We often associate winter with gray skies and a monochromatic landscape. But take a look in any Northern California farmers market right now and you’ll see that even in January there is a rainbow of produce available. And just why are some fruits and vegetables green, some orange, some purple and others red? The answer is in the pigments.
Pigments are colorful compounds that absorb some wavelengths of visible light and reflect others. In addition to giving plant structures their color, they perform essential biological functions. By far the most well-known kinds of pigments are chlorophylls, which are responsible for what is arguably the most important biological occurrence on Earth: photosynthesis. In this miraculous process, chlorophyll (contained in cells called chloroplasts) absorbs energy from the sun and transforms it into usable chemical energy. The presence of chlorophyll makes plant tissues appear green, since the pigment absorbs red and blue light waves and reflects green ones. It is why spinach, collards, cardoons, artichokes, leeks and broccoli are green.
Another well-known class of pigments is the carotenoids, first isolated in carrots, from which they got their name. They are considered accessory pigments because they absorb wavelengths of light that chlorophyll cannot, and they pass on the energy to the photosynthetic process. Carotene is one carotenoid especially important for human nutrition; once in our bodies, it can be stored in the liver and released as Vitamin A. Carotene is also an antioxidant and may help to decrease cancer risk. Foods rich in carotene include sweet potatoes, pumpkins, cantaloupe and oranges.
Some stems and leaves also contain considerable amounts of carotene, but its orange hue can’t be seen because of all the verdant reflectivity of the chlorophyll. Grass is one carotene-containing green, and though we don’t eat it directly, some of its carotene ends up in our bodies if we consume meat and dairy products from pastured animals. Carotene is the reason why butter from grass-fed animals is always especially yellow in the spring when fresh grass is abundant and carotene-rich. The creamy yellow color that originally characterized cheeses from the English village of Cheddar is also a result of carotene in the grass eaten by its cows. Today, many cheddar-type cheeses are dyed a bright orangey-yellow, probably an exaggerated attempt to imitate the color of original cheddars.
A carotenoid called lycopene is responsible for red color of watermelons, tomatoes and pink grapefruit. The egg industry often uses lycopene as a supplement in chicken feed to make yolks a brighter yellow. However, eggs from chickens that get to eat bugs and grass and pick through compost are naturally rich in color.
Another class of pigments, the flavonoids, includes anthocyanins, the pigments that give blueberries, grapes, blackberries and other fruits their dark purple, blue and red colors. Anthocyanins are also present in vegetables like red carrots and purple broccoli. Both carotenoids and flavonoids often become more concentrated in fruits as they ripen, signaling that they are ready to eat. In the fields, farmers rely on these color changes to know when fruits like tomatoes, citrus, peaches and figs are ready for market.
In the kitchen, it’s a joy to experiment with color, but some pigments are more easily preserved than others. Carotenoids and chlorophylls are oil-soluble, so while their color might be altered slightly by the level of acidity in a dish, it usually remains relatively intact when cooked. Flavonoids are water-soluble and can easily leach out of fruits and vegetables if they are boiled or braised.
This winter, paint your kitchen with nature’s diverse palette. Here are just a few of the vivid fruits and vegetables you’ll find at the Ferry Plaza Farmers Market this time of year:
Red/pink: beets, potatoes, chard, carrots, cara cara and blood oranges, watermelon radishes, pomegranate juice
Orange: winter squash, carrots, oranges, rutabagas, persimmons
Yellow: beets, carrots, chard, lemons, grapefruit
Green: greens, broccoli, cabbage, leeks
Purple: broccoli, carrots, potatoes, cabbage, orach
Look for some of these colorful items in your local market: