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Medicine and health science fair project:
Can marinating chicken prior to grilling reduce carcinogens?




Science Fair Project Information
Title: Can marinating chicken prior to grilling reduce carcinogens?
Subject: Medicine & Health
Grade level: Middle School - Grades 7-9
Academic Level: Advanced
Project Type: Experimental
Cost: High
Awards: 1st place, 13-14 age group category, Google Science Fair 2011
Winner: Lauren Hodge
Affiliation: Google Science Fair
Year: 2011
Materials, Equipment and Techniques: LC-MS/MS analysis, mass spectrometer, centrifugal evaporator
Description: Chicken breasts were cut into pieces and placed into marinades (leaving a control group of unmarinated chicken). After marinating the chicken was grilled and cooked. After preparation (see link) LC-MS/MS analysis was carried out on chicken samples to determine the number of micrograms of PhIP (a carcinogen in cooked meat) present in each gram of grilled chicken.
Link: http://sites.google.com/site/decreasingcarcinogens/home
Short Background

Marination and Carcinogens

Studies have shown that cooking beef, pork, poultry, and fish at high temperatures can lead to the formation of heterocyclic amines, benzopyrenes, and polycyclic aromatic hydrocarbons, which are carcinogens. However, proper marination may reduce the formation of these compounds. Grilling is often presented as a healthy alternative to cooking with oil, although the fat and juices lost by grilling can contribute to drier food.

As is true of any high-temperature frying or baking, when meat is grilled at high temperatures, the cooking process can generate carcinogenic chemicals. Two processes are thought to be responsible. Heterocyclic amines - HCAs are formed when amino acids (the building blocks of proteins), sugars, and creatine (a substance found in muscle) react at high temperatures. Additionally, polycyclic aromatic hydrocarbons - PAHs are formed when fat and juices from meat grilled directly over an open fire drip onto the fire, causing flames. These flames contain PAHs that then adhere to the surface of the meat. PAHs can also be formed during other food preparation processes, such as smoking of meats.

However it is possible to significantly reduce carcinogens when grilling meat, or mitigate their effect. Garlic, rosemary, basil, mint, sage, savory, marjoram, oregano, olive oil, cherries, and vitamin E have been shown to reduce formation of both HCAs and PCAs. Another method is pre-cooking the meat in the microwave, then draining meat juices so they do not fall onto flames, preventing release of PCAs. Side dishes and drinks rich in antioxidants, such as tea, have also been shown to neutralize the toxins by mixing in one's stomach.

(PhIP) is one of the most abundant heterocyclic amines (HCAs) in cooked meat. It is classified as a IARC Group 2B carcinogen, possibly carcinogenic to humans, and is considered "reasonably anticipated to be a human carcinogen" by the U.S. Department of Health and Human Services National Toxicology Program. PhIP is formed at high temperatures from the reaction between creatine or creatinine (found in muscle meats), amino acids, and sugar. PhIP formation increases with the temperature and duration of cooking and also depends on the method of cooking, as well as the variety of meat being cooked. There is inadequate evidence in humans that PhIP is carcinogenic, however, there is sufficient evidence in experimental animals, as well as in vitro models, for the carcinogenicity of PhIP.

PhIP has been found in cooked beef, pork, chicken, and fish products at concentrations up to 70 ng/g. Estimates of PhIP intake, from the HCA database, suggest that the mean daily intake of PhIP is between 43 and 110 ng/day. However, exposure to PhIP depends on the eating habits of the individual and can vary up to 5000-fold. This exposure is related to the type of meat, doneness, cooking method, and quantity consumed. PhIP can be quantitatively measured as low as 0.1 ppb in cooked ground meat and chicken and up to 500 ppb in well-done flame-grilled chicken. Individual exposures can also differ due to various anti-carcinogens in the diet. Fiber or chlorophyllin, which directly bind to PhIP and prevent absorption, flavonoids, known inhibitors of metabolic activation, and substances that prevent formation of the carcinogen during cooking further complicate the exposure assessment to PhIP. Thus, the dose (exposure) plays a major role in individual risk related to PhIP and merely understanding the degree of doneness of the meat products may not be adequate.

Numerous in vivo and in vitro studies have demonstrated that PhIP is a potent mutagen and can induce tumors of multiple sites in animal models. PhIP was positive in bacterial (Ames) test and induced chromosomal abnormalities in human and Chinese hamster cells in vitro. PhIP has also formed DNA adducts in vivo in both rats and monkeys. PhIP has been tested for carcinogenicity in both mice and rats by oral administration. Increases in lymphomas were seen in mice and increases in adenocarcinomas of the small and large intestine in males and mammary adenocarcinomas in female were seen in rats. Also, an increasing number of epidemiological studies have evaluated the association of well-done meat intake and HCA exposure with cancer risk in humans. In general, these studies have reported that high intake of well-done and/or high exposure to PhIP may be associated with cancer of the colorectum, breast, prostate, pancreas, lung, stomach, and esophagus.

See also:
http://en.wikipedia.org/wiki/Grilling
http://en.wikipedia.org/wiki/2-Amino-1-methyl-6-phenylimidazo(4,5-b)pyridine
http://en.wikipedia.org/wiki/Heterocyclic_amine

Source: Wikipedia (All text is available under the terms of the GNU Free Documentation License and Creative Commons Attribution-ShareAlike License.)

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