In apple beverage manufacture, cider and juice may be stored for a short time prior to pasteurization. Storage time and temperature may affect the subsequent thermotolerance of bacteria in these beverages. This study examined whether prior storage in pH 3.4 apple cider or apple juice affected the thermotolerance of two Escherichia coli O157:H7 strains in the same beverages at 61°C. Both strains exhibited biphasic survivor curves. Strain ATCC 43894 was consistently more thermotolerant than strain ATCC 43889, with 33 to 153% greater D values derived from the linear portion of each survivor curve. Prior storage at 21°C for 2 or 6 h hastened thermal destruction of both strains in apple cider, but not to a statistically significant extent. In apple juice, prior storage at 21 °C for 2 h significantly decreased thermotolerance of strain ATCC 43889, but not of strain ATCC 43894. During 6 h of storage in 21°C apple juice, populations of strains ATCC 43889 and 43894 decreased by 2.1 and 0.5 log10 CFU/ml, respectively, and died rapidly during subsequent heating. Prior storage in apple juice at 4°C for 24 h significantly decreased thermotolerance of both strains, but this effect was not seen after 2 h of storage at 4°C. Experiments with filtered apple cider showed that presence of Alterable pulp enhanced the thermotolerance of both strains. These results show that short-term (≤6 h) room temperature storage of pH 3.4 apple cider and apple juice may enhance the lethality of subsequent pasteurization.
Chitosan inactivates spoilage yeasts but enhances survival of Escherichia coli O157:H7 in apple juice
