甘蔗渣廢棄物為原料以發酵生產γ－－聚麩氨酸之研究

Biorefinery of Sugarcane Bagasse forγ-Poly(Glutamic Acid) Production

以微生物發酵生成之高分子具功能性、生物相容與生物可分解性，是一種非石化資源相關之再生材料，使用時對人體是無害且不會對環境造成污染，因此近年來極受重視。結合生質精煉技術與再生性生質原料為基礎以開發生物高分子材料不但可解決環境問題，同時可生產高經濟價值之產品。本研究建立以甘蔗生質為原料並透過生質精煉與發酵過程生產聚胺基酸類之生質材料，結果發現 Bacillus subtilis D1 可利用蔗渣水解液生產高分子化合物。B. subtilis D1 在蔗渣水解液（含葡萄糖 7.1 g-L 與木糖 2.8 g／L）經 96 h 發酵，可得 γ-PGA 9.1±0.1 g／L，產率為 0.51 ±0.12 g ／g（L-glutamate）。所得之γ-PGA 經純化後可得純γ-PGA 7.9 g／L，其平均分子量（Mn） 為 2 x 106 Da。氨基酸分析與 1H-NMR、13C-NMR 之光譜分析證明純化後之γ-PGA 純度相當高（> 96%），光學異構物之組成比例（D-麩氨酸/L-麩氨酸）比例為 56／44，且比例會隨著培 養基中添加之 Mn2+濃度變化而變化。實驗亦證明本研究之蔗渣水解反應所產生之水解液不會抑制後續之發酵反應，因此極適合作為發酵原料以生產有價值之生化產品。以甘蔗生質為原料並透過生質精煉與發酵過程生產聚胺基酸類之生質材料不但可解決環境問題，又可生產高經濟價值之生化產品，有極高之價值。

As fossil fuel supplies dwindle and environmental awareness increases, the biorefinery process has become the most promising method for producing alternatives to fossil fuels and traditionally oil-based chemicals. In particular, the microbial conversion of biomass for the production of biopolymers is an attractive option because of the high marketing demand for degradable biopolymers and the high quantity of available renewable biomass feedstocks. This study investigated batch cultivation on the production of γ-poly（glutamic acid）（γ-PGA）by Bacillus subtilis D1 by using a hydrolysate of bagasse as feedstock. It was observed that B. subtilis D1 can effectively employ glucose and xylose for γ-PGA production. When B. subtilis D1 was cultivated in bagasse hydrolysate ME9（containing 7.1 g/L of glucose and 2.8 g/L of xylose）, 9.1 ± 0.1 g/L of γ-PGA（yield of 0.51 ± 0.12 g/g L-glutamate）could be obtained. The quality of γ-PGA produced was comparable to an authentic sample obtained from conventional fermentation. Moreover, 7.9 g/L of the purified γ-PGA was obtained, and its average molecular weight（Mn）was 2 x 106 Da. Amino acid analysis and 1H-NMR and 13C-NMR spectra revealed its high purity. The ratio of the optical isomer（D-glutamic acid/L-glutamic acid）was 56/44, and it varied with the concentrations of Mn2+ supplemented in the medium. Experiments further confirmed that no or low concentration of harmful inhibitors was present in the bagasse hydrolysate, thereby rendering it a suitable material for the production of valuable bioproducts in the subsequent fermentation. The biorefinery of bagasse into biopolymers is a sustainable process that can not only solve environmental problems, but also produce high value-added bioproducts.