Study On Enzymatic Hydrolysis And Fermentation Of L - Lactic Acid From Corncobal Cellulose

Corncob is a kind of inexpensive and abundant lignocellulose resources, which has a high reuse value. L-lactic acid as an important organic acids, is widely used in chemical,food, medicine and other industries. It has a big market as material of poly L-lactic acid which is produced plastic. It has an important economic and social value that the corncob is used to produce L-lactic acid. The shredded corncob was sprayed and soaked by the concentrated sulfuric acid, after hydrolysis of vapor, cellulase was added to hydrolyze. At the same time, the effect factors was studied to obtain the high concentration of cellulase hydrolyzate. The laboratory preservation Lactobacillus brevis HF1.71 that the hexose and pentose can be simultaneously fermented, was used to produce L-lactic acid.The corncob was crushed into 1～2cm, sprayed and soaked with the concentration of sulfuric acid of 15%, 1:15（w/w） ratio of liquid/solid, hydrolyzed 3 hours. After acid hydrolyzate, the cellulase was added and the enzymolysis optimum conditions were got.The best single-stage enzymolysis optimum condition was obtained as follows:cellulase adding 40U/g , temperature of 45℃, substrate concentration of 100g/L, acetic acid-sodium acetate buffer of pH 4.8, and metalions of 5.0mg/L of Mg²⁺, 2.0mg/L of Zn²⁺, 8.0mg/L of Fe²⁺, after 48h, the hydrolysis yield reached 74.38%.The reducing sugar concentration reached 10.42% with three-stage countercurrent extraction and hydrolysis by cellulase,and the hydrolyzate was detoxificated.In order to optimizate the fermentation medium, 12.13% bran hydrolyzate, 17.20% hydrolyzate of soybean meal, 1.83% yeast paste were added to the hydrolyzate. The yield of L-lactic acid reached 42.49g/L and the polarimetry purity was 97.63% by determination of HPLC.The innovation in this paper:The corncob was crushed into 1～2cm, after atmosphere acid pretreatment, the three-stage countercurrent extraction and hydrolysis by cellulose was made, decomposed hemicellulose was extracted , and cellulose was hydrolyzed at the same time. In the final, the reducing sugar concentration reached 10.42%, which is satisfied the fermentation requirement of the strain, the vapor was saved to condense hydrolyzate and the comprehensive cost of L-lactic acid fermentation was reduced.