 Comparing these results to an uncooked sample, the study found that phenolics and vitamin C were reduced more than glucosinolates and minerals.Stir-frying with soybean, peanut, safflower or extra virgin olive oil did not reduce glucosinolates, and broccoli stir-fried with extra virgin olive oil or sunflower oil had vitamin C levels similar to uncooked broccoli.These levels were significantly lower with other edible oils.