employed: 5.21 mg KOH per g (Montiel Morte and Hayes, 2009).
In an alternate approach, 33 g (110 mmol) of ricinoleic acid was mixed with 2.2 g
(approximately 9 mmol) of the same polyglycerol source in the presence of 12 wt-%
Novozym 435 (Montiel Morte and Hayes, 2009). The bulk polymerization was conducted
under stirring at 75 °C. This approach yielded an AV of 20 mg KOH per g, thus suggesting
vacuum pressure is required to lower the AV to meet EU specifications. Gel permeation
chromatographic analysis suggested the number-averaged molecular weight and
polydispersity index were 5430 and 3.24, respectively. NMR analyses suggested that of
triglycerol's five hydroxyl groups, only the two primary OH groups could serve as acyl
acceptor sites.

10.5.4 Enzyme-catalyzed synthesis of alkylpolyglucosides
(APGs)
Chemical synthesis of alkyl polyglycosides, or APGs, yields a mixture of -pyranoside

isomers. Anomerically pure glycosides may lead to more consistent and reliable performance
of APGs from batch to batch; their chemical synthesis is complex requiring several protection
and deprotection steps (van Rantwijk et al ., 1999 ).
Enzymatic synthesis of APGs requires two steps: the synthesis of alkyl (mono)glycoside
via glycosidases and the extension of the oligosaccharide group catalyzed by cyclodextrin
glycosyl transferase. The first step has been reviewed (van Rantwijk et al ., 1999 ). Three
examples are provided to describe the current state-of-the-art. Firstly,

α - and β

-glycosidase from
the thermophilic organism Pyrococcus furiosus was employed to catalyze the reaction
between the disaccharide lactose (

β

4)-D-glucose) and hexanol
(Hansson and Adlercreutz, 2002). Immobilized enzyme ( via adsorption onto celite) was
added to a solution of 93 mM lactose in n -hexanol, operated at 75 °C, with its water activity
maintained at 0.79 via equilibration with saturated salt aqueous solution. This approach did
not yield lactoside, due to the enzymatic cleavage of lactose's

β -D-galactopyranosyl-(1 →

β -1,4 glycosidic bond.