The fat, usually oil, coats the exterior of the meat, keeping it from drying out during cooking. Put them together and there isn't a food in creation that can resist their transformational powers. Lemon juice is a popular souring agent in the Mediterranean basin and Central Asia, lime juice in Latin America and the Far East, pomegranate juice in the Near East. Acids in dairy-based marinades range from the yogurt and yogurt cheese mixtures of India, Iran, Iraq and Afghanistan to the buttermilk used in the American South. The fats in a marinade seal in flavor and keep foods moist during grilling.
Olive oil is the preferred oil in California and the Mediterranean.
Sesame oil imparts a pleasing nutty flavor to the marinades of the Far East. Butter is often used in the Near East. If you want the moisturizing benefits of oil without a distinct flavor, use a bland oil, like canola or peanut. The aromatics are the soul of a marinade. Classical French marinades start with a mirepoix , a fragrant dice of onion, celery and carrot.