Study On Fermentative Production Of D(-)-lactic Acid From Glucose By Sporolactobacillus Sp.

The thesis was designed to optimize the cultures of producing D-LA bySporolactobacillus sp. and analyze the effects on fermentation in order to produceD-LA effectively.D-lactic acid(D-LA) is considered to be a very important chemical compoundas a chiral material or intermediate in organic synthesis. D-LA is a prosoma of manychiral compounds with applications not only in the pharmaceutical and cosmetic industry but alsoin highly efficient and lowly toxic pesticide and herbicide. Poly lactic acid(PLA) is abiodegradable and processable high polymer, which is widely used in chemicalengineering, agriculture and pharmaceutical industry. D-LA is hence going to form a hugepotential market.Fermentative production of D-LA by microorganisms is the primary method inindustry, which is applied by several factories abroad. To this day, study on productionof D-LA has not been reported in China, which is urgent to be researched.Fermentative production of D-LA from regenerative materials such as glucose isfeasible in China due to the lower cost, high optical purity, moderate condition and lowerpollution. Lactobacillus delbrueckii, Lactobacillus bulgaricus and Bacilluslaevolacticus are mainly used abroad in fermentative production of D-LA. The thesis wasbased on a strain from Sporolactobacillus sp. with the advantage of D-LA opticalpurity and conversion yield to glucose.The properties, structure, applications, the current production situation of D-LAand the fermentation processes of glucose producing D-LA by Sporolactobacillus sp.were introduced in this thesis. The optimal conditions of D-LA fermentation usingshaking-flask were investigated. The effects of temperature, pH, and anaerobiccondition on fermentation were studied. The effects of medium composition on theyield of D-LA were also studied in shaking-flask culture. Under optimal conditions,40.7g/L of D-LA was produced from 60.0g/L glucose after 72 hours fermentation at37℃, with the mass yield of 67.83%, the mole yield of 135.54% and 96.04%e.e..The method of anaerobic cultivating and fermentation of microorganisms wasresearched and Sporolactobacillus sp. was proved to be micro-aerobic. A series of IImethods, including addtion of liquid petrolatum and glass beads and adjustment offlask loads and rotation speed of swing bed, was founded to be efficient in controllingthe concentration of dissolved oxygen in fermentation medium and enhancing thetransmission of substances. The growth of microorganism and D-LA yield was hencepromoted.For the first time, the thesis applied composite nitrogen sources to fermentationin stead of yeast extrct as single organic nitrogen source. And for the first time, thethesis used NH4NO3 and bran as ingredients of composite nitrogen sources andreduced the concentration of yeast extract and corn steep liquor with the result that thefermentation cost was greatly lowered.The thesis was the first research on fermentative production of D-LA in Chinaand laid a foundation of further researches on producing high optical D-LA effectively.