Fruits and vegetables constitute, together with other groups of food, the essence of what we refer to as the Mediterranean Diet; a diet that should be promoted as favourable in all periods of life. Both fruits and vegetables are an important part of our diet and the benefits they exert on our health become more evident everyday.
When determining the dietary importance of a foodstuff, nutrients often are the only elements considered, whereas in actual fact there are other known food components called ‘non-nutrients’ that are of enormous interest with regard to health. In some cases they have important physiologic properties and are therefore considered bioactive substances. These substances are named “phytochemicals” when they are found in plants. Among these phytochemicals some stand out because, in addition to having beneficial properties, they give fruits and vegetables their colour (Cámara, M., et al.).
Compounds responsible for green colour
The compounds that give green vegetables their colour are called glucosinolates. Glucosinolates are a large group of sulphur-containing amino acid derivatives. Certain glucosinolates and their breakdown products have been linked to a reduction in the prevalence of certain types of cancer. The anticarcinogenic effect of glucosinolates is explained by the activation of enzymes involved in the detoxification of carcinogens, inhibition of enzymes modifying steroid hormone metabolism, and protection against oxidative damage (Hounsome, N. et al.).
Glucosinolates are found in broccoli, cauliflower, Brussels sprouts and cabbage (Heber, D. et al.).
Green leafy vegetables also contain high amounts of iron and folic acid, and the ascorbic acid or vitamin C present in them facilitates iron absorption (Cámara, M., et al.).
Compounds responsible for orange colour
The phytochemicals responsible for orange colour in fruits and vegetables such as carrot, mango, or pumpkin, are the carotenoids α- y β-carotene.
Carotenoids belong to the class of isoprenoid lipids and derive their colour from conjugated carbon-carbon double bonds in the chemical structure. Between 40 and 50 carotenoids are present in our diets that can be absorbed, metabolised, or used by our organism (Aguilera, C. M., et al.). In particular, α and β-carotene are very important in the diet because they are vitamin A precursors, which is why they are also called provitamin A. Vitamin A is involved in hormone synthesis, regulation of cell growth and differentiation, and immune responses (Hounsome, N. et al.).
Compounds responsible for red colour
The red colour of fruits and vegetables such as tomato, watermelon, or grapefruit, is due to the compound lycopene (also belonging to the carotenoids, like α- and β-carotene), and the red-purple colour of grapes, berries, raspberries and cranberries is caused by anthocyanins (Heber, D. et al.).
Lycopene is one of the first carotenoids that occur during the synthesis of this family of compounds, thus constituting the base to synthesize the others. Unlike α- and β-carotene, lycopene is not a vitamin A precursor. It is a carotenoid with a simple aliphatic chain structure of 40 carbon atoms and many conjugated double bonds (de Carlos, P.). It has a very strong antioxidant capacity, plays a role in cell communication, and there is experimental evidence that it protects against prostate cancer, cardiovascular disease, and damage from ultraviolet light exposure and tobacco smoke (Aguilera Garca, C. M., et al.).
Anthocyanins belong to the biggest group of phenolic compounds, called flavonoids. What separates anthocyanins from the rest of the flavonoids is the number of hydroxyl groups, the nature and number of sugars, and the position of these groups. It has been discovered that anthocyanins are absorbed from the diet without being modified.
Anthocyanins have antioxidant properties that have been demonstrated in both in vitro and in vivo experiments. It has also been suggested that anthocyanins are very important in preventing carcinogenesis and mutagenesis (Lazzè, M. C., et al.).
Compounds responsible for orange-yellow colour
The flavonoids, as mentioned above the largest group of phenolic compounds, together with β-cryptoxanthin are responsible for the light orange to yellow colour of fruits such as peach, papaya or orange (Heber, D. et al.).
Dietary flavonoids possess antiviral, anti-inflammatory, antihistamine and antioxidant properties. They have been reported to inhibit lipid peroxidation, scavenge free radicals, chelate iron and copper ions, and to modulate cell signalling pathways. Production of peroxides and free radicals has been linked to cancer, aging, ischemic injury, and neurodegenerative diseases such as Parkinson’s and Alzheimer’s disease. Flavonoids protect low-density lipoprotein cholesterol from being oxidized, thus preventing the formation of atherosclerotic plaques in the arterial wall.
β-cryptoxanthin like β-carotene or lycopene is a carotenoid, and as such has an important function as biologic antioxidant, protecting cells and tissues from oxidative damage (Hounsome. N., et al.).
Compounds responsible for yellow-green colour
These colours in vegetables are due to zeaxanthin and lutein, both pigments that belong to a group called xanthophylls, which in turn are a member of the carotenoid family. They bring about yellowish colours, even though many times they are hidden by the green colour of chlorophyll, e.g. in spinach or avocado.
Apart from the beneficial properties of carotenoids previously described, these two compounds are very important because they selectively accumulate in the retina. Different epidemiological studies have shown that lutein intake and serum levels are associated inversely with risk of ophthalmologic diseases associated to aging, such as cataract or macular degeneration (Aguilera Garca, C. M., et al.).
| Colour || Phytochemical || Fruits and vegetables |
| Green || Glucosinolates || Broccolo, kale |
| Orange || α- and β-carotene || Carrot, mango, pumpkin |
| Red || Lycopene || Tomato |
| Red-purple || Anthocyanins || Grapes, blackberries, raspberries, blueberries |
| Orange-yellow || Flavonoids || Honeydew melon, peach, papaya, orange, tangerine |
| Yellow-green || Lutein and zeaxanthin || Spinach, corn, avocado, melon |
Source: Heber, D. et al.
Fruits and vegetables are very important components of a healthy diet. If we consume them daily in sufficient amounts they could help prevent cardiovascular diseases and certain types of cancer. The World Health Organization recommends eating a minimum of 400 g of fruits and vegetables a day to prevent chronic diseases such as cancer, diabetes and obesity. To reach that number, we can combine the different colours of fruits and vegetables, obtaining all the benefits they bring to our health.
- Aguilera Garca, C. M., et al. Alimentos funcionales. Aproximación a una nueva alimentación. Instituto de Nutrición y Trastornos Alimentarios. Comunidad de Madrid.
- Cámara Hurtado, M., de Cortes Sánchez Mata, M., Torija Isasa, M. (2003). Frutas y verduras, fuente de salud. Instituto de Salud Pública. Consejería de Sanidad y Consumo.
- De Carlos, P. (2007). Propiedades antioxidantes del tomate. Aspectos beneficiosos del licopeno. www.informacionconsumidor.com.
- Elizabeth J Johnson, B Randy Hammond, Kyung-Jin Yeum, Jian Qin, Xiang Dong Wang, Carmen Castaneda, D Max Snodderly, and Robert M Russell (2000). Relation among serum and tissue concentrations of lutein and zeaxanthin and macular pigment density. Am. J. Clin. Nutr.;71:1555–62.
- Heber, D., Bowerman, S. (2001). Applying Science to Changing Dietary Patterns. American Institute for Cancer Research 11th Annual Research Conference on Diet, Nutrition and Cancer.
- Hounsome, N., Hounsome, B., Tomos, D., y Edwards-Jones, G. (2008.) Plant Metabolites and Nutritional Quality of Vegetables. Journal Food of Science. Vol.73, Nr. 4, p. 48-62.
- Lazzè, M. C., Savio, M., Pizzala, R., Cazzalini, O., Perucca, P., Scovassi, A.I., Stivala, L. A. y Bianchi, L. (2004). Anthocyanins induce cell cycle perturbations and apoptosis in different human cell lines. Carcinogenesis vol. 25 nº 8 p.1427—1433.