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.
Highlights
One of the most commonly used procedures for preparation and manufacturing of foods throughout the world is deep-fat frying in which the food is subjected to an elevated temperature of 150-190 oC (Choe and Min 2007)
Antioxidants can be added to frying oils to prevent or slow down the chemical reactions during deep-fat frying by controlling free radical action (Che and Tan 1999)
Among a variety of food and nonfood uses of vegetable oils, this review mainly focuses on the chemical reactions in vegetable oils during deep-fat frying and the applicability of natural extracts to improve the oxidative stability of the frying oil
Summary
One of the most commonly used procedures for preparation and manufacturing of foods throughout the world is deep-fat frying in which the food is subjected to an elevated temperature of 150-190 oC (Choe and Min 2007). Hydrolyzed, oxidized and polymerized products can impart unpleasant odours, flavours, and colours to the food as well as oil (Choe and Min 2007) These reactions limit the re-utilization of oil. Antioxidants can be added to frying oils to prevent or slow down the chemical reactions during deep-fat frying by controlling free radical action (Che and Tan 1999). Synthetic antioxidants such as propyl gallate (PG), butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), and tertiary butylhydroquinone (TBHQ) are used to slow down the oxidation of vegetable oils at room temperature. This review focuses on major chemical reactions and the effects of adding natural extracts and compounds to vegetable oils during the deep-fat frying process
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