Food Protection Trends - July/August 2018 - 264

Figure 6. Numerical estimates for temperature distribution in a
jar cross section. Numerically calculated temperature distribution
at the mid height of the pickle jar for varying times after the start
of the third filling for a non-insulated jar with an initial cucumber
temperature of 40oC: (a) 5 s; (b) 30 s; (c) 60 s; (d) 120 s;
(e) 180 s;( f) 240 s. The colored bar represent the temperature
gradient from 50oC (blue) to 85oC (red) as indicated.

pathogenic Escherichia coli, Salmonella enterica, and Listeria
monocytogenes was found to require an F160 value of 5.6
min, with a z value of 16.7°F (4). These were the minimum
thermal processing conditions targeted for the current study.
However, the majority of acidified products, including most
acidified cucumber spears, have pH values below 4.1, and a
5-log reduction in pathogens can be achieved with an F160
of 1.2 min (with a corresponding z value of 19.5°F) (5).
The data in Table 1 showed that, with cucumbers preheated
to 40°C or 60°C, three repeated fills were sufficient to
achieve a 5-log reduction in vegetative bacterial pathogens.
All treatments except for cucumber spears with an initial
temperature of 20°C in uninsulated jars exceeded the F160
(71.1°C) value of 5.6 min.
Commercial processers also consider quality factors when
processing acidified foods (17). These factors may include
thermal destruction of softening enzymes. Published
processing values to achieve desired quality include
processing at temperatures of 73.9°C (165°F) for 15 min or
71.1°C (160°F) for 20 min (8, 9), with an estimated z value
of 22.4°C. Based on these recommendations, the differences
in processing times for safety vs. quality factors are shown
in Fig. 7. In addition to requiring a 5-log reduction in
bacterial pathogens, acidified food regulations (21 CFR
part 114) (12) also require that spoilage organisms of
non-public health significance do not grow in the product.
However, industry practice often varies considerably from
published thermal process recommendations for quality
factors. Commercial processes typically use the minimal
heat process that exceeds processing requirements for
safety, prevents spoilage microorganisms from growing,
and achieves the desired quality. Time and temperature
parameters for thermal processing of acidified vegetables

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Food Protection Trends July/August

may vary with product type, jar size, the concentration of
spices and other ingredients that may have antimicrobial
activity, and other factors.
Data for the equilibration of center and periphery
cucumbers (Fig. 3) showed that the periphery cucumber
spear equilibrated with the brine quicker than the center
spear. For the 40°C insulated trial shown in Table 1, this
variation was evident by the standard deviation values for
the mean value for hold times for center and periphery
cucumbers at 71.1°C and 73.9°C (3.13 min and 5.25 min,
respectively), with periphery cucumbers being hotter. The
reason for these differences in unclear. It is possible this
occurred because of convection patterns within the jar
(3), and these patterns may have been influenced by the
filling tube location for the experiments shown. In some
trials, this trend was reversed (data not shown), with the
center cucumber spear heating faster. Further research with
alternative packing arrangements, or filling mechanisms that
may be applicable to commercial processes, may be helpful

Figure 7. Processing times and temperatures for quality and safety. The
estimated times for processing to achieve quality factors (triangles) or
safety (circles) are shown. Selected points based on published values (F
values) for quality factors at 71.1oC (20 min) or 73.9oC (15 min) or
safety at 71.1oC (5.6 min) are indicated with data point labels. The z
values for safety and quality were 9.28oC and 22.4oC (respectively).

to determine how these parameters affect heat distribution
(both vertical and horizontal) through the jars.
A numerical model was developed for temperature
predictions that may be useful for optimization of processes
for achieving time-temperature conditions needed for both
safety and quality factors. For commercial application,
the time needed between filling steps may require holding
shunts for jars (allowing jars to accumulate between filling
steps) during processing, to establish processing conditions
Table of Contents for the Digital Edition of Food Protection Trends - July/August 2018
