Betaxanthins

Betaxanthins are a class of betalain pigments that impart yellow to orange colors in plants. They are water-soluble and belong to the two major pigment families of betalains, the complementary red-violet betacyanins. Betaxanthins arise when betalamic acid condenses with amino acids or amines, producing yellow-orange chromophores. By contrast, betacyanins form when betalamic acid condenses with cyclo-DOPA.

Biosynthesis and chemistry: Betalamic acid is a central intermediate in betalain biosynthesis. In tissues producing betalains, enzymes generate betalamic acid from precursors such as L-DOPA, and subsequent coupling with amino compounds yields betaxanthins. The exact hue of a given betaxanthin depends on the attached amino acid or amine and the pH of the environment.

Distribution and occurrence: Betaxanthins are characteristic of plants in the order Caryophyllales and are found in various flowers, fruits, and other tissues, including species such as bougainvillea, Opuntia (prickly pear) fruits, and amaranths. Not all betalains produce betaxanthins, and many species synthesize both betaxanthins and betacyanins to yield a range of colors. Notable betaxanthin examples studied include indicaxanthin and vulaxanthin.

Functions and applications: In plants, betaxanthins contribute to pollinator attraction and fruit coloration. In human use, they serve as natural colorants in foods and cosmetics and are studied for antioxidant properties. Betaxanthins, like other betalains, are typically more stable in neutral to mildly acidic conditions than many plant pigments, but degrade with heat, light, and extreme pH changes. They are used in research and commercial colorant formulations as alternatives to synthetic dyes.