苯乙醇因具有特殊的玫瑰香氣而被大量的應用在香水、化妝品及食品香精中，年產量在全球香料市場中佔有一席之地。利用微生物發酵法，依循Ehrlich pathway的生成途徑，可以透過Saccharomyces cerevisiae將苯丙胺酸轉化成苯乙醇，但在發酵過程中，面臨最大的限制在於產物的抑制效應，會對細胞產生毒性的影響。而且在微生物發酵中，不同培養溫度也會影響微生物的生理狀態和發酵行為，因此本研究主要的目的是在於探討「溫度」環境因子對於S. cerevisiae生產苯乙醇之影響，探討不同培養溫度對於菌體的生長及產物的變化，並結合萃取技術來改善產物抑制的問題。 研究結果發現在溫度為25℃下最適合S. cerevisiae的生長，但在溫度為35℃下則比較有助於單位菌重轉化成產物的能力，於是設計一種兩階段溫度轉換的策略同時提升菌體及產物的產量，在此操作模式下，苯乙醇的產量可以高達2.53 g/L，與在單一發酵溫度25℃跟35℃時相比下分別提升了15.48 %及22.38 %，最後再結合連續萃取發酵裝置，以Hytrel®作為吸附劑的角色，透過 in situ product removal 技術，減輕產物對於菌體生長的限制，最終苯乙醇的累積濃度可達到4.506 g/L。 ;2-Phenylethanol (PEA) is one of the important flavor and fragrance compound in the world with a rose-like aroma. In addition, it is widely used in the cosmetics, perfume, and food industries.
PEA can be produced from L-phenylalanine (L-Phe) through Ehrlich pathway using yeasts. In the fermentation process, the growth of yeast will be limited by product inhibition, cultivation temperature will also has a strong connection with microbial growth and fermentation behavior.
In this work, we have explored the effects of temperature on bioconversion of L-Phe into PEA using Saccharomyces cerevisiae BCRC21812 as well as develop strategies to enhance PEA production. Experimental results showed that at 25°C, the optimum cells growth was achieved and favored bioconversion yield. But at 35°C was more favorable for product yield based on biomass. Therefore, two-stage batch fermentation by temperature control was conducted. PEA concentration using two-stage fermentation was 2.53 g/L which corresponds to 15.48 % and 22.38 % higher than single-stage fermentation at 25°C and 35°C, respectively.
To increase the PEA production, the extractive fermentation will be conducted using Hytrel®. In the preliminary test, it showed that Hytrel® can adsorb PEA to reduce the inhibitory effect and non-toxic effect on yeast growth. After the successive extraction and feeding fermentation, the final concentration of PEA was achieved 4.506 g/L.
