基于动力学分析提高黑木耳多糖产量的pH控制策略

为了实现黑木耳(Auriculariaauricula)深层发酵生产胞外多糖的高产量和高生产强度的统一,在7L发酵罐中研究不同pH对A.auricula分批发酵生产黑木耳多糖的影响.A.auricula细胞生长的最适pH为5.0,而黑木耳胞外多糖合成的最适pH为5.5.恒定pH有利于合成黑木耳多糖,但降低了黑木耳多糖的生产强度.发酵液中较高的pH不利于葡萄糖的消耗,使得发酵结束时的残余葡萄糖含量随pH的升高而升高.分析不同pH条件下A.auricula发酵生产黑木耳多糖动力学参数,发现较低pH有利于加快底物消耗,而较高的细胞生长速率则出现在pH5.0,pH5.5时细胞则具有较高的胞外多糖合成速率和对葡萄糖的得率.在此基础上提出了A.auricula发酵生产黑木耳多糖的两阶段pH控制策略:0~48h控制发酵液pH5.0,48h后控制pH5.5.实验结果表明,采用两阶段pH控制策略,A.auricula胞外多糖产量比控制pH5.5时提高了8.1%,残留葡萄糖含量降低了15.2%,产生最大胞外多糖的时间缩短至96h,且黑木耳多糖的生产强度比pH5.5时提高了35.1%.图4表1参21

Application of pH Controlled Strategy for Enhancing Exopolysaccharide Production by Auricularia auricula

In order to achieve a high concentration and high productivity of exopolysaccharide (EPS) from Auricularia auricula, the effect of pH on the performance of EPS production in submerged fermentation was investigated. It was showed that the maximum yield of EPS (7.54 g/L) was obtained at pH 5.5, but the mycelial growth rate was enhanced at pH 5.0 and the maximum dry cell weight (DCW) was 14.46 g/L. The lowest concentration of residual glucose (3.90 g/L) was observed at pH 4.5. Based on kinetic parameters analysis, a two-stage pH control strategy was proposed, in which pH was controlled at 5.0 in the first 48 h and then switched to pH 5.5. This strategy was experimentally proved to be successful. High yield of EPS (8.15 g/L) and high productivity of EPS (0.085 g L -1 h -1) were achieved by this strategy. The yield and productivity of EPS were improved by 8.1% and 35.1%, respectively, and the residual glucose decreased by 15.2%, compared with that of the constant pH 5.5. Experiment results demonstrated that EPS production by A. auricula was very sensitive to pH variation in submerged fermentation. In addition, the idea of controlling different environmental conditions at different culture stages, according to the metabolic characteristics of cells, could be applied to the production of other bioactive metabolites from macrofungi in submerged fermentation. Fig 4, Tab 1, Ref 21