3. Results
3.1. Average temperature-time histories of peanut butter
The temperatures of creamy peanut butter during treatment
with 27.12 MHz RF energy are shown in Fig. 2. Although the
temperatures of all samples rapidly increased with increasing
treatment time, the heating rates of the middle cracker sandwich
and the bottom cracker sandwich were higher than that of the top
cracker sandwich. After 90 s of RF heating, the creamy peanut
butter of the middle and bottom sandwiches reached ca. 86 C, and
the top one reached 77 C. In order to raise the creamy peanut
butter temperature from room temperature to 60 C, RF heating for
a maximum of 66 s in the top cracker sandwich was required. Fig. 3
shows temperatures of chunky peanut butter during RF treatment.
The pattern of temperature increase of the top, middle and bottom
cracker sandwiches did not differ from those of creamy peanut
butter. The maximum heating time for the top cracker sandwich to
reach 60 C from room temperature was 65 s and the temperature
reached after heating for 90 s was a minimum of 78 C in the top
cracker sandwich.
3.2. Inactivation of pathogenic bacteria by RF heating
The survival of S. Typhimurium and E. coli O157:H7 in creamy
peanut butter during 90 s of RF heating are shown in Table 1. The
populations of both pathogens decreased with increasing treatment
time. Significant (P > 0.05) reductions were not observed for
50 s compared to the control. However, treatment for 70 s significantly
(P < 0.05) reduced levels of S. Typhimurium and E. coli
O157:H7 by 2.77 and 2.93 log CFU/g in creamy peanut butter,
respectively. After 90 s of RF treatment, the reductions of S.
Typhimurium and E. coli O157:H7 were 4.29 and 4.39 log CFU/g in
creamy peanut butter, respectively. Table 2 shows populations of S.
Typhimurium and E. coli O157:H7 in chunky peanut butter during
90 s of RF heating. There were no significant (P > 0.05) reductions in
microbial levels until 30 s of treatment had occurred. However,
significant reductions of S. Typhimurium and E. coli O157:H7 were
observed after 50 s of treatment. Treatment for 90 s significantly
(P < 0.05) reduced levels of S. Typhimurium by 4.55 log CFU/g andE. coli O157:H7 by 5.32 log CFU/g.
3. Results3.1. Average temperature-time histories of peanut butterThe temperatures of creamy peanut butter during treatmentwith 27.12 MHz RF energy are shown in Fig. 2. Although thetemperatures of all samples rapidly increased with increasingtreatment time, the heating rates of the middle cracker sandwichand the bottom cracker sandwich were higher than that of the topcracker sandwich. After 90 s of RF heating, the creamy peanutbutter of the middle and bottom sandwiches reached ca. 86 C, andthe top one reached 77 C. In order to raise the creamy peanutbutter temperature from room temperature to 60 C, RF heating fora maximum of 66 s in the top cracker sandwich was required. Fig. 3shows temperatures of chunky peanut butter during RF treatment.The pattern of temperature increase of the top, middle and bottomcracker sandwiches did not differ from those of creamy peanutbutter. The maximum heating time for the top cracker sandwich toreach 60 C from room temperature was 65 s and the temperaturereached after heating for 90 s was a minimum of 78 C in the topcracker sandwich.3.2. Inactivation of pathogenic bacteria by RF heatingThe survival of S. Typhimurium and E. coli O157:H7 in creamypeanut butter during 90 s of RF heating are shown in Table 1. Thepopulations of both pathogens decreased with increasing treatmenttime. Significant (P > 0.05) reductions were not observed for50 s compared to the control. However, treatment for 70 s significantly(P < 0.05) reduced levels of S. Typhimurium and E. coli
O157:H7 by 2.77 and 2.93 log CFU/g in creamy peanut butter,
respectively. After 90 s of RF treatment, the reductions of S.
Typhimurium and E. coli O157:H7 were 4.29 and 4.39 log CFU/g in
creamy peanut butter, respectively. Table 2 shows populations of S.
Typhimurium and E. coli O157:H7 in chunky peanut butter during
90 s of RF heating. There were no significant (P > 0.05) reductions in
microbial levels until 30 s of treatment had occurred. However,
significant reductions of S. Typhimurium and E. coli O157:H7 were
observed after 50 s of treatment. Treatment for 90 s significantly
(P < 0.05) reduced levels of S. Typhimurium by 4.55 log CFU/g andE. coli O157:H7 by 5.32 log CFU/g.
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