Amino acid composition and betaxanthin formation in fruits from Opuntia ficus-indica.

In contrast to earlier reports high levels of taurine (2-aminoethanesulfonic acid) were found in fruit juices of three cultivars of Opuntia ficus-indica (L.) Mill. Whereas the occurrence of taurine in plant tissue was thought to be restricted to algae, fungi, and the endosperm of some higher plants, prickly pear proved to be a rich source of dietary taurine. Using L-taurine as the amino compound, a new betaxanthin was synthesized by partial synthesis. On the basis of chemical and spectral evidence its structure was determined to be the taurine-immonium-conjugate of betalamic acid. Also betalamic acid could be detected in yellow and orange coloured cultivars of Opuntia ficus-indica for the first time. In spite of the high levels of L-taurine accompanied by the occurrence of betalamic acid, the corresponding betaxanthin could not be detected in the fruit tissue.