The purpose of the graduation thesis was to review the recent scientific literature about the effect of present or added antioxidants on quality of the oil. Based on the reviewed literature, frying causes formation of undesirable products that are harmful to health and cause rancidity. The products formed in frying oil pose a problem because they also pass into the food and thus reduce its safety, quality and nutritional value. Oil stability is mostly dependent on oil fatty acid composition, antioxidant content and frying conditions. Polyunsaturated fatty acids, the absence of antioxidants, temperature and time of frying, the presence of oxygen and other prooxidants all might affect the oxidative stability of oil. For oil protection during frying, antioxidants have to be well soluble and stable at elevated temperatures. Synthetic antioxidants are mainly suitable for protecting oil during storage, though only some synthetic antioxidants are stable at high temperatures and suitable for use in frying oils. Among natural antioxidants the phenols and polyphenols are the most effective. Their usefulness and solubility in frying oils is increased by the moisture that enters the oil from food. To increase the solubility or lipophilicity of (poly) phenols, structural transformations of these molecules are possible. To increase efficiency, researchers also suggest the use of a mixture of different compounds that complement each other.
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