Marinades are designed to flavour and tenderise your food, they function similar to a Wet Brine, they differ a little in that most of them are thicker and contain sugars. Some will have quite strong flavours.
Some will use an Enzyme to tenderise the meat.
Usually, we will include an acid in a marinade and the common belief is that marinades tenderise the meat, in fact, more often than not, the opposite is true.
Acids come in several forms, in cooking, Wine, Lemon (Citrus) Juice, Vinegar, Verjuice (from unripened grapes), Acetic Acid, Lactic Acid and Citric Acid are most common.
Fish is more susceptible to the effects of acids and will oxidise quite quickly. Ceviche is a good example of a dish prepared by the acidulation of fish from the addition of citrus juice. The acid promotes the coagulation of the proteins making the fish firmer.
Marinades often contain wine and/or citrus acids however, we do this for flavour rather than tenderising. Marinades only penetrate a few millimetres into the flesh so, the effect on tenderness is negligible, it is the flavour that we are looking for! It is advisable to cook off the alcohol before adding wine so the coagulation of the proteins is minimised.
Exposure to acids causes the denaturing of the proteins, this simply means the bonds that hold them together as tight bundles are broken and they unravel. Quite quickly a denatured protein will encounter a neighbouring denatured protein and will bond to it. This cross linking of bonded denatured proteins forms a matrix which absorbs and holds liquids.
The muscle fibres are wrapped in collagen packets, and this prevents the penetration of the marinade. In reality, Dry Brine is as effective as a marinade but of course it’s difficult to get the flavour of wine for example in a dry form.
Enzymatic marinades work by breaking down muscle fibres and connective tissue (collagen) but can quickly turn meat to mush. I am wary when using ingredients with enzymes
Raw Figs, Ginger, Kiwi Fruit, Papaya, Pineapple, and some melons all contain enzymes, known collectively as proteases (protein enzymes).
Dairy products like buttermilk and yogurt work to tenderise meat. These products contain lactic acid but are only mildly acidic, and also contain enzymes in low concentration, so they don’t toughen the way strongly acidic marinades do.
The important thing to remember with a Marinade is that it is only the salt and the water in a marinade that penetrates the meat (like in a brine) most of the other ingredients will only ever sit on the top of the meat, some flavour is transported into the meat with the water.
Think about what is in your Marinade and how it will behave in the cooking process and what will you be left with, maybe the leftover can be cooked down to make a Sauce or Gravy?
Sugars will burn if the cooking environment is over 140°C (285°F) other components could dry out or even turn bitter, honey will burn at temperatures over 70°C (160°F).
More often than not, you would be better using a Brine rather than a Marinade