Steaming and sous-vide: Effects on antioxidant activity, vitamin C, and total phenolic content of Brassica vegetables

The present study evaluated the effect of thermal processing on the colour, antioxidant activity, vitamin C content, and total phenols of six Brassica vegetables. The landrace Grelo was the best source of total phenols (162.7 +/- 3.5 mg/100 g; p < 0.05). Cavolo Nero di Toscana, also known as "black cabbage", showed the highest content of vitamin C, calculated as 290.6 mg/100 g (p < 0.05). The concentration of total antioxidants, phenols, and vitamin C was significantly reduced after both steaming and sous-vide processing (p < 0.05). Overall, no differences were oberved between both cooking strategies. However, for some of the studied vegetables, sous-vide processing resulted in higher losses when compared to steaming (p < 0.05). Uncommon Brassica vegetables such as Grelo can be as nutritious and healthy as commonly consumed ones. However, the effect of cooking on the content of nutritious compounds should be considered when calculating their dietary intake from cooked crucifers.