Premature changes cause meat to be rejected by consumers and consigned to the 'offers' section of the meat cabinet. The colour change from bright red to brown in beef (pink to grey in pork) is due to oxidation of the muscle pigment myoglobin. Unsaturated (soft) fats also oxidise, leading to the production of compounds which have 'off' odours and flavours.
In the early stages of fat oxidation, 'free radicals' are produced which can promote other oxidation changes affecting colour and the ability of meat to retain moisture. When meat is minced, the cell walls are ruptured and oxidation proceeds more quickly than in fresh meat. Addition of salt, longer ageing, freezing and thawing and exposure to ultraviolet light also speed up oxidation and reduce shelf-life. There is therefore huge interest in incorporating antioxidants into meat to inhibit or slow oxidation and extend shelf-life.
Vitamin E, an effective antioxidant, is found at high levels in grass-fed beef because it is present in grass. Manufactured vitamin E can be added to diets and is taken up into the animal's tissues during growth. Antioxidants can also be incorporated at the processing stage into mince, sausages and pâtés. Recent studies have concentrated on replacing synthetic antioxidants such as BHT (butylated hydroxytoluene) with natural plant extracts. These include extracts of rosemary, thyme and other herbs and the leaves and fruits of various plants. Some may also have antimicrobial effects. They can be classified as 'nutraceuticals', increasing the appeal of meat to health-conscious consumers as well as extending shelf-life.