Survival of Listeria monocytogenes on Fresh Blueberries (Vaccinium corymbosum) Stored under Controlled Atmosphere and Ozone

Listeria monocytogenes is a foodborne pathogen that represents a high risk for consumers because it can grow under refrigeration conditions and can also develop acid tolerance. Fresh blueberries are hand-picked, packed, and transported under refrigeration without receiving a microbial inactivation treatment. The aim of this work was to study the survival of L. monocytogenes in fresh highbush blueberries stored at 4 or 12 degrees C under different controlled atmosphere conditions, including air (control); 5% O-2, 15% CO2, 80% N-2 (controlled atmosphere storage [CAS]); or ozone gas (O-3), 4 ppm at 4 degrees C or 2.5 ppm at 12 degrees C, at high relative humidity (90 to 95%) for a total of 10 days. Fresh blueberries inside a plastic clamshell were spot inoculated with the bacteria and were stored at 4 or 12 degrees C in isolated cabinets under air, CAS, and O-3 atmospheric conditions. Samples were evaluated on days 0, 1, 4, 7, and 10 for microbial growth using modified Oxford agar. CAS did not delay or inhibit L. monocytogenes growth in fresh blueberries after 10 days. O-3 achieved 3- and 2-log reductions when compared with air treatment at 4 and 12 degrees C, respectively. Low concentrations of O-3 together with proper refrigeration temperature can ensure product safety throughout transportation. O-3 is a strong antimicrobial that safely decomposes to oxygen and water without leaving residues and can be used as an alternative method to prevent bacterial growth during a long transport period.