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Institute of Grassland and Environmental Research
The fatty acid composition of ruminant products, has become increasingly important in recent years, because ofconcerns regarding the fatty acid composition of dietary fat for humans linked to cardiovascular and other lifestylediseases. As a result, methods of altering the fatty acid composition of these products are of great interest. The Department of Health has recommended an increase in the intake of unsaturated fatty acids, and in particular theomega-3 polyunsaturated fatty acids (PUFA) found in fish because they are thought to be beneficial to human health, especially in reducing the risks of coronary heart disease. Green plants are the primary source of omega-3 fatty acids. Fish, which derive their omega-3 fatty acids from marine plankton, are used extensively in concentrated animal feeds, but forage plants would represent a more natural and environmentally sustainable source of these fatty acids.
At IGER, we have investigated the potential to exploit this source of omega-3 fatty acids. Fresh grass contains a high proportion (50-75 %) of total fatty acids as the omega-3 a-linolenic acid (C18:3 n-3) and this varies with plant factors such as stage of maturity and light treatments. There are approximately 10 major fatty acids in grasses. These can be used to define fatty acid profiles or `fingerprints' which are distinctive to particular species and in broad agreement with other evidence about how closely one species is related to others. This confirms that the fatty acid composition of grasses is under considerable genetic control and highlights the potential to select for grasses with higher levels or altered types of fatty acids.
Fatty Acids and Beef
We have investigated the opportunity to manipulate the fatty acid composition of beef, and the resulting effects on meat quality, by feeding animals on feed sources which are rich in omega-3 fatty acids. Animals were fed on grass silage plus one of four concentrates .for 120 days, megalac (experimental control, rich in saturated palmitic acid, C16:0), whole linseed (a-linolenic acid, C18:3 n-3), fish oil (eicosapentaenoic acid, C20:5 n-3 and docosahexaenoic acid, C22:6 n-3) and, finally, linseed plus fish oil in equal amounts. In comparison to the control,feeding linseed doubled the concentration of linolenic acid and significantly enhanced eicosapentaenoic acid,C20:5 n-3 in the meat (see figure). This is particularly interesting because it suggests that synthesis of this longer chain fatty acid, C20:5 n-3, may be encouraged by feeding animals on feed sources rich in a-linolenic acid. Feeding fish oil doubled the levels of C20:5 n-3 and C22:6 n-3, whilst the mix gave results intermediate between feeding linseed and fish oil. This work clearly demonstrates that quality feeds can be translated into quality meat.
Effects of fatty acids on meat appearance and flavour
Increasing the levels of PUFA in meat may sometimes lead to accelerated colour changes from red to brown, due to oxidative changes. Muscle samples from animals fed on fish oil showed higher oxidative changes during retail display and faster colour deterioration. However, animals fed on a linseed supplemented diet produced beef with as long a shelf-life as the controls. The level of anti-oxidants in the muscle play a key role in limiting the extent of these oxidative changes and hence feeding high levels of anti-oxidants are important when manipulating the PUFA content.
We know that the fatty acid composition of muscle lipids has important consequences for meat flavour, because lipid degradation products such as aldehydes, participate in the flavour forming reactions which occur during cooking. In this study, the high levels of long chain C-20 and C-22 PUFA from fish oils produced the greatest oxidative lipid changes in meat, and this coincided with generally negative comments on odour and flavour from a taste panel. However, taste and appearance were good in meat derived from the linseed diet, with a high concentration of a-linolenic acid and medium levels of C-20 and C-22 PUFA. Other studies have suggested that the UK consumer prefers grass-fed to concentrate fed beef. Since grass contains high levels of a-linolenic and normal concentrates do not, this suggests that the oxidation reactions in meat resulting from a-linolenic are not deleterious to taste. These studies are now progressing to examine ways of enhancing the uptake of omega-3PUFA from grass into beef, and to study the subsequent effects on meat quality., with the objective of producing healthy beef with enhanced flavour characteristics.
This work is being carried out in collaboration with Professor Jeff Wood and his team at the University of Bristol.