ORIGINAL ARTICLE Optimization of a reconstituted skim milk based medium for enhanced CLA production by bifidobacteria A.A. Hennessy 1,2 , R.P. Ross 1,3 , R. Devery 2 and C. Stanton 1,3 1 TEAGASC, Biotechnology Centre, Moorepark Food Research Centre, Fermoy, Co. Cork, Ireland 2 National Institute for Cellular Biotechnology, Dublin City University, Dublin, Ireland 3 Alimentary Pharmabiotic Centre, Cork, Ireland Introduction Conjugated linoleic acids (CLA) have been reported to exert health benefits, including prevention and regulation of a number of human medical conditions such as cancer, cardiovascular disease, diabetes, obesity and bone disor- ders as well as antioxidative and growth promoting prop- erties (Roche et al. 2001; Belury 2002; Wahle et al. 2004; Beppu et al. 2006; Bhattacharya et al. 2006). These bio- genic fatty acids exist naturally as a mixture of positional and geometric conjugated isomers of linoleic acid (C 18:2 c9, c12 octadecadienoic acid), of which the cis-9, trans-11 (c9, t11), trans-9, trans-11 (t9, t11) and trans-10, cis-12 (t10, c12) isomers have been the most extensively studied. The c9, t11 CLA isomer is the most common form found in nature and is primarily associated with ruminant fats. Its presence in ruminant fat is a result of the microbial biohydrogenation of dietary linoleic and linolenic acids to stearic acid in the rumen via the action of the enzyme linoleic acid isomerase (Kepler et al. 1966) or through the endogenous conversion of vaccenic acid to CLA via the action of the enzyme D 9 -desaturase (Corl et al. 2001; Griinari et al., 2000). These processes lead to CLA con- centrations of 0Æ2–3Æ7% in bovine milk fat (Sebedio et al. 1997). However, despite the high concentration of CLA found in dairy products, it is estimated that our current dietary intake is much lower than that needed for CLA to exert its health promoting activities (Ip et al. 1994), and as a result strategies designed to increase dietary CLA intake have received increased attention. In recent years, a number of dairy cultures and probi- otic strains with the ability to convert linoleic acid to the c9, t11 and t9, t11 CLA isomers have been identified, including a number of bifidobacteria (Coakley et al. 2003; Keywords bifidobacteria, conjugated linoleic acid, fermentation, milk. Correspondence Cathesine Stanton, Moorepark Food Research Centre, Teagasc, Fermoy, Co. Cork, Ireland. E-mail: catherine.stanton@teagasc.ie 2007 ⁄ 1227: received 2 August 2008, revised 27 August 2008 and accepted 30 September 2008 doi:10.1111/j.1365-2672.2008.04098.x Abstract Aims: To determine the effect of a range of supplements on the bioconversion of linoleic acid to conjugated linoleic acid (CLA) by Bifidobacterium breve NCIMB 702258 in reconstituted skim milk (RSM). Results: Seven supplements (yeast extract, casein hydrolysate, tryptone, l-cyste- ine hydrochloride, sodium acetate, sodium butyrate and sodium propionate) were identified as increasing the bioconversion of linoleic acid to c9, t11 CLA. Using these supplements, the percentage bioconversion of linoleic acid (0Æ35 mg ml )l ) to the c9, t11 CLA isomer was elevated from 15Æ5±1Æ1% in 20% RSM (w ⁄ v) to 48Æ1±2Æ2% in the supplemented RSM. Through additional supplementation of 20 mg m1 )1 inulin and optimization of inoculum and linoleic acid concentration, the percentage bioconversion to c9, t11 CLA was increased to 55Æ0+3Æ2%. Conclusions: Through supplementation, the concentration of CLA produced by bifidobacteria in RSM can be increased to levels comparable to those observed in the synthetic medium cys-MRS. Significance and Impact of the Study: The impact of 22 supplements on the production of the c9, t11 CLA isomer by the strain B. breve NCIMB 702258 in milk has been determined. The results provide an understanding of the factors, which influence CLA production by bifidobacteria in RSM. Journal of Applied Microbiology ISSN 1364-5072 ª 2009 The Authors Journal compilation ª 2009 The Society for Applied Microbiology, Journal of Applied Microbiology 106 (2009) 1315–1327 1315