The value of marinades is two-fold: tenderizing tough, inexpensive, cuts of meat (skirt steak, beef chuck, and pork shoulder, for example) and adding depth of flavor to grilled sides and entrees. Addanother bonus for marinating: Recent studies have found that they may also have protective power against some type of cancer-causing agents!
Lately there have been rumblings of a possible link between grilling and cancer. Some studies have shown that a reaction between creatine in muscle meats and amino acids caused by flame cooking at high temperatures produces a cancer-causing agent known as heterocyclic amine (HCA).
Thankfully, new research indicates that marinades may discourage formation of certain HCAs in char-grilled meat. Scientists aren't sure exactly how marinades act to reduce the formation of carcinogens but there is evidence that they may act as a barrier or that their protective powers may lie in their ingredients.
Acidic ingredients like vinegar or citrus juices, as well as herbs, spices, and oils, seem to contribute to the prevention of HCA formation.
Immersion in an acid-based marinade for as little as forty minutes resulted in a decrease of 92-99% of heterocyclic amines (HCA's) in recent tests by the American Institute for Cancer Research. (About 1⁄2 cup of marinade is needed for every pound of food, although large pieces may need more to cover the food's surface adequately. Total immersion is not necessary, but the food should be turned occasionally, so that all surfaces will be in contact with the marinade long enough to benefit.)
More studies are being conducted, but the acidic component in marinades seems to do the trick.
The key tenderizing ingredient in a marinade is the acid: fruit (kiwi, pineapple, papaya, apple, citrus) fruit juice, vinegar, wine, buttermilk, coconut milk, and yogurt. These break the protein strands and cause the structure of the meat to soften.
Marinating is currently the best known method of discouraging the formation of HCAs, so keep on grilling.