Microbial production of palatinose through extracellular expression of a sucrose isomerase from Enterobacter sp. FMB-1 in Lactococcus lactis MG1363

Sucrose isomerase (SIase) has been used to produce palatinose, a structural isomer of sucrose, which has many beneficial health properties, such as low-glycemic and low-insulinemic indices. A gene corresponding to SIase from Enterobacter sp. FMB-1 was expressed in Lactococcus lactis MG1363 using the P170 expression system. The autoinducible promoter (P170) and an optimized signal peptide (SP310mut2) were used to induce and secrete SIase in L. lactis. One-step Ni–NTA affinity chromatography and Western blot analysis demonstrated that SIase was successfully secreted to the culture supernatant, although 60% of the recombinant enzymes were retained inside the cells. The production of the recombinant SIase was highly correlated with pH (pH 6) and glucose concentration (30 g/L) of the medium. The extracellularly produced recombinant SIase was functionally active, effectively transforming 50 g/L sucrose to 36 g/L palatinose, with a conversion rate of 72% in the culture supernatant.