Abstract:

The traditional Yongchuan Douchi has a unique flavor and is always greatly loved by consumers. Its unique
flavor is produced by interaction of the complex microbial flora. Nested polymerase chain reaction (Nested-PCR) and
denaturing gel gradient electrophoresis (DGGE) were adopted to analyze the microflora ecological evolution of Yongchuan
Douchi during fermentation and it was found that in the koji-making process, the amounts of molds and bacteria exhibited
a logarithmic growth trend and the total number of colonies rapidly declined during the late stage of fermentation and
then remained stable at a lower level. A variety of lactic acid bacteria increased during the early stage of koji-making and
the number of species of lactic acid bacteria decreased during the late stage due to the growth inhibition by molds. At the
late stage of fermentation, Bacillus odysseyi, Lactobacillus oligofermentans and Lactobacillus lindneri were the dominant
bacteria. Besides, it was also found that infectious microbes such as Escherichia fergusonii grew at the beginning of kojimaking.
The dominant mould of Yongchuan Douchi during the entire koji-making period was always Mucor racemosus,
which was accompanied by the growth of Rhizopus sexualis, Rhizopus stolonifer, Syzygites megalocarpus, and Rhizopus
oryzae as well as Zygosaccharomyces sp. during the late phase of fermentation.

Key words: Yongchuan Douchi, microflora, nested-polymerase chain reaction (PCR), denaturing gel gradient electrophoresis (DGGE)