Survival of Listeria monocytogenes on blueberries post-sanitizer treatments and subsequent cold storages

This study evaluated the fate of Listeria monocytogenes (Lm) on blueberries with different inoculation methods during antimicrobial interventions and subsequent refrigeration and frozen storages. Survival of Lm was highly dependent on the inoculation method. Dip-inoculated Lm was much more resistant to sanitizer interventions compared to spot-inoculated Lm on blueberries. In the storage studies, Lm on blueberries without sanitizer treatment maintained a stable population during both 4 and -15 degrees C storages regardless of the inoculation method or inoculation level. For dip-inoculated blueberries, there was about similar to 0.9 Log(10) CFU/g reduction of Lm post 0.4% Neo-Pure treatment during 14-day refrigeration storage. Over 28-day frozen storage of blueberries with dip-inoculated Lm, 0.4% Neo-Pure and 100 ppm chlorine treatments elicited similar to 3.0 and 1.1 log(10) CFU/g reduction, respectively. Blueberry background flora including total plate count (TPC) and yeasts and molds counts (Y/M) on untreated blueberries were similar to 4.0 and 5.0 Log(10) CFU/g, respectively, throughout cold storage. Neo-Pure treatment at 0.4% coupled with cold storages reduced TPC and Y/M counts by similar to 0.8 and 1.6 Log(10), CFU/g, respectively. The inhibitory effect was mostly maintained throughout storage. In summary, the inoculation method plays an important role in Lm resistance to sanitizer interventions and researchers need to be careful in interpretation of antimicrobial efficacy from different experiments. Including Neo-Pure prior to cold-storage is beneficial to control Lm on blueberries.