Agriculture Reference
In-Depth Information
fruits and vegetables. In most cases, a short thermal treatment (usually referred to
as
blanching
) is used as a pretreatment to inactivate enzymes in fresh fruits and
vegetables before dehydration or further thermal processing (
canning
). Therefore,
only a limited amount of thermal resistance data is available concerning foodborne
pathogens in fresh fruits and vegetables. Some data were actually obtained from juices
of fruits (Mazzotta 2001a). Table 13.1 lists the D and z values for
Escherichia coli
O157 : H7,
Salmonella spp.
, and
Listeria monocytogenes
in selected fruits and
vegetables.
It is readily noted from Table 13.1 and Figure 13.1 that the common foodborne
pathogens (
E. coli
O157 : H7,
Salmonella spp.
, and
L. monocytogenes)
are in general
not very heat resistant, and can be destroyed easily by mild heat. Figure 13.1 illustrates
the time needed to achieve a 5-log reduction in
E. coli
O157 : H7 in single - strength
orange juice (the most heat resistant shown in Table 13.1). Apparently, a very short
time (
1 s) is needed to achieve a 5-log reduction in the bacterial counts if the tem-
perature of the products can be increased to above 70 °C. If the bacteria survive after
a food has been heated at or above 70 °C for more than 1 s, it is usually an indication
that bacteria are located inside of the food at an internal temperature substantially
lower than the surface temperature, which can be easily illustrated in the following
case study.
<
1000
100
10
1
0.1
0.01
0.001
0.0001
0.00001
0.000001
50
60
70
80
90
100
T (°C)
Figure 13.1.
Time (min) needed to achieve a 5-log reduction of
E. coli
O157 : H7 in
single-strength orange juice (calculated based on Table 13.1 and Eq. 13.6).
