Selective Enrichment of Conjugated Linoleic Acid Isomers in Their Mixtures Using Combined Chemical and Enzymatic Methods

The aim of this study was to selectively enrich t10,c12-conjugated linoleic acid (t10,c12-CLA) and c9,t11-CLA in commercial CLA mixtures using a combination of urea crystallization and lipase-catalyzed esterification. The objective of the urea fractionation is to remove saturated and monounsaturated fatty acids (FA) from the CLA mixtures. CLA-enriched free FA (FFA) mixtures containing 53.8 wt% t10,c12-CLA and 39.1 wt% c9,t11-CLA were produced from the CLA mixtures containing ~34 wt% each of the two CLA isomers by a urea crystallization using methanol and the urea-to-FA weight ratio of 2.5:1. The CLA-enriched FFA mixtures were partially esterified with dodecan-1-ol in a recirculating packed-bed reactor using an immobilized lipase from Candida rugosa to further enrich the t10,c12-CLA and c9,t11-CLA in an FFA fraction and an FA dodecyl ester fraction, respectively, under the optimal conditions, i.e., temperature, 20 °C; FA-to-dodecan-1-ol molar ratio, 1:1; water content, 2 wt% of total substrates; residence time, 5 min; and reaction time, 24 h (for t10,c12-CLA enrichment) and 12 h (for c9,t11-CLA enrichment). After the reaction, an FFA fraction with 72.6 wt% t10,c12-CLA was obtained. Another FFA fraction with 62.0 wt% c9,t11-CLA was recovered after the saponification of the FA dodecyl ester fraction. The yields of t10,c12-CLA and c9,t11-CLA in the FFA fractions were 43.6 and 21.5 wt%, respectively, based on their initial weights in the CLA mixtures.