Food Protection Trends - September/October 2017 - 344

harder as variability in core temperatures increases. In fact,
processors typically devote considerable effort to ensuring
that each batch of fish processed is as uniform as possible,
because this process actually impacts profit by maximizing
fish yield and processing efficiency. The sampling strategy
being proposed to ascertain the adequacy of the heat
treatment should be suitable for the variability resulting
from typical commercial tuna processing operations.
Prior to the start of the process, the fish should be
segregated by species and then sorted by weight (i.e.,
"sized") into pre-established weight class categories. Fish
from each size category should be processed together
in batches of like-weight fish of the same species.
Sizing cascades to provide consistent post-thawing fish
temperatures and consistent precooking initial temperatures
(ITs), thereby providing consistent precooking heating
rates during precooking and consistent post precooking
core temperatures. The suggested maximum ranges of
weight for sorting the fish are one or two kg for smaller fish
(under 10 kg) and five kg for larger fish (over 10 kg) (3).
Efficient reliable equipment and techniques for thawing
the fish are needed to reduce IT variability. The thawing
water should be temperature-controlled and should have
adequate circulation (8) to provide consistent thawed fish
temperatures. Optimizing the efficiency of the thawing
equipment results in uniformly thawed fish, which helps to
make the rest of steps in the process more efficient.
Processors typically establish stringent operating
parameters and monitor the thawing process and the fish
exiting the thawing step to ensure the fish have thawed
sufficiently to continue processing. In particular, processors
should ensure that no individual fish are still frozen at the
core because this (a) makes the fish difficult to butcher and
split, if required, and (b) may cause a very slow and variable
precooking time.
The personnel assigned to work on the butchering
line are typically trained to detect and alert management
if the fish gets too hard to butcher because it is still
partially frozen internally. Partially-frozen fish should
be segregated from properly-thawed fish, as they
might need to be precooked as a separate batch or held
back until they finish thawing and before they can be
precooked. The personnel should also be trained to alert
the management if the fish arriving from the thawing
step are not properly "sized" or have been assigned the
wrong size class category, i.e., in the lot identification
documentation available for the fish.
For the larger fish sizes that require splitting and
cutting, the cutting equipment must be properly adjusted
and capable of consistently cutting the fish into pieces
of uniform size and shape. The allowed variation for cut
pieces should be pre-determined, and the splitting and
cutting operation should be monitored to ensure the fish
pieces conform to the specifications.

344

Food Protection Trends September/October

After butchering and splitting, the fish must be divided
into batches made up of individual pieces of uniform size,
shape, and racking arrangement. At the fish racking station,
individual pieces from each batch should be sampled
by measuring and/or weighing to make sure the correct
precooking time is selected. The size and shape class
category and the racking arrangement of each batch should
be documented in the precooking records. Any piece that
is significantly larger than the rest in the batch should be
checked by measuring and/or weighing prior to racking
to make sure that it belongs to the same size/shape class
category as the rest of the fish in the batch. Pieces that
belong to a different category should be culled out and
precooked as a separate batch; otherwise, the precooking
time applied to the batch should be chosen according to
the largest fish size category in the batch, because the larger
pieces will have slower heating rates (3).
Each precooking rack or trolley that will be used to
take the fish into the precooker must be loaded only with
fish that belong to the same batch. To minimize heating
variation during precooking, the precooking racks and
baskets must have essentially the same construction
and physical characteristics, and all the fish in the batch
must be arranged in the racks with the same loading
configuration, i.e., same orientation and disposition of
individual pieces and same number of pieces per layer or
per precooking basket.
If the batch has some individual pieces that are noticeably larger than the average piece size, then the racking
personnel would have to ensure these larger pieces are
located in specific pre-established positions in the racks or
marked in some consistent fashion so their core temperatures can be measured before and after precooking. Likewise, if the precooker has any consistent "cold spots" that
were identified during the temperature distribution studies, then the rack(s) that will be located in this area of the
precooker during the process must be tagged or marked to
ensure that their fish are included in the sample that will
have its core temperature measured after precooking.
ACCEPTANCE SAMPLING
There are two methods of acceptance sampling:
sampling by attribute or sampling by variable (17). A
simple technique that uses attribute sampling to measure
temperature and time for the vacuum precooker (VPC)
is described. For conventional atmospheric precookers
(CAPs), an Excel spreadsheet using the variable sampling
method (6) was developed to be used to analyze the
core temperatures of the fish exiting the precooker. This
spreadsheet will analyze the log-lethality of the heat
treatment of precooking and test the core temperatures
for normality. As an alternative, for a factory that has no
computer support, an acceptance technique was developed
using the median and range/d2 method described by

Table of Contents for the Digital Edition of Food Protection Trends - September/October 2017