DEAR DR. BLONZ: You have written about different methods of cooking and how they affect a food’s nutrients, but can you talk about how boiling, roasting, microwaving and frying compare? -- K.B., Las Vegas
DEAR K.B.: As a general rule, the longer the time from field to plate, the more nutrients fresh foods will lose. Cold can slow down this process, but it’s heat that serves as the prime nutrient destroyer. The greater the heat and the longer the time of exposure, the greater the nutrient destruction.
Minerals are the only nutrients that are unaffected by heat. Proteins, carbohydrates and fats have a reasonable degree of heat stability, but they, too, will succumb if the heat is high enough. Vitamins tend to be the most vulnerable nutrients, with water-soluble vitamins being the most affected. Vitamin C, thiamin and folic acid, for example, can be destroyed by heat; fat-soluble vitamins can also be destroyed by extended cooking times. There is less data on other plant chemicals (phytochemicals), but it is probable that they would be vulnerable to heat destruction as well.
A list of cooking methods from quickest to slowest might look something like this: microwaving, sauteing, stir-frying, pressure-cooking, steaming, deep-fat frying, roasting, broiling, boiling and baking. Cooking times, of course, can vary from food to food.
Look at potatoes, for example. Because it is cooked rapidly, a microwaved potato will have the greatest amount of vitamin C, whereas a baked potato will have the least. A boiled potato will fall somewhere in the middle.
Nutrients can be lost in ways other than outright destruction. The use of water with boiling can pose a problem, in that some nutrients will dissolve in water. If the water is then discarded, these nutrients are then lost in addition to those destroyed by the heat. Steaming and pressure-cooking also use water, but it’s less of an issue because less water is used with these methods.
DEAR DR. BLONZ: In a recent column, a reader remarked, when comparing lemon juice with vinegar, that the latter took their breath away. This is because the acetic acid in vinegar is volatile, and the citric acid in lemon juice is not. Vinegar can be “tasted” by both the nose and the tongue, whereas the citric acid in lemon juice is only tasted by the tongue. A useful feature of vinegar’s volatility is that it can be reduced in a recipe if it’s too strong simply by heating with the lid off.
This is from a chemist who has smelled a lot of things in his career. -- M.M., via email
DEAR M.M.: Thanks for your helpful comment. As you correctly point out, it is important to consider all the senses when considering a flavor impression.
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