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

Authors: Hwang, Hong-Sik; Moser, Jill; Liu, Sean

Submitted to: Journal of the American Oil Chemists' Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/16/2022
Publication Date: 4/1/2022
Citation: Hwang, H., Winkler-Moser, J.K., Liu, S.X. 2022. Antioxidant activity of amino acid sodium and potassium salts in vegetable oils at frying temperatures. Journal of the American Oil Chemists' Society. 99(5):407-419. https://doi.org/10.1002/aocs.12585.
DOI: https://doi.org/10.1002/aocs.12585

Interpretive Summary: During deep fat frying, which is one of the most popular cooking methods, oil quality is deteriorated, and toxic substances are produced. Although vegetable oils such as soybean oil have many health benefits, these oils are easily oxidized. Therefore, palm oil and other tropical oils are widely used by the food industry and restaurants, which are more stable than healthy vegetable oils during frying but can cause many health problems. To replace unhealthy oils with vegetable oils as frying oils, strong antioxidants are needed. In this study, we developed new natural antioxidants by modifying amino acids and examined performance in soybean oil at a frying temperature. The modified version of 12 amino acids had stronger antioxidant activity than the corresponding amino acids in soybean oil, and among them the modified version of phenylalanine had the strongest antioxidant activity. The modified version of phenylalanine had stronger antioxidant activity than phenylalanine in other vegetable oils including olive, high oleic soybean, canola, avocado, and corn oils. A frying study with potato cubes in soybean oil showed that the modified version had significantly stronger antioxidant activity than 0.02% tert-butyl hydroquinone, a widely used synthetic antioxidant. These new materials can replace the potentially toxic synthetic antioxidants used in frying oils. They can stabilize vegetable oils during frying indicating that unhealthy palm oil and other tropical oils can be replaced with healthy vegetable oils.

Technical Abstract: In this study, the carboxylic acid group of amino acids was converted to a carboxylate group (-COO-Na+ or -COO-K+), and a heating study was conducted to examine the antioxidant activity of 5.5 mM amino acid salts in soybean oil at 180 ºC. Sodium salts of amino acids including alanine, phenylalanine, and proline and disodium glutamate had significantly stronger antioxidant activity than the corresponding amino acids, and potassium salts had 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. Phenylalanine potassium salt had stronger antioxidant activity than phenylalanine in other vegetable oils including olive, high oleic soybean, canola, avocado, and corn oils. A frying study with potato cubes in soybean oil showed that phenylalanine potassium salt at 5.5. mM had significantly stronger antioxidant activity than 0.02% (1.1 mM) tert-butyl hydroquinone, a synthetic antioxidant.