Inactivation of Salmonella enterica serovars and Escherichia coli O157:H7 surrogate from baby spinach leaves using high voltage atmospheric cold plasma (HVACP)

Leafy greens are ideal hosts for pathogens like Salmonella enterica and E. coli O157:H7. In the current study, baby spinach leaves inoculated with Salmonella enterica serovars and E. coli 25,922 (an E. coli O157:H7 surrogate) were subjected to a high voltage atmospheric cold plasma (HVACP) with 100% nitrogen gas at high humidity at 80 kV for 5 min in the indirect exposure. HVACP is a novel, non-thermal technology reducing bacteria with minimal effect on product quality. Microbial reductions were enumerated for up to 14 days of post-treatment storage at 4 °C. After 24 h, a 2.11 log 10 CFU/sample and 2.14 log 10 CFU/sample were observed for Salmonella enterica and E. coli, respectively. After 14 days, HVACP-treated Salmonella enterica infected leaves showed a 3.18 log 10 CFU reduction per sample while E. coli infected leaves showed 3.77 log 10 CFU/sample reductions compared to untreated infected leaves. This study also explored Enterococcus faecium as a potential surrogate for Salmonella enterica with a D-value of 37.14 and 5.79 h, respectively for an indirect cold plasma with nitrogen as working gas, applied voltage of 80 kV for a maximum treatment time of 10 min and post treatment storage of up to 24 h tested.