Purpose: The objective of this research was to quantify the fate of Escherichia coli O157:H7 and Salmonella on bruised and unblemished blueberries at two maturity levels, ripe (dark blue) and commercially ripe (light blue), stored at shipping (2°C) and retail display (15.5°C) temperatures.
Methods: Harvested blueberries were sorted into dark and light blue fruit. Half of the blueberries from each group were bruised by dropping fruit from a height of 21 cm five times. Twenty microliters of a five-strain rifampicin-resistant E. coli O157:H7 or Salmonella cocktail (ca. 106 CFU/ml), was spot inoculated onto 5 blueberries and dried for 1 h. Blueberries were stored at 2°C and 15.5°C, and sampled at 0, 1, 3, and 7 days (n= 6). Pathogen populations were enumerated on selective and non-selective media supplemented with rifampicin.
Results: Populations of E. coli O157:H7 and Salmonella decreased under all experimental conditions. At 2°C, E. coli O157:H7 and Salmonella population decreases ranged from 1.2-1.6 and 1.4-1.8 log CFU/berry, respectively, over 7 days. When stored at 15.5°C, declines of E. coli O157:H7 (1.4 and 1.3 log CFU/berry) and Salmonella (1.2 and 1.1 log CFU/berry) populations were seen on light blue bruised and unblemished blueberries. Populations of E. coli O157:H7 and Salmonella decreased significantly less (P ≤ 0.05) on dark bruised blueberries (0.7 and 0.9 log CFU/berry) when compared to dark unblemished blueberries (1.6 and 1.7 log CFU/berry).
Significance: Bruising did not significantly affect the fate of E. coli O157:H7 or Salmonella populations on light blueberries or on dark blueberries stored at 2°C. However; the slower population decline of E. coli O157:H7 and Salmonella on bruised dark blueberries than on unblemished berries at 15.5°C may increase risks.