Recent Listeria outbreaks and recalls associated with intact apples establish a novel link between human listeriosis and apple consumption. These occurrences surprised the producers and public health officials since intact apples had not been previously implicated in foodborne outbreaks. Apples can get contaminated pre-harvest in the field, post-harvest in the processing plants and during storage and shipping. In fact, studies demonstrate that Listeria can survive on apples under refrigeration and ambient storage conditions. Thus, there is a critical need for antimicrobial strategies, which are effective, and sustainable along the production continuum. In this regard, lactic acid bacteria (LAB) serve as excellent candidates for reducing pathogen levels on fresh and minimally-processed produce. Since LAB occupy the same ecological niche as Listeria and can survive under conditions that promote Listeria survival, LAB based biocontrol can provide sustained antimicrobial effect through the production process. Hence, the proposed study will investigate the potential application of LAB for improving the microbial safety of apples. Specifically, this study will evaluate i) spray application of LAB to control Listeria on apples during storage at the packing-house and ii) LAB application through fruit finish and Listeria control on apples during storage at the packing-house, retail store and at home. In addition, this study will investigate the ability of LAB to prevent subsequent Listeria transfer into the fruit while cutting. Overall, successful completion of this study will help develop a sustainable, biocontrol strategy that can be incorporated as part of a multi-hurdle approach to control foodborne pathogens on produce.
Project objectives from proposal:
The overall objective of the proposed study is to determine the antimicrobial efficacy of select lactic cultures for controlling L. monocytogenes at high (5 log CFU/fruit) and low inoculation (3 log CFU/fruit) levels on apples. A high inoculum level (5 log CFU/fruit) will be used to enable measurement of several log reductions in pathogen counts during the study (Beuchat et al., 2002). Additionally, this study will incorporate a low level of inoculum (3 log CFU/fruit) in order to simulate low levels of pathogen contamination that are likely to occur under normal postharvest handling and storage conditions (Behrsing et al., 2003). In order to simulate commercial conditions, Listeria control on apples will be specifically evaluated following: 1. Spray application of LAB and fruit storage under conditions simulating cold storage at the packing- house 2. Application of LAB containing fruit finish and apple storage under conditions simulating storage at the packing-house, retail outlet and home. 3. Application of LAB containing fruit finish and effect on subsequent pathogen transfer while cutting.