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Quality, Research and Development Manager at the Cairo Company for Oil Extraction and Refining.
In any industry that relies on oils and fats, care should be taken of the six enemies to maintain the quality of the oil for as long as possible and increase the induction period (the period before the appearance of rancid taste and smell due to oxidation reactions).
In this article, we will learn about the six enemies and their prevention: -
Heat also has an important and effective role in refining operations, but may be one of the main factors in the deterioration of the quality of refined oil. The removal phase is the most dangerous stage of refining (200-260 degrees Celsius and a vacuum of no more than 2 mbar). Using temperatures above 260 leads to thermal decomposition of glycerides. F.F.A free fatty acids are formed in addition to trans fatty acids and polymers. It should be noted that in the case of refining palm oils and their derivatives, relatively lower temperatures (200-230) are used to prevent the formation of GE, 3MCPD compounds. It is worth noting that the ideal storage temperature is up to 25 degrees Celsius, but in hot countries such as Egypt, it is allowed up to 40 degrees Celsius, taking into account the rest of the factors for a shorter storage time.
Oils, especially liquid oils containing a high percentage of unsaturated fatty acids, are oxidized when exposed to oxygen in what is known as self-oxidation (auto-oxidation), especially that oxygen dissolves in oil nine times faster than its solubility in water, leading to the rapid formation of peroxide and hydroperoxide compounds and they break down over time into secondary oxidation compounds (aldehydes, ketones, polymers, hydrocarbons...) Responsible for bad flavors and unwanted smells. Therefore, preventing or reducing the presence of oxygen in the production and storage stages is a crucial step in maintaining the quality of oils. Therefore, it is recommended to inject inert gas and antioxidants directly into the refined oil coming out of the removal device and reduce voids in tanks while making a blanket with nitrogen gas to isolate them from atmospheric air. When filling, it should be under the pressure of an inert gas in narrow-mouthed containers with a small peak vacuum.
When oil is exposed to direct and indirect sunlight and store lighting, especially UV rays, it stimulates photo oxidation reactions that lead to the degradation of oils more quickly than self-oxidation, specifically with the presence of chlorophyll, which leads to the formation of Singlet oxygen, which is a thousand times faster than triplet oxygen in oxidation processes and can lead to oil deterioration in several hours. Therefore, chlorophyll should be treated carefully in the refining stages by using the appropriate type of earth and activated charcoal to bring its concentration below 30 ppb. In cold pressed oils such as olive oil, it is best to pack them in dark glass and store them away from light.
Moisture stimulates the hydrolysis of triglyceride molecules, leading to an increase in the percentage of free fatty acids, which makes the oil unpalatable and reaches the maximum percentage of free acids (0.3%) before the expiration of the shelf life (12-24 months). It is wrong to think that moisture levels have been controlled in the refining stages, especially with vacuum, at almost all stages. However, moisture can form in refined oil after the completion of refining operations during the storage and packaging stages.
When oil is stored in tanks that are not thermally insulated or exposed to different temperatures between night and day, water vapor condenses on the walls, especially with a gas vacuum in the tank without oil. In addition, in highly humid areas, when opening the tank lid to take samples, it helps in the condensation of water vapor, especially with newly produced oils, which are relatively warm.
During filling, internal leakage may occur in the oil-cooling heat exchangers. Nitrogen gas from the nitrogen extraction unit, which is injected if it is not well dried from water vapor, will certainly be a source of moisture as relying on the purity of nitrogen gas alone is not sufficient. Finally, oil containers that have been stored in highly humid places may maintain internal moisture on the walls or cover.
The presence of heavy metals in oils is caused by the oilseeds themselves as a result of their absorption from the soil, the most famous of which is iron (Fe²/Fe³), which has a harmful effect on the oil, just like light and heat. It can be considered a pro-oxidant as it stimulates the rapid formation of free radical, whether from fatty acids or hydroperoxide compounds, to produce free radicals, which speeds up oxidation rates as minerals reduce the activation energy needed to initiate oxidation reactions. Therefore, activated bleaching earth, citric acid and phosphoric acid are used as chelating agents in refining, in addition to not using metals in production and packaging lines. Stainless steel and monitoring the percentage of iron in the steam used is necessary to control it. It should also be taken into account that some bad types of bleaching dust may be a direct source of heavy metals.
These are active biological proteins that stimulate chemical reactions in vegetable oils. They come naturally from oilseeds, especially those that are injured or poorly stored, and cause several damages to the oil, such as the enzyme Lipase, which works to degrade triglycerides in the presence of moisture by breaking the ester bond between glycerol and fatty acid and increasing the percentage of free fatty acids. Lipoxygenase helps in oxidation processes through the formation of hydroperoxide compounds without the need for catalysts for the production of free radicals. Fortunately, the refining heat is sufficient to inhibit the action of these enzymes, but it is better to control it before extraction through heat treatment of seeds and good storage.
The question remains whether refined oil can be exposed to these enzymes after refining processes? The answer is yes if the oil is contaminated during storage and transportation by microorganisms that secrete these enzymes. This is caused by unclean tanks and tanks containing moisture or crude oil residues.
Maintaining the quality of refined oil requires careful control at every stage of production, from seed to storage, while controlling these six factors:
Heat - Air - Light - Humidity - Minerals - Enzymes.
Awareness of these factors helps producers extend product life and ensure quality until the end of the shelf life.
