Development of novel extractive fermentation process of lactic acid with solvent-tolerant bacteria

乳酸主要用于传统食品工业中的添加剂，近年来作为生产可生物降解聚乳酸的原料引起了人们的关注。随着对环境友好材料需求的增加，发酵法生产乳酸受到了人们的关注。然而，该过程的经济性取决于开发一种有效的从发酵液中回收乳酸的方法，因为分离和纯化步骤占生产成本的50%。溶剂萃取法已被认为是一种很有前途的回收技术，可以替代传统的沉淀法。近年来，从抑制最终产物(乳酸)抑制和提高反应器效率的角度出发，在发酵液生产乳酸的过程中，通过溶剂萃取同时回收乳酸的原位萃取发酵工艺被认为是有吸引力的。在本研究中，为了抑制萃取剂和有机溶剂的毒性，我们开发了以果糖乳杆菌NRIC0224为菌种的原位萃取发酵新工艺，该菌具有嗜酒性，可以在1-脱醇存在下生长。三正辛胺(TOA)对乳酸的萃取率最高。发酵液中的酵母膏和蛋白胨对乳酸的提取有抑制作用。测定了TOA对果食性乳杆菌NRIC0224的毒性。在TOA和碳酸钙(CaCO3)的存在下，该菌能够生长、消耗葡萄糖和产生乳酸。基于这些结果，我们考察了用含有细胞和碳酸钙的海藻酸盐胶囊填充的色谱柱对乳酸提取发酵的适用性。从菌体生长和减少最终产物抑制的角度来看，乳酸的提取发酵是成功的。

Lactic acid is mainly used in the traditional food industry as an additive, and has recently drawn attention as the raw material for the production of biodegradable polylactic acid. With an increase in demand for environmentally friendly materials, lactic acid production by fermentation methods has gained interest. The economics of the process, however, depend on the development of an effective recovery method for lactic acid from the broth, because the separation and purification steps account for up to 50% of the production costs. Solvent extraction has been proposed as a promising recovery technique as an alternative to the conventional precipitation process. Recently, in situ extractive fermentation processes, in which lactic acid is simultaneously recovered by solvent extraction during the production of lactic acid in the fermentation broth, have been deemed attractive from the perspectives of suppression of the end-product (lactic acid) inhibition and enhanced reactor efficiency. In the present study, in order to repress the toxicity of the extractant and organic solvent we developed the new process for in situ extractive fermentation by using Lactobacillus fruclivorans NRIC0224 (hiochibacterium), which was alcoholophilic and could grow in the presence of 1-deanol. Tri-n-octylamine (TOA) in decanol gave the highest extractability of lactic acid. It was found that yeast extract and peptone in fermentation broth inhibited to extract lactic acid. The toxicity of TOA to Lb.fructivorans NRIC0224 was tested. In the presence of TOA and calcium carbonate (CaCO_3), the bacterium could grow, consume glucose, and produce lactic acid.Based on these results, we examined the applicability of a column packed with alginate capsules containing the cells and calcium carbonate to the extractive fermentation of lactic acid. The extractive fermentation of lactic acid was successful from the points of view of cell growth and reduction of the end-product inhibition.