Survival of Listeria monocytogenes on d’Anjou Pears Coinoculated With Bacillus thuringiensis, Aureobasidium pullulans, and Penicillium expansum During Nine Months of Cold Storage

Pears may be stored under controlled atmosphere (CA) storage conditions for up to 9 months. The Pacific Northwest pear industry identified the need to understand how pear microbiota influences the survival of Listeria monocytogenes during long-term storage. This research evaluated the survival of L. monocytogenes on pears co-inoculated with Bacillus thuringiensis, Aureobasidium pullulans, and Penicillium expansum under industry-relevant storage conditions. D’Anjou pears (n=1620), intact or mechanically damaged, were inoculated with L. monocytogenes alone or alongside one of the selected organisms. Pears were stored in bulk or wrapped in commercial tissue paper containing 1.3% copper carbonate and 0.1% ethoxyquin under CA conditions (3℃; 2-3% O2 and 1% CO2) for 9 months. L. monocytogenes was enumerated and, using the most probable number method, the limit of detection (LOD) was 0.38 log MPN/pear. Co-inoculum populations were also determined throughout storage (LOD: <2.67 Log CFU/pear). No treatment supported L. monocytogenes growth (p<0.05), though the pathogen persisted for up to seven months under some conditions. Wrapped pears showed significantly lower levels of L. monocytogenes, B. thuringiensis, and P. expansum throughout storage (p<0.05). A significant increase in P. expansum population on injured pears (p<0.05) caused L. monocytogenes to fall < LOD after 3 months in storage. B. thuringiensis and A. pullulans persisted on intact pears for 9 months. These findings revealed the impact of species within the pear microbiota and industry practices on L. monocytogenes survival. The efficacy of copper-ethoxyquin tissue paper to simultaneously improve food safety and P. expansum decay on pears was demonstrated.