聚乙烯醇──海藻酸鈉包埋固定納豆菌以生產菌果聚醣

Immobilization of Bacillus Subtilis Natto by using Polyvinyl Alcohol and Sodium Alginate for Levan Production

本研究以聚乙烯醇及海藻酸鈉進行Bacillus subtilis natto之固定化，以回應曲面實驗設計法探討固定化之最佳條件，所得之固定化菌體可用於以批次式及連續式發酵生產菌果聚醣（Levan）。結果顯示當顆粒製作之最適條件為攪拌時間2.45 h，聚乙烯醇（PVA）濃度9.05 g／100 mL，海藻酸鈉（SA）濃度0.91 g／100 mL時，所得菌體顆粒在SM生產培養基培養30小時後，菌果聚醣（Levan）之最高產量為79.14 g／L，且固定化菌在培養期間顆粒依舊保持完整無破碎。以一次一因子方式探討固定化菌批次發酵生產菌果聚醣條件，發現當硫酸銨濃度為2％、蔗糖濃度為250 g／L、溫度為37℃、pH值為6.5時，Levan產量高達80.63 g／L。經過五個批次生產Levan後，固定化菌仍依舊完整無破碎，但Levan產量已降低至5.49 g／L。以連續式發酵探討固定化菌生產菌果聚醣時，發現當硫酸銨濃度為2％、蔗糖濃度為250 g／L、曝氣量為0.02 vvm、pH值為6.5時，Levan產量在第30小時達到最高63.81 g／L，同時發現進行208小時連續式發酵生產Levan後，菌體顆粒依舊完整無破碎。連續式生產Levan之產量雖不及批次式之產量，但於節約能源、減少人力成本及便於自動化控制均有利於連續式生產。本研究可提供工業化大量生產Levan之參考依據，對生物高分子方面之研究具有學術及應用上之價值。

In this study, immobilization of Bacillus subtilis natto was performed using polyvinyl alcohol (PVA) and sodium alginate (SA). The optimal conditions for immobilization were investigated using response surface methodology. The obtained immobilized cell beads can be used for levan production using batch and continuous fermentation. The optimum conditions for immobilization were a mixing time of 2.45 h, PVA concentration of 9.05 g/100 mL, and SA concentration of 0.91 g/100 mL. The highest yield (79.14 g/L) of levan was obtained when the immobilized cells were cultivated in SM medium for 30 h, and the immobilized cell beads remained intact during cultivation. In levan production using batch fermentation, one-factor-at-the-time was used to investigate the optimal conditions. The result showed that levan production was highest (80.63 g/L) when ammonium sulfate and sucrose concentration were 2% and 250 g/L, respectively, temperature was 37 ℃, and pH was 6.5. The obtained immobilized cell beads remained intact after five repetitions; however, levan production decreased significantly to 5.49 g/L. In levan production using continuous fermentation of immobilization cells, levan production was highest (63.81 g/L) when ammonium sulfate concentration was 2%, sucrose concentration was 250 g/L, aeration was 0.02 vvm, and pH was 6.5 at 30 h of fermentation. The obtained immobilized cell beads remained intact after 208 h of continuous fermentation. Levan production using continuous fermentation was less efficient than it was in batch mode; however, it was conducive for continuous production because of energy saving, labor cost reduction, and easy automation control. This study can provide a reference basis for industrial mass production of levan and has academic and application values for research on biopolymers.