Abstract:Ball-milling was employed to pretreat the sugarcane leaves，followed by ultrasound-assisted extraction for polysaccharides. The extract was characterized via Fourier transform infrared spectroscopy（FT-IR），and the in vitro antibacterial activity and free radical scavenging activity of the extract were determined.The optimal extract yield was obtained when the milling was performed at the frequency of 20 Hz and the ball-tomaterial ratio of 45 ∶1（g/g）for 70 min.Under these conditions，the yield of polysaccharides from sugarcane leaves was 8.52 mg/g.After the response surface optimization，the extraction conditions for polysaccharides from sugarcane leaves were determined as ultrasound treatment time of 66 min，ultrasound power of 230 W，extraction temperature of 65 ℃，and liquid-to-material ratio of 25 ∶1（mL/g）.Under such conditions，the yield of polysaccharides from sugarcane leaves was 10.10 mg/g，which increased by 18.54%compared with that without ultrasound treatment.The polysaccharides from sugarcane leaves showed antibacterial activity against Escherichia coli and Staphylococcus aureus，especially for the latter.Moreover，the polysaccharides exhibited good DPPH and hydroxyl radical scavenging activities only slightly weaker than VC.The FT-IR results unveiled that ball milling did not change the groups in the polysaccharides of sugarcane leaves and the extract exhibited typical absorption peaks of polysaccharides.