Influences of rare sugar D-allulose on the fermentation ability of baker's yeast and the physical properties of bread

The rare sugar D-allulose (Alu), which has only 10% calories of sucrose (Suc) and an anti-obesity effect, was added to bread, and the effects of Alu on the fermentation ability and physical properties of baked bread were investigated. Alu, unlike its epimer D-fructose and D-glucose, was not metabolised by the baker's yeast and caused a decrease in the amount of CO2 generated through respiration. The expansion rate of the Alu-added dough was lower than sugar-free (control) and Suc-added dough in primary fermentation, indicating that Alu partially inhibits dough fermentation. The addition of Alu did not affect the rheological properties of gluten; however, Alu-bread had much higher hardness and gumminess than control and Suc-bread. Therefore, the high hardness and gumminess were due to the low CO2 production rate of yeast. 94% of Alu added to bread remained in Alu-bread after baking. Furthermore, Alu-bread, when stored at room temperature, was lower in hardening rate than control and Suc-bread. The present study reveals that the sole use of Alu as a sugar material is not preferable in terms of texture, but most Alu remains in bread without degradation and has an effect on preventing the bread from texture-deteriorating during storage.