Biocatalytic synthesis of lactosucrose using a recombinant thermostable β-fructofuranosidase from sp. 10138.

As a prebiotics, lactosucrose plays an important role in maintaining human gastrointestinal homeostasis. In this study, a thermostable enzyme from sp. 10138 was screened from six β-fructofuranosidase-producing strains for the lactosucrose production and the coding gene was heterologously expressed in for efficient expression. Recombinant β-fructofuranosidase was purified and biochemically characterized by MALDI-TOFMS spectrometry. The transfructosylation product by this recombinant enzyme was determined to be lactosucrose rather than other oligosaccharides or polysaccharides by HPLC and LC-MS. Efficient extracellular secretion of β-fructofuranosidase was achieved by the optimization of signal peptide and induction conditions. It was found that with the signal peptide torT, the highest extracellular activity reached 111.01 U/mL, which was 38.4-fold higher than that with the OmpA signal peptide. Under the optimal conditions (pH 6.0, temperature 50°C, enzyme amount 40 μg/ml, sucrose 150 g/L and lactose 150 g/L), 109 g/L lactosucrose was produced with a molar conversion ratio of 49.3%. Here the thermostable β-fructofuranosidase from sp. 10138 can be used for efficient synthesis of lactosucrose, and this provides a good startpoint for the industrial production of lactosucrose in the future.