Volatile components of the frying process

In the course of deep fat frying, food contacts oil at about 180 °C and is partially exposed to air for various periods of time. Thus frying, more than any other standard food process or handling method, has the greatest potential for causing chemical changes in fat, and sizeable amounts of this fat are carried with the food (5-40% fat by weight is absorbed). During frying, oxidative reactions involving the formation and decomposition of hydroperoxides lead to such compounds as saturated and unsaturated aldehydes, ketones, hydrocarbons, lactones, alcohols, acids and esters. Sulfur compounds and pyrazine derivatives may develop in the food itself or from the interactions between the food and oil. Food absorbs varying amounts of oil during deep-fat frying (potato chips have a final fat content of about 35%). The food itself can release some of its endogenous lipids (e.g., fat from chicken) into the frying fat and consequently the oxidative stability of the new mixture may be different from that of the original frying fat. The changes that occur in the oil and food during frying should not be automatically construed as undesirable or harmful. In fact, some of these changes are necessary to provide the sensory qualities typical of fried food. On the other hand, extensive decomposition, resulting from lack of adequate control of the frying operation, can be a potential source of damage not only to sensory quality of the fried food but also to nutritional value.