To grade the oil, we need to consider the fatty acid composition. It affects how oils survive the storage environment, perform in cooking, and ultimately change our health.

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There are several trends in edible oil manufacturing industry, some are looking for new kind of oil, while others improve techniques to produce same oil. All of them want to make the oil healthier, lasts longer, preserves the natural nutrients, cooks and tastes better. 

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High Stability Oil

One of the trend is high stability oil. High oleic oils are oil rich in oleic acid in the fats molecules, it is monounsaturated meaning there is one double bond in the fatty acid carbon chain which change the way it reacts with air and our body. It has higher resistance against oxidation compared to polyunsaturated (2 or more double bonds in fatty acid carbon chain), which means they reacts to air and breakdown much slower. Scientific researches shown that monounsaturated fatty acids help regulating blood cholesterol (Lower "bad" cholesterol, higher "good" cholesterol). This benefit is important as many heart and blood vessel diseases, or known as cardiovascular diseases, are related to blood cholesterol level.

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High oleic sunflower and high oleic canola oil are common high oleic oils found in market. They are particularly good for high temperature cooking as their smoke point are as high as 450°F (232°C). Deep frying with these oils produce food that stay crispy, without making food taste and smell oily or rancid, in other words it keeps the nature taste of food.

 

Extra Virgin Oils

Extra Virgin oils are another popular kind of oil. Extra Virgin meaning oil is mechanically made without heat, low free fatty acid (some refers as free oleic acid, not to mix up with oleic acid bound in fat molecules), and without any sensory flaws. Cold pressed is the common term used to describe the process to produce extra virgin oils. This process is expensive compared to normal refinery where the oils are produced with heat and chemicals. It is good for preserving aroma of oil, and some natural micronutrients such as vitamins, minerals and antioxidants. It is commonly used to produce olive oil since olives are rich in these micronutrients.

 

Extra virgin olive oil is the most common extra virgin oil and it has been used for long time in the Mediterranean diet. Due to the relatively high, 55%-85% oleic acid in olive oil, it also benefits heart health as well as providing anti-oxidative function. 

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High oleic oils and extra virgin oils are highly ranked due to the their high stability and health benefits respectively.

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Polyunsaturated & Saturated Oils

Meanwhile, oils high in polyunsaturated fats or saturated fats are less healthy and rank lower.

 

Polyunsaturated fatty acids e.g. omega-3, omega-6 are also good for heart and vessel. However, polyunsaturated fatty acids are unstable and could be easily oxidised in cooking temperature. Most manufacturers need to add antioxidants in order to preserves oil during storage and transport.

 

Saturated fatty acids e.g. palmitic acid, stearic acid, are quite stable against oxidation, but the high intake of saturated fatty acids in our diet increase risk of cardiovascular diseases. Most of our diet, i.e. include plenty of meat, some cheese, which also provide saturated fatty acids. Hence it is not preferred to use oil rich in saturated fats. As a result, oils with these characteristics such as Rapeseed, Cottonseed, Flaxseed, Corn, Peanut, Palm, Coconut oils have lower ranking.