微生物轉換甘蔗汁以生產聚醣及聚酯化合物

Microbial Conversion of Sugarcane Juice for the Production of Polyfructan and Polyester

近幾年來由於全球暖化、環保意識抬頭、化石燃料之即將用罄與原油價格日漸提升，使得尋找經濟、有效、能永續之替代能源與可再生利用之生質原料以取代傳統石化原料已是追求永續發展之重要課題。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（生態材料），因此近年來極受重視並已於食品、化妝品、醫藥及環保等領域之應用。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，如此對環境友善之綠色製程，值得開發。本研究探討以甘蔗汁為基質並以納豆菌（Bacillus subtilis natto）進行發酵生產菌果聚醣，探討氮源、初始pH值、溫度、轉速對其生產菌果聚醣之影響，並找出最佳生產條件。結果發現納豆菌可有效利用甘蔗汁生產菌果聚醣。納豆菌以NB培養基活化後，於不額外添加氮源之甘蔗汁培養基，轉速175rpm，溫度37℃、初始pH6.5進行搖瓶培養48h，結果顯示菌果聚醣之產量可高達18.0g／L（26％，以蔗糖消耗計）。發酵液經超過濾膜濃縮後可得純化之菌果聚醣，而其過濾液中含葡萄糖（約55g／L）與果糖（約40g／L）。以過濾液作為Cupriavidus necator生產聚酯化合物之碳源並探討初始pH值、溫度、轉速對其生產PHA之影響，以尋找出最佳生產條件。結果發現C. necator以NB培養基活化後，於含碳源之過濾液培養基，轉速200rpm，溫度30℃、初始pH7.0進行搖瓶培養48h，結果顯示可得菌體生質量12.02 g／L，PHA濃度為1.60 g／L，PHA含量為13.30 wt％。 As fossil fuel supplies dwindle and environmental awareness rises, the biorefinery process has emerged as the most promising method for the production of alternatives to fossil fuels and traditional, oil-based chemicals. In particular, the microbial conversion of biomass for biopolymer production is attractive because of the substantial demand for degradable biopolymers and wide availability of renewable biomass feedstock. Microbial biopolymers are biodegradable, edible, biocompatible, and nontoxic for humans and the environment; they do not rely on oil resources; and their applications are versatile, safe, and environmentally friendly. Microbial biopolymers offer a variety of industrial applications in the fields of cosmetics, foods, pharmaceuticals, and the environment. The purpose of this study is to investigate the feasibility of a tandem production of two invaluable biopolymers, levan and polyhydroxyalkanoates(PHA), by using microbial fermentation with sugarcane juice as a feedstock. In the first section of the study, factors affecting levan production by fermentation of Bacillus subtilis(natto)Takahashi in a medium containing sugarcane juice were studied. The highest yield of levan production(18.0 g/L at 24 h; 26.0% by sucrose consumption)was obtained when the bacteria were cultured in a medium containing sugarcane juice(with 78 g/L sucrose)at a pH of 6.5, temperature of 37°C, and agitation speed of 175 rpm. The fermentation broth was concentrated using ultrafiltration membranes. The levan was harvested from the concentrate through precipitation by adding 4 volumes of cold ethanol; the filtrate containing glucose(~55 g/L)and fructose(~40 g/L) was proven to be a suitable substrate for the production of PHA by Cupriavidus necator. In the second section of the study, the factors affecting PHA production by fermentation of C. necator in a medium containing waste filtrate from levan fermentation were studied. The highest yield of PHA production (1.60 g/L; 13.30 wt%)was obtained when the bacteria were cultured in the medium for 48 h at a pH of 7.0, temperature of 30°C, and agitation speed of 200 rpm.