On the Fermentation Properties of Wheat Flour-yeast Dough Mixed with Rice Flour and its Change in Sugar Content during Fermentation

Abstract

Gelatinized rice flour(GRF)and untreated raw rice flour(URRF)were replaced with wheat flour by 20%. The changes in the fermentation properties and in sugar content of the wheat flourrice flour-yeast mixed dough during the fermentation were investigated. At the early fermentation stage, the CO₂ production of the dough containing URRF was increased, whereas in the case of the dough containing GRF, the increment was observed only at the latter stage. There were not much differences in the total sugar content between wheat flour dough and URRF containing dough during fermentation, but in the case of the dough containing GRF, it was 2 to 3 times higher than that of wheat flour dough. In the wheat flour dough, the amount of glucose decreased during early fermentation stage and that of maltose decreased only latter fermentation stage. On the other hand, the dough containing URRF had 2 to 3 times more glucose than that of wheat flour dough and the maltose content decreased during early fermentation stage. The maltose content of the dough containing GRF was 2 to 3 times higher than that of wheat flour dough during the fermentation. These results indicated that the increased CO₂ production of the dough containing URRF observed at the early fermentation stage was due to the hydrolysis of maltose by α-glucosidase derived from URRF. On the other hand, in the case of GRF, all enzymes were inactivated by the heat treatment and starch were hydrolysed only by β-amylase in the wheat flour. Therefore, the CO₂ production increased at the latter fermentation stage.