Abstract: This paper reports the optimization of the ultrasonic microwave-assisted extraction of water-soluble polysaccharides from tillering onion by one-factor-at-a-time method and response surface methodology. The response was polysaccharide yield. The optimum conditions were determined as follows: liquid-to-solid ratio, 17:1 (mL/g); ultrasonic power, 360 W; microwave power, 200 W; and irradiation time, 16 min. Under the optimized conditions, the polysaccharide yield was (11.92 ± 0.13)%. Solubility results showed that the extracted polysaccharide was soluble in water but insoluble in organic solvents. The results of color reaction experiments showed that the water-soluble polysaccharide did not contain starch or phenolic compounds but contained uronic acid. As indicated by ultraviolet-visible spectroscopy measurement, the water-soluble polysaccharide had no characteristic absorption peaks of nucleic acid and protein. Fourier transform infrared spectroscopy showed that the water-soluble polysaccharide had the characteristic absorption peak of polysaccharide. The weight average molecular weight was analyzed by high performance gel permeation chromatography. It was found that the water-soluble polysaccharide was not composed of homogeneous components.

Key words: tillering onion, water-soluble polysaccharide, ultrasonic microwave-assisted extraction