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Choose Cooking Oils Wisely! Test on 50 Samples Revealed Harmful Contaminants in 90% and Genotoxic Carcinogens in Almost 60% Samples Understand “Good” and “Bad” Fatty Acid Ratio and Nutrient Values

  • 2022.07.18

Oil is an essential ingredient for cooking and many discerning home cooks would even use different types of cooking oils for preparing specific cuisines. According to the Consumer Council’s recent test on 50 samples of cooking oil, 47 samples (94%) were detected with 1 or more types of harmful contaminants, amongst which 40% (20 samples) were even found with 3 types or more. A point of concern was that almost 60% (29 samples) were detected with the genotoxic carcinogen glycidol, 2 of which even exceeded the European Union’s (EU) standard. 2 other samples were found with another genotoxic carcinogen benzo[a]pyrene, of which 1 sample’s detected amount exceeded the EU standard. Besides, 1 sample had detected levels of plasticiser that exceeded the action level of the Centre for Food Safety (CFS) and the EU’s upper limit. Overall, only 3 of the tested samples were not detected with any contaminants. Despite this being unsatisfactory, it shows that it is possible to ensure that the cooking oil is free from contaminants in the manufacturing process. As cooking oil is an indispensable ingredient in everyday cooking, manufacturers should have the responsibility to ensure their quality and safety, and prevent any harmful contaminants, so as to safeguard the health of consumers. Besides, the healthy and harmful fatty acid ratios varied amongst the samples. The Council recommends consumers to select cooking oils that mainly contain unsaturated fatty acids (UFAs), and those with lower trans fatty acid (TFA) and saturated fatty acid (SFA) contents. When cooking, be mindful of the smoke points of different cooking oils to prevent emission of a large amount of cooking fumes which could lead to health risks.

Besides, the test also revealed that 8 samples had a variance between their actual and declared nutrient content that exceeded the stipulated tolerance limit (20%). The most severe case was the polyunsaturated fatty acid (PUFA) content for 1 sample, which had a variance of 85% with the labelled value. The Council urges manufacturers to promptly rectify discrepancies on the product labelling and provide consumers with accurate information.

The Council sourced 50 samples of common varieties of cooking oils from supermarkets and department stores, covering 13 categories, including 14 extra virgin olive oils, 2 olive oils, 2 avocado oils, 3 coconut oils, 2 camellia oils, 2 sunflower oils, 2 rice bran oils, 2 grapeseed oils, 3 corn oils, 6 canola oils, 1 soybean oil, 6 peanut oils and 5 blended oils. Test items included the food safety and nutrient content, while the accuracy of the nutrient labelling was also compared.

60% Samples Detected with Genotoxic Carcinogens or Harmful Contaminants

Some types of cooking oils need to undergo high-temperature refinement during the manufacturing process. 3-MCPD esters (3-MCPDE) and glycidyl esters (GE) are formed during the deodorisation process. Research has shown that upon hydrolysation in the gastrointestinal tract, 3-MCPDE and GE would release the toxic 3-MCPD and genotoxic carcinogen glycidol respectively. Excessive consumption of 3-MCPD over a prolonged period would adversely affect the kidney functions, central nervous system, and male reproductive system of laboratory animals. In the Council’s previous test on 60 samples of cooking oil covering 10 categories in 2017, 70% (42 samples) were detected with 3-MCPD, while 77% (46 samples) were found with glycidol. Although the performance of the current test showed slight improvement as compared with the 2017 test results, there were still approximately 60% samples detected with 3-MCPD (30 samples) and glycidol (29 samples) respectively.

The test found a significant variance in both the 3-MCPD and glycidol contents (per kg) amongst the samples. In terms of the content of the genotoxic carcinogen glycidol, the samples with the lowest (100μg) and highest (2,000μg) levels could vary by as much as 19 times. 1 coconut oil and 1 peanut oil samples were detected with 1,100μg and 2,000μg glycidol respectively, both of which exceeded the maximum level of 1,000μg/kg set out in the EU standard. The content of the harmful contaminant 3-MCPD also varied by more than 13 times between the samples with the lowest (130μg) and highest (1,900μg) levels. The highest 3-MCPD content was found in 1 sample of blended oil, yet it did not exceed the EU standard, and would probably not pose health risks when consumed in regular portions.

It should be noted that as extra virgin olive oils and cold-pressed oils are extracted through a mechanical process, the manufacturing process theoretically would not involve high temperatures or other chemicals, and thus such oils should not contain 3-MCPD and glycidol. EU legislation also states that extra virgin olive oils do not contain GE, 3-MCPD and their esters. However, the test found both 3-MCPD and glycidol in 1 sample of extra virgin olive oil and 2 samples of camellia oil which claimed to be cold-pressed. Despite the levels not exceeding the EU standard, it was suspected that the samples may have been treated with high temperature, or had been contaminated with non-cold pressed oils. As they were possibly in violation of the Trade Descriptions Ordinance, the relevant information had been passed to the Customs and Excise Department (C&ED) for follow-up.

Besides, 2 samples were detected with the genotoxic carcinogen benzo[a]pyrene, of which the concentration in 1 sample of corn oil (2.1μg/kg) slightly exceeded the EU standard (2.0μg/kg).

The test also found plasticisers in around 70% (35 samples) of the samples, approximately the same percentage of the 2017 test results. However, 5 samples in the 2017 test had exceeded the action level of the CFS and the maximum limit of the EU, whereas only 1 sample of extra virgin olive oil in the current test exceeded such limits, showing signs of improvement.

Fatty Acid Ratios and Smoke Points Varied Amongst Cooking Oil Categories

Aside from the taste, aroma and aesthetic of the dish, consumers should also be mindful of the health aspect when cooking. When selecting cooking oils, comprehensive consideration should be made based on their nutritional value. Out of the 13 cooking oil categories in the current test, some only covered 1 to 3 samples and could not exhaustively represent all other products of the same category on the market. However, the relevant nutritional values of each category could still serve as useful reference for consumers when selecting cooking oils.

The monounsaturated fatty acids (MUFAs) and PUFAs in cooking oils could lower the levels of “bad” cholesterol, and help in controlling the levels of “good” and “bad” cholesterols in the body. Based on the content per 100g, in the test, the 3 categories with the highest average MUFA content were camellia oil, olive oil and extra virgin olive oil; whereas the highest average PUFA contents were found in the 2 categories grapeseed oil and corn oil, and the sample of soybean oil.

Based on the content per 100g, a 74-time variance was found between the samples with the highest (74.8g, 1 peanut oil sample) and the lowest (1.0g, 1 coconut oil sample) MUFA content. As for PUFA, the variance between the samples with the highest (64.3g, 1 grapeseed oil sample) and lowest (0.6g, 1 coconut oil sample) contents even reached 106-fold. The Council reminds consumers that although UFAs have health benefits, they are still fats and excessive consumption over a prolonged period could lead to weight gain.

The fatty acid content and nutrient value of coconut oil has long been controversial. The test results indicated that coconut oil was the lowest in both MUFA (3.8g) and PUFA (2.0g) content amongst all categories. Despite the fact that the samples did not contain TFAs, their SFA content were also the highest (86.8g) of all categories. 

In terms of the average SFA content (per 100g), blended oil and rice bran oil ranked second and third highest, after coconut oil. The categories with the lowest average SFA content were canola oil and sunflower oil. The samples with the highest (87.8g, 1 coconut oil sample) and lowest (6.2g, 1 canola oil sample) SFA contents showed an approximately 13-time difference.

The Council reminds consumers to reduce the intake of foods containing SFAs and TFAs, in order to prevent increasing the bad cholesterol levels in the body. TFAs could even lower the levels of good cholesterols, resulting in even greater health risks than SFAs. Apart from coconut oil, the extra virgin olive oil category in the test was found with an average TFA content of almost 0 (based on the content per 100g), with only 1 out of the 14 samples detected with trace (0.1g) TFA. Similarly, the olive oil, avocado oil and canola oil categories also had a relatively low average TFA content. On the other hand, those with a higher average TFA content were the soybean oil sample, and the grapeseed oil and corn oil categories. The samples with the highest TFA content of all were 1 corn oil and 1 soybean oil (1.0g).

When deep-frying food at high temperatures, consumers should select cooking oils with a higher MUFA content as they are more stable under high temperatures. Besides, cooking oils with a lower smoke point would emit a large amount of cooking fumes during high-heat cooking, which could lead to health risks if inhaled over prolonged periods. In the test, 26 samples of cooking oil from different categories had a smoke point at or higher than 200°C, meaning that they are more suitable for high-temperature frying, grilling or baking. 7 samples had a smoke point lower than 180°C, and would be more suitable for low-temperature cooking methods, such as for preparing salads. The Council recommends consumers to reduce using high-temperature cooking methods that require a large amount of oil, regardless of the type of oil used, so as to safeguard one’s health.

A point of concern was that 8 samples of cooking oil in the test were found with a discrepancy between their declared and actual nutrient content that did not comply with regulations. Out of these samples, the SFA content for 1 sample, MUFA content for 1 sample, and PUFA content for 4 samples had a discrepancy of over 20% compared with the labelled value, exceeding the tolerance limit set out in the CFS’ “Technical Guidance Notes on Nutrition Labelling and Nutrition Claims”. The most severe discrepancy was the PUFA content in a sample of sunflower oil, which was 62.6g per 100g on the food labelling but was found to be 9g only in the test, a discrepancy of 85.7%.

The test results also showed that the TFA content of 2 samples did not comply with the benchmark to be claimed as “0” on the labelling, while 1 other sample did not indicate its TFA content on the nutritional labelling. For 1 sample of blended oil comprising rapeseed oil and peanut oil, “rapeseed oil” was placed first in the ingredient list, yet the product name only showed “peanut”, which might lead consumers into buying a product based on the name which did not reflect its actual ingredient composition. Besides having referred the relevant results to CFS for follow-up, the Council also urges the industry to clearly label the various types of cooking oils in blended oils, or the content or ratio of fatty acids, to provide consumers with more practical product information.

When selecting cooking oil, aside from paying heed to the information on the packaging, and selecting products with a higher nutritional value, consumers are reminded to switch the cooking oil type regularly to ensure a balanced nutrient intake. Besides, consumers could use a non-stick pan to reduce the amount of cooking oil used, and reduce the cooking time for high-temperature cooking methods to reduce the emission of cooking fumes.


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