This article outlines what edible oil is, how it is produced, how it is tested, and the parameters required to assess its quality and safety.
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What is Edible Oil?
Edible fats or cooking oils are suitable for human consumption and are mostly used in food or cosmetic products. They contain important vitamins, as well as saturated and/or unsaturated fatty acids. Both edible fats and oils are mostly comprised of water-insoluble esters of glycerol and fatty acids, known as glycerides.
Fats and oils are usually classified depending on whether they are liquid or solid at room temperature. A basic distinction is made between vegetable fats and oils that are derived from the seeds and fruits of oil plants, and fats and oils that are derived from animal sources. However, synthetic edible fats and oils can be developed from raw materials using chemical processes, including the Fischer–Tropsch process.
Generally, fats and oils with higher proportions of unsaturated fats (particularly polyunsaturated fatty acids) are healthier. Sunflower, safflower, rapeseed, soybean, and olive oils are especially high in unsaturated fatty acids and polyunsaturated fatty acids. These oils can be used for cooking and frying, but they are best consumed in their natural states. Conversely, coconut, palm kernel, butterfat, and palm oils are high in saturated fats. They are therefore mostly used for frying, roasting, baking, and for the production of industrial soaps and cosmetics.
Examples of Edible Oils
Sunflower Oil
Sunflower oil is a popular choice as it can be used for frying foods at very high temperatures. Due to its high smoke point and neutral flavor, it is often used in baking to improve the texture and flavor of baked goods. It is also used in skincare products for a variety of reasons, including its unsaturated fatty acid and vitamin E content, its moisturizing and anti-inflammatory effects, its UV protection, and its emollient properties.
Rapeseed Oil
Rapeseed oil is also known as canola oil. It is tasteless and retains its fluidity even at lower temperatures. It is commonly used in mayonnaise because it has a light color and neutral flavor, and gives mayonnaise a creamy consistency. Due to its high smoke point and neutral flavor, it is also used to make fried foods and crunchy snacks, such as popcorn and French fries.
Coconut Oil
Coconut oil is often used in food products because it adds a slightly coconutty taste and aroma and remains stable at higher temperatures. Its high saturated fat content means it is a solid at room temperature, but it melts at roughly 24 °C. Because of this, coconut oil is often hydrogenated for use in warmer climates, raising its melting point to around 36–40 °C. Coconut oil is a popular choice in vegan baking since it acts as an alternative to butter. It is also used in the cosmetics industry, especially in body and hair moisturizers.
Storage and Quality Considerations
Product quality and shelf life are crucial considerations. Edible fats and oils can deteriorate during storage, ferment, become contaminated with traces of pesticides or natural substances associated with the oil's source, or even be intentionally adulterated.
These products can become rancid via autoxidation, in which long-chain fatty acids are degraded, and short-chain compounds are formed, such as butyric acid. The hydrolysis of oils and fats promotes triacylglycerols to split and form free fatty acids (FFA), mono-, and diacylglycerols. These free fatty acids can undergo extra autoxidation. In addition, triacylglycerol oxidation catalyzes carboxylic acid formation, with a glycerol backbone, which increases the oil’s acidity.1
How is Edible Oil Made?
Edible oils are obtained through various methods, typically using direct extraction techniques. The main processes include pressing (Figure 1), extraction with volatile solvents, and refining or purification using caustic chemicals (bleaching).
Pressing is categorized as either cold-pressed or hot-pressed, which results in completely different finished products. Oil is extracted at room temperature during cold pressing. Because the acid value of cold-pressed edible oils is relatively low, they do not need to be refined, so the final product is acquired after precipitation and filtration. Hot pressing involves extracting edible oils at high temperatures. As a result, the acid value rises substantially, and the oil loses the majority of its natural qualities, they must, therefore, be refined so that they can be consumed.
Different categories of oils include: native (virgin), refined, unrefined, hydrogenated, transesterified, fractionated, finished (manufactured), and cold-resistant.
Native/ Virgin Edible Oils
Native edible oils, also known as virgin edible oils, are acquired using gentle mechanical processes without adding heat, so as to preserve beneficial compounds. These oils are generally high quality and are especially valuable and healthy. For example, virgin olive oil is fairly resistant to oxidation as a result of its fatty acid composition, which is characterized by a high monounsaturated-to-polyunsaturated fatty acid ratio. This is a major factor in providing oil oxidative stability. It also contains polyphenols, which are powerful antioxidants. The majority of these compounds are removed during refining and are therefore present in much lower amounts in refined edible oils than in virgin oils.2
Unrefined Edible Oils
Unrefined edible oils are acquired by pressing, centrifuging, or melting. These processes are often employed to produce edible oils of animal origin. Heat is often added or tolerated. Such oils are not treated chemically and still contain many valuable components that have survived the elevated temperatures.
Refined Edible Oils
Refined edible oils are subject to extra mechanical and/ or chemical treatments. For example, they may be filtered, deoderized, deacidified, and bleached. As a result, they are usually considered to be less healthy and are used more for industrial purposes in cosmetics and food, rather than direct consumption.
Hydrogenated Edible Oils
Hardened edible oils are refined fats, whose fatty acids have been further modified via hydrogenation. They are considered unhealthy and have been criticized due to the trans-fatty acids that are produced during the hydrogenation process. They can negatively impact cholesterol and fat metabolism levels.
Transesterified Edible Oils
Transesterified edible oils are refined edible oils, or blends thereof, that are produced under the additional influence of catalysts. This changes the melting behavior and fatty acid arrangement.
Fractionated Edible Oils
Fractionated edible oils are created from refined or unrefined edible oils by cooling and then separating the stearin from the oleic components. This process can be employed for the creation of particular properties in the final product.
Finished / Manufactured Edible Oils
Finished edible oils (also known as manufactured edible oils) are produced through hydrogenation, transesterification, and fractional distillation, or by combining these processes.
Cold-Resistant Edible Oils
Cold-resistant or cold-stable edible oils are produced by winterizing either refined or unrefined oils. During winterization, the oil is cooled and the precipitating fractions are filtered. The filtered product can then be stored at low temperatures without flocculation.
More processed edible oils are generally lower quality. Various testing parameters should be used to check and analyze edible oil quality.
References
- Sakaino, M., et al. (2022). Carboxylic acids derived from triacylglycerols that contribute to the increase in acid value during the thermal oxidation of oils. Scientific Reports, [online] 12(1), p.12460. DOI: 10.1038/s41598-022-15627-3. https://www.nature.com/articles/s41598-022-15627-3.
- José A. et al. (2013). Rapid Determination of Olive Oil Oxidative Stability and Its Major Quality Parameters Using Vis/NIR Transmittance Spectroscopy. Journal of Agricultural and Food Chemistry, 61(34), 8056–8062. DOI: 10.1021/jf4021575. https://pubs.acs.org/doi/10.1021/jf4021575.
This information has been sourced, reviewed and adapted from materials provided by Metrohm Middle East FZC.
For more information on this source, please visit Metrohm Middle East FZC.