In the strictest sense, phytochemicals are defined by plant scientists as chemicals produced by plants. However, confusingly the term is generally used by both human nutrition and plant science to describe chemicals from plants that may affect human health and well-being, but are not essential nutrients, e.g. caffeine. To prevent confusion a more appropriate term to point to this group of phytochemicals is the usage of “non-essential” or “non-nutrient” phytochemicals. As there are no known effects or symptoms as a consequence of their deficiency, also no target levels have been determined for intake2. It is recommended to daily consume five to eight portions (400–600 g) of fruits and vegetables, in order to reduce risk of cardiovascular disease, cancer, poor cognitive performance, and other diet-related diseases, as well as for the prevention of micronutrient deficiencies (WHO). Much of this potential of fruits and vegetables in disease prevention is thought to be provided by their complex mixture of phytochemicals, among which the preventive activity of antioxidants is most well documented (Rodriguez-Casado 2016; van Breda and de Kok 2018). Therefore, the use of supplements or fortification with only one phytochemical will probably not be effective to improve health. There is a consensus that whole fruit and vegetable intake is more important in providing health benefits than that of only one of their constituents, because of additive and synergistic effects (Rodriguez-Casado 2016). More than 200.000 phytochemicals have currently been identified (Chapter 3). An overview of several classes of phytochemicals is shown in Table 2.3.
Table 2.3: Chemical classification of the main phytochemicals and their main plant based food (Table copied from: van Breda and de Kok 2018)
Category | Chemical class | Chemical subclass | Example | Plant-based food sources (examples) |
Carbohydrates | Polysaccharides | Non-starch | Cellulose | Whole grains, almost all plants Pears, apples, citrus fruits |
(dietary fiber) | polysaccharides | Pectins | ||
Steroids | Phytosterols | Sterols | Campesterol | Whole grains, legumes, nuts, seeds, pulses, banana, apples, cruciferous vegetables, asparagus, onions |
β-sitosterol | ||||
Stigmastrerol | ||||
Stanols | ||||
Organic acids | Short-chain organic acids | Aldonic acids | Ascorbic acid (vitamin C) | Pepper, kiwi, cruciferous vegetables, berries, citrus fruits, |
Aldaric acids | Tartaric acid | Grapes, cranberries | ||
Sulfur compounds | Thiosulfinates | Allicin | Garlic, leek, onion, chives | |
Diallyl sulfide | ||||
Nitrogen | Amines | Benzylamines | Capsaicin | Chili peppers |
containing | Tryptamines | Psilocybin | Mushrooms | |
compounds | Cyanogenic glycosides | Amygdalin | Seeds of apricot, apple, peach and plum | |
Glucosinulates | Aliphatic glucosinulates | Sulforaphane | Broccoli, Brussels sprouts, cabbage, cauliflower | |
Sinigrin | ||||
Benzyl isothiocyanate | ||||
Allyl iosthiocyanate | ||||
Phenethyl isothiocyanate | ||||
Aromatic glucosinulates | Glucobrassicin | Cabbage, broccoli, mustards, woad | ||
Purines | Xanthines | Caffeine | Coffee bean | |
Other nitrogen | Indole alcohols | Indole-3 carbinol | Broccoli | |
compounds | ||||
Alkaloids | Pyridine alkaloids | Trigoneline | Potatoes, oats, peas, arabic coffee | |
Betalain alkaloids | Betacyanins | Betanin | Red beet | |
Betaxanthins | Indicaxanthin | Beets, red dragonfruit | ||
Phenolics | Flavonoids | Anthocyanins | Cyanidin | Apple, berries, peach, red grape, carrot, red cabbage, red |
Delphinidin | onion, red grapes | |||
Malvidin | ||||
Flavanols | Catechin | Apple, berries, red-purple grape, apricot, peach, green bean | ||
Epicatechin | Green tea | |||
Proanthocyanidins | Green tea | |||
Epicatechin gallate (ECG) | ||||
Epigallocatechin-3-gallate | ||||
Flavonols | Quercetin | Apple, apricot, berries, citrus fruits, cruciferous vegetables, | ||
Kaempferol | onions, sweet potato, tomato, cherry | |||
Myricitin | ||||
Flavones | Apigenin | Carrot, celery, parsley | ||
Isoflavonoids | Genistein | Legumes, soy-bean, currants, alfalfa sprouts | ||
Flavonones | Naringenin | Grapefruit, oranges, tomato | ||
Dihydrochalcones | Phloretin | Apples, apricot | ||
Phenolic acids | Hydroxybenzoic acids | Gallic acid | Blackberry, cherry, mango, red/purple grapes, pomegranate | |
Ellagic acid | Berries, pomegranate | |||
Hydroxycinnamic acids | Ferulic acid | Apple, blackberry, blueberry, grapefruit, Brussels sprouts, | ||
Chlorogenic acid | corn, tomato, cabbage, pepper | |||
Caffeic acid | ||||
Para-Coumaric acid | ||||
Salicylates | Tomato, radish, pepper, broccoli, grapes, cherries, apples | |||
Lignans | Pinoresinol | Banana, cranberry, orange, peach, broccoli, cabbage, carrot, | ||
tomato, onion, potato, pumpkin | ||||
Coumarins | Coumarin | Tonka bean, vanilla grass, mullein, sweet woodruff | ||
Coumestans | Coumestrol | Lima beans, alfalfa sprouts, soy beans | ||
Furanocoumarins | Psoralen | Celery, parsley | ||
Benzodioxoles | Apiole | Celery, parsley | ||
Curcuminoids | Curcumin | Turmeric | ||
Hydroxyphenyl-propenes | Eugenol | Basil, cinnamon, nutmeg | ||
Stilbenoids | Resveratrol | Red grapes, berries, plums, peanuts | ||
Pterostilbene | Blueberries | |||
Piceatannol | Grapes | |||
Terpenoids | Mono-terpenoids | Limonene | Grapefruit, lemon, orange, tangerine, carrot, celery | |
Triterpenoids | Phenolic terpenes | Vitamin E | Spinach, nuts, avocado | |
Saponins | Ursolic acid | Rosemary, basil | ||
Phytosterols | Campesterol | Banana, pomegranate, pepper, grapefruit, onion | ||
Tetrapenoids | Carotenoids | α- carotene | Carrot, pumpkin, sweet potato, tomato, apricot, mango, | |
β-carotene | cabbage, winter squash, cruciferous vegetables, spinach, | |||
Lycopene | peach, red/pink grapefruit | |||
Lutein | ||||
β-cryptoxanthin | ||||
Zeaxanthin |