A Research On Rice Straw Solid-State Sacchrification And Fermentation For Lactic Acid

Rice straw, wheat straw, corn stalks and other crops stalks accounted for the main part of plant fiber resources in our country. Rice straw was chosen for studying as raw materials according to abundant production of rice straw in China. It is great significance for the comprehensive utilization of resources and environmental protection. The contents of our research were as follows:1) The best enzymatic hydrolysis condition for Trichoderma reesei straw powder was obtained by the use of single-factor experiment with solid-state fermentation of cellulose decomposition bacterium: carbon resource was the mixed cooperation of straw powder (treated by 2% NaOH) and wheat bran with 3:1 ratio. Nitrogen resource was 2% (NH₄)₂SO₄. When the initial pH was 5.0, the ratio was 1:3, the inoculum amount was 0.50ml, and culture temperature was 30℃for 72h static fermentation, the enzyme activity of cellulose filter paper and C_X was 277.58 U/g and 1651.88 U/g respectively which achieve the best.2) It was significant effect that the compound bacteria (Trichoderma reesei and Aspergillus niger) product the glucose better than single Trichoderma reesei or single Aspergillus niger. Based on this, the cellulose culture condition of solid-state fermentation was obtained by orthogonal experiment: 3g straw powder, 1g wheat bran; 0.36g (NH₄)₂SO₄, 12 ml water, initial pH 5.0 and 30℃for 3 days. The sequence according to the effects of various factors to filter paper and C_X enzyme activity was as follows: ammonium sulfate, water multiples, straw powder, wheat bran powder.3) Through the analyze of lactic acid which was fermented with glucose as raw material, the best fermented condition for Lactobacillus brevis was as follows: glucose about 80mg/ml, peptone 5.0mg/ml, yeast extract 5.0mg/ml, anhydrous magnesium sulfate 0.5mg/ml, chlorine Sodium 0.1mg/ml, KH₂PO₄ 0.5mg/ml, pH 5.5. The conversion rate was 83.0%. Also the best fermented condition for Rhizopus oryzae was as follows: nitrogen resource 2mg/ml, KH₂PO₄ 0.005%, MgSO₄·7H₂O 0.025%, CaCO₃ 5%, pH 5.0, added CaCO₃ in batches. The conversion rate was 84.3%. 4) The lactic acid amount and lactate rate were 15.0 g/l, 43.9% with separate hydrolysis and fermentation (SHF) and 16.1 g/l, 50.3% with simultaneous sacchrification fermentation (SSF) by Rhizopus oryzae. Also, the lactic acid amount and lactate rate were 15.3 g/l, 46.6% with SHF and 19.4g/l, 60.6% with SSF by Lactobacillus brevis.5) It was concluded that the production of lactic acid by SSF was bigger than that by SHF for Rhizopus oryzae and Lactobacillus brevis. Through the single factor experiment of ferment, the effects to lactic acid were obtained by several factors which involved addition time of bacteria vaccination and enzyme, temperature of saccharifying fermentation; inoculum amount and fermentation time.6) Compared with traditional processes for ethanol and single cell protein production process, SSF process with the resource of cellulose can promote the material conversion rate and production value. Thus it has important significance to accelerate use of renewable resource and implement sustainable development strategy.