Correction: Highly porous core–shell chitosan beads with superb immobilization efficiency for Lactobacillus reuteri 121 inulosucrase and production of inulin-type fructooligosaccharides

Correction for ‘Highly porous core–shell chitosan beads with superb immobilization efficiency for Lactobacillus reuteri 121 inulosucrase and production of inulin-type fructooligosaccharides’ by Thanapon Charoenwongpaiboon et al., RSC Adv., 2018, 8, 17008–17016.

The authors regret that Fig. 9 in the original article was displayed incorrectly. The correct version is shown below.Open in a separate windowFig. 9Batch reusability of INU-CSBs for IFOS synthesis. Reaction condition: 10 U mL⁻¹ of biocatalysts were incubated with 200 g L⁻¹ sucrose in acetate buffer pH 5.5, 40 °C and 2 h per batch.The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.     

Rational re-design of Lactobacillus reuteri 121 inulosucrase for product chain length control

Fructooligosaccharides (FOSs) are well-known prebiotics that are widely used in the food, beverage and pharmaceutical industries. Inulosucrase (E.C. 2.4.1.9) can potentially be used to synthesise FOSs from sucrose. In this study, inulosucrase from Lactobacillus reuteri 121 was engineered by site-directed mutagenesis to change the FOS chain length. Three variants (R483F, R483Y and R483W) were designed, and their binding free energies with 1,1,1-kestopentaose (GF4) were calculated with the Rosetta software. R483F and R483Y were predicted to bind with GF4 better than the wild type, suggesting that these engineered enzymes should be able to effectively extend GF4 by one residue and produce a greater quantity of GF5 than the wild type. MALDI-TOF MS analysis showed that R483F, R483Y and R483W variants could synthesise shorter chain FOSs with a degree of polymerization (DP) up to 11, 10, and 10, respectively, while wild type produced longer FOSs and in polymeric form. Although the decrease in catalytic activity and the increase of hydrolysis/transglycosylation activity ratio was observed, the variants could effectively synthesise FOSs with the yield up to 73% of substrate. Quantitative analysis demonstrated that these variants produced a larger quantity of GF5 than wild type, which was in good agreement with the predicted binding free energy results. Our findings demonstrate the success of using aromatic amino acid residues, at position D418, to block the oligosaccharide binding track of inulosucrase in controlling product chain length.

Blocking the binding track of inulosucrase to control the chain length of the products.     

Highly porous core–shell chitosan beads with superb immobilization efficiency for Lactobacillus reuteri 121 inulosucrase and production of inulin-type fructooligosaccharides

With the aim to overcome the limitations of hydrogel chitosan beads (HGBs), various types of chitosan, core–shell chitosan beads (CSBs), and dried chitosan beads (DBs) were synthesized. Physical and chemical properties were compared with those of HGBs. CSBs were proved to be an effective support because they displayed higher stability and capacity over the HGBs, and thus, were selected for enzyme immobilization. Recombinant inulosucrase (INU) from Lactobacillus reuteri 121 was immobilized on CSBs using glutaraldehyde as a cross-linker. Immobilized biocatalysts (INU-CSBs) were then used for the synthesis of inulin-type fructooligosaccharide (IFOS). Biochemical characterization revealed that the optimum pH of both INU-CSBs and free enzyme was unaltered at 5.5 whereas the optimum temperature of INU-CSBs shifted from 50 °C to 60 °C. Moreover, pH stability and thermostability of INU-CSBs significantly improved. For batch synthesis of IFOS, INU-CSBs retained approximately 45% of their initial catalytic activity after being reused for 12 cycles. IFOS was also continuously synthesized in a fixed-bed bioreactor for a reaction duration of at least 30 h. The high efficiency of INU-CSBs makes them very attractive for industrial applications.

Inulosucrase immobilized on chitosan bead in core–shell format has proved to be an attractive biocatalyst for the synthesis of inulin-type fructooligosaccharides.