Assessment of Antioxidant Potential and Polyphenol and Mineral Content in Selected Green Vegetables Subjected to Sous Vide Cooking and Steaming

Green vegetables are rich sources of bioactive substances, including polyphenols and minerals, whose content and biological activity change during various technological processes. The aim of this study was to evaluate the effect of sous vide cooking at three different temperatures (80 °C, 85 °C, and 90 °C) and steaming on the content of minerals, total polyphenols, the profile of selected polyphenols, and the antioxidant potential of green asparagus, broccoli, spinach, and kale. Acidified methanolic extracts were prepared from raw vegetables and vegetables subjected to the four technological processes using ultrasound-assisted extraction. The prepared extracts were used to determine the total polyphenol content using the Folin–Ciocâlteu reagent, the profile of selected polyphenols using HPLC-UV-VIS, the mineral content using ICP-MS, and the antioxidant activity using the ABTS radical assay and the CUPRAC assay. The results showed that for most of the green vegetables studied, the sous vide method ensured the greatest retention or increase in the content of polyphenolic compounds and minerals, as well as antioxidant potential, compared to other thermal processing methods such as steaming. The sous vide process not only contributes to the preservation of selected bioactive substances in the tested vegetables but also to their increased measured concentration.