Vegetables are rich sources of nutrients such as fiber, minerals, vitamins, and antioxidants. Vegetables also contain various free-form amino acids, which improves their nutritional and palatable value. Cooking alters the content of free amino acids in vegetables, which affects their nutritional values. In this study, free amino acid levels were evaluated after cooking vegetables by different methods, boiling, roasting in an oven, and using a microwave. Results showed that many vegetables analyzed contain aspartate and glutamine abundantly. On the other hand, hydroxyproline, cysteine, ornithine and citrulline are the free amino acids existing at low or undetectable levels in all vegetables tested. The total free amino acid content in vegetables tended to decrease after boiling, and almost the same amount of free amino acids was obtained in the cooking liquid. Roasting of vegetables in an oven resulted in an increase in the content of specific amino acids, including γ-aminobutyric acid (GABA). Thus, it is important to choose the right cooking methods to prevent the loss of free amino acids. The results of the present study emphasize the changes in the contents of free amino acids during cooking with methods that are typically used on a daily basis. Our study on the dynamics of free amino acids caused by various cooking methods provides ample information for future nutritional studies.
Keywords: HPLC; NBD-F; amino acid analysis; cooking liquid; thermal cooking process.