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It was 2002 when Swedish researchers announced that they had found surprisingly large amounts of acrylamide in cooked foods. Apart from the public scare that followed, this news generated a new area of research as teams around the world vied to publish new data on the type of food implicated and the mechanism of acrylamide formation. The concern arose from its potentially harmful effects, since acrylamide causes cancer in lab rats, although little is known about its effects on humans via the diet. The Joint Food and Agriculture Organisation and the WHO declared recently that current levels of dietary exposure might be of concern, so efforts should be made to reduce acrylamide levels in food. It is not formed in all cooked foods. For instance, microwaved or boiled foods appear to be acrylamide free, as is raw food. However, the starch-rich foods are affected the most when they are fried, grilled, baked or toasted. Foods like potato chips, potato crisps, bread, crispbread and coffee. It is the presence of reducing sugars like glucose that initiate the formation of acrylamide via the Maillard reaction with amino acids, either in free form or within proteins. A whole series of compounds can be produced and many contribute to the flavour and aroma of cooked foods. There have been numerous suggestions for reducing acrylamide levels such as changing the cooking conditions, reducing the acrylamide precursors before cooking by blanching or soaking, and treating food by microwaving or with enzymes before cooking. A further idea involves the use of antioxidants. A recent report stated that natural extracts of green tea and bamboo leaves alleviated acrylamide formation, although this was in direct contrast to a second report showing that ascorbic acid increased acrylamide in cooked potato. The difference probably lies in the type of antioxidant, since there are many different classes such as flavonoids, tannins, coumarins, lignans and stilbenes. However, this reduction in acrylamide has prompted scientists to see if other types of plant extract can produce the same effect. Harold Corke, Fan Zhu and Yi-Zhong Cai from the University of Hong Kong and Jinxia Ke from the Republic Polytechnic, Singapore, examined the effects of 35 aqueous plant extracts on a model food system. They also studied the effects of a set of 12 individual phenolic antioxidant compounds. Corke recognised that GC/MS and LC/MS methods for measuring acrylamide exist already that would work well in his study. However, he pointed out that they are relatively expensive to operate and are not freely available in developing countries. HPLC was his preferred choice due to its ease of operation and low cost, so his team devised a new HPLC method with diode array detection. From a set of three columns tested, they selected a commercial alkyl RP bonded phase designed to retain hydrophilic and other compounds when using highly aqueous mobile phases. With this column and a mobile phase of pure water, acrylamide eluted within 12 minutes and was detected at a wavelength of 200 nm. There was no interference from other compounds produced during the model reaction or derived from the extracts. Although reputed to be stable under these conditions, the researchers found that the column suffered from phase collapse after 10 days of use, so had to be replaced. Nevertheless, the performance before deterioration was good. Using an external acrylamide standard, recoveries of 88.5-92.3% were achieved and the calibration curve was linear up to 2.5 µg/mL. The model reaction they chose was the Maillard reaction between asparagine and glucose. It was carried out in the presence and absence of the plant extracts from species such as mint, mulberry, coriander, grape, clove, buckwheat and lemongrass, as well as the phenolics. Acrylamide was extracted from the solution with ethyl acetate for analysis. Surprisingly, 34 of the 35 extracts reduced the acrylamide content, with cuts ranging from 11-74.5%. Mint leaves, cumin seeds and star anise fruit were the best performers with reductions of 74.5, 73.1 and 68.9%, respectively. Only one extract tested raised the acrylamide level and that was Huanggang Ku-Jing-Cha leaves, a type of tea. This behaviour might be explained in terms of a synergistic effect, since there are many components present in plant extracts. Other, perhaps amino acids, water-soluble proteins or saccharides, might also contribute. For the phenolic compounds tested, 10 reduced acrylamide, with p-coumaric acid the best at 53.4% down. Citric acid, which was also tested, had a greater effect with a 60.5% reduction. Only two of the phenolics, ferulic acid and hesperetin, had an adverse effect, raising acrylamide by 4.5 and 8.6%, respectively. At this stage, it appears that aqueous extracts of plants or individual phenolic compounds could be used to lower the amounts of acrylamide produced in cooked food, in line with the WHO recommendation. The team will continue this line of research, with future work focusing on more types of plant extract while seeing if the effects are mirrored in real cooked foods such as potato chips and crisps. Related links:
The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd. |
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