The term "salad oil" comes from the West, and as its name suggests, it's specifically used in salads. In Western cuisine, salads are typically made with raw vegetables and various seasonings to enhance flavor and nutrition. To make the dish more appealing, a thin layer of oil is often added on top—this is what we call salad oil. To preserve the natural color and taste of the vegetables, this oil must be colorless and odorless. Additionally, since cold dishes are often refrigerated, the oil needs to remain liquid even at low temperatures, such as 4.4°C. This means that non-triglyceride components in the vegetable oil must be removed as much as possible, which is why salad oil is usually derived from refined vegetable oils.
Cooking oil, also known as cooking oil or frying oil, can be either plant-based or animal-based (though in most cases, it refers to vegetable oil). It should be liquid at room temperature, have good fluidity, and retain the natural nutrients of the oil without any strong or unpleasant odors. However, it's important to note that cooking oil and frying oil are not exactly the same. The key feature of frying oil is its ability to withstand high temperatures (around 160–180°C) without breaking down due to thermal oxidation or hydrolysis.
In Europe and the United States, both cooking oil and frying oil fall under the broader category of shortenings, differing mainly in their physical properties. Salad oil, on the other hand, is specifically referred to as a cold-liquid oil. In Japan, the distinction between cooking oil, cold oil (salad oil), and frying oil is more precise, with each type having unique characteristics.
In China, according to national standards, edible oils include primary oil, secondary oil, premium cooking oil, and salad oil. In most regions, there is no clear distinction between cooking oil and salad oil, as people primarily use it for cooking. However, with the introduction of advanced refining technologies and increased consumer awareness, some cities have started to shift toward using refined oils like salad oil. This trend reflects rising living standards and a growing preference for purer, more refined food products. That said, from a nutritional standpoint, using salad oil for cooking may not be ideal and requires further exploration.
From a chemical perspective, most natural oils and fats consist mainly of triglycerides made up of saturated and unsaturated fatty acids, along with small amounts of other lipid substances. These include phospholipids, free fatty acids, sterols, vitamins, pigments, waxes, and other compounds. While many of these are harmless or even beneficial, some may contain toxic components that need to be removed during refining. The process of refining crude oil into salad oil typically involves degumming, deacidification, decolorization, deodorization, and sometimes dewaxing. These steps significantly alter the composition and nutrient content of the oil.
Phospholipids, for example, are naturally present in crude vegetable oils, with soybean oil containing about 1–3% of them. They play an important role in metabolism, brain function, and cholesterol regulation. However, they can cause discoloration, cloudiness, and spoilage if left in the oil. For this reason, phospholipids are largely removed during the refining process.
Free fatty acids (FFA) are another component found in oils, often resulting from lipase activity or oxidation. High levels of FFA can affect the taste and quality of the oil but are generally not harmful to human health. Pigments like carotenoids and chlorophylls contribute to the color of oils and also offer nutritional benefits, such as antioxidant properties and vitamin A precursors. In most cooking oils, these pigments are not removed unless the oil is intended for specific uses like salad oil or cosmetics.
Sterols, such as cholesterol in animal fats and various phytosterols in plant oils, are also present in different quantities. Some studies suggest that sterols may help reduce cholesterol absorption and support heart health. However, they are often removed during refining to improve the oil’s stability and appearance.
Overall, the refining process ensures that the final product meets specific quality and safety standards, while also influencing its nutritional profile. As consumers become more aware of food quality, the demand for refined oils like salad oil continues to grow.
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