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Histamine is a biogenic amine and a food safety hazard, and it is the only biogenic amine regulated by statute or hazard analysis and critical control point guidance. This article reviews the regulations for histamine levels in fish in countries around the world, including maximum limits or levels and sampling procedures in different fish preparations. The maximum histamine levels, sampling plans, and fish products are listed. The country-by-country regulations for maximum histamine acceptance levels in some food products vary by a factor of 8, from 50 ppm in some countries to a maximum of 400 ppm in other countries. For similar food products, the maximum histamine levels vary by a factor of 4 (from 50 ppm to 200 ppm) in, for example, fresh tuna. The country-by-country sampling plans vary widely as well, and these, too, are covered in detail.

This review covers 18 years of voluntary recalls of tuna sold commercially in the United States. Recall information is a valuable indicator of failure to implement procedures for food safety. The voluntary recalls involve tuna that was fresh, frozen, processed, hermetically sealed, retorted in a shelf-stable pack (i.e., canned), and formulated into other tuna products. U.S. Food and Drug Administration regulations address the capture, processing, transportation, and sale of raw and processed seafood. These regulations include current good manufacturing practices, the Food Modernization Act, emergency permit controls, and guidelines for low-acid canned foods, seafood hazard analysis and critical control points, food labeling, and sanitary food transportation. Traceability and the food safety culture are important for successfully preventing or implementing recalls. The recalls themselves were separated into product treatment groups: uncooked products, canned shelf-stable products, and products in which tuna was used as an ingredient. The recalls were further categorized and summarized by reason or cause, such as biological and chemical contamination, undeclared ingredients, underprocessing, and foreign materials. The primary causes of recalls of the reviewed tuna products were (in order) Listeria monocytogenes, undeclared allergens, elevated histamine concentrations, and underprocessing of retorted tuna products. The recalls for elevated histamine concentrations primarily affected uncooked (raw) tuna. Recalls for Listeria contamination and the presence of undeclared allergens were primarily class I recalls, and recalls for elevated histamine concentrations and underprocessing were almost always assigned to the less serious recall class II.

An experiment to validate the precooking of tuna as a control for histamine formation was carried out at a commercial tuna factory in Fiji. Albacore tuna (Thunnus alalunga) were brought on board long-line catcher vessels alive, immediately chilled but never frozen, and delivered to an on-shore facility within 3 to 13 days. These fish were then allowed to spoil at 25 to 30°C for 21 to 25 h to induce high levels of histamine (>50 ppm), as a simulation of \"worst-case\" postharvest conditions, and subsequently frozen. These spoiled fish later were thawed normally and then precooked at a commercial tuna processing facility to a target maximum core temperature of 60°C. These tuna were then held at ambient temperatures of 19 to 37°C for up to 30 h, and samples were collected every 6 h for histamine analysis. After precooking, no further histamine formation was observed for 12 to 18 h, indicating that a conservative minimum core temperature of 60°C pauses subsequent histamine formation for 12 to 18 h. Using the maximum core temperature of 60°C provided a challenge study to validate a recommended minimum core temperature of 60°C, and 12 to 18 h was sufficient to convert precooked tuna into frozen loins or canned tuna. This industrial-scale process validation study provides support at a high confidence level for the preventive histamine control associated with precooking. This study was conducted with tuna deliberately allowed to spoil to induce high concentrations of histamine and histamine-forming capacity and to fail standard organoleptic evaluations, and the critical limits for precooking were validated. Thus, these limits can be used in a hazard analysis critical control point plan in which precooking is identified as a critical control point.

Precooking tuna is an essential part of the process of manufacturing traditional canned tuna. This article briefly describes the manufacturing processes for precooking tuna in a conventional atmospheric precooker. Fish thickness and weights were measured to determine thickness variation by fish size. A finite difference simulation model was used to study the impact of three factors (fish size, initial backbone temperatures, and ambient steam temperatures) on precooking times. Results obtained with the simulation model indicate that the factors affecting precooking times are, in decreasing order, fish thickness, initial temperatures, and ambient steam temperatures. A multiple regression analysis indicates that the combination of fish size (thickness) and initial backbone (core) temperatures can account for 95% of the variation in predicted precooking time, with most of the variation based on fish thickness. Suggestions are offered for optimizing recovery of precooked fish and using the End Point Internal Product Temperatures to control precooking results.

The advent of higher flux neutron sources has made the use of sample changers appropriate across the instrument suites at neutron scattering facilities. We examine the efficiency, design, and operation of two sample changers used at the thermal chopper spectrometers at the Spallation Neutron Source. We also present case studies of sample holders designed to accommodate multiple single crystal or powder samples for the Cold Neutron Chopper Spectrometer at the Spallation Neutron Source. [This manuscript has been authored by UT-Battelle, LLC under Contract No. DE-AC05-00OR22725 with the U.S. Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (http://energy.gov/downloads/doe-public-access-plan).]

The time and temperature controls for processing canned tuna to control histamine formation were first published in the 1998 edition of the Fish & Fishery Products Hazards & Controls Guide from the U.S. Food and Drug Administration (FDA). The controls have been refined since then with validation studies and FDA warning letters. To control histamine formation, the latest precooking validation study allows a 12-h thawing and butchering time limit, a critical limit of a minimum precooking temperature of 60°C at the backbone of the fish, and a 12-h critical limit from the end of precooking until the inhibitory temperatures is reached in the cold spot in the can in the retort. The largest tuna cannot be thawed within the initial 12-h limit prior to precooking. We propose a tempering phase in ambient air of -3 to -4°C to increase the enthalpy of the still frozen tuna so the thawing time in water can be shortened and the critical limits can be met. The potential for growth of bacteria that form histamine and the formation of histamine at temperatures near 0°C was evaluated based on published data. At the proposed ambient tempering temperatures of -3 to -4°C, there is minimal risk of the growth of histamine-forming bacteria and the formation of histamine.

A Heat of Summation model was developed to compare the number of minutes of temperatures over 60°C to which tuna meat is subjected during precooking in conventional atmospheric and in vacuum precookers, using various steam heating profiles. The Heat of Summation model was developed using finite difference methods. Lower precooking temperatures resulted in lower Heat of Summation values, but longer times were required to precook the fish to a core temperature of 60°C. In the end, the available precooking capacity combined with the desired product appearance and texture will determine which cooking temperature profile and equipment to use.

This paper presents practical procedures that allow processors to determine when a batch of tuna fish is heated sufficiently to achieve a 5-log reduction in Morganella morganii, the most heat-resistant histamine-forming bacteria. The core temperatures of the largest, coldest fish in the batch are chosen to estimate the minimum temperature of the batch, because they will have the slowest heat penetration rate. The prerequisites and validations required for this procedure are presented, as well as the corrective actions that might be needed to comply with FDA seafood HACCP guidelines. An Excel spreadsheet was developed to allow for simple data input and to provide output of a decision as to whether to accept the tuna, wait, or recook the tuna. The consistent use of these procedures will produce a safe precooked tuna product, thereby allowing for an extra 12 h for tuna preparation and processing.

Critical Limits (CLs) to prevent histamine formation while processing commercially canned tuna are developed for tuna precooking, using core temperatures and time. The CLs are developed from the thermal death times of Morganella morganii, the most heat-resistant of the histaminogenic bacteria in tuna. These CLs will deliver a 5 log reduction of this bacterium and ensure that histamine formation will be sufficiently restricted to allow enough time to continue processing tuna until the finished product is canned and retorted. The US-FDA Seafood HACCP Guide (4th ed) allows an intermediary heating phase Critical Control Point if the total processing time extends over 12 hours. More than 12 hours total processing time is required to process larger tuna fish, thus the need for this CCP and associated CLs. Based on prior work, a critical limit of 60°C for 1 min in the cold spot of the fish has been shown to result in a 5.68 log reduction in Morganella morganii. Alternative CLs, using cold-spot core temperature and holding time proposed for a reduction of more than 5 logs, are: 59°C for 2 min (5.41 logs), 58°C for 4 min (5.59 logs), 57°C for 7 min (5.30 logs), and 56°C for 12 min (5.30 logs).