Abstract: This study is aimed to figure out the structure of the microbial community in the traditional sourdough and to determine the flavor components of steamed bread made with it. The pH, titratable acidity and total bacterial colony counts of sourdough samples collected from Shanxi (SX), Hebei (HB), Qinghai (QH), Gansu (GS) and Henan (HN) provinces were measured, and the composition of the microbial communities in the five samples were determined by high-throughput sequencing. Besides, solid phase micro-extraction coupled to gas chromatography-mass spectrometry (SPME-GC-MS) was used to determine the flavor compounds in steamed bread. The results showed that the pH of these sourdoughs was between 3.69 and 3.83, the total titratable acidity (TTA) ranged from 3.73 to 4.30 mL, as determined by titration with 0.1 mol/L NaOH, and the number of lactic acid bacteria and yeasts ranged from 4.89 to 8.31 (lg(CFU/g)) and 4.75 to 6.08 (lg(CFU/g)), respectively. Lactobacillus, Lactococcus and Weissella were the dominant bacteria in the sourdoughs, and the dominant fungi were Saccharomyces, Pichia and Candida. Besides, the relative abundance of the dominant bacterial and fungal genera was different among the different samples. In total, 42 volatile compounds were identified in all samples, including alcohols, aldehydes, esters, aromatics and hydrocarbons, 30 of which were found in sample HB, 26 in samples SX, QH and GS, respectively, and 25 in sample HN. The total contents of flavor compounds in steamed breads made with the five sourdoughs were ranked in decreasing order as follows: SX > HN > GS > QH > HB.

Key words: sourdough; flavor compounds; microbial community diversity; high-throughput sequencing; gas chromatograph-mass spectrometry