D-Tagatose production by Lactococcus lactis NZ9000 Cells Harboring Lactobacillus plantarum L-arabinose Isomerase

D-tagatose is a functional sweetener present in medicine, food, and dairy products and with broad market prospects, and L-arabinose isomerase gene (araA) can mediate the bioconversion of D-galactose into D-tagatose. In this study, a Lactococcus lactis NZ9000 strain harboring exogenous L-arabinose isomerase was constructed to produce D-tagatose. Lactobacillus plantarum CGMCC 8198 exhibits L-arabinose isomerase activity and its genome has been sequenced. The araA gene of Lactobacillus plantarum CGMCC 8198 encoding L-arabinose isomerase was identified by sequence analysis and was successfully cloned and expressed in Lactococcus lactis NZ9000. The D-tagatose production by the whole cell of the recombinant strain was optimized. The optimal condition for conversion reaction was at 50°C, pH 7.0 and with 300 mmol/L Mn2+ and 60 g/L galactose added. The D-tagatose yield and conversion rate at the optimal condition was determined and reached 40.2 g/L and 67%, respectively.