Abstract: Postharvest microbial contamination of strawberries has become a topical issue for safety and quality control in the logistics process. In this study, the effect of combined cold plasma-activated water (PAW) and dielectric barrier discharge (DBD) treatment on the sterilization and quality of strawberries was explored. One-factor-at-a-time experiments were carried out to investigate the effect of PAW preparation time, salicylic acid concentration, and soaking time as well as DBD working voltage, time and frequency on the total bacterial count (TBC) on the surface of strawberries. The significant variables affecting the response variable were determined using Plackett-Burman (PB) design and were optimized using Box-Behnken design. Results showed that the TBC on the surface of strawberries decreased first and then leveled off with increasing PAW preparation time and salicylic acid concentration, while it continuously decreased with increasing DBD working voltage and time. Nevertheless, when DBD working voltage and time exceeded 60 kV and 150 s, respectively, the appearance of fruit color was faded and even damaged. Soaking time and working frequency had no significant effect on the TBC (P > 0.05). Besides, salicylic acid concentration, PAW preparation time and DBD working voltage were the significant variables affecting the TBC (P < 0.001), ranked in decreasing order of importance. The critical values of salicylic acid concentration and DBD working voltage both showed a linear downward trend with PAW preparation time. The optimum values of PAW preparation time, salicylic acid concentration and DBD working voltage were found to be 96 s, 1.1 mmol/L and 46 kV, respectively. Under these conditions, the TBC decreased from 3.64 (lg (CFU/g)) to 0.83 (lg (CFU/g)) and the sterilization rate was 99.8%. The combined treatment could obviously inhibit the growth of microorganisms at 20 ℃ for 8 days, effectively maintain the quality and extend the shelf life of strawberries .

Key words: strawberry; cold plasma sterilization; salicylic acid; total bacterial count; storage period; fresh fruit quality