Thermal Food Processing

378 Thermal Food Processing: New Technologies and Quality Issues
overprocessing is allowed, in order that the thermal process delivered
to the product thermal center is sufficient. Chilled or frozen storage is
used for the ready meal, and end-product testing for microbiological
activity is usual.
4. Time–temperature integrators (TTIs) can be applied to gather process
data similar to those from microorganisms. 17,18 Section 12.3.3 discusses
TTIs because this method is one of the most exciting to have emerged
in recent years.
One of the core activities involved with establishing a thermal process is the
selection of worst-case conditions likely to be experienced during normal production.
19–22 This is independent of the method chosen for process validation. The
current methodology used by most food companies is to validate the microbiological
process safety under worst-case conditions so that, by default, the process
will be safe under normal production conditions.
To prove that the thermal process has achieved the target process value or
F value during manufacture, it is necessary to conduct validation studies using
an approved method. Various methods can be selected from the list above, and
their choice depends on the costs and nature of the food and process type.
Temperature measurements usually provide the cheapest method but are not
appropriate for all foods.
12.3.1 TEMPERATURE PROBE SYSTEMS
It has been stated above that the process validation study should be conducted
using worst-case conditions. Therefore, by inference it should not be possible for
a normal production batch to heat more slowly than the combination of factors
evaluated as worst case. To determine the worst-case conditions it is necessary
to first consider the product, process, and package separately, and second consider
the influences of interactions. The following lists suggest the factors that should
be addressed in a process validation study, although the lists are not intended to
be exhaustive. This thought process, to arrive at the set of conditions that heat
the slowest, is typical for in-pack processing, but is also appropriate for continuous
processing.
Product factors:
• Formulation (weight variation in ingredients, e.g., high starch levels
that could lead to increased viscosity)
• Fill weight (percent overfill of the key components, e.g., solids
content)
• Consistency or viscosity of the liquid components (before and after
processing)
• Solid components (size, shape, and weight before and after processing,
potential for matting and clumping)
• Preparation methods (e.g., blanching)