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Outline
[Objective] To elucidate the enzymatic-producing properties and environmental tolerance of culturable microorganisms from medium-high temperature Daqu, as well as their regulatory effects on the solid-state fermentation system of Baijiu, to investigate the differences of functional microorganism distribution across different Daqu grades, and to provide a theoretical basis for the development of fortified microbial starters and the optimization of brewing processes. [Methods] The isolation of functional microorganisms, along with the evaluation of enzyme-producing characteristics, growth properties, and environmental tolerance, was conducted on post-fermentation medium-high temperature Daqu of superior-grade and premium-grade used in the production of Nongjiangjianxiangxing Baijiu (strong-sauce aroma-type Baijiu). Moreover, solid-state simulated fermentation experiments were conducted to investigate the regulatory effects of four dominant strains on the physicochemical properties and volatile flavor compounds of the fermented grains. [Results] In this study, a total of 44 strains were isolated from Daqu of premium-grade and superior-grade used in the production of Nongjiangjianxiangxing Baijiu (29 from premium-grade Daqu and 15 from superior-grade Daqu), belonging to 5 phyla and 8 genera, with Bacillus being the dominant genus (accounting for 43.2%). A total of 28 amylase-producing strains (20 from premium-grade, 8 from superior-grade) and 4 cellulase-producing strains (3 from premium-grade, 1 from superior-grade) were primarily screened. Although the premium-grade Daqu contained a higher number of enzyme-producing strains, the strains from the superior-grade Daqu exhibited greater average enzyme production capacity. After secondary screening, strains T41, Y46, and T47 were identified as high-yield amylase-producing functional microorganisms, and strain Y22 as a high-yield cellulose-producing functional microorganism. The tolerance assays revealed that Y46 exhibited the strongest adaptability to high temperature, ethanol stress, and lactic acid stress, and Y22 exhibited the strongest acid tolerance whereas T41 showed the best performance under glucose stress. The results from the solid-state simulated fermentation indicated that all four tested strains contributed to maintaining fermentation ecosystem stability. The strains significantly enhanced starch degradation, achieving reduction rates (from 7.0% to 9.5%), with Y22 exhibiting the most pronounced degradation efficiency. The differential regulatory effects were observed on reducing sugar utilization and volatile flavor compound synthesis, particularly esters. Notably, T41 showed the most pronounced enhancement in flavor compound accumulation. [Conclusion] Post-fermentation medium-high temperature Daqu harbors abundant enzyme-producing functional microorganisms. Significant differences were observed in the quantity and enzyme-producing performance of functional strains across Daqu of different grades, with amylase-producing strains exhibiting a higher isolation rate than cellulase-producing strains. The four screened functional strains possess excellent enzymatic properties and environmental adaptability. In the simulated Baijiu fermentation system, these strains maintained acidity stability, enhanced starch utilization efficiency, and promoted the formation of flavor compounds. Among them, strains T41 and T47 exhibited superior overall fermentation performance and demonstrated considerable potential for practical application. These findings provide valuable microbial resources and a scientific basis for the development of functional microbial starters and the operation of Baijiu brewing processes.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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