Fruits and vegetables contain their highest level of nutrients when they are harvested at full ripeness and eaten soon thereafter, with only minimal processing. Since substantial vegetable gardening is impractical for most people, the next best alternative is to purchase fruits and vegetables properly harvested and stored or processed to preserve their nutritional value. Frequently, frozen foods are a good choice for produce because they are generally picked at their peak, quickly processed, and stored at nutrient preserving cold temperatures. Store foods properly to prevent significant nutritional losses. A cool, dark place is generally best since vitamin degradation accelerates at higher temperatures and several of the water soluble vitamins, riboflavin and vitamin C in particular, are ve ry light sensitive.
Cooking also contributes to vitamin losses, and many water soluble vitamins are destroyed by heat.
Consequently you should occasionally eat fruits and vegetables raw and keep cooking times to the minimum. Microwave vegetables without water whenever possible to preserve nutrient content.