Conjugated linoleic acids biohydrogenation

Duckett, S. K., Andrae, J.G., Owens, F.N. 2002. Effect of high-oil corn or added corn oil on ruminal biohydrogenation of fatty acids and conjugated linoleic acid formation in beef steers fed finishing diets. J. Anim. Sci. 80, 3353-3360. 

Conjugated linoleic acid (CLA) is naturally present in milk, dairy products, and the meat of ruminants (1). Ruminants are the major dietary source of this fatty acid because of the unique abihty of rumen bacteria to convert linoleic acid into cis-9,trans- CLA (c9,tll-CLA) (1). This reaction is part of a process that takes place in the rumen it is called biohydrogenation and it converts linoleic acid [or, less efficiently, other 18-carbon polyunsaturated fatty acids (PUFA) with double bonds located at 9 and 12 positions] to stearic acid (1). During this process, vaccenic acid (tl 1-18 1) is formed. This acid can be converted to CLA in all organisms that possess A9-desaturase (2). 

In the mid-1900s there was increased interest in the process of biohydrogenation, which occurs in the rumen, and is responsible for the formation of both the trans monoenoic acids and the conjugated linoleic acids found in the rumen and milk. 

The process of linoleic acid biohydrogenation is depicted in Fig. 1.1. Linoleic acid from plant lipids is first acted upon by an isomerase of bacterial origin that creates new geometric and positional isomers, including conjugated dienes. However, no hydrogen addition occurs at this step and the same number of double bonds is maintained within the acyl chain. Additional transformations may follow where double bonds are eliminated from the fatty acyl chain via the action of mio-obial reductases. Reductase action may proceed until the fatty acyl chain is fully saturated. 

Shingfield, K.J., Ahvenjarvi, S., Toivonen, V., Arola, A., Huhtanen, P., and Griinari, J.M. (2002) Fish Oil Inhibits the Biohydrogenation of Fatty Acids in the Rumen Causing an Increase in Milk frans-Octadecenoic and Conjugated Linoleic Acid Content, J. Dairy Sci. 85 (Suppl. 1), 143 (Abstr.). 

Keywords Ruminal biohydrogenation Conjugated linoleic acid Phytochemicals... 

Unpublished results of own experiments also did not confirmed the potential of essential oils to modulate rumen biohydrogenation. None of used essential oils originating from Eugenia caryophyllata, Abies sibirica or Vanilla planifolia improve concentration of conjugated linoleic acid isomers in the rumen and milk of dairy cows. 

The term conjugated linoleic add (CLA) refers to a mixture of positional and geometric isomers of linoleic add with a conjugated double bond system milk fat can contain over 20 different isomers of CLA. CLA isomers are produced as transient intermediates in the rumen biohydrogenation of unsaturated fatty acids consumed in the diet. However, cis-9, trans-11 CLA, known as rumenic acid (RA), is the predominant isomer (up to 90% of total) because it is produced mainly by endogenous synthesis from vaccenic acid (VA). VA is typically the major biohydrogenation intermediate produced in the rumen and it is converted to RA by A9-desaturase in the mammary gland and other tissues. 

CLA refers to a mixture of positional and geometric isomers of linoleic acid (cis-9, cis-12 octadecadienoic acid) with a conjugated double bond system. The structure of two CLA isomers is contrasted with linoleic and vaccenic acids in Figure 3.1. The presence of CLA isomers in ruminant fat is related to the biohydrogenation of polyunsaturated fatty acids (PUFAs) in the rumen. Ruminant fats are relatively more saturated than most plant oils and this is also a consequence of biohydrogenation of dietary PUFAs by rumen bacteria. Increases in saturated fatty acids are considered undesirable, but consumption of CLA has been shown to be associated with many health benefits, and food products derived from ruminants are the major dietary source of CLA for humans. The interest in health benefits of CLA has its genesis in the research by Pariza and associates who first demonstrated that... 

Fatty acids with two or more conjugated double bonds are found in some plants and animals. In tissues of ruminant animals (and, hence, in meat and dairy products), fatty acids with conjugated diene system were detected as intermediates or by-products in the biohydrogenation of linoleic acid by microorganisms in the rumen. The main isomer, 9-cis, ll-fran -octadecadienoic acid, may account for up to 1% of the total fatty acids of milk fat. 9-cis, ll-fran5-15-cw-octadecatrienoic acid, derived from a-linolenic acid, is present in ruminant tissues only in trace levels. This fatty acid has been shown to have several medical properties, especially anti-cancer and anti-atherosclerosis effects. 

Bessa, R. J. B., Santos-Silva, J., Ribeiro, J. M. R., Portugal, A. V. (2000). Reticulo-rumen biohydrogenation and the enrichment of ruminant edible products with linoleic acid conjugated isomers. Livestock Production Science, 63, 201-211. 

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