Abstract: Weissella confuse J28, which has been found to produce exopolysaccharide (EPS), was inoculated to pure rice flour or 10% sucrose incorporated rice flour and cultured at 30 ℃ for 24 h to prepare low-EPS and high-EPS rice flour sourdoughs, respectively. In order to compare the effects of the two sourdoughs on the dough rheology, microstructure and steaming characteristics of steamed bread, biochemical analysis, dynamic rheological test, texture analysis and sensory evaluation were carried out. The results showed that upon the addition of sugar, strain J28 produced 11.12 g/kg EPS in the rice sourdough. This strain produced acids to activate the endogenous enzymes. The amylase activity in the rice sourdough increased first and then decreased, and the soluble sugar content increased. A large amount of fructose and glucose were produced. Increased proteolytic activity was observed, causing degradation of macromolecular soluble gluten. Compared with steamed bread dough incorporated with rice flour at 25%, the elasticity and viscosity moduli of the steamed bread doughs with rice flour sourdough were reduced, and the protein structure was weakened. The dough with high-EPS sourdough was softer. Compared with the control, the sourdough steamed breads had significantly increased specific volume (P < 0.05) and significantly decreased hardness (P < 0.05), with more uniform and smaller pores. The texture of the steamed bread with high-EPS sourdough was better than of the steamed bread with low-EPS sourdough, as manifested by 7.9% increase in specific volume and 28.7% reduction in hardness. Moreover, the sensory score of the steamed bread with high-EPS sourdough was higher and it was more popular with consumers than the other two groups.

Key words: exopolysaccharides, Weissella confusa, rheological properties, steamed bread incorporated with rice flour, microstructure, steaming characteristics