Downstream processing of algal polyunsaturated fatty acids.

Continuous enzymatic transesterification of high oleic sunflower oil in a packed bed reactor: influence of the glycerol production

This article reviews the application of enzymes in lipid modification. Lipases are the most established biocatalysts used for the synthesis of structured triacylglycerols, fats, and margarine and for the release of flavoring fatty acids for food applications. In addition, the various enzymes, such as P450 monooxygenases, hydratases, lipoxygenases, and certain lyases, used for oxyfunctionalization and the phospholipases used for degumming are covered. Basic aspects of enzyme catalysis and the modern tools used for their discovery and improvement by protein engineering provide insight into how suitable biocatalysts can be identified and optimized for an application. In addition to isolated enzymes, whole-cell engineered microorganisms are also used for lipid modification. Thus, the polyunsaturated fatty acid EPA (eicosapentaenoic acid) can be produced in a yeast using sugar as a renewable resource.

Enzymes in Lipid Modification

Lipase-catalysed transesterification of high oleic sunflower oil

Though designed by nature to effect hydrolysis of lipids, lipases can, under appropriate reaction conditions, promote ester formation through reaction of acids and alcohols (esterification) or of esters with acids (acidolysis), alcohols (alcoholysis), or other esters (interesterification). Compared with chemical processes already carried out on an industrial scale enzymic reactions occur under milder (and ‘greener’) conditions though they may take longer. Of greater significance is the specificity shown by the enzymes which permits the formation of lipid derivatives not easily prepared by conventional laboratory procedures.



This review describes the lipases and their various specificities and reports on their use in hydrolysis and in the production of phospholipids, fatty acids, alkyl esters, mono- and di-acylglycerols, triacylglycerols, other esters, and amides. Some of these have already led to marketable products but for the most part the full potential of these reactions has yet to be realised. The reactions of other enzymes promoting interesting reactions at unsaturated centres are also described.



© 1999 Society of Chemical Industry

Enzymes as biocatalysts in the modification of natural lipids

The crucial role of silica gel in lipase-catalyzed esterification reactions using adsorbed high-polar substates was established. It was found that in these kinds of reactions, the presence of silica gel-adsorbed substrates did not alter the kinetic mechanisms of the synthesis of acylglycerides but improved significantly the conversion yields. An explanation for the critical role of silica gel in these kinds of reactions was proposed whereby the silica gel behaves as a “polar substrate reservoir” and plays a protective role for the immobilized enzyme avoiding its blockage. In this way it was shown that the use of silica gel facilitates reactions at high glycerol concentrations without alteration of reaction rates or conversion yields. It also was demonstrated that highly hydrophilic polyols enhanced blockage of the enzyme. The importance of the presence of an organic solvent in the reaction medium was shown to have a critical role in the conversion yields of the reactions tested. Finally, the influence of different supports used for adsorption of the substrates was compared with respect to their efficiency in protecting the enzymatic activity.

J. Stephane Condoret

Papers

The role of silica gel in lipase-catalyzed esterification reactions of high-polar substrates

Enzymatic Catalysis in Nonconventional Media Using High Polar Molecules as Substrates