بهبود توليد اتانول زيستي و مقاومت ساكارومايسس سرويزيه تحت برخي تنش‌ها به‌منظور كاهش مصرف آب

Bioethanol is known as a widely used biofuel, and improving the bioethanol production process for economic and environmental reasons is a priority research field on an international scale. Bioethanol production is a water-intensive industry, and reducing water consumption is one of the most important challenges for ethanol production units. Some strategies to reduce water consumption include the use of thick bed, fermentation at high temperature and using Persian Gulf sea water instead of fresh water in bioreactors. However, ethanol production under these conditions requires Saccharomyces cerevisiae yeast with the ability to produce high ethanol and tolerance to osmotic and thermal stresses. In this project, 30 isolates were isolated from different sources based on morphological characteristics, and 4 isolates (yeast number 1901, 1902, 1903, 1402) were identified as Saccharomyces cerevisiae yeast with the help of biochemical tests and molecular methods. The isolates were investigated for their ability to grow and ferment under the stresses of high temperature, salinity and high and very high sugar concentration. Finally, 1901 yeast with the ability to grow in one molar salt, 41°C and fermentation in 25 °Brix (270 g/L of glucose) was selected as the superior isolate. In order to improve the tolerance of yeast to salinity, 15 times of serial cultivation were carried out in 0.7 M salt for the adaptive evolution of the yeast isolate. Based on this, the growth of the adapted isolate was observed to be almost ten times that of the parental strain within 24h To eva‎luate the fermentation ability of yeast 1901 under the mentioned stresses, fermentation parameters were assessed in two culture media based on glucose and sugar beet molasses with different °Brix levels at 30°C and 37°C. Additionally, to improve fermentation conditions in the mentioned culture media, the increase in inoculum size and shaking the fermentation medium at 80 and 120 rpm were examined. The highest bioethanol and ethanol yield was achieved at 25 °Brix, shaiking at 80 rpm and 37°C, 8.94% and 44.89%, respectively. The isolated yeast was able to produce 7.45% (v/v) ethanol with an ethanol yield of 42.5% during fermentation at 37°C with 18 °Brix (200 g L−1 glucose), 0.7 M salt and inoculum size of 1.1×108 cells/ml. In the molasses medium with 22 and 26 °Brix and at both temperatures, 57.6% and 7.68% ethanol with productivity of 1.7 and 1.15 g/l/h and theoretical yeild percentage of 97.36% and 93.89% was produced and by increasing the amount of inoculum size almost 4 times and also shaking the culture medium, the productivity of ethanol production increased by 2.4 and 1.6 times respectively. The amount of ethanol was calculated with the help of specific density and reported in terms of weight percent. Based on the obtained results, yeast has the potential to produce bioethanol in saline water equivalent to Persian Gulf sea water. Therefore, based on the obtained results, the isolate has the growth ability and fermentation potential under the stresses of high gravity, high temperature and salinity and can be further eva‎luated, improved and optimized for industrial bioethanol production and reducing water consumption during bioethanol production.

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