Abstract: The impacts of four extraction methods (hot water extraction, acid extraction, enzymatic extraction and ultrasonic-assisted extraction) on the yield, structure and antioxidant activities of okra flower polysaccharides were systematically investigated. The results showed that the yield of polysaccharides was in the following decreasing order: enzymatic extraction ((21.90 ± 0.14)%) > acid extraction ((15.15 ± 0.07)%) > hot water extraction ((12.60 ± 0.28)%) > ultrasonic-assistant extraction ((12.02 ± 0.37)%). The polysaccharides extracted by enzyme-assistant extraction and hot water extraction had higher molecular mass and intrinsic viscosity, while ultrasonic-assisted extraction significantly reduced the molecular mass and intrinsic viscosity of polysaccharides and the extracted polysaccharides had a relatively more uniform molecular mass distribution. The polysaccharides obtained by the four extraction methods had identical monosaccharide composition but varied in the molar ratio of monosaccharides, composed mainly of rhamnose, galacturonic acid and galactose. Fourier transform infrared spectroscopy indicated that all four polysaccharides had typical characteristics of polysaccharides. These polysaccharides possessed different antioxidant activities in terms of measurement of 1,1-diphenyl-2-picrylhydrazyl radical scavenging capacity, with the ones extracted by ultrasonic-assisted extraction showing the strongest antioxidant activity．

Key words: okra flowers, polysaccharide extraction, structure, antioxidant activity