ROLE OF HYDROGEN-PEROXIDE PRODUCED BY BAKERS-YEAST ON DOUGH RHEOLOGY

Baker's yeast, Saccharomyces cerevisiae, has a well-known effect on do ugh rheology during breadmaking. During a 3-hr fermentation, hydrogen peroxide (H2O2) produced by yeast (0.76%, fwb) increased from 1.09 to 2.32 mu mol/g of flour. The spread test, a measure of a dough's rheolo gical properties, showed that yeast had an effect on dough rheology si milar to that of H2O2, an oxidant that makes flour-water dough more el astic. In additional experiments (spread test and H2O2 measurement), g lucose oxidase, an enzyme that produces H2O2 gave results similar to t hose with yeast. The fact that catalase, an enzyme that destroys H2O2, reversed the rheological effect of added H2O2 but did not reverse the effect of either yeast or glucose oxidase suggested that either wheat flour contains an inhibitor to catalase or H2O2 was not the active co mponent. A series of experiments, including use of defatted flour, rem ixing, and mixing dough under nitrogen, all indicated that catalase wa s inhibited by peroxides in the lipid fraction of flour. These results also suggested that H2O2 is responsible for the effects of yeast and glucose oxidase on dough.