Method of producing
DHA-rich oil using lipase
Omega- 3 polyunsaturated fatty acids (PUFAs) such as eicosapentaenoic acid (EPA), docosapentaenoic
acid (DPA), and docosahexaenoic acid (DHA), are recognized as essential nutrition for human beings.
Lipase produced by such microorganisms as Aspergillus, Burkholderia, Candida, Pseudomonas, and
Rhizomucor, can concentrate these nutritional PUFAs in the natural form of “acylglycerols.” Candida
rugosa lipase (CRL) is one of the most popular biocatalysts for this industrial application. This article
describes the unique and key features of CRL.
pRODUcINg DHA-RIcH OIls IN
PUFAs can be concentrated in the acylglycerol fraction in various
ways. For example, “winterization” is a traditional process in which
fatty acids with different saturations are separated based on their
melting point. This is a very simple process in which low temperature enables the triacylglycerols (TAGs) comprising saturated fatty
acids to precipitate. However, achieving the very low temperatures
required to significantly increase PUFA contents consumes large
amounts of energy. The PUFA yield also decreases due to poor separation of PUFAs from other unsaturated fatty acids.
In contrast, enzymatic method is energy efficient, since the
reaction of lipase-catalyzed hydrolysis can occur at room temperature. PUFAs are concentrated efficiently by using fatty acid-specific
lipase. On the other hand, the correct selection of lipase is crucial, since different types of lipase have different specificity to fatty
acids. Because CRL acts extremely weakly on DHA, DHA is enriched
in the glyceride fraction and the yield of DHA increases. It is important to note that this hydrolysis is an equilibrium reaction, and DHA
concentration can only increase to a certain point. For example,
when the hydrolysis of tuna oil that contains about 25% DHA is
catalyzed by CRL, DHA is concentrated to about 45–50%, but it is
difficult to achieve concentrations higher than 50%—even with a
higher dose of CRL. More DHA-enriched oil can be obtained by re-hydrolyzing the DHA-rich oil fraction that separates from the reaction mixture (Fig. 1). DHA can be concentrated to more than 70% in
the glyceride fraction by repeating the separation of DHA-rich oil
fractions and hydrolysis processes. Most DHA-enriched oils used
as health foods or dietary supplements in the Japanese market are
processed with this way.
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