Fatty acids biohydrogenation

Keywords Essentials oils Rumen miCToorganisms fatty acids Biohydrogenation... 

Garton etal, (10) demonstrated that rumen microbial suspensions could hydrolyze triglycerides. It was later established that virtually any ester link between fatty acid and glycerol was subject to hydrolytic cleavage by rumen organisms (7 7). As aconsequence of the activity of the lipolytic enzymes, high levels of free fatty acids are produced in the rumen. The unsaturated fatty acids are substrates in biohydrogenation reactions. 

The first step in the biohydrogenation of linoleic acid to stearic acid by the mmen microorganism, Butyrivibrio fibrisolvens, is the formation of the cis-9, trans-11 CLA isomer (Figure 1). This reaction is catalyzed by a membrane-bound enzyme, linoleate isomerase, which acts only on fatty acids possessing cis double bonds in positions and and a free carboxyl group (72). 

It is not certain that the presence of CLA in tissue lipids is due entirely to the production of cis-9, trans-11 as an intermediate during the biohydrogenation of linoleic acid in the rumen. However, the amount of CLA in milk (7 J) and butter (14) is positively correlated to the level of dietary linoleic acid. Some long chain fatty acid intermediates reach the small intestine and are normally absorbed and deposited into adipose tissue (75). There is seasonal variation in CLA content of milk, with the highest values occurring usually in summer (76). 

Hay and Morrison (1970) identified the monoenoic positional and geometric isomers in milk fat and determined the amounts of each total acid class and percentage of trans isomers. The geometric and positional isomers of the monoenes are primarily the result of biohydrogenation of polyunsaturated fatty acids in the rumen. Stearate is also produced, and cis-9-18 l accounts for most of the monoenes. The several positional isomers in trans 16 1 and 18 1 are due to the positional isomerization of double bonds which accompanies elaidinization. 

Because of animal biohydrogenation, the content of polyunsaturated acids in milk is low, currently reported at about 5% (Smith et al 1978), and is associated mostly with the phospholipids. While quantitatively unimportant, these acids are the most susceptible targets of oxidation and provide the essential fatty acids (EFA), mostly cis, cis-9, 12-18 2. 

Gonthier, C., Mustafa, A.F., Berthiaume, R., Petit, H.V., and Ouellet, D.R. 2004a. Feeding micro-ionized and extruded flaxseed to dairy cows Effects on digestion and ruminal biohydrogenation of long-chain fatty acids. Can. J. Anim. Sci. 84, 705-711. 

Petit, H.V., Tremblay, G.F., Tremblay, E., and Nadeau, P. 2002. Ruminal biohydrogenation of fatty acids, protein degradability, and dry matter digestibility of flaxseed treated with different sugar and heat combinations. Can. J. Anim. Sci. 82, 241-250. 

Figure 4. Developments of cumulative hydrogen yield, pH value, volatile fatty acids (VFAs) and alcohols in the batch reactor during the conversion of the substrate to biohydrogen under the pretreated condition of microwave heating...

Cw-polyenoic acids are present at low concentrations in milk fat, because of the biohydrogenation reactions that take place in the rumen. These acids are comprised almost exclusively of linoleic acid (9c, 12c-18 2), about 1.2 to 1.7% and a-linolenic acid (9c, 12c, 15c-18 3), about 0.9 to 1.2% (Table 1.2). These two fatty acids are essential fatty acids they cannot be synthesised within the body and must be supplied by the diet. In recent times, the usage of the term essential has been extended to include derivatives of these fatty acids, which are not synthesised in significant quantities (e.g., eicosapentaenoic acid, 20 5 and docosahexaenoic acid, 22 6). The proportion of a-linolenic acid appears to be affected by the cow s diet the concentration is higher in milk from pasture-fed cows than in milk from barn-fed cows (Hebeisen et al., 1993 Wolff et al., 1995). In the case of linoleic... 

The presence of Qg tram-fatty acids in milk fat is the result of incomplete biohydrogenation of the unsaturated dietary lipids in the rumen. These fatty acids have attracted attention because of their adverse nutritional affects. Clinical trials have shown that traus-octadecenoic acids, relative to the cis isomer, can increase the LDL-cholesterol and decrease the HDL-cholesterol, thus, producing an unfavourable affect on the LDL HDL ratio (Mensink and Katan, 1993). 

The fatty acids in milk fat are derived from two sources, de novo synthesis of fatty acids in the mammary gland and plasma lipids (see Pal-quist, Chapter 2). De novo synthesis generally involves short-chain and medium-chain fatty acids and some 16 0. The proportions of various fatty acids depend on the specific balance between enzymatic chain elongation and chain termination. The plasma lipids are derived from the diet and also from storage in the body tissues. For non-ruminants, the diet has a large influence on the fatty acid composition but for ruminants, biohydrogenation in the rumen results in much less impact of diet on the final fatty acids absorbed into the bloodstream. 

Ruminant milk fat is of unique composition among terrestrial mammals, due to its great diversity of component fatty acids. The diversity arises from the effects of ruminal biohydrogenation on dietary unsaturated fatty acids and the range of fatty acids synthesized de novo in the mammary gland. 

Future advances in the science of milk fat and nutrition will come from focusing on the unique biological properties of minor milk fatty acids arising from ruminal biohydrogenation and possibly some of de novo mammary origin. 

Incorporation of dietary unsaturated fat into milk fat by ruminants is low because of the efficient ruminal biohydrogenation process (Jenkins, 1993). Nevertheless, dietary fatty acids have profound effects on milk fat composition that have led to a prodigious amount of literature in the past 20 years (for reviews see Sutton, 1989 Grummer, 1991 Palmquist et al., 1993 Kennedy, 1996 Mansbridge and Blake, 1997 Chilliard et al., 2000, 2001). 

Several other procedures have been developed to protect unsaturated fatty acids from ruminal biohydrogenation. Of these, only the amide derivative has extensive research documentation (Jenkins, 1998, 1999), but has not been applied commercially. Often, calcium soaps of palm oil or canola fatty acids are referred to as protected. These are not protected from ruminal biohydrogenation (Table 2.2), but rather are ruminally inert with regard to their effects on the rumen microbial population. 

Shingfield, K.J., Ahvenjarvi, S., Toivonen, V., Arola, A., Nurmela, K.V.V., Huhtanen, P., Griinari, J.M. 2003. Effect of dietary fish oil on biohydrogenation of fatty acids and milk fatty acid content in cows. Anim. Sci. 77, 165-179. 

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... 

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