Nature of Betanin, the Pigment of Red Beet

Abstract

THE interesting communication of R. G. Peterson and M. A. Joslyn on this subject calls for some comment. In the first place, the term “nitrogenous anthocyanin” is used partly chemically (nitrogenous) and largely botanically (anthocyanin) to denote an obviously related group of water-soluble bluish-red colouring matters, such as those of Beta, Atriplex, Celosia, and certain Cactaceae. The only evidence favouring some form of amino-flavylium salt structure, which was the basis of a working hypothesis, was the colour and some other properties of synthetic amino-flavylium salts containing hydroxyl and methoxyl groups¹. There was a certain resemblance between the absorption spectra in the visible region of betanin and 4′-amino-3 : 7-dihydroxyflavylium chloride. However, no phenolic degradation products could be obtained from betanidin². We have always recognized that the relation to the flavylium group was unconfirmed and a purely speculative hypothesis. The evidence in favour of a pyrroloid constitution is not much stronger.