While it is deemed best to eat most vegetables raw, cooking with heat increases its digestibility and deactivates harmful elements present when the vegetables is eaten uncooked. Examples of harmful foods when eaten raw are root vegetables such as yams, casava and legumes and nuts such as fava beans and cashew nuts. Starch in tubers and root vegetables get gelatinized by heat and inactivates anti-amylases enzymes improving digestibility and taste.
Cooking vegetables also removes the ‘raw smell’ by breaking down the responsible enzymes only present in its raw form, thus making the food more palatable.
Although boiling vegetables seems to be an easier option, steaming is a better choice in terms of health benefits. Even though the temperature of steam ( in a domestic setting, not pressurized ) and boiling water ( at sea level ) are essentially the same, there are several reasons why steaming is the way to a more healthful meal.
Loss of water soluble nutrients by boiling :
Vegetables are a rich source of minerals , vitamins and folates , of which vitamins and folates are water soluble and easily destroyed by prolonged exposure to heat. This is especially so when the boiling water is salted, which increases its boiling temperature.
As a result, the nutrients in vegetables can be destroyed in a fairly short time. Being water soluble, vitamins such as vitamin B and C will be lost in the boiling liquid. Most preparation practices requires the boiled vegetables to be cooled under running water to stop its cooking, thereby further increasing the loss of the nutrients.
Although minerals are not destroyed by heat in cooking, they can be lost together with the water which is discarded upon boiling.
Retention of nutrients by steaming :
Nutrient loss in vegetables can be reduced by steaming ; less water soluble vitamins is leached as steaming removes the need for blanching or running over cold water. When well prepared, most vegetables can be cooked by steaming in a couple of minutes, thereby retaining its nutrients, shape, texture and color.
Ease of preparation by steaming :
Beside the use of the traditional stove steamer and steaming basket, vegetables can also be steamed by microwaving. Simply wash and drain them before cutting. Arrange the vegetables on a microwavable dish and cover with a cellophane wrap. Most vegetables can be cooked under two minutes prepared in this manner, looking brilliant green with its shape retained.
Cooked on a serving dish, the steamed vegetables can even be served from steamer to freezer, reducing the need for a separate warmed plate.