Traditional ways of cooking, such as boiling certain vegetables, can deplete water-soluble vitamins, such as vitamin C and the B vitamins, as well as flavonoid phytonutrients. I found out that up to 80% of the folic acid in carrots and 66% of the flavonoids in broccoli are destroyed through boiling for extended periods of time.
You may be surprised to find that according to recent research some vegetables, such as carrots and tomatoes, actually offer greater availability of antioxidants after they have been cooked. The release of carotenoids through cooking can be measured. In carrots, for example, about 40% more carotenoids are released and made available through cooking. Studies on the effects of cooking on the phenolic phytonutrients in zucchini, beans and carrots found that these antioxidants are best retained if cooked in small amounts of water.
A study published in the Journal of the Science of Food and Agriculture found that light steaming was the clear winner when comparing different types of cooking methods and their effects on the retention of phytonutrients, such as carotenoids and flavonoids that act as powerful antioxidants. You will maximize nutrient retention, losing only around 5–10% of vitamins, while the loss of minerals and other nutrients is even less.
Cocinar al vapor durante máximo 5 minutos: brócoli, coles de bruselas, judías, maíz, repollo, zanahorias.
Cocinar al vapor durante máximo 7 minutos: calabacín.
Cocinar al vapor durante máximo 10 minutos: patatas, boniatos.
Cocinar al vapor durante máximo 15 minutos: remolacha
fuente: "the world’s healthiest foods"