Studies On Amylase Production And Ethanol Fermentation By Saccharomycopsis Fibuligera A11 Strain

Cassava is a root crop of tropical American origin and is the fourth most important staple crop in the tropics.It is also cultivated in many provinces in the south of China. The cassava plant is extremely robust, is resistant to disease and drought, and can grow in relatively low-quality soils. Therefore, cassava starch is also a good starchy material in food and fermentation industry in China. Cassava starch is composed of unbranched amylose(20±5%) and branched amylopectin (80±5%), both of which can be hydrolyzed enzymatically (either with pure enzymes or amylase-producing microorganisms) to release their constituent glucose and maltooligosaccharides.Amylase exists widely in microorganisms, and there are mainly a-amylase, glucoamylase and so on.α-amylase is a endonuclease which can catalyze the cleavage of 1,4-a-glycosidic bonds in starch molecules while glucoamylase is a exonuclease which can catalyze the release of glucose from the non-reducing ends of starch molecules.We discovered that S. fibuligera can produce amylase with high activity which is able to hydrolyze the cassava starch. We optimized the solid fermentation condition of a strain S. fibuligera A11.First, Response Surface Methodology (RSM) was used to optimize the medium compositions and cultivation conditions for amylase production by S. fibuligera in solid fermentation, the optimal parameters obtained with RSM were the initial moisture 61.5%,the amount ratio of wheat bran to rice husk 0.42,inoculum 2%(v/v),cassava starch 2.0%(w/v), temperature 28℃,natural pH. 4296 U/gram of dry substrate (gds) of amylase activity was reached in the solid fermentation culture of strain S.fibuligera within 120h under the optimized conditions whereas the predicted maximum amylase activity of 4222 U/gds was derived from RSM regression. Then, the conditions for immobilization of S. fibuligera cells were optimized and the optimal parameters were PVA 8.0%(v/v),sodium alginate 2.0%(w/v),CaCl23.0%(w/v),inoculum size 5%(v/v),time of immobilization 4h. After the conditions for amylase production by the immbibilized cells were optimized,the amylase activity attached 329.0 U/ml while the amylase activity produced by its free cells was only 244.0 U/ml.On the basis of the results obtained above, we took advantage of the amylases produced by strain A11 to hydrolyze cassava starch, further; the hydrolysate was fermented into ethanol by Saccharomyces sp WO.Finally, the ethanol concentrations obtained were 10.5%;(v/v) from the cassava starch hydrolyzated after 72 h of the fermentation.