What makes up a marinade?  A marinade is always a combination of at least two of the following base ingredients:

The marinading process breaks down the proteins in the meat tissue into a simpler form.  This is called denaturalization.  We denature foods all the time when cooking with heat, dry aging meat, and ,as in this case, chemically.  Since you are chemically breaking down the structure if you leave your meat in the marinade for move the 24 hours you’re most likely going to have gelatin left when you get to using the meat.

The marinade process also allows you to force out the tasteless moisture in the meat and replace it with your newly created flavorful liquid.  If you marinade fish and seafood, the tissue will actually get tougher in the process.

Here is a quick look at some the ingredients in a couple of marinades:

Angelyn’s Marinade

soy sauce(acid and flavor enhancer from salt), white wine (acid), sesame oil (oil), garlic (spice), ginger root (spice), cilantro (aromatic)

Full Recipe: http://allrecipes.com/Recipe/Angelyns-Marinade/Detail.aspx

Mexican Ceviche:

limes (acid), tomatoes (acid), green pepper (aromatic), chopped parsley or chopped cilantro (aromatic), salt (flavor enhancer), pepper (spice), oregano (aromatic), jalapeno peppers (spice and acid), white vinegar (acid), onion (aromatic), cilantro (aromatic), Tabasco sauce (acid)

Full Recipe: http://www.recipezaar.com/Mexican-Ceviche-8899