Abstract: The invention provides a D-psicose crystal and a preparation method thereof. The method comprises: adding a seed crystal to a D-psicose solution and stirring uniformly, subjecting the solution to crystallization by gradient cooling and constant-temperature crystallization alternately at 50-30° C., stopping the crystallization until the temperature of the solution is 30° C., separating the crystal by centrifugation, washing and drying, to obtain a D-psicose crystal. Rather than evaporative crystallization, organic solvent-assisted crystallization and ultrasonication, controllable crystallization by gradient cooling, constant-temperature crystallization, and other technical means are employed. Thus, the invention has low requirements for equipment, simple process, low energy consumption, and low preparation cost, and thus particularly suitable for large-scale industrial production and processing. The purity of the D-psicose crystal obtained is ?98.

Abstract: The present invention relates to the technical field of microbial fermentation engineering, and specifically to a method for producing psicose 3-epimerase by high-density fermentation. In view of the low expression level of psicose 3-epimerase and other problems existing in the current fermentation, by controlling the feeding rate in the fermentation process, improving the culture temperature in the middle and late stages of fermentation and other measures in the present invention, the OD value during the fermentation with recombinant Bacillus subtilis and the total enzyme activity of psicose 3-epimerase in the fermentation broth are significantly increased, the expression of psicose 3-epimerase is markedly improved, and the production cost of allulose is reduced. Therefore, the present invention has a very broad prospect of application in industry.

Abstract: The invention provides a D-psicose crystal and a preparation method thereof. The method comprises: adding a seed crystal to a D-psicose solution and stirring uniformly, subjecting the solution to crystallization by gradient cooling and constant-temperature crystallization alternately at 50-30° C., stopping the crystallization until the temperature of the solution is 30° C., separating the crystal by centrifugation, washing and drying, to obtain a D-psicose crystal. Rather than evaporative crystallization, organic solvent-assisted crystallization and ultrasonication, controllable crystallization by gradient cooling, constant-temperature crystallization, and other technical means are employed. Thus, the invention has low requirements for equipment, simple process, low energy consumption, and low preparation cost, and thus particularly suitable for large-scale industrial production and processing. The purity of the D-psicose crystal obtained is ?98.