利用根黴菌在氣舉式醱酵槽中生產L型乳酸銨

Production of Ammonium L-Lactate by Culture of Rhizopus in an Air-lift Bioreactor

劉芝妤(Chih-yu Liu)

指導教授 ： 許垤棊

大同大學/工程學院/生物工程學系所/碩士(2009年)

摘要

L型乳酸因為可以用來合成生物可分解以及生物相容性聚合物，所以受到相當的重視。傳統的方法是用根黴菌醱酵葡萄糖或澱粉以生產L型乳酸，醱酵過程使用碳酸鈣當酸鹼中和劑，但是在後續純化乳酸的過程產生大量的固體廢棄物（硫酸鈣）。假如用氨水取代碳酸鈣，則醱酵產物是L型乳酸銨，可免除硫酸鈣的產生；另外氨也是根黴菌的氮源，甚至氨可回收重複利用。
氨水對根黴菌(Rhizopus sp.)是有毒性的，因而導致L型乳酸產量的降低。第一，氨水的成分是氫氧化銨，它具有化學腐蝕性，可殺菌，甚至可殺死病毒。第二，高濃度的銨離子，可能抑制根黴菌的生物活性。
本研究使用3.5公升的氣舉式生物反應槽，利用根黴菌Rhizopus arrhizus BCRC 33071以及Rhizopus oryzae ATCC 9363醱酵葡萄糖生產L型乳酸，醱酵過程經由玻璃擴散器饋入酸鹼中和液（含10% NH3、2%碳酸氫銨以及1%尿素）。碳酸氫銨具有緩衝酸鹼度的功能，可降低NH3對於黴菌細胞的傷害，尿素則是被黴菌的酵素分解成NH3和CO2 時產生緩衝作用，同時CO2氣體使菌絲球成多孔狀，有利於氧氣、葡萄糖和L型乳酸的質傳。
最高的產量， R. oryzae在pH 5.25醱酵32小時產生92 g/L的L型乳酸，而R. arrhizus在pH 5.25醱酵34小時，產生高達102 g/L的L型乳酸。

關鍵字

氣舉式生物反應槽 ； 氨 ； L型乳酸 ； Rhizopus arrhizus ； Rhizopus oryzae

並列摘要

Interest in L-lactic acid production has increased due to its ability to serve as raw material for the manufacture of biodegradable and biocompatible polymers. Traditionally, L-lactic acid is produced through the fermentation of glucose or starch with Rhizopus strains, using calcium carbonate as neutralizing agent. In the downstream process for the purification of lactic acid, large amount of calcium sulfate, a solid waste, is formed. When calcium carbonate, the neutralizing agent during the fermentation, is replaced by ammonia water, the product is mainly ammonium L-lactate and the formation of calcium sulfate during the purification of lactic acid is avoided. Ammonia can serves as a nitrogen source for the fungus. Furthermore, ammonia may be recovered from ammonium L-lactate by means of ion exchange or electro-dialysis.
Ammonia is toxic to the fungus, leading to a decreased production of lactic acid. Firstly, the main component in ammonia water is ammonium hydroxide, which is caustic and thereby inactivates germs and even viruses. Secondly, high concentration of ammonium ions in the fermentation medium might reduce the bioactivity of the fungus, slowing down the formation of lactic acid.
In this work, L-lactic acid fermentation was carried out in an 3.5-L air-lift bioreactor by Rhizopus species including Rhizopus arrhizus BCRC 33071 and Rhizopus oryzae ATCC 9363. A mixture of ammonium bicarbonate, urea and ammonia water served as the neutralization agent through a porous glass device. Both ammonium bicarbonate and urea provide buffer effect against ammonia water, reducing the damage of ammonium hydroxide on fungal cells. Urea was converted into ammonia and carbon dioxide through the catalysis of urease on fungal cells.
Optimum production of L-lactic acid was achieved when the fermentation was controlled at pH 5.25. After a 32-h fermentation with R. oryzae or a 34-h fermentation with R. arrhizus, final concentration of lactic acid at 92 g/L or 102 g/L was obtained, respectively.

並列關鍵字

air-lift bioreactor ； ammonia ； L-lactic acid ； Rhizopus arrhizus ； Rhizopus oryzae

參考文獻

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