Rancidity or oxidation in food

Rancidity or oxidative rancidity is mainly responsible for the deterioration of foods rich in lipids, such as meat, as it results in undesirable changes in the color, flavor, aroma and consistency of the food. Lipid oxidation involves an extremely complex series of chemical reactions that occur between atmospheric oxygen and unsaturated fatty acids in lipids.

Fat is naturally present in meat and can be added to some formulations, either homogenized, such as sausages, mortadella or emulsified cooked sausages, or in larger pieces, such as salami. But both the fat present in meat and that added to formulations undergo oxidation processes.

The reaction of oxygen with lipids is the most common process that leads to oxidation, a process called self-oxidation. Oxidation forms volatile aromatic compounds that are perceived as off-flavours. You off-flavors detected depend on the fatty acid composition and degree of oxidation, although oxidation conditions can also affect the volatile compounds produced and the sensory properties. Aldehydes often contribute to the off-flavors that develop during lipid oxidation.

In addition to the rancid aroma, lipid oxidation can cause changes in color due to reactions with pigments, especially carotenoids, and reactive intermediates, called free radicals, which are formed during lipid oxidation. Free radicals can also lead to a reduction in nutritional quality, as they react with vitamins.

Is it important to control light in meat products?

Yes, the call photo-oxidation, which occurs mainly in products that will undergo long periods of maturation, curing or display for sale. Photo-oxidation, in this case the excitation of lipids or the excitation of oxygen, can occur in the presence of light and sensitizers. Photo-oxidation is characterized by the transfer of hydrogen atom or the transfer of electrons, producing free radicals or free radical ions. Autoxidation can then proceed.

Do antioxidants help prevent rancidity?

Antioxidants in foods can be defined as any substance capable of postponing, delaying or preventing the development of rancid flavor or other aromatic deteriorations in foods, resulting from oxidation. Antioxidants slow the development of off-flavors.

Antioxidants can inhibit or delay oxidation by scavenging free radicals (scavenging action), in which case it is described as a primary antioxidant or by a mechanism that does not involve direct free radical scavenging activity, in which case the compound is a secondary antioxidant. .

Secondary antioxidants act through a variety of mechanisms, including binding metal ions, scavenging/scavenging oxygen, converting hydroperoxides to nonradical species, absorbing UV radiation, or deactivating singlet oxygen. Typically, secondary antioxidants only exhibit antioxidant activity when a second, smaller component is present. This can be observed in the case of sequestering agents, such as citric acid, which are effective only in the presence of metal ions, and in the case of reducing agents, such as ascorbic acid, which are effective in the presence of tocopherols or other primary antioxidants.

What factors influence oxidation in foods?

1. Amount of oxygen present, since oxidative rancidity does not occur in the absence of O²;
2. Fat composition, that is, the type of unsaturated fatty acid and the degree of saturation have a significant influence on oxidation (linoleic and linolenic acids oxidize 64 and 100 times faster than oleic acid, respectively);
3. Exposure to light, which accelerates oxidation reactions and, therefore, as far as possible, its direct impact on foods susceptible to oxidation should be avoided;
4. Storage temperature, the higher the temperature, the greater the speed at which the reaction develops. With every 10ºC increase in temperature, the reaction of oxygen with unsaturated fat doubles.
5. Presence of catalysts, called pro-oxidants, which accelerate the oxidation reaction (metals and damyoglobin heme group);
6. Water activity (aw) of foods, with the presence of free water increasing the catalytic activity of metals, therefore, the risk of oxidation increases as the water activity increases

References
ADDITIVES $ INGREDIENTS – insumos.com.br/aditivos_e_ingredientes/materias/209.pdf
FOOD INGREDIENTS BRAZIL Nº 29 – 2014 – loja-fi.com.br/upload_arquivos/201606/2016060396904001464897555.pdf