2.2. Sample preparation and inoculation
Experiments were performed using commercially processed
creamy and chunky peanut butter. A peanut butter sample (60 g)
was aseptically placed in sterile 250-ml glass beaker. For inoculation,
2.0 ml of culture cocktail was applied to the sample and gently
but thoroughly mixed for 1 min with a sterile spoon to ensure even
distribution of the pathogens. It was then dried for 1 h inside
a biosafety hood (22 2 C) until the aw of the sample equaled that
of a non-inoculated sample (ca. 0.4). During the drying interval the
sample was stirred gently at 10 min intervals to prevent pockets of high moisture. Commercially-produced saltine crackers were
purchased at a local grocery store (Seoul, Korea) and were used to
simulate commercially-prepared foods that contain peanut butter.
Crackers (5.0 cm in diameter) were first sterilized for about 10 min
under a germicidal UV lamp before 3 g of inoculated peanut butter
was coated between two crackers for minimizing other interruptive
bacterial factors. Three peanut butter cracker sandwiches (ca. 25 g)
were placed parallel to each other in the middle of a sterile polypropylene
bowl (11.0 cm in diameter and 4.5 cm deep) for each RF
treatment.