Betalains are a plant pigment and phytonutrient that were originally extracted from beets, thus the name, which is derived from the Latin word for beet, beta vulgaris. They are somewhat rare in the plant world, because they are only found in one order, the Caryophyllales, and then in only some of the plants of this order. (An older method of naming plant orders calls this the Centrospermae.)
Betalains consist of aromatic rings, although they are not flavonoids. They are attached to a glucose molecule and also have nitrogen in their structure. They replace anthocyanins in the plants where they are found, and plants will only have one or the other of these substances. The two main types of betalains are betacyanins and betaxanthins. These absorb light differently because of their different structures, so each type gives a different spectrum of color to a plant. Among these groups there are 24 different betalains we know of.
As with most of the plant pigments, betalains work as an antioxidant, scavenging up and neutrializing the damaging oxidative substances in our bodies. They have anti-inflammatory properties, and are also being studied for their protection against cancer. Many of these studies are being done with the prickly pear or Nopal cactus. The Nopal cactus is said to contain all 24 varieties of betalain.
Read more about betalains and Nopal.
Betacyanins give certain flowers and foods their red, blue or purple colors. They are commonly found in beets, amaranth, cacti and Swiss chard.
Betanin is a betacyanin pigment found in beets and the other foods mentioned above, and used by the food industry as a red dye. It's food additive number is E162. Light, heat and oxygen cause it to degrade, so it is usually used in frozen foods or foods with a short shelf life. It can be found in ice cream, powdered drinks, sugar confections, soup, tomato and bacon products. It's color is pH sensitive. The higher the pH, the more it changes from bluish red to bluish violet. At a lower pH it will turn yellow. Because of its widespread use in the food industry, betanin is getting a lot of scrutiny for its antioxidant and anticancer properties.
Betaxanthins are a yellow pigment which is also present in beets, but usually in lesser amounts than betacyanins, so that the red color of the betacyanins dominates the vegetable. There is a variety of "golden" or yellow beet which is higher in betaxanthins, and this phytonutrient is also found in cacti and some varieties of Swiss chard.