Antioxidant activity of amino acid sodium and potassium salts in vegetable oils at frying temperatures

Abstract: Strong antioxidants are needed to protect vegetable oils from oxidation during frying, which are prone to oxidation due to the high content of unsaturated fatty acids. In our earlier studies, it was found that several amino acids had strong antioxidant activity in vegetable oils under frying conditions. In this study, amino acids were converted to sodium and potassium salts, and their antioxidant activities at 5.5 mM were examined in soybean oil heated at 180 ºC. Sodium salts of alanine, phenylalanine, and proline and disodium glutamate had significantly stronger antioxidant activity than the corresponding amino acids. Potassium salts had even stronger antioxidant activity than sodium salts. Potassium salts of alanine and phenylalanine more effectively retained tocopherols in soybean oil than the corresponding amino acids during heating. Potassium salt of phenylalanine had stronger antioxidant activity than phenylalanine in other vegetable oils such as olive, high oleic soybean, canola, avocado, and corn oils. A frying study with potato cubes showed that phenylalanine potassium salt at 5.5 mM more effectively prevented oil oxidation than tert-butyl hydroquinone (TBHQ), a synthetic antioxidant, at its legal concentration limit (0.02%). This study showed that converting an amino acid into its sodium or potassium salt significantly improved the antioxidant activity of amino acid at frying temperatures.