L-lactic Acid Production By Fermentation From Agriculture By-products

Lactic acid and its derivatives are widely used in the food,pharmaceutical,chemical, feed industries and environmental protection.Recently,lactic acid consumption is increasing considerably because of its role as a monomer in the production of biodegradable PLA.PLA is well-known as a sustainable bioplastic material,which has similar properties of glossiness and processibility as polystyrene,With the use of PLA,it is hopeful to resolve the problem of "white pollution".The objective of this research was to reduce the L-lactic acid production cost using agriculture by-products in place of glucose or starch.To realize the objective of this research,we studied the condition of L-lactic acid fermentation from sweet potato pulp and corn stover by Rhizopus oryzae PW352.1.This paper described the conversion of sweet potato pulp into L-lactic acid by Rhizopus oryzae PW352 in 250mL flask.The affecting factors such as nitrogen source, inorganic salts,calcium carbonate,inoculation volume,temperature,humidity and thickness of materials on L-lactic acid production were investigated by orthogonal design and uniform design.The highest lactic acid production of 38.36(±0.51)%(w/w)was obtained when Rhizopus oryzae was cultured for 72h under the following condition:10g sweet potato pulp/250mL flask,(NH₄)₂SO₄ 1.5%,MgSO₄ 0.2%,ZnSO₄0.05%,MnCl₂ 0.05%,glucose 0.5%,Tween 80 0.05%,CaCO₃ 30g/(100g dry medium),humidity 66.7%,volume of seeds is 1mL/10g culture medium(1.0×10⁷ spores/mL) and culture temperature is 36℃.2.The enlarged experiment of L-lactic acid production in trays from sweet potato pulp was studied on the base of solid state fermentation in flasks.The size of tray is 20cm×12cm×5cm,each tray was put into 50g sweet potato pulp.The lactic acid production of 26.78(±0.85)%(w/w) was obtained when Rhizopus oryzae PW352 was cultured in solid state substrate in 36℃for 48h under the same condition as optimal flask fermentation.3.L-lactic acid in solid state fermentation was extracted and purified.The lactic acid was separated and purified by filtrate,decolor,ion exchange resin and concentrated by the technology of vacuum distillation.The concentration of purified lactic acid was about 75.22%.4.The hydrolyzation of corn stover by sulfuric acid and lactic production from corn stover were studied.The corn stover was hydrolyzed by sulfate acid.Rhizopus oryzae PW352 was cultured at 36℃,180rpm with fermentable sugars in the hydrolyzing liquid as carbon source,and lactic acid production of 1.98(±0.18)g/L and conversion rate to reducing sugars of 5.36(±0.49)%were gained.But the production of lactic acid was 7.69(±0.99) g/L,and conversion rate to reducing sugars was as high as 64.06(±8.23)% when using glucose and xylose complex(glucose:xylose=7:3,the reducing sugars concentration of culture medium is 12g/L) as carbon source.When the corn stover was decolored by neutral detergent and hydrolyzed by sulfate acid,lactic acid production of 9.31g/L and conversion rate to reducing sugars of 39.66% were obtained by fermentation of Rhizopus oryzae.The conversion rate to reducing sugars raised 6.4 times than the undecolored group.