The Study On Batch And Fed-batch Ethanol Fermentation From Sugarcane Juice By Saccharomyces Cerevisiae GJ2008

Sugar utilization is very important for ethanol fermentation, especially for highgravity sugarcane fermentation as it often causes sluggish or stuck of the use of fructose,unmetabolized fructose results in lower ethanol yield, which is rather disadvantageous forethanol production industry. It is necessary to find out what causes the slowdown of sugarutilization during the final stages of the fermentation with the aim of better controlling thefermentation process and improving the overall fermentation performance.Firstly, YPF, YPD and YPDF medium were used to carry out the experiments toevaluate the environmental factors such as the type of sugar, the total sugar concentrationand temperature on the discrepancy in fructose and glucose utilization. Secondly,completely hydrolyzed sugarcane juice was simulate the sugarcane juice to perform theethanol fermentations to evaluate the environmental factors such as the timing of nitrogenaddition, temperature and feeding operation on the discrepancy in fructose and glucoseutilization as well as on other parameters. The results are as follows:(1) Fermentation with either glucose or fructose as the sole carbohydrate source hadclearly different sugar consumption rates but almost the same specific production rates atthe sugar concentration ranging from140g l-1to180g l-1. The specific production rate alsodiversified from each other when the sugar concentration higher than250g l-1. Theglucose was consumed relatively faster than fructose due to the nature of the yeast GJ2008,which was independent as to whether glucose was contained in medium or not. Whenfermentation with both sugars(50%/50%), S.cerevisiae GJ2008always showed a slightlyhigher preference for glucose than fructose, and so the fructose consumption was alwaysunder competitive inhibition. As far as the effect of environmental factors on theconsumption of both sugars, fructose consumption was affected more than glucoseconsumption by initial sugar concentration, and lower sugar concentration could result in alower discrepancy in fructose and glucose utilization, in contrary fructose fermentationwas less strongly affected by the temperature gradient and lower temperature could relievefructose sluggish phenomenon. Another aspect of this study was the investigation into theeffect of hexose ratio, micro-aeration and temperature on the discrepancy in fructose andglucose consumption in the presence of11%(v/v) ethanol, results showed that the initialconcentration of glucose accounted for more than40%is highly influential on fructosemetabolism. In addition, mircro-aeration could effectively reduce the discrepancy infructose and glucose utilization, and ethanol productivity was enhanced by61.70%.Meanwhile low temperature is obviously helpful to maintain the final biomass and sugardegradation was less severely affected by external ethanol than that produced by the yeast.However the environmental factors did not affect the preference for glucose than fructosementioned above. (2) Completely hydrolyzed sugarcane juice was adjusted with an equivalent amountof fructose and glucose to give a total sugar concentration ranging from220g l-1to340g l-1.The juices were supplemented with nitrogen sources at various stages at the sugarconcentration of220g l-1. Results again indicated that S.cerevisiae GJ2008always showeda slightly higher priority for glucose than fructose, fructose consumption always laggedbehind glucose consumption. Nitrogen addition could reduce the discrepancy in glucoseand fructose utilization effectively when added in the early stages of the fermentation. Inaddition, two-stage temperature strategy was investigated, and it turned out two-stagetemperature strategy could effectively reduce the discrepancy in fructose and glucoseutilization, and the ethanol productivity was enhanced by2.71%. The ethanol productioncould reach up to153.86g l-1in the fermentation liquor in the fermentation time of60husing the two-stage temperature strategy. Finally, the juices above containing total sugarcontent of250g l-1were supplemented with nitrogen sources at0h, and two-stagetemperature strategy was applied, non-sterilized equivalent amount of fructose andglucose was added at fermentation time of13h to adjust the actual total sugarconcentration up to340g l-1. Results showed that the final ethanol content could reach upto146.36g l-1in the fermentation liquor. The ethanol productivity and yield efficiencywere2.71g l-1h-1and84.94%at the fermentation time of54h, which were enhanced up to2.15%and8.86%respectively as compared to batch fermentation.