Over the years, the animal nutrition industry has been constantly evolving. In the urban context, it was necessary to set guidelines to achieve and maintain the established production goals and, as early as the 20th century, globalization brought the need to increase competitiveness by incorporating the use of additives.
The main additives used to limit the deterioration caused by lipid oxidation, increasing the useful life of the food, were the antioxidants. These substances prevent an oxidative process that is carried out by autoxidation or hydrolysis.
Autoxidation or oxidative rancidity modifies the organoleptic qualities and reduces the nutritional value of fats. Sometimes it generates toxic compounds as a result of exposure to oxygen.
It is a process in which oxygen is added to the alpha carbon of the double bond, forming a hydroperoxide, more historically known as peroxides. It is completely irreversible but can be delayed thanks to the addition of antioxidants, vacuum packaging or packaging in an inert gas atmosphere, proper storage or the use of appropriate packaging.
The oxidation of fatty acids is divided into three phases:
- Initiation created by external energy that produces active free radicals
- Propagation: free radicals form peroxide radicals that attack fatty acids. These peroxides later decompose into highly volatile by-products that cause bad odor.
- Termination: the reactive compounds interact with each other by decreasing the amount of peroxide radicals.
Hydrolysis or hydrolytic rancidity is due to the presence of moisture, catalytic agents or lipases. As a result of this process, glycerol is released.
Methyl ketones, lactones and their esters can be formed by hydrolytic reactions. It is even believed that hydrolytic reactions, including lipolysis, give rise to free fatty acids so that they can progress more rapidly towards self-oxidation.
Antioxidants exist naturally but are easily lost during the processing or storage of products, so it is often necessary to add exogenous antioxidants.
In general, the selection of antioxidants depends on the products, compatibility and regulatory guidelines. Occasionally, synergistic mixtures of antioxidants are used for a more effective result.
Antioxidants are classified into two large groups: synthetic and natural.
Synthetic antioxidants are obtained artificially. The most used in animal nutrition are:
- BHA and BHT: they are the most used synthetic antioxidants in the sector. They are very effective in animal fats and to a lesser extent in fats and vegetable oils. However, they are extremely volatile at high temperatures.
3-tert-butyl-4-hydroxyanisole represents 90% of commercial BHA, and can stabilize a free radical by sequestering it, thus avoiding subsequent free radical reactions.
BHT is used in conjunction with BHA for greater efficiency since it is not as thermally stable as the BHA.
Both have a slight phenolic smell and can affect the palatability of the product.
- TBHQ: is an aromatic compound derived from hydroquinone, more effective in vegetable oils than BHA and BHT and useful in the prevention of oxidation in thermal processes. It shows a good synergy with citric acid, BHA and BHT.
- Propyl gallate: it is a white crystalline powder that is used in foods in which the use of other fat-soluble synthetic antioxidants is not adequate.
- Ethoxyquin: it is an antioxidant derived from quinoleins that oxidizes easily, forming ethoxyquin nitroxide. Its metabolism generates unsafe substances, so in June 2017 the authorization of ethoxyquin as a feed additive in the European Union was temporarily suspended.
Natural antioxidants are produced by the organisms themselves to protect lipids. Therefore, the acceptance requirements are lower than in the case of synthetic antioxidants. The most important are:
- Tocopherols: are fat-soluble antioxidants that are very frequently found in plants. They are formed by 4 isomers (alpha, beta, gamma and delta) with different antioxidant capacity and vitaminic power.Tocopherols and synthetic antioxidants of phenolic origin prevent the oxidation of lipids by stopping chain reactions of free radicals. However, tocopherols are less volatile than synthetic antioxidants, which allows them to stay more effectively in the final product.Thanks to the structure of the tocopherols, they have a high solubility in lipid medium that allows to protect the food with greater efficiency.It is a safe antioxidant, effective and easy to incorporate into the productive process. In addition, its use is allowed in all countries of the world.
- Rosemary Extract: it is an antioxidant extracted from the rosemary rosemary and is very functional in animal fats. It is composed of phenolic antioxidants such as Rosmarinic Acid, Camosol and Carnosidic Acid.
- Green tea extract: obtained from the leaves of Camellia sinensis and presents polyphenol antioxidants. It is usually used as a complement to the activity of vitamins E and C in animal feed.
- Ascorbic acid and its derivatives: can occur in the form of vitamin C, in its water-soluble salts or liposoluble esters. Its antioxidant activity is due to interactions with tocopherols, citric acid and certain synthetic antioxidants.
Regarding its mechanism of action, two types of antioxidants are considered: primary and secondary.
- The primary antioxidants break the oxidation reaction by adding hydrogen and generating more stable radicals. The main antioxidants of this type are: phenolic antioxidants, breakthrough phenols and eventual primary.
- The secondary antioxidants inhibit peroxidation mainly by metal chelation, regeneration of primary antioxidants, decomposition of hydroperoxides and elimination of oxygen. The main types are: antioxidants oxygen receptors, chelating agents, secondary and eventual antioxidants.
Another type of classification is according to their properties, so they are classified as technological and physiological antioxidants.
- The technological antioxidants control the lipoperoxidation processes of the raw materials with greater energy intake and palatability. Usually synthetic molecules are used that slow down the oxidation of fats but do not exert any effect on the physiological functions. However, natural antioxidants containing alpha-tocopherol are also used, which provides more benefits than the technological ones.
- The physiological antioxidants are important antioxidants against the reduction of oxidative stress resulting from the imbalance between the production of free radicals and the antioxidant action. There are numerous factors that can increase the production of free radicals and / or weaken the antioxidant system. Therefore, antioxidant supplementation provides both in-vivo and post-mortem benefits through the prevention of oxidative stress.
Therefore, when choosing the most suitable antioxidant for each product, they will take into account that they meet the following requirements:
- Safe and without negative effects for animal health
- Effective at low concentrations
- Effective to extend the useful life of products
- Able to reduce the use of other antioxidant nutrients in the diet