Microbial production of conjugated fatty acids

Conjugated fatty acids have attracted much attention as a novel type of biologically beneficial functional lipid. Some isomers of conjugated linoleic acid (CLA) reduce carcinogenesis, atherosclerosis and body fat. Considering the use of CLA for medicinal and nutraceutical purposes, a safe isomer‐selective process of production is required. The introduction of biological reactions for CLA production could be an answer. We screened microbial reactions useful for CLA production and found several unique reactions in microorganisms. Lactic acid bacteria produced CLA from linoleic acid. The CLA, which was obtained as the free fatty acid form, comprised a mixture of cis‐9,trans‐11‐octadecadienoic acid (18:2) and trans‐9,trans‐11‐18:2. Furthermore, lactic acid bacteria transformed ricinoleic acid [12‐hydroxy‐cis‐9‐octadecenoic acid (18:1)] to CLA (a mixture of cis‐9,trans‐11‐18:2 and trans‐9,trans‐11‐18:2). Castor oil, rich in the triacylglycerol form of ricinoleic acid, was also found to act as a substrate for CLA production by lactic acid bacteria with the aid of lipase‐catalyzed triacylglycerol hydrolysis. Filamentous fungi transformed trans‐vaccenic acid (trans‐11‐18:1) to cis‐9,trans‐11‐18:2 by Δ9 desaturation. This CLA was obtained as a triacylglycerol. In addition, lactic acid bacteria produced conjugated trienoic fatty acids from α‐ and γ‐linolenic acid. The trienoic fatty acids produced from α‐linolenic acid were cis‐9,trans‐11,cis‐15‐octadecatrienoic acid (18:3) and trans‐9,trans‐11,cis‐15‐18:3. Those produced from γ‐linolenic acid were cis‐6,cis‐9,trans‐11‐18:3 and cis‐6,trans‐9,trans‐11‐18:3.