| As one of six distilled liquors in the world, Chinese spirits is very prevalent in China, with a rich cultural heritage. If lactic acid and ethyl lactate content is too high, it will result in a fall in liquor ratio and flavor, even not have wine. The speedy growth of lactobacillus can produce lactic acid in the Daqu and fermented grains. As carbon source, lactic acid could be used by propionibacterium which produces propionic acid, and realizes the effect of ethyl propionic acid-increasing and ethyl lactate-decreasing, thereby enhancing the quality of Chinese liquors.Propionibacterium isolated and identified from pit mud and Daqu of Te-type liquor was studied in this research, including having a great impact on the main factors of its growth and propionic acid production, reducing lactic acid and ethyl lactate, esterifying liquid on propionic acid being applied to cross-steaming and blending in Chinese spirits. The primarily study results are as follows:1. A sensitive screening method to isolate and identify propionibacterium from pit mud was constituted in this paper. In MRS medium, microbes from pit mud and Daqu of Te-type liquor were selected from 58 strains,28 different colony morphometrics. As bacteria, propionibacterium was isolated approximately 15 species by colony morphology. According to metabolizing lactic acid, there were four strains by microscopy, physiological and biochemical tests and propionic acid productivity from the second screening. With the highest propionic acid productivity, CF7-1 strain was from pit mud of Te-type liquor. It was determined to its 16s rDNA sequences, and denominated propionibacterium jensenii.2. The main research included the effect of propionibacterium jensenii CF7-1 with different pH, temperature and inoculation. Propionibacterium jensenii CF7-1 produced propionic acid with the optimal condition and medium. The results were obtained:For propionibacterium jensenii CF7-1, its fermentation cycle was 8 days. The production of propionic acid was achieved to 9.3g/L.The optimal culture pH was 6.5 to 7.0, the culture temperature was 30 to 34℃, the culture inoculation was 5% to 7%. The optimal medium was:glucose 60g/L, peptone 15g/L, yeast extract 15g/L, KH2PO43g/L, MgSO40.3g/L, CoCl 10mg/L. 3. It included the ability of propionibacterium CF7-1 using different carbon sources and reducing lactic acid with the variety of Te-type liquor. The results were obtained:Compared with single carbon source, mixed source was more conducive, and the conversion of lactic acid is higher than glucose. The culture inoculation ratio of propionibacterium and lactobacillus was 3:1. In Te-type liquor production, when the content of propionibacterium raised 6.7×105/g in fermented grains, compared with control sample, lactic acid and ethyl lactate content was reduced by 3.67mg/100mL and 80.6mg/100mL, and ethyl propionic acid content was increased by 0.5mg/100mL, with the Te-type liquor style features and taste better.4. It was researched on the preparation technique of esterifying liquid on propionic acid with esterifying enzyme. Investigation on the influence of esterifying enzyme, propionic acid, ethanol and temperature, ethyl propionic acid was composited by Monascus sp and Te-type Daqu. Propionic acid mixed with last distillate esterified was applied to steaming and blending in Chinese spirits. The main results included:The suitable esterifying temperature was 35℃, the concentration of propionic acid and ethanol was 1.5mL/100mL and 16mL/100mL; the dosage of esterifying enzyme of Monascus sp and Te-type Daqu was 9g/100mL and 7g/100mL. Te-type Daqu was high tolerance for propionic acid concentration, ethanol concentration and temperature, and less for the dosage of esterifying enzyme. Esterifying liquid on propionic acid mixed with last distillate (ratio 1:1), compared with ordinary base liquor, the string-based total ester content of distilled liquor was increased, and improved the quality of liquor rate. |
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