Molecular Microbiology Research, 2025, Vol.15, No.2, 45-58 http://microbescipublisher.com/index.php/mmr 47 and at the same time injects modern innovation elements (Liu et al., 2024). Yuyue established a provincial brewing technology research and development center and began to scientifically record and improve traditional processes. In recent years, Yuyue has launched a series of new products that retain both traditional flavors and meet modern needs, such as strengthened soy sauce with iron added, healthy soy sauce with reduced salinity, and orange vinegar and lotus seed sauce wine developed in combination with local specialties. In terms of process equipment, Yuyue invested in the transformation of sauce drying yards and fermentation containers, introduced facilities such as stainless steel pipe temperature control drying yards to partially replace manual labor, and at the same time, it combined traditional skills with industrial tourism through glass observation windows and model displays. Figure 1 Field view of traditional soy sauce fermentation using earthenware vats in natural environments 3 Microbial Fermentation System: from Natural Inoculation to Bacterial Breeding 3.1 Traditional sauce-based microbial community Traditional soy sauce fermentation is a complex microbial synergistic process carried out in an open natural environment. In the ancient method of fish jumping, artificial bacteria are not actively added during the rumbling process, but instead use mold spores that naturally exist in the environment to inoculate them by themselves. After several days of indoor incubation under warm conditions, the soybean-bran mixture becomes covered with fluffy Aspergillus mycelia, forming what is known as “jiangqu” (fermentation starter). Research has shown that under traditional conditions, fungi of the genus Aspergillus, such as Aspergillus oryzae, often dominate during the koji-making stage. These fungi produce amylases and proteases, which break down macromolecules in soybeans and wheat flour into fermentable substrates (Wang et al., 2023). When the koji is mixed with brine to initiate high-salt moromi fermentation, the environment—characterized by approximately 20% salt concentration, high humidity, and low oxygen—favors the enrichment of halotolerant microbial communities. Lactic acid bacteria (e.g., Tetragenococcus halophilus) and yeasts (e.g., Zygosaccharomyces rouxii) are the major functional microbial groups in traditional moromi fermentation, each becoming dominant at different fermentation stages (Chin et al., 2024). In the natural fermentation system since the Northern Song Dynasty, the source of microorganisms completely relies on the environment and raw materials, and naturally select bacterial species that are suitable for the conditions of the soybean mash. Research on traditional Korean soy sauce also found that under the conditions of adding sterile species, communities composed of various bacteria and fungi will be spontaneously formed, including salt-resistant lactic acid bacteria, Pseudomonasaceae and a small amount of yeast, etc., which work together to form the flavor and quality of soy sauce. 3.2 Pure breeding fermentation and breeding of bacteria With the development of modern microbiology, the soy sauce industry has begun to introduce the concept of purebred fermentation, that is, artificial inoculation of specific excellent bacterial strains to replace natural fermentation that is completely dependent on the environment (Liu et al., 2025). As early as the late 19th century, Japan isolated and purified excellent Aspergillus and used it for soy sauce koji, achieving the stability of purebred
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