The Production Of D-tagatose By Lactose Fermentation In Recombinant Escherichia Coli

D-tagatose, one of rare sugars, is a hexoketose monosaccharide sweetener, which is an isomer of D-galactose and is rarely found in nature.It has an excellent sucrose like taste,but has30%of sucrose energy,it possesses special functionality as a low calorie sweetner.D-tagatose can be composed by chemical method or biological method from D-galactose. The biological method includes enzymatic method in vitro and whole cell fermentation method.Both principles are the same. But the report about fermentation method are few. Besides, the enzyme method and chemical method have many disadvantages such as process is complex,the source of matrial is expensive and single, high cost. However, the whole cell fermentation method has many advantages, such as process is simple, the sourec of matrial is cheap and wide, low cost,suitable for industrialized production.This paper mainly researched the process for the convention from Lactose to tagatose by fermentation method,includes optimization of fementation process and preliminary extraction and purification of D-tagatose.In order to increase the production of biomass and tagatose, thefermentation media were optimized. The optimal medium as follows:LB and Lactose medium, the Lactose’s concentration is7g/L,2.5mM Fe2+/Mg2+. Then the fermentation process was studied. The result shows that the fermentation process can be broadly divided into3stages. In the first stages(0-9h), bacterias started to grow while lactose started to be hydrolyzed. In the second stages(9h-30h), the cells entered into logarithmic phase, the TaMAI started to express, and tagatose started to be produced. In the third stages(30h～120h), the cells entered into stable phase, the TaMAI expressed stably, and the D-galactose continues to transform into D-tagatose. Then the fermentation conditions were optimized based on the fermentation characteristics. During fermentation, multi-phase control methodology was adopted, in the first phase(0-30h), the culture condition were37℃,200rpm, pH7.0,0.5N乳糖Borate; in the second phase(30-120h), the culture conditions were60℃,200rpm, pH8.5,0.5N乳糖Borate. The conversion rate of the tagatose after5days fermentation was60%.In the second part of the article,the extraction technology of D-tagatose in the fermentation solution was established, which using the high speed centrifugation, decolorizaation, borate removal, the selective degradation of galactose by Saccharomyces cerevisiae L1cells, protein removal and salt removal. The result showed that the recovery of D-tagatose was64.8%.