Oxidative Enzyme Effects in Malt for Brewing

Malted barley is an important beer-brewing material that strongly affects brewing processes, the aroma, and the taste of beer. In addition to imparting a good aroma, malt not only generates substrates and enzymes, such as starches and some amylase, for alcohol production but also generates beer-quality-degrading substances and enzymes. Four oxidases are specifically addressed in this chapter. First, thiol oxidase in malt is described. The activity of thiol oxidase decreases during malt storage. Next, ascorbate peroxidase was investigated. It has been detected in the acrospires and aleurones of germinating barley. The enzyme has extremely high affinity for hydrogen peroxide. Also, ascorbic acid oxidase (AAO) was investigated. It is developed in the embryo tissues of barley during steeping and during the initial stages of germination. The addition of ascorbic acid to mash leads to the survival of higher levels of polyphenol and thiols into wort and a reduced color in that wort. Finally, oxalate oxidase in barley kernels is described. It is probably less important than other oxidases in scavenging oxygen from mashes, because the enzyme has low affinity for oxygen. Beer quality is expected to be improved by the regulation of oxidant enzymes, such as thiol oxidase or AAO, oxalate oxidase, or substrates, such as oxygen.