Shachar and Yaron (2006) reported that S. Typhimurium was
rapidly killed at 70 C in saline buffer, and a greater than 7-log
reduction was observed within less than 5 min in a heated water
bath. However, in a matrix of peanut butter only a 1.4-log reduction
was observed at 70 C, a 2.2-log reduction was observed at 80 C,
and a 2.5-log reduction was observed at 90 C after 5 min in
a heated water bath. Two sequential treatments also were not
effective for achieving a 7-log reduction. Based on their calculated
parameters of theWeibull model, more than 260 min are needed to
reduce Salmonella by 7 log units at 70 C, and more than 60 min is
required at 90 C when using a conventional hot water immersion method. However, these treatment times are not practical for use
by industry and could adversely affect the organoleptic qualities of
the products by increasing denaturation or browning. Li et al.
(2009) had also reported that a hot water immersion of 71e77 C
for 20 min was not sufficient to inactivate Salmonella Tennessee
in peanut butter. About a 3 log reduction was observed in peanut
butter exposed to 90 C for 20 min. Therefore, conventional
thermal treatments commonly used by industry are not adequate
to inactivate Salmonella in peanut butter. In the present study, the
average bacterial concentrations of S. Typhimurium and E. coli
O157:H7 inoculated into one batch of sample was 6e7 log CFU/g.
These inoculation levels were much higher than would normally
be encountered in peanut butter since such high levels of pathogens
would not occur as post-processing contamination unless
GMPs and sanitation were extremely poor. A high inoculum load
was used to make enumeration of surviving bacteria easier