While fresh vegetables usually have a shelf life of only a few days, preserved vegetables produced using the fermentation or preservation process can be stored for longer periods of time, providing a flavour boost to dishes while some also serve as appetisers. A wide range of preserved vegetables are available on the market, such as kimchi, sauerkraut, and mustard tuber. Preserved vegetables contain dietary fibre, vitamins, and minerals, as well as probiotics produced during the fermentation process. However, as most preserved vegetables are preserved with salt, they are generally higher in sodium. The Consumer Council tested 30 prepackaged preserved vegetable samples and found that over 85% were relatively high in sodium content, which might increase the risk of hypertension and other diseases if consumed regularly. Although over 30% samples contained lactic acid bacteria which could promote intestinal health, some samples were relatively high in sugar and fat content, so consumers should be mindful of “enjoying more by eating less”. In addition, 3 samples of pickled mustard leaf with olive contained relatively more insect fragments and the relevant information has been forwarded to the Centre for Food Safety (CFS) for follow-up. The Council reminds consumers to maintain a balanced diet and not to consume preserved vegetables as a substitute for fresh vegetables.
The Council sourced 30 samples of prepackaged preserved vegetables from supermarkets and department stores, including 8 kimchi, 4 sauerkraut, 5 gherkin, 5 mustard tuber, 4 radish, and 4 pickled mustard leaf with olive samples, priced between $4.3 and $82 per pack, equivalent to unit prices from $4.3 to $26.5 per 100g or 100ml. Test items of preserved vegetables (without liquid) included nutrients, contaminants, preservatives, microorganisms, and light filth content. Results showed that 10 samples received an overall score of 4.5 points, including both higher and lower priced products (price per pack), reflecting that there is no necessary correlation between price and quality.
Over 85% Samples Were “High in Sodium”
To inhibit microbial growth, adding salt to vegetables to create a “dehydrating” effect is a very common preservation method, but the amount of salt used in different preserved vegetables could vary greatly. The World Health Organization (WHO) recommends that adults should consume less than 2,000mg of sodium per day, which is equivalent to about 5g of salt (i.e. slightly less than 1 level teaspoon). According to the reference level provided to consumers by the CFS, a food is classified as “high-sodium” if it contains over 600mg of sodium per 100g solid food. Test results showed that 26 samples were “high-sodium” foods, with sodium content ranging from 641mg to 3,080mg per 100g. The highest sodium content was found in a sample of pickled mustard leaf with olive, which contained 924mg of sodium per serving (30g), equivalent to nearly half of the WHO’s recommended daily sodium intake limit for adults. Sodium could help maintain extra-cellular fluid balance and acid-base balance in the body, and is essential for nerve transmission and muscle contraction, but excess consumption over a prolonged period might lead to an increase in blood pressure thus the risk of cardiovascular and kidney diseases. According to information from the Department of Health, excessive salt intake might also damage the stomach lining and increase the risk of enhancing colonisation of the carcinogenic bacterium Helicobacter pylori, increasing the risk of stomach cancer.
The Council also found that the labelled value of sodium content of some preserved vegetable samples was lower than actual test results, with a maximum discrepancy of over 1.5 times. Apart from possible error in nutrition labelling, another reason may be that the labelled sodium content of the sample is actually of the whole packet of preserved vegetables (i.e. both solid and liquid), and if the product has more liquid, the labelled sodium content of the packet may be lower than that of the preserved vegetable alone. Therefore, consumers should be aware that they might have a higher sodium intake than expected when eating preserved vegetables. The Council urges manufacturers to provide nutrition information on the packaging for both the solid part and the whole product with liquid so consumers could have clearer and more comprehensive information about the product.
2 Samples Were “High in Sugar”
All Pickled Mustard Leaf with Olive Samples Were “High in Fat”
Most of the preserved vegetable samples did not have a high sugar content, with 23 samples found to be low in sugars. However, 2 samples were “high-sugar” foods, containing 25.8g and 34g of sugars per 100g sample respectively. WHO recommends a daily free sugars intake of less than 50g (about 10 cubes of sugar) for adults on a 2,000kcal daily diet. Another 4 samples were high in fat, all were pickled mustard leaf with olives, with total fat content ranging from 46.4g to 69.6g per 100g. Taking the sample with the highest total fat content as an example, assuming that an adult consumed one serving of this sample (30g), they would have a 20.9g total fat intake, which is 31.3% of the WHO’s recommended maximum daily intake of total fat for adults. If the sample was consumed without draining as much liquid (such as oil) as possible, the fat intake would be even higher.
Kimchi Samples Contained the Highest Lactic Acid Bacteria Count
But High Temperatures Could Inactivate Lactic Acid Bacteria
Many fermented foods contain lactic acid bacteria, which could help promote gut microbiome diversity and boost the number of beneficial bacteria, making them beneficial to digestive health, immune system, and overall health. Lactic acid bacteria also possess antioxidant properties that could help reduce inflammation and oxidative reactions in the body. Mesophilic lactic acid bacteria were detected in 10 samples, 7 of which were kimchi, which also had the highest average count. Some experts opined that if preserved vegetables are sterilised at high temperatures, the lactic acid bacteria in them will become inactive. Some manufacturers might also use non-natural fermentation methods to reduce production time and improve quality control, but these products usually do not contain lactic acid bacteria. Ready-to-eat fermented preserved vegetables should not be heated before consumption if lactic acid bacteria intake is intended. In fact, consumers could also absorb lactic acid bacteria from other foods, such as yoghurt and tempeh, whereas preserved vegetables should not be taken as the main source for lactic acid bacteria intake.
Only 1 Sample Not Detected with Light Filth
The main ingredient of preserved vegetables is vegetables, which might be contaminated by insects or other impurities, while foreign substances might also be brought in during the production process. Even though they might not be harmful to humans, if the amount of foreign matter is high, it indicates improvement of product hygiene is needed. The majority of the samples (29 samples) were found to contain light filth, including insects, acarid, hair, metal and plastic fragments. Although most samples did not contain a lot of light filth, 3 samples of pickled mustard leaf with olives contained between 91 and 310 pieces of insect fragments per 100g sample. The Council urges manufacturers to exercise stringent quality control over ingredients, finished products, and the production process to enhance food safety and hygiene.
In terms of preservatives, sulphur dioxide was detected in 2 gherkin samples, while sorbic acid or benzoic acid was detected in 8 samples respectively, all of which met the requirements of the Preservatives in Food Regulation, but 2 samples contained no information on preservatives in their list of ingredients in accordance with the Food and Drugs (Composition and Labelling) Regulations.
Mindful of Sterilisation for Homemade Preserved Vegetables
Some consumers may make their own preserved vegetables at home, but due to technical and environmental factors, the preparation process might not be effective in killing bacteria, thus increasing the risk of food poisoning. Apart from using fresh, whole, and good quality vegetables, consumers should also clean and sterilise all equipment and utensils before pickling, and boil glass containers for at least 10 minutes to kill microorganisms. In addition, nitrite, which has a relatively high toxicity, might be produced in the preservation process, but the content would decrease with the duration of pickling. As the time required for preparing different types of preserved vegetables varies, consumers are advised to refer to recipes from credible sources to make preserved vegetables to reduce the risk of poisoning.
Some tips for consuming preserved vegetables:
- Preserved vegetables generally have a high sodium content. Consumers should moderate their intake and choose fresh vegetables as the mainstay of their daily diet;
- Consider the overall nutritional value of the product, choose preserved vegetables with lower sodium, sugar and fat content, and find out whether preservatives or food colourings, etc. have been added to the product;
- Individuals with gastrointestinal problems such as irritable bowel syndrome, and hypertension, heart diseases, or chronic kidney failure should refrain from eating preserved vegetables;
- People with allergy should try choosing preserved vegetables without added preservatives to avoid allergic reactions caused by excessive intake;
- Avoid products of unknown origin and check carefully for any unusual odour or colour when purchasing.
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