Marinate in Acid : use lemon juice, vinegar or wine for 10 minutes (seafood), a couple hours (poultry) or overnight (meat)
Tenderize with enzymes in fresh pineapple or papaya juice. Be careful as it can cause meat to become mushy if marinate too long.
Tenderize with acidic diary products such as yogurt or buttermilk. Use in marinades for poulty or meat to yield tender, yet still firm, texture and delicious tangy flavor.
Tenderize mechanically by pounding protein (meat, pork or poultry) with teeth-side of mallet.
Tenderize with a meat needler, also known as a "jaccarder" (device with numerous needles or small blades which pierce the meat), to cut through muscle fibers and connective tissue before marinating.