Acids like lemon juice, lime juice and vinegar break down raw meat, allowing the marinade's oil and spices to deeply penetrate and infuse the meat with flavor and moisture. They dig out little pathways in the meat and allow the marinade to seep in. The scientific term for this breakdown is "denaturation," which is the process in which protein loses its structure by application of a strong acid, base, salt, alcohol or heat. Basically, the scientific process that cooks meat with heat in the oven is the same one that cooks it with acid. The results may taste a little different -- fish cooked in the oven is flaky, whereas fish cooked by lemon juice (a.k.a. ceviche) has a more raw-tasting consistency -- but the process is the same.
dennaturation=变性