2631
Many studies have been conducted with regard to free radicals , oxidative stress and antioxidant activity of food , giving antioxidants a prominent beneficial role , but , recently many authors have questioned their importance , whilst trying to understand the mechanisms behind oxidative stress .
 None
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
 None