Occurrence of Leuco-anthocyanin in Pears

Abstract

THE anthocyanin pigments of plants may occur in two possible colourless forms, as the pseudo-base and as leuco-anthocyanins1,2. In both cases conversion to the corresponding anthocyanin occurs on acidification, but is slower in the latter case. Although leuco-anthocyanins have been isolated only from cacao beans3 and Australian heartwood of Acacia melanoxylon4 their occurrence is implied on the basis of the vanillin test and chromatographic identification of anthocyanins2,5. The occurrence of leuco-anthocyanins in pears (Pyrus communis) was suggested by Joslyn6 to explain the reddening that occurs in tinned pears stacked before they are completely cooled, and by Bate-Smith1 to explain the reddening of stewed pears. Kiesser et al.7 reported the occurrence of leuco-anthocyanins in perry pears on the basis of chemical and chromatographic examination of the insoluble matter causing haze and turbidity and depositing as a sediment in perry. The red pigment obtained by treatment of the sediment with warm dilute acid was found to contain small quantities of phloroglucinoi, protocatechuic acid, catechol and cyanidin but was composed chiefly of complex leuco-anthocyanixs related to cyanidin. We have recently examined Bartlett pears for the occurrence of leuco-anthocyanins and found evidence for the presence of the leuco-anthocyanin related to cyanidin.