利用生產果聚糖及生物柴油之廢棄副產物為原料以生產γ-聚麩胺酸

Production of Poly(γ-glutamic acid)by Utilizing Waste Byproducts of Levan and Biodiesel Production as Raw Materials

γ-聚麩胺酸（γ-PGA）是一種極有應用潛力的微生物聚合物，可用在食品、化妝品、醫藥材料、農業和環境保護等領域，它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，因此極受重視。為促進γ-PGA的工業化生產與降低生產成本，近年來許多研究探討以工業或農業廢棄物為原料來生產γ-PGA。本研究探討以生產果聚糖及生物柴油之廢棄副產物（葡萄糖與甘油）作為原料，經苔蘚桿菌（Bacillus licheniformis CCRC 12826）發酵生產高附加值的γ-聚麩胺酸（γ-PGA）。結果發現B. licheniformis CCRC 12826在含廢葡萄糖與廢甘油之常用培養基E（medium E）中可有效生產γ-PGA，培養基中廢葡萄糖和廢甘油的初始比例會影響麩胺酸和檸檬酸鹽的利用率，並影響γ-PGA的生產和分子量。在發酵槽培養中，將pH值控制在6.5是實現高碳源利用率和γ-PGA生產的最佳選擇。在痕量麩胺酸和檸檬酸鹽的存在下，廢葡萄糖和甘油的混合物可以用作細胞生長和γ-PGA產生的主要碳源。但是，即使保持最佳pH6.5，從培養基中完全去除麩胺酸和檸檬酸鹽則不會有細菌生長和γ-PGA之產生。所產生的γ-PGA的品質與傳統發酵所獲得的γ-PGA樣品相當。

In the fields of food, cosmetics, agriculture, and medicine, γ-poly-glutamic acid（γ-PGA）is a promising microbial polymer with wide applicability and environmental protection effects; it is water soluble, biodegradable, edible, and nontoxic toward humans and the environment. Many recent studies have explored the production of γ-PGA using industrial or agricultural waste as raw materials to promote the industrialized production of γ-PGA and reduce production costs. This study investigated the use of waste glycerol and glucose from biodiesel and levan production as feed stock for the production of high-value-added γ-PGA by Bacillus licheniformis CCRC 12826. It was found that B. licheniformis CCRC 12826 can effectively produce γ-PGA in medium E（a commonly used medium for γ-PGA production）containing waste glucose and waste glycerol. The initial ratio of waste glucose to glycerol in the medium influenced the utilization of both glutamate and citrate and affected the production and molecular weight of γ-PGA. In fermenter cultivation, a pH of 6.5 was optimal for attaining high carbon-source utilization and γ-PGA production. In the presence of trace amounts of glutamate and citrate, the mixture of waste glucose and glycerol could be used as sole carbon sources for cell growth and γ-PGA production. However, the strict exclusion of glutamate and citrate from the medium resulted in the absence of bacterial growth and γ-PGA production even under the optimal pH of 6.5. The quality of γ-PGA produced was comparable with that of an authentic sample obtained from conventional fermentation.