4. Conclusions
The raw kale exhibited the highest carotenoid content out of all of the analyzed samples, while the steamed red cabbage showed the highest anthocyanin concentration. Steaming resulted in maximum levels of total phenolic acids in kale and ascorbic acid in both vegetables. However, the cooking techniques seemed to have no significant effect on TPC in red cabbage. According to all of the antioxidant activity assays (chemical and cellular), the steamed kale displayed the highest antioxidant activity; however, these results were heterogeneous for red cabbage. The effects of the cooking process can be positive since cooking softens the vegetable tissues, facilitating the extraction of bioactive compounds. However, cooking can also be negative, because heat treatment can degrade these compounds. Therefore, considering evidence from the literature, the results found in the present study, from a nutritional point of view, indicate that steaming can be considered to be the best home cooking technique to prepare kale and red cabbage. This technique does not involve the addition of excessive amount of oil, avoids losses by leaching, and in general, results in the highest contents of the bioactive compounds and satisfactory antioxidant activity in the analyzed vegetables. Additionally, these results are important for the improvement of dietary intake recommendations for bioactive compounds.