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The Centre for Food Safety (CFS) of the Food and Environmental Hygiene Department released today (July 29) the sixth report of the First Hong Kong Total Diet Study (HKTDS), which covers the dietary exposure of the local population to acrylamide. According to the study, the dietary exposure of the local population to acrylamide was found to be low, relative to other countries and regions (including the United States, Canada, Europe, New Zealand and the Mainland). However, the CFS' risk assessment of the estimated dietary exposure of the local population to acrylamide may indicate a human health concern.
Acrylamide is an industrial chemical used in the production of polyacrylamide. Recent research has found that it is formed when foods are cooked or processed at high temperature, mainly via the Maillard reactions. Upon heating, the free amino acid, asparagine, in food reacts with reducing sugars to form acrylamide.
A spokesman for CFS said, "The chemical is a genotoxic carcinogen and is considered to possibly cause toxic effects on the nervous system, and adverse reproductive and developmental effects in experimental animals. However, epidemiological studies do not provide any consistent evidence to show a positive correlation between the level of dietary exposure to acrylamide and the incidence of cancer in humans."
He noted that CFS had conducted several studies on acrylamide in food, mainly on foods reported to contain high levels of acrylamide. A risk assessment study in 2010 suggested that the dietary exposure to acrylamide of the local population might indicate a human health concern. As a result, acrylamide was selected in the first HKTDS with a view to obtaining an estimate of dietary exposure to acrylamide from the whole diet.
The acrylamide content of a total of 133 food items (with 17 fruit items excluded) was analysed.
Results showed that among the food groups, the highest acrylamide level was detected in the food group "snack foods" (mean: 680 microgramme/kg), followed by "vegetables and their products" (mean: 53 microgramme/kg) and "legumes, nuts and seeds and their products" (mean: 40 microgramme/kg). However, the majority (95%) of samples for "fish and seafood and their products", and all samples of "eggs and their products" and "beverages, alcoholic" were not detected to contain acrylamide.
Among the food items, potato chips were found to contain the highest level of acrylamide (mean: 680 microgramme/kg), followed by fried potato (mean: 390 microgramme/kg) and zucchini (mean: 360 microgramme/kg).
The dietary exposure to acrylamide of the average and high consumer in the local population was 0.21 and 0.54 microgramme per kg of body weight per day respectively, and their Margins of Exposure (MOE) were all well below 10 000 (847 – 1 459 for the average population, 334 – 576 for the high consumers). This may indicate a human health concern because of the relatively low figures for a genotoxic carcinogen. The MOE value is defined as the ratio of the benchmark dose lower confidence limit for a 10 per cent extra risk of tumours (BMDL10) from an animal study to the estimated dietary exposure to acrylamide of the local population. The Joint Food and Agriculture Organisation / World Health Organization Expert Committee on Food Additives adopted the MOE approach for assessing the risks of acrylamide to human health. For genotoxic carcinogens, an MOE value below 10,000 would be of concern from a public health point of view. The lower the MOE, the greater the health concern.
The influence of different cooking methods in the formation of acrylamide in vegetables is worth noting in analysing the results of this study.
According to the current study, the main dietary source of acrylamide for the local population was from "vegetables and their products", particularly stir-fried vegetables (44.9%), including Chinese flowering cabbage, water spinach, zucchini and onion. Nevertheless, some kinds of stir-fried vegetables, such as Chinese spinach, watercress, spinach and Chinese lettuce were detected to have low levels of acrylamide, and non-cooked, boiled or steamed vegetables like European lettuce, cucumber and hairy gourd were even not detected to have acrylamide.
Since the formation of acrylamide while frying vegetables may be affected by many factors (such as the presence of asparagine and reducing sugars in the vegetables, and the frying temperature and time), further testing on the formation of acrylamide in stir-frying vegetables with and without cooking oil added under different cooking conditions was conducted. Samples of fried vegetables prepared by restaurants were also taken for testing of acrylamide.
The findings indicated that a higher level of acrylamide was formed where the vegetables were fried at a higher temperature and for a longer time. Lower acrylamide levels were found in the vegetables sampled from restaurants compared with HKTDS samples of the same kind of vegetables. As blanching of vegetables before stir-frying was common in restaurants, such a practice may help reduce the formation of acrylamide. However, no obvious associations were observed in acrylamide levels for frying vegetables with or without cooking oil added.
Since the acrylamide levels detected in both the above experiment and stir-fried vegetables sampled from restaurants were lower than the HKTDS samples, the HKTDS study might have overestimated the estimated dietary exposure to acrylamide from stir-fried vegetables. Moreover, it should be noted that the formation of acrylamide is influenced by many variables, such as batch to batch variation, food composition (e.g. contents of reducing sugars and amino acids) and processing conditions (e.g. cooking temperature and time), etc. When producing fried food, members of the public should not cook for too long or at too high a temperature, and should avoid charred food or excessive browning.
The spokesman stressed that the public should maintain a balanced and varied diet, consume at least three servings of vegetables a day, and moderate the consumption of fried foods such as potato chips and fried potatoes. To reduce the formation of acrylamide, food should not be cooked for too long or at too high a temperature.
To reduce the level of exposure to acrylamide from vegetables, members of the public may consider blanching the vegetables before frying, or cooking them by boiling or steaming. Some vegetables may also be eaten raw after washing.
The spokesman also advised the food trade to find ways to reduce the level of acrylamide in food. CFS has updated the "Trade guidelines on reduction in acrylamide level" issued in 2011. Members of the trade may refer to the trade guidelines in seeking ways to reduce the level of acrylamide in food during the selection of raw materials and the formulation of recipes and food processing conditions. Taking potato products such as French fries and potato chips as an example, the food trade may consider selecting potato varieties with low reducing sugar levels and optimise the cooking temperature and time to avoid overcooking.
The First Hong Kong Total Diet Study was launched in March 2010 and will be completed in 2014. This is the sixth report in the series. The first five reports that have been released cover the following substances: dioxins and dioxin-like polychlorinated biphenyls (PCBs), inorganic arsenic, polybrominated diphenyl ethers, pesticide residues and metallic contaminants.
The Study aims at estimating the dietary exposure of the general population and various population subgroups to a range of substances, including contaminants and nutrients. The purpose is to assess any associated health risks. It focuses on the total diet of the population rather than individual foods.
A total of 150 food items were chosen for the study according to the food consumption pattern of the Hong Kong population. They are being used for testing the level of over 130 substances, including pesticide residues, persistent organic pollutants, metallic contaminants, mycotoxins, macro nutrients and elements. By combining the test results with food consumption data, the dietary exposure of the population to the selected substances may then be estimated.
The full report on the study on acrylamide is available on CFS' webpage at www.cfs.gov.hk. Study results concerning other substances will be released in phases.
Ends/Monday, July 29, 2013
Issued at HKT 17:09
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