Goji berry (also known as wolfberry) is a traditional Chinese medicine (TCM) commonly used in many home-cooked dishes such as steamed chicken, stewed soups, and dessert soups, etc. In Europe and the USA, goji berries have become a “superfood”, with claims of anti-oxidising and antiviral properties, and as a result many dried goji berry snacks have recently emerged. There are 2 main species of dried goji berries on the market: Lycium chinese and Lycium barbarum L., which are very similar in appearance but differ in properties and composition. The Consumer Council tested 27 samples of dried goji berries and genetic test results showed that all samples were Lycium barbarum L., while results also revealed that goji berries are rich in carotene, vitamin C and various minerals, consistent with TCM theories of goji berries being beneficial in nourishing the liver, kidneys, virility, and eyes. However, all samples were detected with different types of heavy metals, with 2 samples found with lead concentration close to the maximum level permitted under relevant Hong Kong regulation. In addition, over 70% of the samples were found to contain pesticides, 1 of which was even detected with 7 pesticides, which may cause a “cocktail effect” and pose health risks. The Council urges the industry to reduce the use of pesticides and other chemical pest control methods to reduce risks to humans and the environment.
The Council collected 27 dried goji berry samples from the market in August and September 2022, of which 23 were prepackaged and the remaining 4 non-prepackaged. 3 samples were labelled “ready-to-eat” and 7 were labelled “organic”. Prices ranged from $5 to $146 per packet, equivalent to a unit price of $9 to $64.3 per 100g, a price difference of over 6 times. Test items included DNA, nutrient content, heavy metals, common food colourants, mycotoxins and pesticides. 15 samples received an overall rating of 4 points or above, including the highest and lowest priced samples, while 1 sample with an overall score of only 2.5 was over 2.5 times more expensive than the cheapest sample rated 4 points, reflecting that product quality may not be directly proportional to the price.
β-carotene Detected in All Samples
Possesses Eye Protection and Antioxidant Effects
Many people consume goji berries with the anticipation of promoting eye health and achieving anti-oxidising effects, for which carotene is proven effective. All samples contained the more common β-carotene, with levels ranging from 0.272mg to 1.13mg per 100g. The 2 samples with the highest β-carotene content contained 1.13mg and 0.964mg per 100g respectively. β-carotene, as the form of carotene most easily converted into vitamin A, possesses anti-oxidising properties. Sufficient vitamin A intake is essential for eye health, and vitamin A deficiency may lead to night blindness and dry and coarse eyes.
Goji Berries Rich in Iron and Copper
Helpful Mineral Supplement for Vegetarians
The human body requires various minerals to promote growth, development, and maintain normal body functions. Iron was found in all 27 samples, with 6 meeting the definition of “iron-rich food” (i.e. no less than 4.5mg iron per 100g solid food) under the Food and Drugs (Composition and Labelling) Regulations, out of which the sample with the highest level contained 7.36mg of iron. Although it was commonly known that the absorption rate of non-heme iron from plant foods is lower than that of heme iron generally found in meat or seafood, the moderate to high levels of vitamin C (from 3.84mg to 18.93mg per 100g among samples) in goji berries can help to promote iron absorption in the human body, making goji berries a possible day-to-day supplementary source of iron for vegetarians or people who cannot consume meat.
Copper can boost immunity, reinforce bones, assist transport of iron, and helps with cholesterol and glucose metabolism. The copper content in 26 samples met the definition of “copper-rich food” under current regulations, i.e. no less than 0.45mg copper per 100g solid food. 1 sample contained 2.26mg copper per 100g (equivalent to 22.6mg per kg), which exceeded maximum limit of heavy metals in goji berries set out in the Pharmacopoeia of the People’s Republic of China which stated that the copper content in goji berry shall not exceed 20mg per kg. However, based on the tolerable upper intake levels (12mg/day for males and 10 mg/day for females) listed by the World Health Organization, adults would have to consume over 500g of this sample per day to exceed the limit, therefore normal consumption would unlikely pose any health risks.
Lead Content in 2 Samples Close to Regulatory Upper Limit
Industrialisation and modernisation of agriculture have increased the risk of farmland contamination, with plants absorbing heavy metals from the soil and accumulating to even higher concentrations along the food chain. According to the test results, all 27 samples were detected with different types of heavy metals, with 21 samples found to contain lead at levels ranging from 0.018mg to 0.29mg per kg, 2 of which had detected amounts of 0.284mg and 0.29mg per kg respectively, which, after conversion, were close to the upper limit set in the Hong Kong Food Adulteration (Metallic Contamination) Regulations. The Council has referred the results to the Centre for Food Safety for follow-up. Studies have shown that chronic dietary intake of lead through the diet can adversely affect the neurodevelopment and mental development of children, as well as the systolic blood pressure of adults. Therefore, consumers should avoid consumption of any levels of lead as much as possible. Besides, cadmium was detected in all samples, chromium in 3 samples and arsenic in 2 samples, but the levels were below the regulatory limit.
1 Sample Detected with 7 Pesticides Possibly Causing “Cocktail Effect”
Many farmers spray their goji berry shrubs with pesticides to tackle infestation, and the Council’s test results revealed that 19 samples were detected with a total of 14 different pesticides. Among them, 2 samples were detected with 0.062mg/kg of Chlorfenapyr and 0.071mg/kg of Chlorothalonil respectively, which exceeded the European Food Safety Authority’s (EFSA) maximum residue limit (MRL) for goji berries, but were lower than the requirements for fruiting vegetables (other than cucurbits) under Hong Kong’s Pesticide Residues in Food Regulations. According to statistics from the Joint Food and Agriculture Organization of the United Nations/World Health Organization Meeting on Pesticide Residues, the maximum tolerable daily intake of Chlorfenapyr and Chlorothalonil are 0.03mg and 0.02mg per person respectively. A 60kg adult would have to consume over 29kg or 17kg of these 2 samples per day respectively to pose a health risk. Pesticide levels in the other 17 samples were lower than relevant Hong Kong and European requirements.
Furthermore, 4 samples were found to contain 5 or more different pesticides, and 1 sample was even detected with 7 types of pesticides. The combination of pesticides may result in a multiplying “cocktail effect” which could pose health risks. Although views on the possibility of the “cocktail effect” vary internationally, the Council anticipates the industry to engage raw material suppliers with good agricultural practices, prioritising physical pest control measures, and reducing the use of chemical methods such as pesticides to minimise risks to humans and the environment.
In recent years, goji berries have become a highly sought-after “superfood”, and they are indeed nutritious and healthy. Consumers should take note of the following when buying and consuming:
- Goji berries are susceptible to mould after the packaging is opened and should be stored in an airtight container in a cool and dry place;
- Before consumption, wash then soak the goji berries in cold drinking water for 15 to 20 minutes to remove the harmful residues from the surface. Avoid soaking for too long, while prolonged cooking at high temperature is also inadvisable, as these may result in the loss of soluble nutrients such as vitamin C and minerals;
- According to TCM research, goji berries are suitable for people with a yin-deficient constitution, used for addressing symptoms such as soreness and pain in the loins and knees, dizziness and tinnitus, and blurred vision. However, people with spleen deficiency, “heat” and “dampness” in the body, and shortness of breath with phlegm should not consume goji berries regularly.
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