Fatty acid ascorbyl esters are liposoluble substances that possess good
antioxidative properties. These compounds could be synthesized by using
various acyl donors for acylation of vitamin C in reaction catalyzed by
chemical means or lipases. Enzymatic process is preferred since it is
regioselective, performed under mild reaction conditions, with the obtained
product being environmentally friendly. Polar organic solvents, ionic
liquids, and supercritical fluids has been successfully used as a reaction
medium, since commonly used solvents with high Log P values are inapplicable
due to ascorbic acid high polarity. Acylation of vitamin C using fatty acids,
their methyl-, ethyl-, and vinyl esters, as well as triglycerides has been
performed, whereas application of the activated acyl donors enabled higher
molar conversions. In each case, majority of authors reported that using
excessive amount of the acyl donor had positive effect on yield of product.
Furthermore, several strategies have been employed for shifting the
equilibrium towards the product by water content control. These include
adjusting the initial water activity by pre-equilibration of reaction
mixture, enzyme preparation with water vapor of saturated salt solutions, and
the removal of formed water by the addition of molecular sieves or salt
hydrate pairs. The aim of this article is to provide a brief overview of the
procedures described so far for the lipase-catalyzed synthesis of fatty acid
ascorbyl esters with emphasis on the potential application in food,
cosmetics, and pharmaceutics. Furthermore, it has been pointed out that the
main obstacles for process commercialization are long reaction times, lack of
adequate purification methods, and high costs of lipases. Thus, future
challenges in this area are testing new catalysts, developing continuous
processes for esters production, finding cheaper acyl donors and reaction
mediums, as well as identifying standard procedures for purification of
products which will not require consumption of large amounts of
non-biocompatible organic solvents.
Enzymatic synthesis and application of fatty acid ascorbyl esters