A survey of anthocyanins. I

Abstract

ALTHOUGH the details of the constitution and properties of the anthocyanins can only become known as the result of their isolation in substance and the study of the pure individual pigments following the lines of the pioneering researches of Willstaitter and his collaborators [1913-16], yet it is also true that much can now be gleaned from an examination of the colouring matters in solution and there are many obvious advantages attaching to this procedure. For example, the formation and occurrence of anthocyanins can be instantly recognised by inspection and the development of a method of analysis is a necessary step towards the utilisation of this property in making attempts to solve the problems of the origins and functions of these pigments. Moreover, phylogenetic investigations are often facilitated by a knowledge of the antho-cyanins of the varieties, and more rapid methods than those demanding the collection of kilograms of the dried petals are urgently required. Finally a preliminary survey should afford evidence of the existence of interesting new types of anthocyanins, and thus pave the way for extensions of the large scale investigations. In all cases we have employed cold 1 % aqueous hydrochloric acid in order to extract the coloured materials and the best results were obtained by using fresh flowers and by examining the solutions as soon as possible following their preparation. Colour offlowers and of the extracts-co-pigments. The colours of the flowers or fruits themselves do not afford trustworthy indications, but whilst orange-scarlet shades indicate the occurrence of a pelargonidin derivative no blue flower-pigments are derived from pelargonidin. On the other hand not very dissimilar bluish-red Phlox, crimson Dianthus and crimson-scarlet Linum contain anthocyanins derived respectively from pelargonidin, cyanidin and delphinidin. More reliance can be placed on the colour of the acid extracts provided these are observed at the boiling-point of the solution. Under these conditions the order from orange-red to blue-red is that of anthocyanins based on pelar-gonidin, peonidin, cyanidin, malvidin and delphinidin. The necessity for this precaution arises from the existence in the solutions of substances (co-pigments) which intensify and modify the colour. Willstiatter Biochem. 1931 xxv 107