Injury of Salmonella enterica on apple and tomato following sequential treatments with cold plasma and organic acid antimicrobial.

Authors: UKUKU, DIKE - Retired ARS Employee; Olanya, Ocen; Mukhopadhyay, Sudarsan; Niemira, Brendan; Huang, Lihan

Submitted to: Acta Scientiarum Polonorum. Technologia Alimentaria
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/29/2025
Publication Date: N/A
Citation: N/A

Interpretive Summary: The contamination of produce by foodborne pathogens continues to be problematic for consumers with costly recalls, despite substantial gains in food safety measures. In this research, inactivation measures of cold plasma technology and organic acids on Salmonella Typhimurium were determined and quantified on tomato and apple. Cold plasma treatments of apple reduced survival of Salmonella by >4 logs and a similar pathogen reduction was recorded on tomato. Organic acid treatments also considerably reduced Salmonella survival on apple and tomato. Similarly, further reductions of survival were observed when cold plasma treatment was combined with organic acids. Combination treatments of produce and subsequent cold temperature storage can enhance the microbial safety of tomato and apple at post-harvest.

Technical Abstract: The increased consumption of fresh-cut salad contaminated with bacterial pathogens has resulted in foodborne illness and costly recalls. The objectives of this study were to determine effects of cold plasma and organic acids treatments on inactivation, survival and recovery of aerobic mesophilic bacteria, Salmonella Typhimurium populations and recovery of injured cells following storage. Tomato and apple stem scars were inoculated with Salmonella at 5.8 logs and 5.7 log CFU/g, respectively; by spotting 10µL sequentially up to 0.1 mL inoculum. Produce types were treated with cold plasma (0-40 kV range) and organic acids (100µL) for 0, 120s and 180s, then stored at 5C, 15C, and 20C for 0 to 36 h. To recover surviving populations, samples were homogenized in neutralizing buffer and 0.1mL aliquots were plated on TSA and XLT-4 agar and incubated at 37C for 24 h to enumerate populations and calculate injured bacterial cells. Cold plasma treatments of apples for 120s and 180s reduced survival of Salmonella populations to 2.2 log and 1.4 log CFU/g, respectively and 43.6 % and 49.2 % of bacterial cells were injured. A similar reduction of Salmonella populations and injury of bacterial cells (%) were recorded on tomato. On apples treated with organic acids at 120s and 180s, Salmonella survival was reduced to 1.6 log and 1.1 log CFU/g, respectively; as 35.8 % and 46.2 % of the populations were injured cells. However, bacterial survival were reduced to < 0.6 log CFU/g with combination treatment (cold plasma + organic acids) and <10 % populations consisted of injured cells. Produce storage at 5C led to further reduction of injured cells (<5% after 24 h), implying that cold temperature storage subsequent to treatment would enhance the microbial safety of tomatoes and apples designated for fresh-cut salad.