Biocontrol of Listeria monocytogenes and Salmonella enterica on Fresh Strawberries with Lactic Acid Bacteria During Refrigerated Storage

Small fruits such as strawberries have been increasingly implicated in outbreaks of foodborne illnesses. Salmonella enterica and Listeria monocytogenes may contaminate strawberries leading to potential public health concern. The objective of this study was to investigate the efficacy of a combined lactic acid bacteria (LAB) treatment of Lactobacillus plantarum and Pediococcus pentosaceus for controlling S. enterica and L. monocytogenes on fresh strawberries during storage at 4°C and 10°C. Strawberries purchased from a local grocery store were separately dip inoculated with Salmonella Newport, Salmonella Tennessee, Salmonella Thompson, or a three-strain cocktail of L. monocytogenes at ∼9 log colony-forming unit (CFU)/mL and allowed to air-dry for 1 h. Inoculated strawberries were then divided into three groups: (1) Control (pathogen alone), (2) Man, Rogosa, Sharpe (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 4°C or 10°C for 7 d in vented clamshell containers. Surviving Listeria, Salmonella, and LAB populations on strawberries were determined on 0, 1, 3, and 7 d post-treatment by plating on selective agars. At both 4°C and 10°C, LAB treatment significantly decreased Listeria populations by up to 2 log CFU/g compared to controls after 3 d of storage (p < 0.05). When strawberries were stored at 4°C, LAB treatment reduced ∼2.5 log, ∼2.7 log, and ∼2.9 log CFU/g in Salmonella Newport, Salmonella Tennessee, and Salmonella Thompson populations, respectively, compared to control on day 7. Similarly, ∼2.5 log CFU/g reductions of Salmonella populations were observed with LAB treatment at 10°C on day 7. LAB populations remained at ∼7.5 log CFU/g levels on strawberries at both temperatures throughout the entire study. Results of this study suggest that a combined LAB treatment can be potentially used as biocontrol agents against Salmonella and L. monocytogenes on strawberries at postharvest level.