The Study on the Relationship of Invertase Activity and Leavening Ability in Sweet Dough

The leavening abilities in sweet dough and the invertase activities were determined in several strains of Saccharomyces cerevisiae to investigate their correlations. There was a general tendency that the higher invertase activity yeast cells showed, the less leavening ability the strain possessed in sweet dough containing sucrose. The changes of glucose contents detected in high sucrose model liquid dough (HSMLD) mediums further confirmed that strains with higher invertase levels were exposed to high osmotic stress faster and greater in HSMLD mediums than strains with less invertase activities, thus causing that their CO₂-producing capacities were inhibited seriously. Then a mutant BM-8 was obtained from baker´s yeast strain BY-6 mutated by ultraviolet irradiation. Its invertase level was reduced by 24.9%, while the fermentative activity was proved to be increased by 22.9%. The changes of glucose contents of the mutant BM-8 and its parent BY-6 in HSMLD mediums indicated that compared to the parent BY-6, the mutant BM-8 exposed itself to a less osmotic stress condition during the whole fermentation process. These results showed that the less invertase levels is undoubtedly helpful for the improvement of leavening ability of baker´s yeast and BM-8 was an excellent strain useful in bread production.