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estimate of the lowest temperature from a batch of precooked
fish and is suitable for use in determining compliance with
the CL.
Histamine and the tuna canning business
The canned tuna business is a multi-billion-dollar business
spread throughout the world. Hamilton et al. (23) estimated
that, in 2008, there were at least 144 tuna processing facilities
around the world capable of producing either canned tuna or
cooked, cleaned, and frozen tuna meat in loin bags destined
for canning. The total capital investment in the global canned
tuna industry was $15 billion U.S. dollars, the processing
capacity was over 14,000 metric tons per day, and a round
weight of 3 million metric tons was processed annually.
The vast majority of tuna processing factories precook the
tuna before further processing, with the average precooker
capacity per cycle of about five metric tons. Based on these
estimates, there are ca. 2,800 daily precooking cycles and ca.
600,000 precooking cycles performed annually.
The process and equipment used for precooking tuna and
the factors that have the most impact on the heating rates and
precooking time for commercially processed tuna have been
described previously by DeBeer et al. (8).
All seafood processed and/or sold in the United States
must be processed under the U.S. Food and Drug Administration's (FDA) Seafood HACCP regulations (18). The
FDA has issued a series of recommendations for processing
seafood in various HACCP guidance documents, with the
latest issued in 2011 (15). Histamine is one of the hazards
that tuna processors are required to control. Histamine forms
after the tuna dies, if the tuna is not chilled properly aboard
the fishing vessel or is exposed to conditions conducive to
histamine formation during processing at the factory (26).
These conditions allow histamine forming bacteria (HFB) to
convert the free histidine found in certain fish to histamine
by the inducible enzyme, histidine decarboxylase (HDC)
(41). What sets histamine apart from other seafood toxins is
that its formation is 100% preventable, with timely and proper cold or heat treatments (22, 26). The defect action level
(DAL) for histamine in seafood in the United States is 50
ppm, with an action level of 500 ppm based on toxicity (16).
A 50 ppm DAL is associated with relatively small samples
sizes and is most often viewed as evidence of mishandling
and the possible presence of higher levels of histamine within
the lot (41).
The workflow for processing whole tuna, from receiving
at the factory until shipping canned product, is shown
in Fig. 1. Typically, there are 10 steps from thawing until
retorting the canned product, usually processed in batches.
The FDA's 2011 Seafood Hazard Analysis Critical Control
Point (HACCP) guide (15) recommends a maximum
exposure limit of 12 hours when temperatures are over 21°C
for processing frozen tuna, in the absence of an approved
intermediate heat (precook) step. However, 12 h may be not

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be sufficient for processing large tuna (30), unless the fish
are precooked to a minimum inhibitory core temperature
(MICT) in order to pause histamine formation for an
extended period of time. Under these circumstances, the
MICT then becomes a Critical Limit (CL) in a HACCP plan.
The FDA HACCP Guide (15) allows for a heating stage
(precooking) for tuna but gives no guidance on the time
and temperature of the heat treatment or the MICT. In the
early 1970s, Peterson (36) recommended 57.3°C (135°F)
as a minimum core temperature. Hence, that minimum core
temperature has been the de facto standard for precooking
tuna for almost 50 years.
Minimizing the risk of histamine formation during and
after precooking
By the time the tuna is ready to be precooked, it will
have passed the required initial HACCP histamine and
organoleptic screening and is safe for processing into
shelf-stable containers. The risk of histamine formation as
a result of the precooking heating step is that a portion of
some fish might not achieve the time and minimum fish core
temperature necessary to reduce the HFB, which then might
grow during the time the fish is cooled and cleaned, after
precooking. The fish core temperature can be monitored in
one of two ways: (a) the fish can be tested after precooking
with thermometers at the backbone or geometric center or
(b) the fish can be continuously monitored with temperature
probes during precooking (30).
Multiple factors can contribute to variability of the core
temperatures of precooked tuna. These factors include fish
size, thawing, initial core temperature before precooking,
placement of the tuna on the trolleys, temperature distribution of the precookers, steam supply, and precooker
maintenance. All of these factors need to be managed as
much as possible. Some of the variation can be minimized
by capital construction and simple maintenance, while
other operational sources of variation can be minimized but
not eliminated.
The canned tuna industry relies completely on the capture
of free-swimming, wild tuna that weigh from 0.25 kg to
100 kg (5). The fish is sorted by size when it arrives at the
processing factory. The range of sizes within the size group
has been reviewed elsewhere (8). Even fish with the same
weight can have different thicknesses, so there is always
a thickness variation within a batch of fish from the same
size category (8), which can cause fish to thaw and heat
differently. This size variation needs to be accounted for and
dealt with accordingly, because it cannot be eliminated.
Several procedures can be implemented to minimize the
temperature variation after precooking (33). These include:
(a) making certain there is a consistent, even temperature
distribution throughout the precooker, (b) providing
sufficient steam supply to maintain the targeted ambient
steam temperatures, and (c) conducting proper maintenance

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