Isolation And Identification Of A Probiotic Strain Capable Of Producing Glycerol And Optimization Of Fermentation Conditions For The Strain

Energy metabolism disorder of transition period dairy cows, based on a negative energy balance, is a kind of diseases threatening dairy farming with great severity. Glycerol, an excellent glucogenic precursor, with which glucose could be produced through gluconeogenesis pathway by dairy cows, provides energy for the body. A yeast strain capable of yielding glycerol was isolated, and identified as Saccharomyces cerevisiae. The yeast culture from fermentation, rich in glycerol and containing plenty of viable yeasts, given to transition period dairy cows as feed additive, may alleviate the negative energy balance, meanwhile play a role of probiotics, and provide a good opportunity for developing a kind of microbial ecological agent preventing and treating energy metabolism disorder.Experiment 1. A glycerol producing yeast strain was isolated and identified. A glycerol producing yeast strain, isolated from honey, was named NAU-ZH-GY1. By morphology, physiology and biochemistry assays, and 26S rDNA D1/D2 domain sequences analysis, the strain was identified as Saccharomyces cerevisiae, which is a kind of probiotics permitted for feed by laws. The yeast culture from fermentation, included 12.2 g/L glycerol and 107 CFU·mL-1 viable yeasts.Experiment 2. Optimization for the culture conditions of glycerol producing yeast NAU-ZH-GY1 was finished. Optimization with shaken-flask assays for the culture medium of glycerol producing yeast NAU-ZH-GY1, by single-factor and orthogonal design, was carried out, showing the optimal culture medium containing glucose 20%, urea 0.4%, corn steep liquor powder(CSLP) 0.5% and NaCl 2%. While the optimal parameters for fermentation resulted from another orthogonal design were temperature 32℃, incipient pH 5.0, inoculum 10%, time 2 d and speed of the shaking table 180 rpm, respectively, and the production of glycerol reached 24.3 g/L with DCW(Dry Cell Weight) 25.7 g/L.Experiment 3. Effects of pH and DO (Dissolved Oxygen) during fermentation on the glycerol production of glycerol producing yeast NAU-ZH-GY1 in the fermenter were investigated. First, the variation of pH during fermentation (initial pH 5.0) was detected, then, effects of different constant pH on fermentation were studied, and fermentation at different DO levels was evaluated. Results showed that a constant pH value of 5.0 and DO concentration at 70% was proper for fermentation, and the glycerol production reached 32.7 g/L, with DCW 31.6 g/L.