The rich, enticing colors that add eye appeal to new fruits, vegetables, leaves and flowers can change when heated or subjected to acid. Fall leaves go from green to bright, glowing hues. French hydrangeas (Hydrangea macrophylla), hardy in U.S. Department of Agriculture plant hardiness zones 6 through 9, have pink flowers when planted in alkaline soil and blue flowers when in acidic soil. Four kinds of plant pigments act differently when subjected to heat or acidity, making colour changes.
Chlorophyll pigments give plants their green colour, and many changes happen when a green tea belongs into boiling water. First, a brighter green colour develops, brought on by the growth of gases and their escape from spaces between plant cells. The collapse of the quite cloudy pockets of gas reveals the bright-green chloroplasts within cells. Another color change happens in response to acidic water: The calcium ion in the middle of the chlorophyll molecule is replaced with a hydrogen molecule, causing the green to dull. Chlorophyll-a gets gray-green pheophytin-a, and chlorophyll-b turns into yellow pheophytin-b. When the boiling water is slightly alkaline, then chlorophyll stays greener. Fried vegetables change to a duller green colour when temperatures reach 140 degrees Fahrenheit. The heat damages chloroplasts, releasing organic cell acids to turn green to olive-green.
Red and Blue
Reds, blues and purples happen because of a concentration of various kinds of anthocyanins, water-soluble pigments held in plant cell sap. Heating doesn’t change them, however, they’re red in acidic conditions and blue or purple in alkaline conditions. The colour of fall leaves happens when the leaf chlorophyll expires. Intense reds and purples of anthocyanins, which can be made up of anthocyanidins plus glucose molecules, form finest in reaction to heat, sunny fall days with cool night temperatures that don’t fall below freezing. Those conditions result in abundant sugar formation and better anthocyanin production. Leaves turn reddish when cell sap is contaminated and purplish or blue when cell sap is more alkaline. Vegetables and fruits with anthocyanins can change colour completely in response to acidity or alkalinity. Under alkaline conditions, sometimes red cabbage leaves flip blue-purple when cooked, blueberry fruits become green in garlic and sausage cloves turn green or blue when pickled.
Yellow and Orange
Carotenoids are more soluble in fat than in water, and so their colors do not fade much in reaction to heat. Some change happens, but with carrot taproots moving from red-orange to more yellow when cooked. When colorful apricot and bright-red tomato fruits are sun-driedthey lose much of their brightness unless they’re treated with the antioxidant sulfur dioxide. Carotenoids also have less-intense color under acidic conditions.
White or colorless to start with, anthoxanthins are water-soluble. They get white when in polluted environments and yellowish when alkaline conditions prevail. They turn dark in excess heat. If plant cells with anthoxanthins are cooked in aluminum, tin or iron containers, their pigments may respond with that alloy’s ions and shape colors like grey, blue, red, green and brown.