Bioconversion in vitro of conjugated linoleic acid by lactic acid bacteria.

VAN NIEUWENHOVE, C.; GONZÁLEZ, S.,

S. M. de Tucumán

Simposio; III Simposio Internacional de Bacterias Lácticas; 2009

CERELA

BIOCONVERSION IN VITRO OF CONJUGATED LINOLEIC ACID BY LACTIC ACID BACTERIA C. Van Nieuwenhove1,2, S. González. 1,3  1CERELA-CONICET. CCT-TUCUMÁN. Chacabuco 145. 4000. S.M. de Tucumán- Argentina. 2Facultad de Ciencias Naturales e IML-UNT. Miguel Lillo 205. 4000. S.M. de Tucumán. 3Facultad de Bioquímica, Química y Farmacia-UNT. Ayacucho 471. 4000. S.M. de Tucumán-Argentina. E-mail: carina@cerela.org.ar   Conjugated linoleic acid (CLA) refers to positional and geometric isomers of linoleic acid with a double conjugated bond. Many biological effects have been attributed to CLA like anticarcinogenic, anti-obesity and immunomodulatory among others. The main natural CLA isomers are c9,t11 and t10,c12, having different biological effects. Many bacteria can produce CLA, included lactic acid bacteria which can be added to fermented products or used as probiotic strains for CLA production at intestinal level. The aim of this work was to determine CLA bioconversion in lactic acid bacteria, evaluating their tolerance to substrate and isomers produced by each. Strains of Lactobacillus (Lb.) acidophilus, Lb. casei, Lb. plantarum, and Lactococcus (Lc) lactis were cultured in MRS or LAPTg media, supplemented with 80 µg/ml of linoleic acid (LA) for 24 h at 37ºC. Total CLA level was determined by UV spectrophotometry (233 nm). Strains selected by CLA production were cultured in presence of higher LA concentrations (100-600 µg/ml) to determine tolerance and CLA isomers produced by gaseous chromatography. Lipids were extracted by using chloroform/methanol solution (2:1, v/v), saponified with NaOH/methanol and derivatized with HCl/methanol. CLA production rate varied among strains from 16 to 55 %. The highest values were detected in Lc. Lactis, followed in turn by Lb. plantarum. In all evaluated bacteria a marked substrate inhibition effect was observed when LA concentrations higher than 400 µg/ml were used. CLA production was observed after 5 h of incubation at the different substrate concentrations. The highest CLA production was determined after 15 h of incubation approximately. Some bacteria were inhibited by higher LA concentrations, but were able to form CLA even under this condition. CLA isomer formation was strain-dependent. Some lactic acid bacteria were able to produce the c9,t11 isomer exclusively, such as Lb.  casei and Lb. plantarum, while a mixture of c9,t11 and t10,c12 isomers were produced by Lc. lactis and Lb. acidophillus. This study demonstrates that lactic acid bacteria differ in their ability to produce CLA and the type of isomer produced is strain-dependent. Bacteria selection must take into account CLA production conditions and the type of isomer formed. Lb. plantarum and Lc. lactis were selected according to CLA production rate to be added as adjunct or starter cultures for fermented dairy product manufacture. These studies are in progress in our laboratory.