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Identification and quantification of chromophoric substances in barley (Hordeum vulgare L.)
Häge, D., Reichenbacher, M. Bernhard, M., Schneider, K., Krause, B., Zarnkow, M., Lindemann, M.

The contents of colouring substances in different cultivated varieties of barley (Hordeum vulgare L.) were recorded qualitatively and quantitatively to identify which substances contribute to their colour. HPLC was used to quantify the 3-O-glucosides of the anthocyanidins malvidin, peonidin, pelargonidin, cyanidin and delphinidin. Of the varieties examined, only the ancient spring barley variety Weihenstephaner Schwarze Nackte contained anthocyanins, with delphinidin-3-glucoside accounting for the largest proportion. In addition, another substance was detected, which is most likely also an anthocyanin. The total anthocyanin content was at the upper end of the values previously known from black varieties. MALDI-TOF mass spectrometry was used to try to shed more light on the structure of the dark pigments in the outer layers of the black barley grains. The results suggest that the dark substance is a heterooligomer of different, partly phenolic substances. Specifically, the repeated occurrence of a 180 Da monomer could be detected. Since plant melanins are usually synthesised from the phenolic acids found in the plant, this substance could be caffeic acid and would thus be similar to allomelanin from oats (Avena sativa L.), which is a homooligomer of p-coumaric acid. The development of anthocyanins during malting were recorded photometrically. A clear decrease in the total anthocyanin content could be observed, however, clear weaknesses of the method used to date became apparent.

Descriptors: Anthocyanins, allomelanin, coloured barley, HPLC, MALDI-TOF, polyphenols

BrewingScience, 76 (September/October 2023), pp. 97-106