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Ask Tufts Experts July 2015 Issue

Q. I’ve read that high temperatures destroy vitamin C, yet potatoes are listed as a source of vitamin C and are never eaten raw. Why isn’t the vitamin C destroyed by cooking? Similarly, do canned fruits and vegetables have less vitamin C because of the heat in the canning process?

A. C-Y. Oliver Chen, PhD, associate director of Tufts’ HNRCA Antioxidants Research Lab, explains: “The content of vitamin C in raw potatoes in the USDA National Nutrient Database is 11.4 milligrams per 100 grams, and the value decreases to 7.6 milligrams in canned potatoes. Humans do not consume fresh potatoes and the vitamin is known to be susceptible to degradation by food preparations used in home and commercial food processing. Boiling in water can quickly decrease vitamin C content in potatoes by 10% in 10 minutes. However, baking and microwaving can retain more than half of vitamin C because vitamin C does not leach out from potatoes into water and then degrade. Thus, vitamin C content in cooked potatoes can be varied depending on style of preparations.

“Similarly, canned fruits and vegetables may contain less vitamin C because of water and heat used in the process. However, vitamin C may stay high if additional vitamin C is added during processing.”

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