Effects of the integrated treatment of plasma-activated water and ultrasound on the microbial inactivation and quality of radish sprouts

This study evaluated the effects of ultrasound (US) treatment using plasma-activated water (PAW) as the medium (UP treatment) and a sequential treatment consisting of US followed by PAW (US→PAW treatment) on the inactivation of indigenous mesophilic aerobic bacteria and the color and antioxidant activity of radish sprouts. The PAW was generated by applying a surface dielectric barrier discharge to 1 L distilled water for 60 min. The UP treatment involved immersing 5 g of radish sprouts in 500 mL of PAW followed by ultrasound treatment (700 W, 19.8 kHz) for 10 min. In the US→PAW treatment, the sprouts were treated with ultrasound and then immersed in PAW for 5, 10, 20, or 30 min. The pH, electrical conductivity, and oxidation-reduction potentials of the PAW were 2.15±0.1, 2,653.3±223.1 µS/cm, and 578.4±25.0 mV, respectively. The UP treatment inactivated the indigenous microorganisms in radish sprouts by 2.4±0.1 log CFU/g and the microbial reduction rates rose from 1.6 to 3.3 log CFU/g as the US→PAW treatment duration increased from 5 to 30 min. The UP-treated radish sprouts had similar colors and antioxidant activity to those treated with water (p>0.05). These results suggest that the UP treatment could potentially be used as an effective microbial decontamination method while maintaining the quality of radish sprouts.