植物乳杆菌(Lactobacillus plantarum)是一种多功能乳酸菌,所产胞外多糖(exopolysaccharides,EPS)具有很多优良功能特性。但发酵生产EPS时,原料和操作成本高,EPS产量低限制了其工业化应用。该研究在5 L罐中,使用常规流加发酵、生物催化、生物催化结合液液萃取和基于pH-Stat自动流加葡萄糖法的反复生物催化等策略发酵,旨在提高EPS产量、降低原料和操作成本。其中,生物催化法仅使用葡萄糖即可将EPS质量浓度提升至3.34 g/L,较摇瓶发酵水平提高110%。使用基于pH-Stat自动流加葡萄糖法的反复生物催化策略,可以连续回用各反复发酵中的残存细胞,第2次反复发酵批次的EPS质量浓度达到3.33 g/L。由于在收集处理细胞时,细胞总量下降,导致EPS产量下降,但EPS/细胞量不变,细胞活性稳定。可以通过加大首批次发酵的装液量、提高细胞总量,解决EPS产量不断下降的问题。用基于pH-Stat法的反复生物催化策略进行EPS发酵,提升了EPS产量,省去了昂贵MRS培养基的使用,降低了原料成本,实现了自动化控制。该发酵策略还可联产具有一定价值的副产物40 g/L DL-乳酸。
The extracellular exopolysaccharide (EPS) produced by Lactobacillus plantarum, a kind of multifunctional lactic acid bacteria, has many excellent functions and properties. However, the high raw materials and operation costs and low EPS yield in scaled fermentations limit its industrial application. The strategies of traditional fed-batch fermentation, bio-catalysis, bio-catalysis combined with liquid-liquid extraction and pH-Stat automatic glucose feeding based “repeated bio-catalysis” were implemented in a 5 L tank. The yield of EPS was 3.34 g/L with glucose by the bio-catalysis method, which was 110% higher than in shake-flask fermentation. With the pH-Stat glucose feeding based repeated bio-catalysis method, the cells harvested in each run could be reused consecutively for the next batch. EPS yield in the second repeated run could still reach a high level of 3.33 g/L. However, the total cell amount gradually decreased due to the cells amount loss during the collection/treatment process, leading to the consecutive decline of EPS concentrations, but the EPS/cell-amount remained constant and the cell metabolic activities were stable. The consecutive reductions of EPS concentration could be solved by enlarging the working volume in the first run and increasing the total cells amounts due to the cells amount loss during the collection/treatment process. The proposed pH-Stat glucose feeding based “repeated bio-catalysis” strategy increased EPS concentration, eliminated the expensive MRS medium utilization, reduced raw materials cost and realized automatic process control. In addition, the proposed strategy could also simultaneously produce 40 g/L DL-lactic acid.
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