POSSIBLE IMPLICATIONS OF FOUR OXIDOREDUCTASES (POLYPHENOLOXIDASE, CATALASE, LIPOXYGENASE, AND PEROXIDASE) PRESENT IN BREWERY'S BARLEY AND MALT ON ORGANOLEPTIC AND RHEOLOGICAL PROPERTIES OF MASH AND BEER

摘要

Organoleptic quality of beer during storage can be dramatically altered as a result of enzymatic oxidation of endogenous polyunsaturated lipids and phenolic compounds originating from brewery's barley. Enzymatic-mediated oxidative reactions can take place during the 3 stages of the process viz barley germination, malt kilning and at the beginning of mashing. In this respect, the action of oxidoreductases can lead to flavour deterioration (development of staling and off-flavours), occurrence of haze,modification of bitterness and astringency, as well as a modification of the colour of the processed product (1,2). Both polyphenoloxidase (PPO) and peroxidase (POD) are able to catalyze the O_2- or H_2O_2 mediated oxidation of endogenous polyphenols inreactive quinonic compounds and give rise to secondary oxidations altering the quality of beer. Moreover, POD are also susceptible to realize oxidative cross-linkings between proteins and / or soluble pentosans (3) and, consequently, may hinder lautering and filterability of beer.