A recent question I received from one of my blog readers was how ripeness and cooking affects the nutritional value of foods. This is a great question and one that I felt deserved some attention.
In general, the longer that something is cooked, the more nutritional value it will lose. If something is cooked in water, it will potentially lose more water-soluble vitamins such as vitamins B and C. Different methods of cooking will result in minimal differences to overall nutritional value of a food.
I found one research study from 2011 that examined the effects of cooking and ripening on plantains (bananas). Baiyeri et al stated, “that nutritional qualities of plantain fruits vary with the stage of ripeness and cooking/processing method employed.” Carb content increases with ripeness, but fat, iron and beta-carotene (vitamin A) decreased with ripeness. Beta-carotene levels decreased up to 50-70%.
According to the same study, boiling or baking partially ripened foods may lead to 10% loss of nutrients. Fully ripe fruits could lose 50-70% of nutrients during boiling.
Another study by Kimura found about a 30-40% loss of mineral contents in cooked foods compared to raw or uncooked foods, especially in the case of vegetables. Recommendations from this study to preserve some of the mineral content lost in cooking include adding a small amount of salt to boiling water when cooking, limit overcooking, and using cooking methods that will lead to less mineral loss such as stewing, frying or parching.