Effects of fatty acids on meat quality: a review
Introduction
There has been an increased interest in recent years in ways to manipulate the fatty acid composition of meat. This is because meat is seen to be a major source of fat in the diet and especially of saturated fatty acids, which have been implicated in diseases associated with modern life, especially in developed countries. These include various cancers and especially coronary heart disease. In the UK, the Department of Health (1994) recommended that fat intake be reduced to 30% of total energy intake (from about 40%) with a figure of 10% of energy intake for saturated fatty acids (from 15%). At the same time, the recommended ratio of polyunsaturated fatty acids (PUFA) to saturated fatty acids (P:S) should be increased to above 0.4. Since some meats naturally have a P:S ratio of around 0.1, meat has been implicated in causing the imbalanced fatty acid intake of today's consumers. For this reason, ways to improve the P:S ratio during meat production are required. More recently, nutritionists have focussed on the type of PUFA and the balance in the diet between n-3 PUFA formed from α-linolenic acid (18:3) and n-6 PUFA formed from linoleic acid (18:2) (Williams, 2000). The ratio of n-6:n-3 PUFA is also a risk factor in cancers and coronary heart disease, especially the formation of blood clots leading to a heart attack (Enser, 2001). The recommendation is for a ratio of less than 4 and again some meats are higher than this. As with the P:S ratio, meats can be manipulated towards a more favourable n-6:n-3 ratio.
The increasing awareness of the need for diets to contain higher levels of n-3 PUFA has focused on the importance of meat as a natural supplier of these to the diet. The ratio of n-6:n-3 PUFA is particularly beneficial (low) in ruminant meats, especially from animals that have consumed grass which contains high levels of 18:3. Ruminants also naturally produce conjugated linoleic acids (CLAs) which may have a range of nutritional benefits in the diet (Enser, 2001).
Fatty acids are involved in various “technological” aspects of meat quality. Because they have very different melting points, variation in fatty acid composition has an important effect on firmness or softness of the fat in meat, especially the subcutaneous and intermuscular (carcass fats) but also the intramuscular (marbling) fat. Groups of fat cells containing solidified fat with a high melting point appear whiter than when liquid fat with a lower melting point is present, so fat colour is another aspect of quality affected by fatty acids. The ability of unsaturated fatty acids, especially those with more than two double bonds, to rapidly oxidise, is important in regulating the shelf life of meat (rancidity and colour deterioration). However, this propensity to oxidise is important in flavour development during cooking.
The aim of this article is to summarise the main effects of fatty acid composition on meat quality and to review recent work showing the effects on meat quality of changes in fatty acid composition achieved during production.
Section snippets
Fatty acid composition of meat
A survey conducted by Enser, Hallett, Hewett, Fursey, and Wood (1996) illustrated the differences in fatty acid composition and content between beef, lamb and pork. Fifty loin steaks or chops from each species were purchased from four supermarkets to represent the meat on sale to the public (Table 1). The total fat content of the steaks (obtained by dissection) was highest in lamb, probably because of a lower level of fat trimming during butchery. The total fatty acid composition of the
Components of meat quality
The components of technological meat quality influenced by fatty acids are fat tissue firmness (hardness), shelf life (lipid and pigment oxidation) and flavour. Although there have been suggestions that dietary fatty acids influence tenderness and juiciness, these are more likely to be affected by the total amount of fatty acids rather than individual ones. The effect of fatty acids on firmness is due to the different melting points of the fatty acids in meat. In the 18C fatty acid series,
Acknowledgements
We are grateful to our collaborators in providing many of the results presented here, including Institute of Grassland and Environmental Research, Harper Adams University College and University of Reading. Funding was provided by Department for Environment, Food and Rural Affairs (DEFRA), Meat and Livestock Commission, ABN Ltd, JSR Farms Ltd, Tesco Stores Ltd, Roche Products Ltd, International Fishmeal and Oil Manufacturers Association and Southern Counties Fresh Foods Ltd. We gratefully
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