Impact of cultivar, harvesting method, and storage time on blueberry microbiota and Listeria monocytogenes survival using antimicrobial packaging

Blueberries are a high-value fruit crop in the United States, with Georgia ranking among the leading producers. The increasing use of mechanical harvesters have raised concerns regarding microbial safety, particularly following recent Listeria monocytogenes contamination events. This study evaluated the survival of L. monocytogenes in two cultivars, ‘Georgia Dawn™’ and ‘Powderblue’, harvested manually or mechanically and stored with or without antimicrobial packaging. Blueberries were inoculated with L. monocytogenes and stored at 3 °C and 90% relative humidity for 30 days in clamshells containing tissue papers impregnated with copper carbonate (1.3% w/w), copper (1.3% w/w) plus ethoxyquin (0.1% w/w), non-antimicrobial paper, or no paper (control). L. monocytogenes , yeast and mold populations, and fruit quality parameters were evaluated every 10 days. Concurrently, the microbiota of non-inoculated control blueberries was analyzed throughout storage using long-read Oxford Nanopore 16S rRNA sequencing. L. monocytogenes declined by ∼1 log CFU/g across control samples from both cultivars and harvest methods, with a faster die-off rate observed in ‘Georgia Dawn™’ harvested by hand compared to mechanically harvested ( P < 0.05). After 30 days, antimicrobial packaging showed limited efficacy compared to the control treatment. Plain paper increased L. monocytogenes persistence and the growth of yeasts and molds in mechanically harvested blueberries, without significantly affecting other fruit quality parameters. Microbiota analysis showed that ‘Georgia Dawn™’ exhibited higher microbial alpha-diversity, and both harvesting method and cultivar significantly influenced beta-diversity ( P < 0.05). These findings suggest cultivar, harvesting method, and packaging may influence blueberry safety and quality.