VEGETABLE OIL OXIDATION PROCESS AND TECHNOLOGIES FOR ITS PREVENTION

ABSTRACT

Under the influence of oxygen in the air, various oxidation derivatives appear on vegetable oils. Most of them dramatically change the organoleptic and technological properties of oil. Oils that have begun to oxidize lose their stability during further storage and cause problems in processing.

АННОТАЦИЯ

Под действием кислорода воздуха на растительных маслах появляются различные производные окисления. Большинство из них резко меняют органолептические и технологические свойства масла. Масла, начавшие окисляться, теряют стабильность при дальнейшем хранении и вызывают проблемы при переработке.

Keywords: Oxidation, peretherification, radical, ketones, triglycerides, refining and deodorization.

Ключевые слова: Окисление, переэтерификация, радикал, кетоны, триглицериды, очистка и дезодорация.

The President of the Republic of Uzbekistan, Sh. Mirziyoev, in his Address to the members of the «OliyMajlis» Senate and the Legislative Chamber on the results of 2019, stated that the requirements for quality in the production of products will increase, and set a number of tasks for improving the health of the population and raising the standard of living. .

In the Action Strategy for the further development of the Republic of Uzbekistan, the tasks of "Development of agriculture, use of local raw material resources and creation of technologies for their processing" are defined.

Industrially produced vegetable oils are a complex mixture of triglycerides, compounds and non-fatty substances.

The presence of plant tissue particles, moisture and other non-oily substances in the composition reduces the quality and nutritional value of vegetable oils.

Today, as a result of research carried out by local and foreign researchers, lipids are not only effective energy reserves with high satiety, but also metabolically active substances depending on the balance of complex physiological active substances in the fatty acid content of edible oil.

Oxidation derivatives of different levels appear on vegetable oils under the influence of oxygen in the air. Most of them dramatically change the organoleptic and technological properties of oil. Oils that have begun to oxidize lose their stability during further storage and cause problems in processing.

The main reason for our attention to this issue in the analysis is that any impact on vegetable oils causes their physico-chemical changes. In particular, it is desirable that the improper conduct of the processes of pre-esterification and coupling not only prevents their deterioration during further storage processes, but also increases their stability.

Oxidized oils have a toxic effect on the body. Earlier, vitamins and other necessary substances were damaged in this process, but today their direct toxic properties are being identified.

Modern views on the mechanism of oxidation are based on Bach-Engler's peroxide theory and Semenov's chain radical process theory. According to the theory of peroxides, unstable peroxides are formed during the initial oxidation of oils. The subsequent splitting of the peroxide leads to deep changes and the emergence of stable derivatives.

Radical chain processes are understood as the repetition of one or a number of reactions of radicals that preserve one or a number of active centers. The number of repeated radical reactions determines the chain length.

The formation of two radicals from the transformation of one radical in the chain process is considered a branched radical-chain process. An example of such processes is the oxidation of organic substances under the influence of oxygen. The appearance of branches is the result of radical decomposition of hydroperoxide.

In the formation of free radicals, oxygen molecules, which are active biradicals at room temperature, are considered, and they take protons (primarily hydrogen atoms in the alpha position of double bonds) from the fatty acids themselves.

Also, as factors causing the formation of radicals:

• metal ions with variable valency that exchange electrons in the oxidation-reduction process;
• various organometallic compounds;
• temperature effect;
• light and others can serve.

Free fatty acids help dissolve metals in oil and accelerate oxidation processes.

In the initial process of oxidation, oxidation is slow. As the number of radicals increases, the process accelerates according to the chain reaction. As a result, stable carboxylic groups (aldehydes, ketones) are formed that have the ability to decompose oxygen-retaining radicals.

In the process of deepening of oxidation, under the influence of oxidation derivatives, the mechanism of oxidation changes fundamentally. Under the influence of chains in the oxidation process, a number of reactions begin to take place in parallel. These derivatives can not only accelerate the oxidation process, but also slow it down.

It is difficult to explain the process of oxidation of fats and oils with some kind of stoichiometric equation. Because, depending on the composition of the oil, oxidation and chain reactions take place differently.

Regardless of how the process proceeds, 90% of the hydroperoxides formed have double bonds in the trans configuration.

Polyunsaturated linoleic and linolenic acids are very sensitive to oxygen. During their oxidation, linoleate and lenolenates are formed, and the hydroperikis formed during their subsequent transformations are unstable and easily transform into various oxygen-retaining derivatives. The presence of double bonds indicates a tendency to the formation of low molecular volatile substances on the one hand, and to the formation of polymers on the other hand.

Taking into account the above-mentioned conditions, the following conditions should be identified in the oxidation of triglycerides:

• acyl structure of fatty acids included in triglycerides;
• oil storage temperature;
• presence and amount of oxidation catalysts in the oil;
• presence and amount of oxidation inhibitors in the oil;
• rays, radiation and other irradiating effects on the oil.

It is known that the rate of oxidation of a mixture of fatty acids depends on the molar fraction of each component and its activity in the chain reaction. Also, the selective effect of fatty acid residues in the mixture of triglycerides is important. For example, sunflower oil, which is rich in palmitic and oleic fatty acids, is more resistant to oxidation than oil rich in linoleic acid.

Natural antioxidants contained in oils are able to effectively maintain the oxidation process. Natural antioxidants include tocopherols, sesamol, gossypol, phospholipids, polyphenols and a number of other substances.

Among the antioxidants, tocopherols (vitamin E) are of great importance. Tocopherols actively protect oils from oxidation, but they themselves are oxidized, losing their vitamin properties. Tocopherols are quite resistant to high temperatures in the presence of oxygen, but they are resistant to the effects of ultraviolet rays and some oxidants.

In the technological processes of extracting vegetable oils, the processes aimed at transferring natural inhibitors into the oil composition are important in preventing the oxidation of oils. During the process of heat, pressure and other effects during oil separation, it is necessary to try to preserve not only the oxidation of the oil, but also the natural preservation of tocopherols, carotenoids and other necessary substances included in its composition.

The results of the latest research show that when oils are marketed as natural as possible, despite the fact that the appearance of the product is slightly lower, the useful substances in it are preserved more. For example, after primary purification of sunflower oil, it is very useful to release it without refining and deodorization.

Refined oils are inferior to unrefined oils in their indicators, especially in terms of oxidation stability. Cold-pressed oils have higher quality indicators than hot-pressed oils. However, unrefined oils differ in their instability to hydrolytic decomposition.

In the process of storing oils, it was found that the stability to oxidation increases by 1.5-2.0 times when they are poured into brown or green packaging compared to transparent containers.

References:

1. Address of the President of the Republic of Uzbekistan Sh.M. Mirziyoev aimed at setting the results of 2019 and priority tasks for 2020. https://www.gazeta.uz/uz/murojaatnoma
2. http://strategy.regulation.gov.uz/uz/document
3. Annex to the Decision No. 43 dated March 31, 2020 of the Economic Commission of the Economic Commission for the Eurasian Economic Union. http://www.eurasiancommission.org/ru/nae/news.
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