Sesame seeds are high in nutritional value, including fatty acids that can protect cells, regulate metabolic function, and reduce bad cholesterol in blood; as well as protein, minerals, vitamins, and dietary fibre which help promote hair health, relieve constipation, prevent anaemia and osteoporosis, and possess anti-inflammatory, antioxidant, and regulate immune responses. Sesame products are available in different forms and ways of serving, such as sesame oil to add aroma to cooking, sesame powder to enhance food texture, and sesame paste which is more commonly used as spread on bread. The Consumer Council tested 35 common sesame products on the market and detected plasticisers in 3 samples of sesame oil and 1 sample of sesame powder at levels higher than the action level set by the Centre for Food Safety (CFS). Some studies suggested that prolonged excessive consumption may affect the development of the reproductive system as well as the health of organs such as liver and kidneys in experimental animals. The genotoxic carcinogen glycidol was detected in 13 samples of sesame oil. Among these, the detected glycidol level in 1 sample exceeded the upper limit of European Union (EU) standards. In addition, the declared nutrient values of 10 samples did not tally with the actual test results. The Council urges manufacturers and agents to rectify the various problems promptly to ensure product safety.
The 35 samples of sesame products tested include 20 sesame oils, 10 sesame powders, and 5 sesame pastes. Test items included levels of plasticisers, pesticides, and nutrient content; as well as contaminants in sesame oil, and mycotoxins and pathogens in sesame powder and sesame paste. The price of the samples varied among different brands. For example, the price of sesame oil ranged from $11.9 to $68.7 per 100g, with the greatest difference of over 4.7 times, while the highest-priced and one of the lowest-priced samples both scored the highest 5 points in the overall rating, indicating that there is no definite correlation between price and product quality.
4 Samples Exceeded Plasticisers Limit, the Highest by 79 Times
Phthalate is a plasticiser that can improve the elasticity and flexibility of plastics. Studies have shown that long-term excessive consumption of plasticisers may affect the development of the reproductive system of experimental animals, and damage the health of organs such as the liver and kidneys. The migration of plasticisers would also be higher in foods with higher temperature, longer contact time, higher fat content and acidity. In Hong Kong, action levels for 5 plasticisers, namely DBP, DEHP, DIDP, DINP and BBP have been set. The action level for DBP is not more than 0.3mg/kg and that for DEHP is 1.5mg/kg, while the sum for DINP and DIDP is set at not more than 9mg/kg, and that for BBP is no more than 30mg/kg.
Test results showed that DBP was detected in 6 samples and DEHP in 20 samples. Among them, 3 sesame oil samples and 1 sesame powder sample were detected with DBP or/and DEHP at levels exceeding CFS action levels, with the levels of DBP and DEHP detected in 1 sesame oil sample exceeding limits by 79 times (24mg/kg) and more than 46 times (71mg/kg) respectively. If an adult consumes more than 15.7g (about 1 tablespoon) of this sesame oil sample per day, it would exceed the group tolerable daily intake (group-TDI) set by the European Food Safety Authority (EFSA); on the other hand, if a 5-year-old girl of 19kg body weight consumes 5.0g (about 1 teaspoon) of the same sample, it would already exceed the EFSA’s group-TDI. Furthermore, DINP was detected in 5 sesame oil samples and 1 sesame powder sample, but the levels did not exceed the CFS action level.
The Council reminds the manufacturers concerned to step up inspection of plasticisers in their products, obtain test reports on raw materials from suppliers, and review the production process to ensure product safety. The Council has also forwarded information of the relevant samples to the CFS for follow-up.
16 Detected with Glycidol or 3-monochloropropane-1,2-diol (3-MCPD)
Glycidol Detected Levels of 1 Sample Exceeded EU Limit
Fats and oils are the main component of sesame products. During the high-temperature deodorisation process of oils at over 200°C and over 160°C, the harmful process contaminants glycidyl fatty acid esters (GE) and 3-MCPD esters (3-MCPDE) are formed respectively. After these substances enter the human gastrointestinal tract and are substantially hydrolysed, they would respectively release the genotoxic carcinogen glycidol and toxic 3-MCPD, which affects experimental animals’ male reproductive system and damages kidney function and the central nervous system. Glycidol was detected in 13 sesame oil samples (ranging from 120μg/kg to 2,100μg/kg), with the highest being 2,100μg/kg, 1.1 times higher than EU standards (1,000μg/kg GE, expressed as glycidol). Furthermore, 13 samples were found with 3-MCPD (ranging from 120μg/kg to 2,300μg/kg), all of which did not exceed EU standards (2,500μg/kg of 3-MCPD and 3-MCPDE in total). Among them, 10 samples were found to contain both 3-MCPD and glycidol.
Glycidol and 3-MCPD and their fatty acid esters should not be found in virgin oils and cold-pressed oils that are pressed by mechanical methods without refinement at high temperatures and chemical extraction. However, 2 sesame oil samples claiming to be cold-pressed or extra-virgin were detected with 3-MCPD, and 1 of them was simultaneously detected with glycidol. Although detected levels did not exceed the upper limit of EU standards and should not pose any health risk in normal serving sizes, the results suggest that these products may have been subjected to high-temperature refining processes or contaminated by non-cold-pressed or refined oils, and there are also studies indicating high-temperature roasting of seeds significantly increases the levels of these contaminants in pressed oils. The Council has forwarded the information of the relevant samples to the Customs and Excise Department for follow-up.
At present, neither the Codex Alimentarius Commission (Codex) nor Hong Kong has set a standard for regulating the levels of 3-MCPD, 3-MCPDE, glycidol and GE in edible oils. According to reports by the Joint Food and Agriculture Organization/World Health Organization Expert Committee on Food Additives (JECFA) and the EFSA, prolonged daily excessive intake of 3-MCPD in test animals could impair kidney function, the central nervous system, and male reproductive system. JECFA has set a provisional maximum tolerable daily intake (PMTDI) for 3-MCPD and 3-MCPDE at 4μg per kg of body weight, whereas EFSA has set the tolerable daily intake (TDI) for 3-MCPD and 3-MCPDE at 2μg per kg of body weight. As for glycidol, which is a genotoxic carcinogen, JECFA and EFSA recommend that intake of genotoxic carcinogens should be as low as reasonably practicable/achievable and therefore a safe level of intake (SLI) for glycidol is not established.
Sesame Seeds Contain Unsaturated Fatty Acids but Prolonged Excessive Consumption May Lead to Obesity
Sesame products contain different types of fatty acids, including saturated fatty acids (SFAs), which increase bad cholesterol in the blood; trans fatty acids (TFAs), which increase bad cholesterol and reduce good cholesterol in the blood at the same time; as well as unsaturated fatty acids (UFAs), which are more beneficial to the body. Taking for example polyunsaturated fatty acids (PUFAs), which contribute to the development of skin, retina and brain nerves in foetuses and developing children, the average PUFAs content per 100g sample was 39.0g in the sesame oil group, 22.4g in the sesame paste group, and 21.6g in the sesame powder group. However, consumers should note that UFAs are still fats, and prolonged excessive consumption will still lead to weight gain. Consumers should therefore eat more vegetables and fruits to maintain a balanced diet.
Nutrition Labelling of 10 Samples Did Not Match Actual Content
According to the Technical Guidance Notes on Nutrition Labelling and Nutrition Claims (“Technical Guidance Notes”) issued by the CFS, discrepancies between the nutrition declared value on the label and actual content for prepackaged food should be within tolerance limits. However, the measured TFAs and SFAs contents of 1 sesame oil sample showed a discrepancy of 169% and 112% respectively from declared values stated on the nutrition label. The trans fatty acid test result of another 1 sesame oil sample was 89.7% higher than the declared value, and the saturated fatty acid test result of 1 sesame powder sample was 25.9% higher than the declared value. In addition, according to the Technical Guidance Notes, the TFAs test results of 7 samples did not meet its definition of “0” for labelling (less than or equal to 0.3g per 100g or 100ml). Incorrect nutrition labelling information may mislead consumers, especially those with chronic diseases such as heart disease and diabetes.
Consumers may refer to the following tips when purchasing and consuming sesame products:
- Check the product description on the packaging and pay attention to the ingredients list. Choose sesame pastes without added sugar, and sesame products with only sesame seeds as the ingredient, or with sesame seeds listed at the top of the ingredients list (indicating a relatively higher ratio of sesame);
- Choose sesame products with higher UFAs content (if any) and lower SFAs and TFAs contents as shown on the nutrition label. Also choose sesame paste products with a higher protein content and less sugar and sodium;
- After purchase, products should be stored in a cool and dry place away from direct sunlight. Refrigerate after opening and consume within 2 to 3 months. If the sesame product smells rancid, or the sesame powder becomes mouldy after exposure to moisture, it means the product has gone off and should be discarded immediately;
- Some people may be allergic to sesame seeds and may suffer from rashes, itching, facial swelling, etc. after consumption. In severe cases, this may lead to allergic reactions such as airway swelling, breathing difficulty, dizziness, fainting, and low blood pressure, and even death in extreme cases. Therefore, individuals allergic to sesame seeds should be extra cautious.
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