Microbial quality of blueberries for the fresh market

Abstract

Harvested blueberries are sorted in packinghouses to remove pre-mature fruits and plant debris, packaged in polyethylene clamshells, and cooled in refrigeration facilities before being shipped to the fresh markets. This study determined the microbial quality of fresh blueberries collected from berry packinghouses. Unpacked and packed blueberries (n = 124) were collected in duplicate at the beginning of the day, lunchtime, and the end of the day from six different packinghouses in Georgia in the summer of 2015 and 2017. Collected berries were rinsed or homogenized in 0.1 M phosphate buffered saline and appropriate dilutions were inoculated on tryptic soy agar, MacConkey agar, Enterococcus agar and potato dextrose agar. Resulting microbial colonies were enumerated and presumptive fecal coliforms and enterococci confirmed. Eleven berry samples from three packinghouses tested positive for fecal coliforms and one sample tested positive for enterococci. Mean total aerobic counts, total yeast and mold counts and total coliform counts of the berries were 3.89, 4.42 and 1.42 log CFU/g, respectively. Sampling time had significant influence (P ≤ 0.05) on the recovery of all three groups of microorganisms. On average, berry samples collected at the end of the day had the lowest microbial counts. Homogenization of berries recovered significantly higher numbers of yeast and mold and total coliform cells than rinsing. In general, packing process had no significant influence (P > 0.05) on recovered microbial counts, however, unpacked berries had numerically higher aerobic counts and yeast and mold counts than packed berries. This study suggests that sorting of blueberries before packing for the fresh market does not lead to significant reductions in microbial counts.