Ascorbic acid oxidase in barley and malt and its possible role during mashing

Abstract

Ascorbic acid oxidase (AAO) develops in the embryo tissues of barley during steeping and initial stages of germination. Two AAO enzymes have been identified. One of them is of remarkably low molecular weight (<10,000). Both are very heat tolerant and capable of acting over a broad pH range. Both enzymes would be expected to function during conversion temperatures of mashing. Indeed, addition of ascorbic acid to mashes results in the survival of higher levels of polyphenol and thiols into wort and a reduced color in that wort, commensurate with AAO preferentially consuming oxygen which, thus, is less readily available for other reactions in mashes, including thiol oxidation and polyphenol oxidation. © 2014 American Society of Brewing Chemists, Inc