Deep-fat Frying of Vegetable Oils: Major Chemical Reactions and Effect of Natural Extracts on Oxidative Stability - A Review

Abstract

Deep-fat frying is a popular cooking technique in the world and vegetable oil is widely used as the frying medium in this process. Deep-fat frying produces both desirable and undesirable compounds through various chemical reactions. Undesirable chemical compounds are formed mainly through hydrolysis, oxidation and polymerization reactions. These compounds lower the oxidative stability thereby, the quality of oil and food. Antioxidants are added to improve the oxidative stability of oil during deep-fat frying by lowering the free radical action in frying oil. Even though artificial antioxidants are added to frying oils to lower the effects of undesirable chemical reactions and their products, the efficiency of artificial antioxidants decrease with increasing temperature and may cause adverse health effects to the consumer. Natural extracts of rosemary (Rosmarinus officinalis), sage (Salvinia officinalis), tea (Camelia sinensis), oregano (Origanum vulgare) and barley (Hordeum vulgare) are stable under frying conditions and act as effective antioxidants during deep-fat frying. Despite confirmation by numerous research, the use of natural compounds as antioxidants in deep-fat frying is not popular in the food industry. Hence this review explores the major chemical reactions in vegetable oils during deep-fat frying and the effect of natural compounds and extracts in interrupting these undesirable chemical reactions.