Optimization of the One-Step and Two-Step Transformation Methods of Mannitol by Lactobacillus buchneri

Mannitol, an important raw material in food industry and medical fields, is always expected to be produced by the method of biotransformation. It was found in our previous work that Lactobacillus buchneri CGMCC 7300, isolated from traditional fermented sauerkraut, showed the ability of high-producing mannitol. In this study, the production methods of mannitol by L. buchneri CGMCC 7300 with one-step or two-step transformation strategy were optimized using the mixture of fructose and glucose as the substrate. One-step method involved the cell growth and mannitol production in a single process. The result indicated the mixture of fructose and glucose with a total concentration of 90 g/L and ratio of 3:2 was the optimal substrate to produce mannitol, reaching a yield of mannitol 48.82 g/L. On this basis, a two-step transformation strategy was tried and optimized to produce mannitol. In this method, the cells were firstly cultured, then collected and added into the 3 substrate for biotransformation. The optimal transformation conditions were found as follows: the total concentration of the fructose and glucose mixture 120 g/L, transformation time 36 h at 32 °C, medium pH 5.0. Under the above conditions, mannitol’s yield reached 63.71 g/L, 30.5% more than the yield of the one-step transformation method, showing that the two-step transformation method had a great advantage in mannitol production. The results will be significant for further industrial-scale production of mannitol.