Forschungs- & Entwicklungsinformationsdienst der Gemeinschaft - CORDIS

Identification of important CLA pre-cursors in the rumen for biologically efficient enrichment of CLA in milk

Nutritional quality is becoming a major issue in food choices because of growing consumer awareness of the link between diet and health. Numerous studies have established that cis-9, trans-11 conjugated linoleic acid (CLA) has a number of potential health benefits to man. Milk and dairy products are the main source of CLA in the human diet and therefore there is a need to develop effective strategies for enhancing milk fat CLA concentrations. Cis-9, trans-11 CLA is considered to be derived from ruminal biohydrogenation of C18:2 n-6 and also through endogenous conversion of trans-11 C18:1 in the mammary gland. Trans-11 C18:1 is produced as an intermediate of C18:2 n-6 and C18:3 n-3 metabolism in the rumen. Research in this project provided essential information on the relative importance of both ruminal and endogenous CLA synthesis in the dairy cow. Measurements of milk fatty acid composition in response to post-ruminal infusions of cis-9, trans-11 CLA and trans-11 C18:1 allowed the transfer of these fatty acids into milk and bioconversion of trans-11 C18:1 to cis-9, trans-11 CLA to be calculated. It was shown that 39.9 % of cis-9, trans-11 CLA at the small intestine was transferred into milk. Post-ruminal infusions of trans-11 C18:1 increased both the concentrations of trans-11 C18:1 and cis-9, trans-11 CLA confirming that endogenous synthesis is an important source of cis-9, trans-11 CLA in milk. Moreover, 8.1 and 21.4 % of the amount of trans-11 C18:1 infused was recovered in milk as cis-9, trans-11 CLA and trans-11 C18:1, respectively. Through examining the relationship between the output of cis-9, trans-11 CLA with the sum of trans-11 C18:1 and cis-9, trans-11 CLA in milk, it was possible to show that 27:8 % of trans-11 C18:1 available to the mammary gland was bio-converted to cis-9, trans-11 CLA. Overall the relative biological value of trans-11 C18:1 produced in the rumen was shown to be equivalent to 20 % of cis-9, trans-11 CLA synthesized in the rumen. This is the first study to show that endogenous synthesis of cis-9, trans-11 CLA in the mammary gland is not appreciably altered by relatively large changes in the availablity trans-11 C18:1 and directly compare ruminal versus endogenous synthesis of cis-9, trans-11 CLA in the dairy cow. These findings are of importance in the formulation of dairy cow diets to enhance milk fat CLA content and indicate that ingredients which alter ruminal lipid metabolism causing preformed cis-9, trans-11 CLA or trans-11 C18:1 to accumulate would be effective. More research is required to identify diets or feed ingredients that alter lipid metabolism in the rumen and enhance the amounts of trans-11 C18:1 and cis-9, trans-11 CLA available for absorption. Furthermore, these findings provide further evidence to suggest that trans-11 C18:1 in milk also serves as a substrate for endogenous cis-9, trans-11 CLA synthesis in humans.

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Reported by

MTT Agrifood Research Finland
Animal Production Research
31600 Jokioinen
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