Chapter 22 - Fatty acids in meat: effects on nutritional value and meat quality

Abstract

Fatty acids are increasingly seen as important metabolic compounds. Apart from their role in energy provision, they are also involved in cell signaling and gene expression. Their different melting points (−44 to +75°C) regulate the fluidity of muscle membranes and adipose tissue deposits, which is important in cell signaling, fluidity being maintained through changes in enzyme activity. A key enzyme is stearoyl coA desaturase, which converts saturated fatty acids (SFAs) to monounsaturated fatty acids (MUFA) and whose activity is increased by SFA and inhibited by polyunsaturated fatty acids (PUFA). The four main species used for meat production have different melting points in adipose tissue: the ruminants beef and sheep have high melting points due to a high ratio of SFA to PUFA, and pork and chicken have low melting points due to high percentages of PUFA, especially the n-6 fatty acid linoleic acid (LA), which is particularly high in chicken. This fatty acid is common in diets and is incorporated unchanged into tissues in pork and chicken but is hydrogenated in the rumen in beef and sheep. The rate of incorporation into tissues is higher than for the main n-3 PUFA, α-linolenic acid (ALA). Both LA and ALA form long-chain derivatives, which produce eicosanoids involved in the control of inflammation in the body. Those from ALA are less inflammatory than those from LA so medical advice is to increase n-3 PUFA levels in diets to benefit cardiovascular health. Many studies have explored ways of increasing n-3 PUFA levels in meat so it can be labeled and sold as a “source” of n-3 PUFA. In pork and chicken, ALA can be raised to “source” levels using linseed/flaxseed. In all the species, the long-chain n-3 PUFA can be increased to “source” levels using marine algae, but oxidation of these relatively unstable fatty acids can occur during processing, leading to off-flavors in cooked meat, even when tissue levels of the antioxidant vitamin E are raised by adding “supranutritional” levels to the diet. Grass feeding in beef and sheep raises levels of n-3 PUFA in muscle and rumenic acid in adipose tissue compared with concentrate (grain) feeding. The different flavors produced on cooking may be liked or disliked according to previous experience.