玉米芯稀酸水解及L-乳酸发酵研究

对玉米芯稀硫酸水解条件及糖化液发酵L-乳酸进行了初步研究。结果表明,玉米芯木聚糖最适水解条件为2%H2SO_4、120℃、30 min、固液比1:10,糖化液还原糖含量可达40.8 g/L,主要成分为木塘。细菌A-19可以利用水解液中的葡萄糖和木糖产酸,最适发酵条件为45℃、pH 6.5,从45℃～51℃、pH 5.5～pH 6.5产量均较高。用未浓缩的水解液发酵24 h,L-乳酸产量为30.6g/L,残糖为1.6 g/L,糖酸转化率为82.6%;用浓缩1倍的水解液发酵48 h,L-乳酸产量为41.4 g/L,残糖4.1g/L,糖酸转化率为68.2%,在发酵48 h后继续补料发酵至72 h(补料液为浓缩3倍的水解液),L-乳酸产量为50.9 g/L,残糖6.3 g/L,糖酸转化率为71.8%。该研究为利用木质纤维素生产L-乳酸奠定了一定基础。

Corncob saccharification by diluted sulphuric acid and fermentation of L-lactic acid

The corncob saccharification conditions by diluted sulphuric acid and fermentation of L-lactic acid by bacteria A-19 were investigated. The optimal conditions for saccharification were ascertained： 2%H2SO4, 120 ℃, 30 min, solid/liquid ratio of 1/10. Under the optimal conditions, 40.8 g reducing sugar/L were obtained with xylose as the major component. Bacteria A-19 could produce L-lactic acid using glucose and xylose in corncob hydrolysate neutralized by CaCO3. The optimal fermentation conditions were： pH 6.5, inoculum size 10% and 120 r/min at 45℃. Using the unconcentrated corncob hydrolysate as fermentation substrate, the L-lactic acid yield reached 30.6 g/L after 24 h, and the residual sugar and the conversion rate of sugar were 1.6 g/L and 82.6 %, respectively. Using the concentrated （ 1 time） corncob hydrolysate as fermentation substrate, the L-lactic acid yield reached 41.4 g/L after 48 h. The residual sugar and the conversion rate of sugar were 4.1 g/L and 68.2 %, respectively. Using a further 24 h fed batch cultivation feeding with corncob hydrolysate （concentrated by 3 times）, L-lactic acid yield reached 50.9 g/L, and the residual sugar and the conversion rate of sugar were 6.3 g/L and 71.8 %, respectively.