These same chemicals have been proven to have a profound effect on the human immune system. Although in the past, phytonutrients in fruits and vegetables were classified as vitamins, nowadays they are grouped according to their similar protective functions and similar chemical characteristics. Cartenoids consist of bright yellow, orange and red plant pigments found in vegetables such as tomatoes, parsley, oranges, pink grapefruit, spinach and red palm oil. Limonoids are a subclass found in citrus fruit peels. Phytosterols occur in most plants, highly concentrated in the seeds of the plants.
Phenols are the blue, blue-red and violet colorations seen in berries, grapes and purple eggplant.
Flavonoids are a phenol subclass and they enhance the effects of ascorbate-vitamin C. Anthocyanidins or flavonals provide cross links that connect and strengthen the intertwined strands of collagen protein. Catechins, Gallic Acids, differ slightly in chemical structure of other flavonoids, but share their chemoprotective properties. Catechins are found in green tea, and are thought to be responsible for the protective benefits of this beverage. Isoflavons of this phenol subclass come from beans and other legumes and are a distant cousin of flavonoids. Thiols are a sulfur-containing class of phytonutrients and are present in garlic and cruciferous vegetables.