| The role of dietary factors in the prevention of cancer is under intensive investigation. Evidence from the studies suggests that conjugated linoleic acid (CLA) originating mainly from dairy products can efficiently prevent carcinogenesis. It has been observed however, that the concentration of CLA in natural products is not sufficient to play such a role. Hence, our research aimed to enhance CLA levels in dairy products by providing insight into the mechanism of CLA production.; CLA levels in milkfat could be enhanced by urea complexation. Milk fat was hydrolyzed and crystallized with urea. Long-chain unsaturated fatty acids, including CLA, were concentrated and the highest CLA level was obtained (2.5-fold increase) by the first crystallization with a 2:1 urea/fatty acid ratio. The C18:1/C18:0 fatty acid ratio was also increased up to 25-fold.; We also studied the factors affecting CLA production by Butyrivibrio fibrisolvens A38. The organism did not produce significant amounts of CLA until the LA concentration was high, biohydrogenation was arrested, and the cell density declined all of which indicated that the flow of CLA from the rumen may be due to LA-dependent bacterial lysis. Extended research was performed on mixed rumen bacteria from cattle fed different diets. Mixed rumen bacteria from cattle fed 90% grain were more active in biohydrogenation and trans-10, cis-12 CLA production than from cattle fed a hay diet. A bacterium isolated from a mixed rumen culture that was enriched in medium containing lactic acid produced 6 times more trans-10, cis-12 CLA than cis-9, trans-11 CLA. This organism was identified as Megasphaera elsdenii YJ-4 by 16S-rDNA assay.; Lactic acid bacteria were screened for CLA producing ability using sunflower oil as a substrate. Among them, Lactococcus lactis IO1 was the best. The addition of dry powder and glucose in the culture increased the CLA concentration, proportionally to bacterial cell growth. Elevated bacterial cell number accelerated milk fermentation but the low pH created during the fermentation decreased CLA concentration. The addition of potassium phosphate buffer (50 mM) maintained the pH at neutral for a longer period of time and increased the CLA content up to 2.3 fold. |
