Phytochemicals – a colorful rainbow that is edible

Natural light separates into seven different colors through a prism, which is red, orange, yellow, green, blue, indigo, and purple. Luckily these are the colors you can find on your dinner table, a full spectrum of the rainbow that is edible. Colorful food is a visual delight, the diversified colors are not just an enhancement of the appearance of food but also beneficial to our health in many ways. In this article, the colors are referred to as the part of the fruits and vegetables consumed rather than the appearance. For instance, a banana that has yellow peel but whitish pale-yellow flesh. Apples that have different peel colors that share similar colors flesh are not discussed in detail as some of us might not consume the peels of the apples due to the concern of the layer of edible wax and residues of the pesticides.

Fruits and vegetables have fibers as well as other beneficial nutrients including those reflected by their colors. The pigments are an indication of the presence of phytochemicals or secondary metabolites that include a large group of compounds. Secondary metabolites are considered as the “by-products” of the primary metabolism and do not participate directly in plant growth and development. What are the functions of phytochemicals in the first place then? The primary purposes are mainly for self-defense and protection from biotic stress such as pests, diseases, other herbivores, and abiotic stress such as drought, freezing and increased UV-radiation. Meanwhile, they provide numerous benefits for human health in various ways including detoxification, wound healing, digestive health, energy improvement, immune system support, and cancer prevention.

When talking about fruits and vegetables, what color comes first in your mind? Yes, it’s green! As the most abundant color on earth, the list for green food goes endless such as lettuce, broccoli, cabbages, celeries, cucumbers, green grapes, green peppers, bitter gourds, honeydews, kiwis, okras, spinaches, watercress, and zucchinis, etc. The color of green is mostly reflected by chlorophyll in the chloroplasts. Chlorophyll absorbs red to blue light and reflects green light so that chlorophyll-containing tissues are green. Green leafy vegetables also contain high quantities of lutein, glucosinolates, folate, isothiocyanates, folic acid, potassium as well as vitamin C and K. Glucosinolates and isothiocyanates are mainly found in cruciferous vegetables from the family of Brassicaceae such as cabbage, mustard, broccoli, cauliflower, and horseradish. Besides being responsible for the pungent and bitter taste, glucosinolates also protect plants against pests and herbivores and have been shown to have antimicrobial, antiviral, antifungal, and anticarcinogenic properties. Lutein is a xanthophyll and synthesized only by plants. Lutein is largely used in treating age-related macular degeneration in the eyes. Overall, the consumption of green food help to prevent macular degeneration, boost the immune system and maintain healthy bones and teeth.

White-colored fruits and vegetables like cauliflower, the flesh of coconuts, soursops, cloves of garlic, turnips, white radish or daikon, white asparagus, white flesh dragon fruits, and white onions. As a group, white vegetables provide plenty of vitamins, minerals, allyl sulfides, allicin, and beneficial nutrients. Onions are members of the allium genus that contain quercetin, a phytonutrient with anti-inflammatory and antioxidant power. Sulfur-containing chemicals are found in garlic and onions that helps to inhibit certain cancers and maintain cholesterol levels.

Red-colored fruits and vegetables can be found from cherries raspberries, strawberries, tomatoes, pomegranates, red flesh watermelon, red flesh dragon fruits, red chilies, red bell peppers, and beetroots. Red-colored fruits and vegetables contain active plant compounds such as lycopene, anthocyanins, calcium, vitamin C and D, flavonoids, resveratrol, and folates. Flavonoids are polyphenolic compounds that are widely distributed in fruits, vegetables, and nuts that can be further classified as flavones, flavonols, flavones, isoflavones, and catechines. Flavonoids are powerful antioxidants and have been widely involved in the treatment of anti-inflammatory, anti-allergic, and anti-cancer activities. Luckily, flavonoids rich foods usually are attractive by their aromatic and colorful appearance such as yellow or red color that is commonly found citrus fruits and berries. The red pigmentation in the swollen roots of the beet is due to the presence of betanin and isobetanin. These phytochemicals help to reduce tumor growth and cancer and promoting memory. They are also beneficial in terms of healthy aging, cardio, and prostate health.

Orange-colored foods are mostly found in fruits and roots such as apricots, oranges, peaches, mangoes, pumpkin, carrots, butternut squash, sweet potatoes, turmerics, papayas, and cantaloupes. And less common ones like yellow flesh watermelon, yellow peppers, corn kernels, jubilee, yellow squash, starfruits, pineapples, yellow figs, and golden kiwifruits. Yellow color indicates the presence of carotenoids such as alpha-carotene and beta-carotene. Carotenoids pigments are found in chloroplasts. There are over 600 known carotenoids that occur in roots, stems, leaves, flowers, and fruits. Carotenoids have two important functions in plants. First, they can contribute to photosynthesis. Second, they protect plants from over-exposed to sunlight. In the absence of carotenoids, this excess light energy could destroy proteins, membranes, and other molecules. Carotenoids are beneficial for reducing cancer risk and heart disease.

Blue can be found from the blueberries and butterfly pea flowers. Purple is available from fruits and vegetables such as blackberries, black currants, elderberries, peel of the eggplants, purple asparaguses, purple cabbages, purple carrots, purple peppers, purple potatoes, and raisins. Blue and purple fruits and vegetables consist of those active compounds similar to that of red-colored fruits and vegetables which are lycopene, anthocyanins, calcium, vitamin C and D, flavonoids, resveratrol, and folates. Their effects are also similar. The only difference is the concentration of the compounds and pH of the plants due to the presence of anthocyanin that gives different colors at different pH. Common beverages such as beverages containing the petals hibiscus and butterfly pea flowers in fresh or dried conditions. For butterfly pea flower beverage, the color of the drink is a blue or indigo color which turns into pink or red when acid (lemonade or lime juice) is added. For the hibiscus with red petals, acid turns the drink into a more vibrant red. Sounds magical right? Do you try this at your home?

When you think of adding colors on dishes, think organically from natural food. Each color represents many beneficial health effects that eventually reflected from the color pigments they carry. Have you ever worried about your children being too picky on the vegetables that have slight bitter taste? Why not making the food colorful and creative so that children also enjoy eating the colors? The colors of the fruits and vegetables not only can be eaten or cooked as dish, they can also be blended and used as natural colorings in culinary. Creative colorful culinary such as porridge, rice, breads, noodles, pasta, smoothies, and desserts are often found as the visual improvements of the recipe that catch the attention of kids. Colorful meal is not only bringing the appearance of the dish to next level but also the “hidden” beneficial effects. It’s happy and joyful to see the rainbow on the table.

Further readings:

Huang, M-. T., Osawa, T., Ho, C-. T., Rose, R. T.. (1992). Food phytochemicals for cancer prevention I. Washington DC: American Chemical Society.

Laura, A., Alvarez-Parrilla, E., & Gonzalez-Aguilar, G. A. (Eds.). (2009). Fruit and vegetable phytochemicals: chemistry, nutritional value and stability. John Wiley & Sons.

Yahia, E. M. (Ed.). (2017). Fruit and Vegetable Phytochemicals: Chemistry and Human Health, 2 Volumes. John Wiley & Sons.