Aspergillus oryzae and method for preparing high purity galacto-oligosaccharides by using same

The invention relates to a method for preparing high purity galacto-oligosaccharides, comprising the following product separation and purification steps: Aspergillus oryzae fermentation, ceramic membrane ultrafiltration, nanofiltration separation and the like. In the method, the Aspergillus oryzae separated from the soil is adopted as an original strain and the Aspergillus oryzae BLB-21 (with preservation number of CGMCC No.2951), a high efficiency transformed strain obtained through mutation screening in the laboratory, is directly used to ferment high concentration lactose solution, thus avoiding the steps of enzyme purification and the like in the process of preparing the galacto-oligosaccharides by an enzyme method and saving time and labor. The high purity galacto-oligosaccharides are obtained by ultrafiltration and nanofiltration separation, the process is ideal, the conditions are mild and the method has extensive industrial production prospect.