Preparation method of milk oligosaccharides and oligosaccharide powder and food prepared thereby

A method for preparing milk oligosaccharides, comprising the steps of:

• performing ultrafiltration of whey liquid for at least three times, subjecting the ultrafiltration permeate to nanofiltration concentration for six times, then subjecting the nanofiltration retentate to chromatographic separation and purification, collecting chromatographic collection liquid containing sialyllactose while removing the fraction containing lactose, subjecting the collection to desalination and drying to obtain oligosaccharide powder, wherein, in the chromatographic separation and purification step, the carrier of the chromatographic packing material is an agarose-based weak anion exchanger, the ion exchange group of which is a diethylaminoethyl group;
• wherein the whey liquid is reconstituted from desalted whey powder and water, and the mass ratio of desalted whey powder to water is 1:4 to 20;
• in the ultrafiltration step, the used ultrafiltration membrane has a molecular weight cut-off of 5 kDa to 30 kDa;
• the ultrafiltration membrane is a composite tubular organic membrane;
• the ultrafiltration is performed under conditions as follows:
• the feed temperature is 20° C. to 45° C., the inlet pressure is 6 to 9 bar, the outlet pressure is 5 to 8 bar;
• the membrane pressure difference is not more than 3 bar;
• in the nanofiltration step, the used nanofiltration membrane has a molecular weight cut-off of 100 Da to 3000 Da;
• the nanofiltration membrane used in the nanofiltration step is a composite tubular organic membrane;
• the nanofiltration is performed under conditions as follows:
• the feed
• temperature is 20° C. to 45° C., the inlet pressure is 16 to 20 bar, the outlet pressure is 14 to 18 bar;
• the membrane pressure difference is not more than 3 bar;
• the desalination is performed by nanofiltration;
• the desalination by nanofiltration comprises:
• separating the chromatographic collection liquid through nanofiltration, washing and filtering with deionized water until the conductivity does not decrease any longer, and concentrating to the minimum cycling volume of the device to obtain a concentrated nanofiltration retentate, at which time the nanofiltration concentration is finished;
• the nanofiltration membrane used in the desalination by nanofiltration has a molecular weight cut-off of 100 Da to 500 Da;
• the nanofiltration membrane used in the desalination by nanofiltration is a composite tubular organic membrane;
• the desalination by nanofiltration is performed under conditions as follows:
• the feed temperature is 20° C. to 45° C., the inlet pressure is 10 to 15 bar, and the outlet pressure is 5 to 10
• bar;
• the membrane pressure difference is not more than 3 bar;
• and
• the drying step is performed by freeze drying;
• the freeze-drying step comprises:
• loading the
• desalted concentrated retentate into a freeze dryer for drying, the freeze-drying step comprises:
• setting the heating program of the vacuum freeze-drying as:
• 20° C. for 2 h, 40° C. for 1 h, and 55° C. until to the end, with the cold trap temperature being set at −50° C., and the vacuum degree at 2.50 to 6.50 MPa, and the drying is not finished until the moisture content on dry basis is less than 5%.