Vitamin C in Foods: Can It Take the Heat?

Overview

Objectives/Goals Reports published by the U.S. National Institute of Health indicate a food's vitamin C oxidizes and denatures at 70° C (or 158° F). I set out to learn if vitamin C could be completely oxidized at normal cooking temperatures. How much vitamin C is lost when fruits such as oranges and tomatoes, and vegetables such as bell peppers and broccoli are cooked at different temperatures? I believed the higher the temperature, the more vitamin C will be lost. If vitamin C is denatured at 158° F, then I thought 50% of the vitamin C would be lost when the food temperature reached 79° F (or 50% of 158° F). I also believed 75% of the vitamin C would be lost when the food temperature reached 119° F (or 75% of 158° F). Finally, I thought all of the food's vitamin C would be denatured when the food's temperature reached 158° F. Methods/Materials I cooked oranges, tomatoes, bell peppers and broccoli at various temperatures in order to test my hypothesis. The effect of heat on the vitamin C for these four foods was determined by redox titration, using household iodine and a starch indicator solution. Results According to my redox titration, the concentration of vitamin C in each of the four foods was not significantly affected (by more than 5%) until the temperature of the cooked foods reached a minimum 158° F. Virtually no vitamin C was lost at an average 79° and 119° F for any of the foods. Conclusions/Discussion Based on my research, I proved the higher the temperature, the more the denaturing of vitamin C but I also proved that vitamin C begins denaturing (not finishes denaturing) when a food reaches 158° F. Therefore, my research disproved the second part of my hypothesis that the vitamin C in foods would be 50% and 75% denatured at 79° and 119° F, respectively. Vitamin C will not significantly begin the denaturing and oxidization process until the average temperature of the food reaches at least 158° F. I learned that in order to maximize the natural vitamin C in raw foods, it's important to cook them as quickly as possible with the lowest amount of heat.

Competition history

• CSEF 2015 Biochemistry/ Molecular Biology · Entry J0509

Resources

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