Media requirements for aerobic cultivation of a yeast strain related to Saccharomyces cerevisiae TMB3400 on softwood hydrolysate

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This thesis work was carried out for SEKAB E-Technology in Örnsköldsvik and the purpose of the study was to design a nutrient medium for the aerobic cultivation of a xylose-utilising yeast related to Saccharomyces cerevisiae TMB-3400. The focus has been to reduce the cost of carbon and nitrogen which represent a significant cost in the yeast production. Carbon is added in the form of beet molasses, a rest product from table sugar production, and nitrogen in the form of ammonia. This work investigates if beet molasses can be interchanged with dilute acid hydrolysate and at which point the yield of yeast will start to decline. Experiments have been performed with different levels of nitrogen to find if nitrogen can be reduced from the levels used today. It was also examined if a decrease in molasses could be compensated with adding nitrogen in excess or by addition of vitamins. Some of the experiments were performed with design of experiments to get statistically significant conclusions. The experimental work showed that it is possible to supply only 10 % of the sugars in the form of beet molasses (and supply the rest as dilute acid lignocellulose hydrolysate) without any significant reduction of the biomass yield. It was not until the molasses addition was below 9 % that a statistically significant reduction in yield was observed. Reducing the assumed nitrogen requirement by 50 % resulted in a statistically significant decrease of the yield. It is not possible to state whether addition of vitamins and surplus of nitrogen can compensate for a decrease in molasses. In future work it is recommended to perform further experiments to design a nutrient medium for aerobic cultivation with lower expenses. The aim should be to find sui...