The effects of vanillin on the fates of Listeria monocytogenes and Escherichia coli O157:H7 at pH values between 3.5 and 4.5 were verified in a model apple juice (MAJ) medium and in apple juice incubated at 4 or 15 degrees C. Viable E. coli O157:H7 cells were recovered from MAJ for up to 10 days, but L. monocytogenes did not survive at pH 3.5. Supplementation with 40 mm vanillin exerted a lethal effect that was species, concentration, pH and temperature dependant. E. coli O157:H7 was more sensitive to vanillin than L. monocytogenes, and viable cells could not be recovered after 2 days incubation at either temperature. L. monocytogenes and E. coli O157:H7 were inoculated (10(5) cfu/ml) in pH adjusted (pH 4.00) or unadjusted (pH 3.42) juice from Granny Smith apples that was supplemented with 40 mm vanillin. Neither species were recovered after 3 days incubation at 4 or 15 degrees C. These findings indicate that vanillin could be useful as a preservative for minimally processed apple products.