CHEMICAL RISKS ASSOCIATED WITH MICROWAVE COOKING
16. Cooking processes, especially the high temperature ones (e.g. grilling, baking, etc.) are known to induce the production of potential carcinogens. There have been concerns that microwave cooking may also increase the production of carcinogens or mutagens in foods.
17.
Currently there is no scientific evidence that the production of any carcinogenic substances would increase upon the application of microwave heating. A study examined mutagen production in cooked lamb and beef found no evidence of mutagenicity in microwave-cooked lamb chops, sirloin steak, leg of lamb or rolled beef loaf9. Results of another study also indicated no adverse
effects of diets cooked by microwaves compared with those cooked conventionally when fed to rats10.
18.
Of the carcinogens, the formation of the chemicals heterocyclic amines (HCAs), polyaromatic hydrocarbons (PAHs) and nitrosamines are of particular concern. Many studies have been conducted to compare the effect of microwave cooking with other conventional methods on the formation of these chemicals and their findings are summarised below –
Heterocyclic amines (HCAs)
19. HCAs are a group of compounds that are present in cooked muscle meat after high-temperature cooking such as grilling / barbecuing, broiling or pan-frying. The International Agency for Research on Cancer (IARC) of the
World Health Organization has classified one of the HCAs, 2-amino-3-methylimidzo[4,5-f]quinoline, as probable human carcinogen (Group 2A)11 and comprehensively genotoxic whereas nine other HCAs as possible human carcinogens (Group 2B). Negligible amounts of HCAs are formed when meats are cooked at or below 100oC and with shorter cooking time12. Hence, cooking methods like microwaving and boiling can result in food with lesser amounts of HCAs.
A study found that the formation of certain types of HCAs in chicken legs could be reduced by microwave cooking when compared with frying13. Also, precook meat in microwave oven before barbecuing would significantly reduce the formation of HCAs1,14. Another study also found that compared with non-microwaved beef patties fried under identical conditions, the amount of selected HCAs decreased three- to nine-fold after microwave pretreatment15.
Polyaromatic hydrocarbons (PAHs)
20. PAHs refer to a large group of organic chemicals containing two or more fused aromatic rings made up of carbon and hydrogen atoms. It is generally considered that incomplete combustion is involved during the formation of PAHs. Food processing or cooking steps such as roasting, grilling, barbecuing and smoking generate PAHs and increase the level of PAHs in the food being cooked16. Charred food of almost any composition contains PAHs17 while only very low level of PAHs was detected when food was cooked by some cooking steps such as steaming and microwave cooking. A study found that significant amount of PAHs was formed when beef cooked in corn oil by conventional frying and reheating whereas negligible amount was formed when cooked by microwave cooking and reheating1.
Nitrosamines
21. Nitrosamines are formed by a reaction between a nitrosating agent (e.g. nitrites) and a secondary or tertiary amine. The reaction may take place in certain types of foods as a result of curing, drying or cooking18. The most common and studied nitrosamine, N-nitrosdimethylamine (or dimethylnitrosoamine, or NDMA), has been classified as a probable human carcinogen (Group 2A) by IARC19.
A study found that microwave cooked bacon samples gave significantly lower levels of nitrosamines than fried samples1. Results of another study revealed that cooking of dried seafood products using indirect heating such as microwave cooking and steaming caused less increase in NDMA, as compared with direct heating such as a gas range20.
22.
In conclusion, microwave cooking did not produce significant amount of HCAs, nitrosamines or PAHs in meat products. The use of microwave cooking to precook meats before grilling or barbecuing has in fact been recommended so as to minimise the formation of HCAs and PAHs. It is probably due to the lower cooking temperature (temperature of microwave cooking normally would not exceed 100oC) and shorter cooking time of microwave cooking.
23.
It has also been alleged that other chemicals may be formed as a result of microwave cooking. However, their associations with microwave cooking have not been documented scientifically.
References
1 Hill, A and ILSI Europe Microwave Oven Task Force. Microwave Ovens. Brussels: ILSI Europe; 1998.
2 Decareau, R.V. Chapter one: History of the microwave oven. In: Microwave foods: new product development. Trumbull: Food & Nutrition Press, Inc.; 1992. p.1-46.
3 Health Canada. Radiation safety of microwave ovens. Available from: URL:
http://www.hc-sc.gc.ca/english/iyh/products/micro_ovens.html
4 Mullin J. Microwave processing. In: Gould, GW, editor. New methods of food preservation. London: Chapman& Hill; 1995. p. 112-134.
5 Ohlsson, T. Domestic use of microwave ovens. In: Macrae R, Robinson, RK and Sadler, MJ, editors. Encyclopaedia of food science food technology and nutrition. Vol. 2. London: Academic Press; 1993. p. 1232-1237.
6 Center for devices and radiological Health. Microwave oven radiation. U.S. Food and Drug Administration; 2000. [cited 04 Aug 17] Available from: URL:
http://www.fda.gov/cdrh/consumer/microwave.html
7 Buffler, CR. Microwave cooking and processing: engineering fundamentals for the food scientist. New York: Van Nostrand Reinhold; 1993.
8 Singh, RP and Heldman, DR. Introduction to Food Engineering. San Diego: Academic Press, Inc.; 1993.
9 Barrington, PJ et al. Mutagenicity of basic fractions derived from lamb and beef cooked by common household methods. Food and Chemical Toxicology 1990; 28(3): 141-6.
10 Jonker, D and Til, HP. Human diets cooked by microwave or conventionally: comparative sub-chronic (13-wk) toxicity study in rats. Food and Chemical Toxicology 1995; 33(4): 245-256.
11 IARC. IQ (2-Amino-3-methlyimidazo[4,5-f]quinoline): Vol. 56. France: IARC 1993. [cited 2003 Oct 31] Available from: URL:
http://monographs.iarc.fr/htdocs/monographs/vol56/05-iq.htm
12 National Cancer Institute. Cancer facts – heterocyclic amines in cooked meats. National Cancer Institute; 1996. [cited 2003 Nov 3] Available from:
http://cis.nci.nih.gov/fact/3_25.htm
13 Chiu CP, Yang DY and Chen BH. Formation of heterocyclic amines in cooked chicken legs. Journal of Food Protection 1998; 61(6): 712-9.
14 Skog K and Solyakov A. Heterocyclic amines in poultry products: a literature review. Food and Chemical Toxicology 2002; 40: 1213-1221.
15 Felton JS, Fultz E, Dolbeare FA and Knize MG. Effect of microwave pretreatment on heterocyclic aromatic amine mutagens/carcinogens in fried beef patties. Food Chemical Toxicology 1994; 32(10); 897-903.
16 Scientific Committee on Foods of EC (SCF). Opinion of the Scientific Committee on Food in the risk to human health of PAHs in food. Brussels: SCF; 2002.
17 Phillips DH. PAHs in the diet. Mutation Research 1999; 443:139-47.
18 Scanlan RA. Nitrosamine. In: Macrae R, Robinson, RK and Sadler, MJ, editors. Encyclopaedia of food science food technology and nutrition. Vol. 5. London: Academic Press; 1993. p.3245-49.
19 IARC. N-nitrosodimethylamine: Vol. 17. France: IARC 1978. [cited 2004 Oct 3] Available from: URL:
http://www-cie.iarc.fr/htdocs/monographs/vol17/n-nitrosodimethylamine.html
20 Lee SJ, Shin JH, Sung NJ, Kim JG, Hotchkiss JH. Effect of cooking on the formation of N-nitrosodimethylamine in Korean dried seafood products. Food Additives and Contaminants 2003; 20(1): 31-6.
