Do tomatoes lose their nutritional value when they are made into tomato sauce? What about canned tomato sauce?
closed as off-topic by KatieK, MandoMando, Chris Steinbach, Jay, talon8 Jun 27 '13 at 22:26
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Nutritional changes in cooking foods (including tomatoes) are not simple to answer: cooking can reduce some nutrients, and it can make other ingredients more available.
Tomatoes are a case in point, as cooking has both effects. According to as study in the Journal of Food and Agriculture, as reported in Cornell Chronical, both effects happen. Vitamin C is reduced as it breaks down under heat, but certain lycoenes and anti-oxidants increased.
See related: Does cooking in a pressure cooker destroy nutrients?