Strength of Salmonella Attachment on Apple and Tomato Surfaces: Effect of Antimicrobial Treatments on Population Reduction and Inactivation

Authors: Ukuku, Dike; Mukhopadhyay, Sudarsan; Olanya, Modesto; Niemira, Brendan

Submitted to: LWT - Food Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/24/2022
Publication Date: 6/10/2022
Citation: Ukuku, D.O., Mukhopadhyay, S., Olanya, O.M., Niemira, B.A. 2022. Strength of salmonella attachment on apple and tomato surfaces: Effect of antimicrobial treatments on population reduction and inactivation. LWT - Food Science and Technology. https://doi.org/10.1016/j.lwt.2022.113605.
DOI: https://doi.org/10.1016/j.lwt.2022.113605

Interpretive Summary: This study was designed to investigate the strength of Salmonella attachment and survival on apple and tomato surfaces. Attachment strength and population reduction is important for food safety and would help in developing non-thermal processing interventions for reducing attached bacteria. Apples and tomatoes were contaminated with Salmonella bacteria at 4.6 and 3.0 log CFU/g, respectively and then washed with water, 200 ppm chlorine, 1.5% hydrogen peroxide and a new antimicrobial solution developed in our laboratory for 5 min. A higher population was washed off within 0 to 30 min of post contamination due to the initial strength of attachment being low. Bacterial reduction at 360 min post inoculation and treatment were reduced and correlated with the increased attachment strength. The new antimicrobial solution reduced and or killed more Salmonella than the chlorine and the hydrogen peroxide suggesting that the new solution would be a better alternative for sanitizing fresh fruits.

Technical Abstract: Understanding the strength of bacterial attachment and survival on produce surfaces is important for food safety and the information obtained would help in developing non-thermal processing interventions for reducing attached bacteria. In this study, the attachment of Salmonella bacteria on apple and tomato surfaces and the efficacy of a new antimicrobial solution developed in our laboratory was investigated. The new antimicrobial solution contains 5g of ascorbic acid, 30g hydrogen peroxide, 5g citric acid, and 30g lactic acid and its bacterial inactivation was compared against three washing treatments (200 ppm chlorine, water, and 1.5 % hydrogen peroxide (H2O2). Whole apples and tomatoes were individually dipped in a Salmonella inoculum at 108 CFU/ml for 4 min, respectively and then allowed to air dry inside a laminar flow biological hood (NuareTM, Plymouth, MN, USA) before treatments were applied at 0, 20 min, 30 min, 60 min, 120 min, 360 min, 540 min and 1440 min, respectively. Salmonella bacteria recovered on whole apple and tomato surfaces after inoculation averaged 4.6 log CFU/g and 3.0 log CFU/g, respectively and the relative strength of attachment on whole apples and tomatoes averaged 0.22 and 0.25, respectively. A 200-ppm chlorine and 1.5% hydrogen peroxide (H2O2) treatment achieved 2.8 log CFU/g inactivation of Salmonella while the new solution led to 3.9 log CFU/g and 2.9 log CFU/g reduction on tomato and apple surfaces, respectively. Strength of attachment increased at 360 min post inoculation and above and affected the activity of all antimicrobial treatments except the organic acid solution in reducing bacteria populations. Results of this study suggest that the attachment strength of Salmonella and inactivation on apple and tomato surfaces stored at 22oC were not significantly (p<0.05) different and the organic acid solution killed more Salmonella bacteria than hydrogen peroxide and chlorinated water suggesting enhanced microbial safety of fresh-apples and tomatoes.