nutrient loss through cooking

Question
We had a lot of tomatoes in the garden this summer.  If I cut these up and turn them into tomato sauce by bringing them to a boil in the microwave and then simmering them uncovered overnight in my slow cooker what percentage all those nutrients do I lose?  

Would it be better to drain off some of the watery juice (to drink) and then cooking the pulp for a shorter period?

Answer
Gerry,
I can't tell you an exact percentage but I can tell you that vitamins are very heat sensitive so you will definitely lose some of the vitamin content.  Minerals will stand up better than vitamins.  The only way to really keep the nutritional value of veggies is to eat them raw or steam them lightly.  As long as you add lots of other veggies to your daily intake I wouldn't worry about one product.  You will still get some nutritional value out of your tomatoes if you use the first process you described.  
May want to check out this site for more info:
http://www.tomato.org/
Kim Tessmer,RD LD
www.Nutrifocus.net

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