Food Protection Trends - January/February 2021 - 37

analysis critical control point (HACCP) food safety system
established in 1997 (27). The fourth edition of the Fish and
Fishery Products Hazards and Controls Guidance (HACCP
Guidance) (69) was published in 2011. This document " is
intended to assist processors ... in the development of ...
HACCP plans. " (69) Occasional updates have been issued
since then, and the latest version of the fourth edition was
published in April 2020 (73). The FDA has issued clarifying
points for critical control points (CCPs) and critical limits
(CLs) by using warning letters for such details as monitoring
times and temperatures or times to reach inhibitory processing temperatures (66-68, 71, 72). These warning letters
are sent to individual processors and are publicly available
on-line. Thus, they have been used to refine the CLs for the
impacted CCPs.
In the past 25 years (1994 through 2020), tuna processing
from the steps of thawing through retorting or refreezing
of cleaned loin meat has gone through four time and
temperature adjustments, and we are proposing an additional
scenario with adjusted CLs.
Scenario 1. The first edition of the HACCP Guidance in
1994 (63) had no restrictions for times and temperatures for
tuna processing prior to the 12-D (12 decimal reduction)
retort process. Thus, there were no time or temperature
limits to thawing, butchering, precooking, cooling, cleaning,
canning, or sealing except for an advisory time limit from the
time the can is sealed until retorting (11, 13).
Scenario 2. The second and third editions of the HACCP
Guidance (64, 65) recommend a 12-h time limit for thawing,
butchering, and precooker staging, with no guidance for time
limits after the precooker. The purpose of this first time limit
was to suppress the growth of histamine-forming bacteria
and thus prevent histamine formation.
Scenario 3. The 2011 HACCP Guidance (fourth edition)
and subsequent warning letters recommended 12 h from the
start of thawing until inhibitory temperatures (high or low)
were reached at the center of the retorted can or the cleaned
and bagged loins while freezing (66-69, 72). This 12-h time
frame was not enough time to process the tuna from thawing
through 60°C in the center of the can in the retort or 4°C
in the center of the loin bag in the freezing chamber. This
recommendation really applies to processing of only small
fish with shorter process times. Larger fish require more time
to process during the various stages of thawing, precooking,
and cooling, so at times tuna with frozen backbones (or
cores) were being precooked.
Scenario 4. Adams et al. (2) provided evidence that a 12-h
thaw and butcher time limit, a precooking CCP with a final
core temperature CL of 60°C, and an additional 12-h CL for
the cleaning and processing time is safe (73). Larger fish can
be processed under this scenario; however, the 12-h time
limit for thawing and butchering still is not effective for the
largest fish. Thus, we are proposing a fifth scenario.

Scenario 5. This scenario adds a tempering step for the
largest fish before the thawing step so these fish can be
properly thawed. To increase the enthalpy in these fish, the
temperature would be raised just before thawing from −20 to
−3°C by putting them in a temperature-controlled room. After
the core of the fish reaches −3°C but is still frozen, the fish
would be moved to the water thawing area, and the thawing
and butchering portion of scenario 4 would be completed.
The purpose of this article is to provide the background
and develop a rationale for tempering large tuna in air to an
equilibrium backbone temperature of −4 to −3°C before
completely thawing them in water to the desired core
temperature needed for precooking. This air tempering
process may extend over more than one full day. Some
factories temper frozen tuna by surrounding them with ice,
but that procedure is not addressed here.
Histamine
Histamine poisoning from fish is caused by the ingestion of
high levels of histamine from temperature-abused fish (33).
Histamine formation from bacterial action in tuna meat is a
food safety concern during the handling and processing of
nonfrozen raw tuna (69). Hungerford (33) and Lehane and
Olley (48) have provided reviews of histamine poisoning.
In 1982, the FDA established a defect action level of
20 mg% (200 ppm) for histamine in tuna as indicative of
decomposition and an action level of 50 mg% (500 ppm)
to signify a hazard to public health (25). In 1995, the FDA
lowered the defect action level to 5 mg% (50 ppm) but kept
the action level the same (26) and included more species of
fish in the compliance document.
Histamine-forming bacteria produce an enzyme, histidine
decarboxylase, that converts free histidine into histamine.
The conversion of histidine to histamine helps to regulate the
pH of their environment (28, 52). Histidine decarboxylase
is the only known enzyme having a pathway to produce
histamine from free histidine (58). When the histamineforming bacteria detect the presence of free histidine
molecules, histidine decarboxylase is formed by the bacteria
and conversion of the histidine to histamine begins. The
reaction rates of different bacterial histidine decarboxylase
enzymes are temperature and pH dependent (37). These
enzymes produce a proton transfer reaction: a histidine
molecule is transferred into the bacterial cell and converted
to histamine. Then the histamine molecule is passed out of
the bacterial cell, and a proton is consumed to provide energy
to the bacteria (41) during this electromotive reaction.
Landete et al. (46) provided an explanation and schematic of
the proton motive force generated by this enzymatic reaction.
Bacteria can be divided into three groups on the basis of
their optimal growth temperature ranges: thermophiles,
which grow best at high temperatures, mesophiles, which
grow best at moderate temperatures, and psychrophiles, that
grow best at cooler temperatures (34). However, Ingraham

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