Combined use of ultrasound-assisted washing with in-package atmospheric cold plasma processing as a novel non-thermal hurdle technology for ready-to-eat blueberry disinfection

Abstract

Ultrasound (US) has limited disinfection efficacy, and it has been recommended to combine it with chemical disinfectants during fresh produce washing. After washing and before packaging, the disinfection effect of US-assisted washing can be weakened; thus, in-package disinfection is important. As a nutritious fruit, there are no packaged blueberries can be directly eaten. Therefore, in this study, blueberry was selected as the model, and the two most commonly used disinfectants (free chlorine [FC] at 10 ppm and peracetic acid [PAA] at 80 ppm) were combined with low-frequency US (25 kHz) during washing, followed by in-package disinfection using dielectric barrier discharge cold plasma (CP). The disinfection efficacy of US-FC and US-PAA against Escherichia coli O157:H7 and Salmonella Typhimurium was significantly higher than that of US, PAA, or FC alone. The highest disinfection efficacy of CP was observed at the pulse frequency range of 400-800 Hz. For US-FC (1 min) + CP (1 min), an additional 0.86, 0.71, 0.42, and 0.29 log CFU/g of reduction for E. coli O157:H7, S. Typhimurium, aerobic mesophilic counts, and mold and yeast was achieved, respectively, compared with US-FC (2 min) alone. For US-PAA (1 min) + CP (1 min) an additional 0.71, 0.59, 0.32, and 0.21 log CFU/g of reduction was achieved for the above organisms, respectively, compared with US-PAA (2 min) alone. Quality loss (in total color difference, firmness, and anthocyanin content) was not observed after treatment with US-FC + CP, US-PAA + CP, US-FC, or US-PAA. After treatment with US-FC + CP or US-PAA + CP, the reactive oxygen species (ROS) content was significantly lower than that in the other groups, and antioxidant enzyme activity was significantly higher than that in the other groups, suggesting that in-package CP can activate the blueberry antioxidant system to scavenge ROS, thereby lowering the risk of quality loss. US-CP combination not only improves the disinfection efficacy but also lowers quality loss caused by ROS, without prolonging the processing time.

Keywords: Dielectric barrier discharge cold plasma; Disinfection; Ultrasound-assisted washing.