Study on the Effect of Key Genes ME2 and adhE during Luzhou-Flavor Baijiu Brewing.

Luzhou-flavor baijiu (LFB) is brewed by the combined action of various microorganisms, and its flavor is affected by the microbial community and the genes they express, but which genes are the key ones during LFB brewing is less clear. Based on our previous studies the genes ME2 and adhE were identified as key genes, but which role they play was also unknown. In this study functional microorganisms were screened based on the key genes ME2 and adhE, and they were identified to be Rummeliibacillus suwonensis, Clostridium tyrobutyricum and Lactobacillus buchneri. Then simulated fermentation experiments were carried out with the functional microorganisms, and during the fermentation process expression of the key genes and the amounts of the main flavors were detected to analyze the role of the key genes. The results showed that the key gene ME2 was significantly positively correlated with the contents of the main acids, however the key gene adhE and the formation of the main esters in the LFB brewing process was a significant positive correlation. This study verified the two key genes ME2 and adhE complement each other in the LFB brewing process, playing an important role in promoting the formation of flavor substances, and are very beneficial to improve the quality of LFB.

Analysis of the difference between aged and degenerated pit mud microbiome in fermentation cellars for Chinese Luzhou-flavor baijiu by metatranscriptomics.

BACKGROUD: Chinese Luzhou-flavor baijiu (LFB) was fermented in an underground cellar, and the bottom and side of the cellar were covered with pit muds (PMs), where the metabolic activity of the microorganisms had a significant effect on the LFB quality. PMs can be divided into aged pit mud (AP) and degenerated pit mud (DP), thus, the qualities of LFB generated from AP and DP were different. In this essay, metatranscriptomics method was applied to illustrate the differences of the two PMs, as well as to search out the pivotal microorganisms and genes influencing the quality of LFB. RESULTS: Archaea, Clostridium and some thermophilic microorganisms might bring significant effect in AP, while the active eukaryota and Anaeromyxobacter would cause degeneration in PM. Also, the metabolism of carbohydrate and amino acid were more active in AP. What is more, carbohydrate, amino acid and their derivant can produce important organic acids via the activity of the microorganisms in PMs. There were eight critical enzymes noticed in the organic acids metabolic pathway, which were more actively expressed in AP, demonstrating active expression of the critical genes related to organic acid metabolism could have a positive effect on LFB quality. CONCLUSION: This study identified specific differences in active microorganisms, active expressed genes and the expression levels of key genes in vital metabolic pathway between AP and DP. Which may be the actual reason for the differences in the quality of LFB made from different PMs. Mastering these results will provide assistance to improve the quality of LFB. © 2021 Society of Chemical Industry.

Co-inoculation of Staphylococcus piscifermentans and salt-tolerant yeasts inhibited biogenic amines formation during soy sauce fermentation.

With the increasing popularity of soy sauce containing high amounts of amino acid nitrogen (AAN) in China and the positive correlation of biogenic amines (BAs) with AAN, reducing BAs formation during soy sauce fermentation has become an urgent task. In this work, the effect of salt-tolerant yeasts and Staphylococcus piscifermentans on BAs formation was extensively studied. Combined inoculation for different osmotolerant yeast strains indicated that Z. rouxii CICC 1417 and T. candida CICC 1019 co-inoculation produced the lowest amount of BAs (89.43 mg/L). Furthermore, co-inoculation of soy sauce mash with S. piscifermentans and salt-tolerant yeasts reduced the BAs production by 31.51% under laboratory-scale experiments. Only 133.40 g/L BAs were produced after S. piscifermentans inoculation in 50-T fermentator, and this value was 63.25% lower than that of the control. Most of the alcohols, aldehydes, phenols, and esters were increased, whereas bacteria, such as Pediococcus, Weissella, and Streptococcus, were inhibited and thus reduced BAs formation. The increased abundance in Zygosaccharomyces and Pichia may contribute to the improvement in volatile compound production. These findings reveal the high potential of the co-inoculation of S. piscifermentans and salt-tolerant yeasts for soy sauce production with limited BAs formation.

Improving RNA content of salt-tolerant Zygosaccharomyces rouxii by atmospheric and room temperature plasma (ARTP) mutagenesis and its application in soy sauce brewing.

Derived from RNA, 5'-ribonucleotides, especially Inosine-5'-monophosphate (IMP) and guanosine-5'-monophosphate (GMP), can enhance the umami taste of soy sauce. In this study, the RNA content of three different salt-tolerant yeasts was examined. The most valuable strain was subjected to atmospheric and room-temperature plasma (ARTP) mutagenesis, which improved its RNA content by 160.54%. Regular fermentation with RNA-enhanced strain failed to increase the amount of 5'-ribonucleotides in the soy sauce due to hydrolysis by phosphatase. A two-stage fermentation strategy was then carried out. Aroma compounds were mainly synthesized in the first stage, and RNA-enriched biomass was massively produced in the second stage followed by heat treatment to inactivate phosphatase. After the proposed strategy was applied, IMP and GMP in the soy sauce reached 68.54 and 89.37 mg/L, respectively. Moreover, the amounts of key aroma compounds and organic acids significantly increased. Results may provide new insights for improving the quality of soy sauce through microorganism breeding and fermentation control.

Longer axial trap distance and larger radial trap stiffness using a double-ring radially polarized beam.

The optical trapping forces acting on a metallic Rayleigh particle are calculated for the case where a double-ring-shaped radially polarized beam is applied. The influence of the off-focus distance and the off-axis distance of a trapping particle on the trapping force is investigated. Compared with the use of the conventional single-ring-shaped radially polarized beam, the longer axial trap distance and the larger radial trap stiffness are predicted using a double-ring-shaped radially polarized beam in an optical trap. These features are useful for improving the trapping ability of an optical trap system where a longer axial trap distance is needed.