The term "salad oil" has its roots in Western culinary traditions. As the name suggests, it's used to dress salads—raw vegetables combined with various seasonings. To enhance nutrition and flavor, a thin layer of oil is applied. This type of oil must be colorless and odorless to preserve the natural color and taste of the vegetables. Additionally, since cold dishes are often refrigerated, the oil needs to remain liquid even at low temperatures (around 4.4°C). Therefore, salad oil is typically refined to remove non-triglyceride components, usually derived from vegetable sources.
In contrast, cooking oil, also known as cooking oil or frying oil, refers to oils used for high-temperature cooking. These oils should be liquid at room temperature, have good flowability, and retain their natural nutrients without any strong odors. However, frying oil is specifically designed to withstand prolonged exposure to high heat (160°C–180°C) without breaking down through oxidation or hydrolysis.
In Europe and the U.S., cooking oil and frying oil fall under the broader category of shortenings, while salad oil is defined as a cold-liquid oil. In Japan, these oils are highly specialized, with distinct characteristics that set them apart.
In China, according to national standards, edible oils include primary oil, secondary oil, premium cooking oil, and salad oil. Most regions still use cooking oil primarily for cooking, rather than distinguishing between salad oil and cooking oil. However, with the advancement of refining technology and increased consumer awareness, some cities have started to prefer salad oil, reflecting a shift toward more refined and purified food choices. Still, using salad oil for cooking may not be optimal from a nutritional standpoint.
From a chemical perspective, most natural oils consist mainly of triglycerides, along with small amounts of other lipid substances like phospholipids, free fatty acids, sterols, vitamins, pigments, and waxes. While many of these are harmless, some may contain toxic compounds that need to be removed during refining. The process generally includes degumming, deacidification, decolorization, deodorization, and sometimes dewaxing.
Phospholipids, for example, can cause discoloration and turbidity in oil, and when exposed to moisture or heat, they can lead to sedimentation and oil degradation. They are largely removed during refining to ensure better stability and processing efficiency.
Free fatty acids (FFA) are another component that affects oil quality. High levels of FFA can impact flavor and may reduce the oil’s shelf life. Pigments like carotenoids and chlorophyll contribute to color and provide nutritional benefits, such as vitamin A and antioxidant properties. While these are valuable, they are often removed in oils like salad oil for aesthetic reasons.
Sterols, found in both animal and plant oils, play a role in cell structure and have health benefits. However, they are typically left in cooking oils unless specific processing is required.
Overall, the refining process significantly alters the composition and nutritional profile of oils, making each type suitable for different uses depending on its intended application.
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