Glaser's "Chemistry is in the News"
To Accompany Wade Organic Chemistry 4/e.
Chapter 19. Amines
Doesn't a juicy, lean steak marinated in a sweet and tangy sauce sound delicious? Not only is that delicious, it's healthy.
There appears to be a link between the consumption of cooked meats and
stomach, colorectal, pancreatic, and breast
ate their beef medium well to well done had greater than three times the
risk of stomach cancer than their counterparts who ate it rare to medium
rare. Those who ate it four or more times a week had greater than twice
the risk of those who ate less frequently.
Creatine and creatinine can be found in muscle meats such as beef, pork, fowl and fish (which have the most amino acids and creatine). These compounds can react with amino acids (and sometimes carbohydrates) at typical cooking temperatures to from heterocyclic aromatic amines HAA's. As meat is left to cook for long periods of time, it shrinks. HAA's are pushed to the surface where temperatures are higher, compounding the effect. Once consumed, HAA's can bind to DNA and cause mutations during replication. These mutations can, in turn, lead to cancer.
Marinating may lower HAA's in meats that are prone to their formation when cooked. To test this theory, researchers bathed chicken overnight in a heavily sugared oil-and-vinegar sauce. When the poultry finally is popped over a sizzling fire, it develops less than one-tenth as much PhIP (an HAA) as unmarinated chicken. In order to shut down the production of HAA’s, creatinine must be bound to either of two amino acids—L-tryptophan or L-proline.
There are four factors that influence the formation of HAA’s: the type of food, cooking method, temperature, and the amount of time the meat is cooked. When meat is cooked at temperatures above 325 degrees Fahrenheit, HAA’s are produced. In order to lower the temperature at which meat is cooked a person can roast it in the oven, boil it, or cook it in the microwave. Another way in which HAAs can be reduced is by marinating. The thicker components of the marinade, which consist primarily of oil and sugar, coat the meat and gum up the high temperature dehydration reaction that forms the HAAs.
On a nice spring Saturday afternoon, why don’t you all do a little of your own testing of marinades on your back porch.
Pertinent Text References
Chapter 19. Amines
Properties: p. 851-856
Substitution: p. 863-867
Reductive amination: p. 886-887
Question 1: Go to "The Cooking Makes a Difference". Using Figure 8, what can you deduce about the effects of cooking temperature and time on the production of HAA's?
Question 2: What are the four factors that influence HAA formation? How are these influential in HAA production?
Question 3: Go to the Science News Online. How does the amount of fat affect the production of HAA's? How are HAA's linked to breast cancer, specifically?
Question 4: Do you think that HAA's will have an affect on how you plan your diet (think about you predisposition for developing cancer)?
Question 5: Using the article about Beer, determine which component of beer may be responsible for the protection against cancer? What evidence is given to support the theory?