Production of d-tagatose, a Functional Sweetener, Utilizing Alginate Immobilized Lactobacillus fermentum CGMCC2921 Cells
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d-tagatose is a ketohexose that can be used as a novel functional sweetener in foods, beverages, and dietary supplements. This study was aimed at developing a high-yielding d-tagatose production process using alginate immobilized Lactobacillus fermentum CGMCC2921 cells. For the isomerization from d-galactose into d-tagatose, the immobilized cells showed optimum temperature and pH at 65 °C and 6.5, respectively. The alginate beads exhibited a good stability after glutaraldehyde treatment and retained 90% of the enzyme activity after eight cycles (192 h at 65 °C) of batch conversion. The addition of borate with a molar ratio of 1.0 to d-galactose led to a significant enhancement in the d-tagatose yield. Using commercial β-galactosidase and immobilized L. fermentum cells, d-tagatose was successfully obtained from lactose after a two-step biotransformation. The relatively high conversion rate and productivity from d-galactose to d-tagatose of 60% and 11.1 g l−1 h−1 were achieved in a packed-bed bioreactor. Moreover, lactobacilli have been approved as generally recognized as safe organisms, which makes this L. fermentum strain an attracting substitute for recombinant Escherichia coli cells among d-tagatose production progresses.
Keywordsd-Tagatose Lactobacillus fermentum Immobilized cells Packed-bed bioreactor l-arabinose isomerase
This work was supported by the National Basic Research Program of China (973) (2009CB724700), the National Nature Science Foundation of China (20906050), the Natural Science Foundation of the Jiangsu Higher Education Institutions of China (no. 08KJA180001), the Natural Science Foundation of Jiangsu Province (BK2009357), and the Specialized Research Fund for the Doctoral Program of Higher Education (20103221120007).
This work was also supported by the State Key Laboratory of Materials-Oriented Chemical Engineering.
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