Abstract: Taking the hydroxyl radical scavenging capacity, moisture content and particle size distribution of product as indexes, the ultrasonic spray drying(USD) of polysaccharides from Ziziphus jujuba Mill. cv. Hupingzao and the effect of different drying methods, i.e. USD, two-fluid spray drying and vacuum freeze drying, on product qualities were studied. The results showed that the optimum technological conditions of USD were inlet air temperature 135 ℃, feed rate 16 mL/min and intake pressure 0.10 MPa. Under these conditions, the outlet air temperature,·OH scavenging rate, moisture content and particle size distribution of the product were 89 ℃, 50.83%, 4.91% and 9.14 μm, respectively. By means of IR spectra, hydroxyl radical scavenging capacity and monosaccharide composition analysis, three drying methods had no effect on the activity, functional group and monosaccharide composition of the product, and the scavenging capacities were all about 50%. The polysaccharide was composed of rhamnose, arabinose, xylose, mannose, glucose and galactose, and their molar ratio was 1:11:2:1:38:5. By means of SEM, moisture content and particle size distribution analysis, the products by ultrasonic spray drying and two-fluid spray drying were granular, but the products by vacuum freeze drying were showed in block, bar and needle shape. The particle size distribution of the product of USD was normal distribution with narrow range of 2-20 μm. The powder product produced by USD was better than the others.

Key words: Zizyphus jujuba Mill. cv. Hupingzao, polysaccharides, ultrasonic spray drying, quality