Abstract:Fresh daylily is susceptible to the contamination of spoilage bacteria，which result in reduced quality and shortened shelf life. To effectively kill spoilage bacteria and extend the shelf life without causing quality deterioration of fresh daylily，a direct-charged low-temperature plasma sterilization instrument was designed.The instrument pumped the compressed air into the double-medium barrier discharger through an air compressor. And then the air after electric treatment was directly passed into the fresh daylily preservation bag to achieve sterilization by low-temperature plasma. The effects of treatment voltage，frequency，and time on the bactericidal rate were studied by single factor experiments. The sterilization conditions were optimized by the response surface methodology with the sensory score and respiration intensity as the evaluation indexes. The results showed that the low-temperature plasma treatment had a significantly bactericidal effect on the surface microorganisms and a significantly inhibitory effect on the respiration intensity of daylily. The optimal sterilization conditions were 110 V，130 Hz，and 70 s. The shelf life of fresh daylily treated under these conditions reached up to 15 d at the storage temperature of 4 ℃，extending by 6 d compared with that of the control group.