Enrichment of CLA isomers by selective esterification with l‐menthol using Candida rugosa lipase

Commercially available preparations of CLA are composed of almost equal amounts of 9‐cis,11‐trans (9c,11t)‐CLA and 10‐trans,12‐cis (10t,12c)‐CLA. Each isomer was fractionated and enriched, for availability as a food supplement, by a process comprising selective esterification with l‐menthol by Candida rugosa lipase, distillation, and n‐hexane extraction. The first selective esterification of CLA isomers was conducted with an equimolar amount of l‐menthol of 30°C. The oil phase of the reaction mixture was fractionated into an l‐menthyl ester fraction (9c,11t‐CLA rich) and an FFA fraction (10t,12c‐CLA rich) by distillation. The FFA fraction was esterified again with an equimolar amount of l‐menthol to enrich 10t,12c‐CLA. The 10t,12c‐CLA preparation was obtained as the resulting FFA fraction by distillation. 10t,12c‐CLA was enriched to 91% with 40% recovery. To enrich 9c,11t‐CLA, the l‐menthyl ester fraction in the first esterification was chemically hydrolyzed, and the resulting FFA were esterified again with an equimolar amount of l‐menthol. The 9c, 11t‐CLA preparation was obtained by chemical hydrolysis of the resulting l‐methyl ester fraction, followed by n‐hexane extraction. 9c,11t‐CLA was enriched to 94% with 42% recovery. This effective process for purification of CLA isomers using l‐methol is applicable to the production of food supplements.