Effects of Different Compositions of Raw Materials on Fungal Flora Composition and Rheological Properties of Sticky Bean Bun Sourdough

The objective of this study was conducted to analyze the effects of different raw materials on fungal community composition and rheological properties of sticky bean bun sourdough. According to the raw materials, 16 sticky bean bun sourdough were divided into four groups (A:glutinous rice+rice, B:glutinous rice+maize, C:maize, broomcorn millet and rice, and D:broomcorn millet+maize). The fungal community composition of sticky bean bun sourdough was investigated by polymerase chain reaction denaturing gradient gel electrophoresis (PCR-DGGE) combined with high-throughput sequencing technique. The rheological properties, the value of pH and total titratable acidity (TTA) also were measured to describe properties of sourdough. The results showed that, at the genus level, Cystofilobasidium, Cryptococcus, Debaryomyces and Trichosporon were presented in the sourdough of both group A and group C Hanseniaspora was also identified in group C, and Penicillium, Epicoccum, Wickerhamomyces and Rhizopus were found in the group A.Cryptococcus and Debaryomyces were found in group B.In group D, Hanseniaspora was identified. The yeast diversity of the sticky bean bun sourdough made by mixing glutinous rice and rice was more abundant than other raw materials. In the sticky bean bun sourdough, Dabaryomyces hansenii was the dominant yeast. The elastic modulus and compound viscosity of raw sourdough had a significant positive correlation with Cyberlindnera (P<0.05). The fermentation of Cyberlindnera could enhance the elasticity of sourdough. The loss factor of raw sourdough was significantly positively correlated with Hanseniaspora, and negatively correlated with Cryptococcus and Naumovozyma (P<0.05), so fungi could affect the fluid properties and solid properties of raw sourdough. Fungi such as Saccharomyces could enhance the fluid properties of cooked sourdough. The pH of sourdough was significantly positively correlated with fungi such as Sporobolomyces, Hanseniaspora, and Spherococcus (P<0.05), and the value of TTA of sourdough was significantly negatively correlated with 8 genera such as Cystofilobasidium, Cryptococcus and Penicillium (P<0.05). The results showed that the low pH and high total acidity of the acid environment inhibited the growth of fungi, such as Sporobolomyces and Cystofilobasidium. Therefore, the composition of raw materials had a certain influence on the fungal community structure (adding corn or broomcorn millet can increase the viscosity and elasticity of sourdough) and the rheological properties of the sticky bean bun sourdough. The rheological properties, pH and TTA had correlation with fungal composition in sourdough dough.