Chemical Hazards Nursel Söylemez Milli · Lipid oxidation · protein oxidation · meat quality · 2 min read
Oxidation is one of the main causes of quality deterioration in meat and meat products, second only to microbial spoilage. Lipid and protein oxidation occur during processing, storage and cooking, and they affect colour, flavour, texture, nutritional value and potentially safety. Because these two processes are closely interconnected, they are increasingly studied together.
Lipid oxidation proceeds mainly through a free radical chain reaction consisting of initiation, propagation and termination steps. Unsaturated fatty acids, particularly those in membrane phospholipids, are the most susceptible substrates. Primary oxidation products, the lipid hydroperoxides, are unstable and decompose into secondary products such as aldehydes, ketones and alcohols. Compounds such as malondialdehyde and hexanal are responsible for rancid off-flavours and are commonly used as indicators of oxidation, for example through the thiobarbituric acid reactive substances (TBARS) assay. Cholesterol oxidation products are also formed and have been associated with potential health risks.
Protein oxidation involves the modification of amino acid side chains and the protein backbone by reactive oxygen species and by lipid oxidation products. Typical consequences include the formation of carbonyl compounds, the loss of thiol groups, the formation of disulphide and dityrosine cross-links, and protein fragmentation or aggregation. Protein carbonyl content is widely used as a marker of protein oxidation. These modifications can reduce water-holding capacity, alter tenderness and juiciness, impair functional properties such as gelation and emulsification, and decrease the digestibility and nutritional value of proteins.
Myoglobin oxidation is of particular importance for meat colour. The conversion of red oxymyoglobin to brown metmyoglobin reduces consumer acceptance, and lipid oxidation products can accelerate this process. Heme iron and free iron released from myoglobin act as pro-oxidants, creating a cycle in which lipid, protein and pigment oxidation reinforce one another.
Numerous factors influence oxidative stability. These include the fatty acid composition of the meat, which depends on species and animal diet, the levels of endogenous antioxidants and pro-oxidants, mechanical processes such as grinding and mixing, salt addition, cooking temperature, exposure to light and oxygen, packaging and storage temperature.
Various strategies are used to control oxidation. Dietary supplementation of animals with vitamin E and other antioxidants can improve the oxidative stability of meat. During processing, synthetic antioxidants or natural alternatives such as plant extracts, essential oils and spices rich in phenolic compounds can be added. Packaging strategies, including vacuum packaging, modified atmosphere packaging with low oxygen levels and active packaging with oxygen scavengers or antioxidant films, are also effective. Cold chain management and protection from light further limit oxidative changes.
The assessment of oxidation relies on a combination of chemical methods, spectroscopic techniques and, increasingly, mass spectrometry-based approaches that allow specific oxidation sites in proteins to be identified. A better understanding of the interaction between lipid and protein oxidation is expected to support the development of more effective strategies for preserving meat quality.