Biocontrol of Listeria monocytogenes and Salmonella enterica on fresh strawberries with lactic acid bacteria during refrigerated storage

Authors: YIN, HSINBAI - Orise Fellow; CHEN, CHI-HUNG - Orise Fellow; COLORADO-SUAREZ, STEPHANIE - University Of Puerto Rico; Patel, Jitu

Submitted to: Foodborne Pathogens and Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/19/2022
Publication Date: 3/15/2022
Citation: Yin, H., Chen, C., Colorado-Suarez, S., Patel, J.R. 2022. Biocontrol of Listeria monocytogenes and Salmonella enterica on fresh strawberries with lactic acid bacteria during refrigerated storage. Foodborne Pathogens and Disease. 19(5):324-331. https://doi.org/10.1089/fpd.2021.0091.
DOI: https://doi.org/10.1089/fpd.2021.0091

Interpretive Summary: Fresh strawberries receive no or minimal processing during harvest and processing, making them vulnerable to contamination by bacterial pathogens. Contaminated strawberries have been implicated in foodborne illnesses previously in the US and elsewhere. Consumers' preference for clean, chemical-free food has led research on natural antimicrobials. The lactic acid bacteria (LAB) were used as natural biocontrols to kill pathogenic bacteria: Salmonella enterica and Listeria monocytogenes on strawberries during refrigerated storage. Strawberries inoculated with pathogenic bacteria were dipped in LAB and stored at 4ºC and 10ºC for 7 days. The LAB treatment significantly killed L. monocytogenes by 2 log CFU/g after 3 days. Similarly, 2.5-2.9 log CFU/g reductions in Salmonella enterica serotypes were observed after 7 days. Yeast and Mold populations were also lower in LAB-treated strawberries after 1 day. Results are helpful to organic farmers in post-harvest control of bacterial pathogens in strawberries. US consumers may prefer probiotic LAB-treated strawberries potentially resulting in increased market value.

Technical Abstract: Small fruits such as strawberries have been increasingly implicated in outbreaks of foodborne illnesses. Salmonella enterica and Listeria monocytogenes may contaminate strawberries leading to the potential public health concern. The objective of this study was to investigate the efficacy of two lactic acid bacteria (LAB) including Lactobacillus plantarum and Pediococcus pentosaceus for controlling S. enterica and L. monocytogenes on fresh strawberries during storage at 4ºC and 10ºC. Strawberries purchased from the local grocery store were separately dip-inoculated with Salmonella Newport, Salmonella Tennessee, Salmonella Thompson, or a three-strain cocktail of L. monocytogenes and allowed to air-dry for 1 h. Inoculated strawberries were then divided into three groups: (1) Control (pathogen alone), (2) MRS control (dipping in MRS broth), and (3) LAB treatment (dipping in a LAB cocktail of L. plantarum and P. pentosaceus). After treatment, strawberries were stored at 4ºC or 10ºC for 7 days in vented clamshell containers. Surviving Listeria, Salmonella and LAB populations on strawberries were determined on 0, 1, 3, and 7 days-post-treatment by spiral plating on selective agars. At both 4ºC and 10ºC, LAB treatment significantly decreased Listeria populations by up to 2 log CFU/g compared to the controls after 3 days of storage (P<0.05). When strawberries were stored at 4ºC, LAB treatment reduced ~ 2.5 log, ~2.7 log, and ~2.9 log CFU/g in S. Newport, S. Tennessee, and S. Thompson populations, respectively, as compared to the control on day 7. Similarly, ~ 2.5 log CFU/g reductions of Salmonella populations were observed with LAB treatment at 10ºC on day 7. LAB populations remained at ~7.5 log CFU/g levels on strawberries at both storage temperatures throughout the entire study. Results of this study suggest that LAB can be potentially used as biocontrol agents against Salmonella and L. monocytogenes contaminations on strawberries at the post-harvest level.