| The widely used feedstock for potable or biofuel ethanol fermentation by yeast,Saccharomyces cerevisiae, is sugarcane molasses. Molasses consists mainly of sugars and it is rich in many nutrients that are essential for microbial fermentation. There are some issues about low concentration of ethanol and prolonging fermentation during very high gravity ethanol fermentation of molasses, especially especially low utilization rate of fructose results in low utilization rate of sugar and lower ethanol yield due to it’s complex composition. As a result, how to remove the inhibitors and enhance cell viability and fructose utilization rate is critically important. Therefore, the influence of inhibitors in molasses by S.cerevisiae GJ2008 on the differences in the glucose and fructose consumption for ethanol production from high gravity sugarcane molasses was studied by this paper. The results are as follows:(1)Ethanol fermentation was carried out by GJ2008 in molasses media with sugar concentrations of 100, 150, 200, 250, 300 g/L in a 500 m L flask. The results showed that the fermentation efficiency reached 78.40 % when the sugar concentration was 200 g/L.Improved the initial sugar concentration was significantly higher residual sugar, more inhibition of yeast cells and prolong the fermentation time, ultimately reduce fermentation efficiency.(2)To explore the impact of sulfite on ethanol fermentation of high concentration of sucrose, ethanol fermentation was carried out by GJ2008 in YPS broth supplemented with sodium bisulfite of 0.00, 0.14, 0.49, 1.14, 1.63 g/L, respectively and with an initial sucrose concentration of 274 g/L. The AUC of OD reached 15.25 and alcohol concentration reached 14.78 %(v/v) and ethanol productivity arrived 2.16 g/(L·h) when the concentration of sodium bisulfite reached 0.49 g/L. Compared to the control,decreased by 8.75 %, 4.34 % and 14.96 %, respectively. The results showed that sodium bisulfite inhibited the vitality of yeast cell and slowed down the rate of sugar uptake with reduced the ethanol productivity. Also, sodium bisulfite led to decrease in the specific sugar uptake rate and specific ethanol production rate. The results also showed that glucose utilization was inhibited to a larger extent than fructose by sodium bisulfite.(3)To explore the impact of metal ion on ethanol fermentation of high concentration of glucose and fructose, ethanol fermentation was carried out by GJ2008 in YPDF broth supplemented with calcium ion of 0.0, 0.3, 0.6, 1.2, 2.4, 4.8 g/L, and with potassium ion of 0, 1, 3, 7, 14 g/L, respectively and with an initial sugar concentration of270 g/L. The AUC of OD reached 28.24 and ethanol concentration reached 114.80 g/L and ethanol productivity reached 2.13 g/(L·h) when the concentration of calcium ion reached0.6 g/L. Compared to the control, decreased by 7.32 %, 6.28 % and 6.17 %, respectively.The AUC of OD reached 29.99 and ethanol concentration reached 119.93 g/L and ethanol productivity reached 2.00 g/(L·h) when the concentration of potassium ion reached 3 g/L.Compared to the control, AUC of OD decreased by 0.30 % and ethanol concentration and ethanol productivity improved 0.33 % and 0.50 %, respectively. The results showed that calcium ion inhibited the vitality of yeast cell and slowed down the uptake rate of glucose and fructose with reduced the ethanol productivity. Also, calcium ion led to decrease in the specific ethanol production rate. The results also showed that fructose utilization was inhibited to a larger extent than glucose by calcium ion. The addition of potassium ions promoted the yeast cell viability, increased the number of yeast cells when the concentration of potassium ion reached 1 g/L and 3 g/L. And the concentration of potassium ion exceeded 7 g/L which could inhibit the growth of yeast cells, the rate of glucose and fructose consumption decreased, and the ethanol production rate decreased.(4)To explore the impact of colloid on ethanol fermentation of high concentration of fructose and glucose, ethanol fermentation was carried out by GJ2008 in YPDF broth supplemented with colloid of 0, 10, 20, 40, 80 g/L, respectively and with an initial sugar concentration of 266.70 g/L. The number of yeast cells reached 3.2×108/m L and ethanol concentration arrived 111.25 g/L and ethanol yield reached 1.85 g/(L·h) when the concentration of colloid of molasses reached 40 g/L. Compared to the control, reduced by5.88 %, 7.84 % and 7.96 %, respectively. The results showed that colloid of molasses inhibited the vitality of yeast cell and slowed down the rate of glucose and fructose uptake with reduced the ethanol productivity. Also, colloid of molasses led to decrease in the specific ethanol production rate. The results also showed that glucose utilization was inhibited to a larger extent than fructose by colloid.(5)Sugarcane molasses followed by flocculation and sulfuric acid, compare with untreated and pretreatment ethanol fermentation in the flask. The residual sugar reached40.69 g/L and the number of yeast cells reached 1.7×108/m L and ethanol concentration arrived 97.84 g/L and ethanol yield reached 1.48 g/(L·h) when the molasses was treated.Compared with the untreated, residual sugars reduced by 40.16 %, and the death rate of cells slowed down, increased by 13.33 %, 13.24 % and 12.98 %, respectively. The results showed that pretreatment increased the rate of sugar uptake and enhanced the ethanol productivity. Also, pretreatment led to improve the specific sugar uptake rate and specific ethanol production rate. |
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