Heterologous overproduction of a dextranase in Bacillus subtilis WB600 and its application in preparation of porous buckwheat starch

The hydrolysis product of dextranase contains highly polymerized oligomeric isomaltose, which can be used as prebiotics to promote the colonization of probiotics, thus adjusting the ecological environment of intestinal flora. In this study, the expression of dextranase (PsDex1711) in Bacillus subtilis WB600 was enhanced by screening signal peptides. Furthermore, the potential application of dextranase for functional starch preparation was explored. Initially, a signal peptide library was constructed to identify the most efficient signal peptide for PsDex1711 secretion. Then, enzymatic hydrolysis was employed to produce porous buckwheat starch with varying pore sizes, and the impact of this enzymatic treatment on the physicochemical and microstructural properties of buckwheat starch was investigated. Signal peptide of the YwoF protein of unknown function demonstrated the highest extracellular PsDex1711 activity at 2.10 +/- 0.036 U/mL. Moreover, scanning electron microscope analysis revealed the development of deeper pores on the surface of starch granules after 18 h of enzymatic treatment, indicating the microstructural alterations induced by the enzymatic process and providing a foundation for further research in this field. The enzymatic hydrolysis also resulted in 40% and 35% increase in the water and oil absorption, respectively, compared to natural starch. Based on x-ray diffraction and Fourier transform infrared spectroscopy, it was inferred that the porous starch had a high degree of short-range ordering, which could provide a theoretical basis for the development and application of porous starch materials.