Guide to Choosing the Right Vegetable Oil for Different Uses

Edible oils are extracted from crushing oilseeds belonging to various plant groups. As a fundamental component of the human diet, they play a crucial role in providing energy and maintaining the body's normal functions. In addition to their sensory and practical cooking properties, these oils are rich in essential fatty acids that are critical to human health. Vegetable oils act as carriers for fat-soluble vitamins and play an effective role in disease prevention.

With the increasing changes in dietary patterns, the global consumption of edible vegetable oils continues to rise. Statistics show that global consumption of these oils reached 212.82 million tons in 2022, a 1.25 fold increase compared to 2014.

The variety in composition and physical and chemical properties of vegetable oils makes choosing the right oil for different uses – including salads, cooking, and frying – essential. In Iran, canola, olive, corn, sesame, and sunflower oils are of particular importance due to their high consumption. By examining fatty acid profiles, the omega-6 to omega-3 ratio, and the smoke point of these oils, more informed decisions can be made for various uses.
 

Fatty Acid Profile

Edible vegetable oils are primarily made up of a compound called triglycerides (which make up 95 to 98 percent of oils) and some other minor compounds (2 to 5 percent). The main component of vegetable oils, triglycerides, are usually made up of fatty acids. The fatty acid profile is recognized as an important indicator for determining the quality and properties of edible oils. In the past, attention was paid only to the high-abundance fatty acids, but today attention to the entire fatty acid family, including low-abundance fatty acids, is of particular importance. These fatty acids are not only used to identify frauds in oils, but also affect the nutritional and health properties of oils.

Fatty acids (FAs) are classified into three main categories based on their chemical structure: saturated fatty acids (SFAs), monounsaturated fatty acids (MUFAs), and polyunsaturated fatty acids (PUFAs). Saturated fatty acids are commonly found in animal fats such as beef, lamb, and pork, but are also present in some vegetable oils. These fatty acids, such as palmitic acid (C16:0) and stearic acid (C18:0), may increase LDL levels (bad cholesterol) in the body, which can lead to cholesterol build-up in the inner walls of blood vessels and increase the risk of cardiovascular disease.

Monounsaturated fatty acids, which usually have only one double bond, can help lower blood sugar and cholesterol levels and improve blood lipid regulation. Oleic acid (C18:1) is one of these fatty acids that is commonly found in diets and can reduce bad cholesterol levels, thereby reducing the risk of cardiovascular disease.

Polyunsaturated fatty acids, which have two or more double bonds in their structure, mainly include omega-3 and omega-6 fatty acid groups. These fatty acids play an important role in maintaining heart and vascular health, reducing inflammation, and improving brain function. They are also essential fatty acids for the body, as the body is unable to produce them and must be supplied through food.
 

• Sunflower Oil

Regular sunflower oil is known for its high concentration of linoleic acid (C18:2) followed by oleic acid (C18:1). Although its fatty acid composition may vary depending on the variety, linoleic acid (C18:2) usually accounts for 65 to 70 percent of the total fatty acids.

The amount of saturated fatty acids in this oil, mainly palmitic acid (C16:0) and stearic acid (C18:0), is usually less than 15 percent of the total fatty acid composition.
One of the positive features of sunflower oil compared to many other oils is its low palmitic acid (C16:0) content, which is known to increase bad cholesterol.

Table 1 shows the acceptable limits of fatty acid composition in various types of sunflower oil according to the Iranian national standard number 1300.

• Canola Oil

Canola oil is extracted from rapeseed with low levels of erucic acid (C22:1). In early rapeseed varieties, high levels of this fatty acid were present in the oil, posing a serious health concern. Studies showed that high levels of erucic acid in rodents led to fat deposits in the heart, skeletal muscles, and adrenal glands and hindered their growth. Although scientific evidence showed that the effects of erucic acid on humans are not as severe as on rodents, concerns about this compound persisted.

In response to these concerns, plant breeding programs began in Canada in 1959. These efforts resulted in the identification of rapeseed varieties with low levels of erucic acid. In 1978, the name "canola" was officially registered and transferred to the Canola Council of Canada in 1980. This name was given to varieties that had less than 5 percent erucic acid in their oil composition.

One of the key achievements in plant breeding was the reduction of the erucic acid chain to oleic acid (C18:1), a turning point in the understanding of fatty acid metabolism. This change led to a dramatic increase in 18-carbon fatty acids in canola oil, with oleic acid now making up about 95 percent of its fatty acid composition.

Today, canola oil is recognized as one of the most nutritious edible oils due to its low erucic acid content (less than 2 percent of the total fatty acid composition) and high oleic acid levels.

• Corn Oil

In the 1950s and 1960s, a prominent marketing feature of corn oil was its high content of polyunsaturated fatty acids. This oil garnered significant attention due to its nutritional composition.

One of the key advantages of corn oil is its low saturated fatty acid content (less than 15%), which helps reduce the risk of cardiovascular diseases. Furthermore, corn oil contains very small amounts of linolenic acid (C18:3).

Linolenic acid (C18:3), due to its susceptibility to oxidation, can lead to rancidity in oil. This characteristic enhances the stability of corn oil compared to oils with higher linolenic acid content, making it a suitable option for daily consumption.
The fatty acid composition of commercial corn oil, according to various standards and sources, is presented in Table 3.

As you can observe, linoleic acid (C18:2) and subsequently oleic acid (C18:1) are recognized as the dominant fatty acids in corn oil. Furthermore, palmitic acid (C16:0) is the most abundant saturated fatty acid in this oil.
Accordingly, corn oil, like sunflower oil, falls into the category of oils with a predominant content of oleic acid (C18:1) and linoleic acid (C18:2).

Table 4 presents the fatty acid composition of refined corn oil according to the Iranian National Standard No. 1447.

• Sesame Oil

As an oil containing polyunsaturated fatty acids, sesame oil has approximately 82% unsaturated fatty acids. Its main fatty acids include oleic acid (C18:1) and linoleic acid (C18:2), which are present in roughly equal amounts. Less than 20% of the fatty acid composition of this oil is made up of saturated fatty acids, primarily palmitic acid (C16:0) and stearic acid (C18:0). Sesame oil also contains very small amounts of linolenic acid. Consequently, sesame oil falls into the category of oils with a predominant content of oleic acid (C18:1) and linoleic acid (C18:2).

Table 5 presents the fatty acid composition of sesame oil based on various standards and sources.

Table 6 presents the fatty acid composition of crude sesame oil according to the Iranian National Standard No. 8636.

• Olive Oil

The level of free fatty acids varies depending on the type of olive oil (extra virgin, virgin, regular, blend of refined and virgin) and is a crucial criterion for determining the quality of olive oil. Generally, the fatty acid composition of olive oil includes:

7.5-20% palmitic acid (C16:0)

0.5-5% stearic acid (C18:0)

0.3-3.5% palmitoleic acid (C16:1)

55-85% oleic acid (C18:1)

7.5-20% linoleic acid (C18:2)

0.0-1.5% linolenic acid (C18:3)

Myristic acid (C14:0), heptadecanoic acid (C17:0), and eicosanoic acid (C20:0) are only found in small amounts. The fatty acid composition may vary from sample to sample, depending on the production site, latitude, climate, olive variety, and stage of fruit ripeness.

Table 7 presents the fatty acid composition of olive oil according to the Codex Alimentarius standard from 1997. This table includes the main fatty acids of olive oil along with their variation ranges in different types of olive oil.

Table 8 presents the fatty acid content in various types of edible olive oil, in accordance with the Iranian National Standard No. 1446.
 

Comparison of Fatty Acid Profiles in Oils (Sunflower, Canola, Corn, Sesame, and Olive)

By examining the fatty acid composition of oils, shown in Diagram 1, we can observe the differences in fatty acid profiles among the oils. Sunflower oil, with approximately 65 to 70 percent linoleic acid (C18:2), falls into the category of oils rich in polyunsaturated fatty acids. Additionally, the saturated fatty acid content in this oil is less than 15 percent.
Canola oil, with a significant amount of oleic acid (C18:1), which makes up about 95 percent of its fatty acid composition, is recognized as the oil with the highest monounsaturated fatty acid content and the lowest saturated fatty acid content. Furthermore, the presence of very small amounts of erucic acid (C22:1) in canola oil alleviates concerns about the adverse health effects of this fatty acid.
Corn oil, like sunflower oil, contains a high percentage of polyunsaturated fatty acids and its saturated fatty acid content is less than 15 percent. Sesame oil, with a balanced composition of oleic acid (C18:1) and linoleic acid (C18:2) and low saturated fatty acid content (less than 20 percent), is considered a nutritious and healthy oil. Olive oil, with a high percentage of oleic acid (C18:1), ranging from 55 to 85 percent of its composition, is also in the category of healthy oils. However, the saturated fatty acid content in olive oil is higher compared to the other oils mentioned, varying between 8 and 25 percent.

Based on this analysis, canola oil has the highest amount of monounsaturated fatty acids and the lowest amount of saturated fatty acids. Sunflower oil also has high amounts of polyunsaturated fatty acids.
 

Essential Fatty Acids and Omega-6 to Omega-3 Ratio

Fats play several vital roles in the body, including providing and storing energy, regulating body temperature, protecting vital organs, and aiding in the absorption of fat-soluble vitamins. Some fatty acids essential for proper body function are not produced by the body and must be obtained through diet. These fatty acids, known as omega-3 and omega-6, are types of unsaturated fatty acids named based on the location of the first double bond in their structure. The human body lacks the necessary enzymes to produce these fatty acids, hence they are called essential fatty acids.

Alpha-linolenic acid (ALA) in the omega-3 group and linoleic acid (LA) in the omega-6 group act as precursors for other important fatty acids in these two families. Essential fatty acids play key roles in many vital bodily processes and are used as dietary supplements, making their adequate intake crucial for overall health.

Both omega-3 and omega-6 fatty acids are essential for health and play numerous roles. For example, omega-3 contributes to maintaining heart health, reducing inflammation, aiding in fetal brain development during pregnancy, and alleviating symptoms of conditions like depression. Omega-6 is involved in processes such as regulating metabolism, providing energy, maintaining bone, skin, and hair health, improving insulin sensitivity, and controlling blood sugar.

Although both omega-3 and omega-6 fatty acids are beneficial, balancing their intake is important. Humans evolved with a diet in which the omega-6 to omega-3 fatty acid ratio (omega-6:omega-3) was approximately 1:1. Today, this ratio has increased, and omega-6 consumption is much higher than omega-3, with ratios around 15:1 to 16.7:1. This high ratio increases the risk of many non-communicable diseases (NCDs), also known as chronic diseases, which are typically long-term and result from a combination of genetic, physiological, environmental, and behavioral factors.
High omega-6 to omega-3 ratios in diets are reported as a risk factor for cardiovascular diseases, hypertension, atherosclerosis, stroke, type 2 diabetes, cancer, and other chronic conditions. Conversely, increasing omega-3 intake and reducing this ratio can have suppressive effects on these diseases. Therefore, it is recommended that the omega-6:omega-3 ratio in the diet be around 1:1 to 4:1, meaning for every unit of omega-3, 1 to 4 units of omega-6 should be consumed.

comparison of Omega-6 and Omega-3 Fatty Acid Amounts and Ratios in Oils (Sunflower, Canola, Corn, Sesame, and Olive)

Based on the fatty acid profiles reviewed, the ratio of linoleic acid (omega-6) to alpha-linolenic acid (omega-3) for the oils studied is calculated in Table 9. This calculation involves dividing the linoleic acid (C18:2) amount by the alpha-linolenic acid (C18:3) amount in each oil.

Based on the data in the table, sesame oil (1045), sunflower oil (125.767), and corn oil (49.904) have the highest omega-6 to omega-3 ratios. Conversely, canola oil (2.389) and olive oil (15.997) have the lowest omega-6 to omega-3 ratios. Considering that the omega-6 to omega-3 ratio is crucial for human health, it is advisable to choose oils with lower ratios. In this comparison, canola and olive oils appear to be more suitable options.
 

Smoke Point

The smoke point is a physical parameter that indicates the temperature at which an oil begins to break down and smoke. Generally, an increase in unsaturated fatty acid content leads to a decrease in the smoke point. When an oil reaches its smoke point, its glycerol and fatty acids begin to decompose and produce compounds like aldehydes, ketones, alcohols, and acrolein. These compounds not only impart unpleasant flavors and odors to the oil and food but can also be toxic and harmful.
For example, acrolein, a reactive compound, can be produced during the thermal processing of oils and fats and may remain in kitchen air, food, and the oil. This toxic compound enters the body through inhalation and ingestion. Acrolein is associated with serious health risks such as cancer, cardiovascular, respiratory diseases and diabetes. According to the International Agency for Research on Cancer (IARC), acrolein is classified as a possibly carcinogenic substance to humans (Group 2A).
This compound can remain in fried foods or be absorbed into heated oils and, through chemical reactions, convert into other toxic compounds like acrylamide. Acrolein production is influenced by factors such as oil type, temperature, frying time, and the frequency of oil use. To reduce acrolein production, it is recommended to use oils with a high smoke point for frying.
Oils with higher smoke points undergo these changes at higher temperatures, so it is recommended to use oils with higher smoke points for frying to minimize acrolein production. The approximate smoke points of the five refined vegetable oils under consideration—sunflower, canola, corn, sesame, and olive—are 209°C, 232°C, 230-238°C, 166°C, and 190-207°C, respectively.

Based on the data presented in Chart 2, refined corn oil has the highest smoke point among the oils studied, at approximately 234 degrees Celsius. It is followed by refined canola oil at 232 degrees Celsius and refined sunflower oil at 209 degrees Celsius. Refined sesame oil has the lowest smoke point at 166 degrees Celsius. Given that a high smoke point is desirable for frying oils, corn, canola, and sunflower oils are more suitable for this purpose.
 

Conclusion

An evaluation of the fatty acid composition, omega-6 to omega-3 ratio, and smoke point of five commonly used vegetable oils, including sunflower, canola, corn, sesame, and olive oil, reveals that each of these oils has unique characteristics and is suitable for various applications.
 

1. Oils Suitable for Deep Frying

Deep frying is a cooking method in which food is completely immersed in hot oil, such as frying potatoes, donuts, fried onions, etc. The ideal temperature for deep frying is usually between 176 and 190 degrees Celsius. Choosing the right oil in this process plays a key role in maintaining food quality (taste, smell, texture, and color), thermal stability, and reducing the formation of harmful compounds.
Oils used for frying should have a high smoke point, i.e., at least 200 degrees Celsius. In addition, they should be resistant to oxidation, meaning they should not react with air oxygen at high temperatures. Therefore, oils rich in polyunsaturated fatty acids are not a suitable choice. It is recommended to use oils with a mild and neutral flavor and aroma for frying, so that the main taste of the food is preserved, although this is a matter of taste. Also, considering that a large amount of oil is needed to immerse the food, it is better to use oils with a reasonable price. Therefore, canola, corn, and sunflower oils can be suitable choices for frying due to their high smoke point.
 

2. Oils Suitable for Light Cooking and Salads

Alll the oils studied in this article, namely sunflower, corn, canola, olive, and sesame oil, are suitable for salads and light cooking, such as sautéing onions or meat until their color changes, and cooking rice.

However, in general, the consumption of sunflower, corn, and sesame oils is not recommended due to their high omega-6 to omega-3 ratio, as this ratio can increase the risk of certain diseases. In contrast, canola and olive oils are considered more desirable options for consumption due to their balanced fatty acid composition, and each has its own benefits.

Therefore, in general, it can be said:

• Canola oil is a better choice for frying.

• Olive oil is a better choice for salads, considering its fatty acid composition and omega-6 to omega-3 ratio, along with its unique flavor and aroma.

• For light cooking, olive and canola oils are both suitable choices, and the choice of a more suitable option depends on various factors and can vary for each individual.