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Volume IV - 9.2 Chemical Indices of Decomposition [Basic]

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Orientation and Training

Food and Drug Administration

DOCUMENT NO.:
IV-09
VERSION NO.: 1.5

Section 9 - Seafood Chemistry

EFFECTIVE DATE: 07-22-04REVISED: 02-14-13

 

While sensory examinations are the primary method used by the agency to determine the decomposed state of seafood, chemical indices provide a significant support mechanism to sensory findings in some products.

Histamine development in fish with high free histidine levels and indole in canned/fresh/frozen shrimp and canned crab products are two important decomposition indicators supported by the agency. These indices may be used to support original and/or confirmation sensory findings in these products. Furthermore, since histamine can develop in the absence of detectable odors of decomposition and since the shrimp industry has employed treatments that mask odors of decomposition, chemical indices meeting the established criteria may be used to support regulatory action in the absence of sensory evidence in some cases. However, since decomposition pathways may develop which do not yield these metabolites, chemical analyses should not substitute or eliminate the need for sensory examination. Product guidance should be referred to for more information on the criteria used to support actions based on chemical indicators of decomposition. The original and check analyses should be used when supporting regulatory action based on chemical indices.

In addition to histamine and indole, there are a number of other indices that may have utility in determining the decomposed state of seafood. Two of the more promising ones are the diamines, putrescine and cadaverine. There may be other decomposition metabolites that may also be supportive if problems arise using the established methods. However, the laboratories should consult with the Office of Regulatory Science (ORS) and the Center for Food Safety and Nutrition (CFSAN) before employing any of these methods in the course of their regulatory activities.

The formation of chemical indicators of decomposition is associated with seafood that was not properly refrigerated after being caught or from mishandling during subsequent storage or processing.  In restaurant situations, storage of "good" product at improper temperatures can result in histamine (scombrotoxin) formation.  Other chemical markers of decomposition have been found in spoiled fish, but their relationship to scombroid poisoning has not been determined.  Histamine can form in both high and low temperature storage conditions, and even before the associated odors of decomposition are apparent.  Histamine-forming bacteria seem to be more sensitive to freezing than spoilage-producing bacteria.  According to the FDA’s Compliance Policy Guide 7108.24, significant decomposition and histamine formation can be avoided by following good handling practices.  This includes icing or rapid immersion of the fresh catch in chilled water (at –1° C) followed by continuous frozen storage.  Leaving fresh catch lying about on deck of a fishing vessel for an extended period of time or interruption of frozen storage are common occurrences in the histories of histamine-contaminated products.  The canning of fish provides additional opportunity for problems associated with poor handling.  Frozen fish are received at the cannery and thawed prior to processing, at which point temperature abuse has another chance to occur.  Additionally, temperature abuse (letting the product get too warm or inadvertently allowing it to thaw) can occur during transportation or retail display if cooling equipment is not held at the correct temperature.

The seafood industry has implemented programs to establish Hazards Analysis and Critical Control Points (HACCP) plans to help producers prevent cases of contamination and foodborne illness.  HACCP plans delineate the most likely locations and scenarios for something to go "wrong" in a process that would result in the food product becoming unfit for consumption.  The HACCP theory can simply be summarized as: if it is known where the problems are most likely to occur, then a prevention and monitoring plan can be put in place to effectively control them.  It is a pro-active approach that places the burden on industry, not a reactive approach to be countered by the government and tax dollars.

9.2.1 Histamine

A. Background

Histamine poisoning is otherwise known as scombroid poisoning.  The name "scombroid poisoning" was coined because histamine ("scombrotoxin") is produced in fish species of the families Scombridae and Scomberesocidae, as well as some non-scombroid fish like Coryphaena and Pomatomus. Histamine-producing species include tuna, mahi mahi, escolar, bonito, yellowtail, bluefish, sardine, pilchard, abalone, and mackerel, to name a few. Fresh product typically has barely detectable levels of histamine.  Histamine can be present in fresh, canned and cooked product – the toxin survives processing. The formation of histamine is typically associated with decomposed product.  However, decomposed product (determined organoleptically) does not always produce histamine, and the presence of histamine does not always occur in decomposed product – thus sensory analysis cannot ensure the presence or absence of histamine.  Histamine can reliably be quantitated by chemical analysis down to 5 ppm (an acceptable level often found in fresh fish) (CPG 7108.24).

The aforementioned species of fish are high in levels of free L-histidine, from which histamine is formed in the muscle after death.  The amino acid L-histidine is decarboxylated by histidine decarboxylase, an enzyme produced by certain bacteria common in fish.  Since the associated bacteria are found in the fish gut, fillet from the anterior section is more likely to be contaminated as the intestine decomposes.  Formation of histamine is dependent upon the growth of these bacteria, which is a function of time and temperature.  Excess L-histidine may also be produced by proteolysis during spoilage, which can further contribute to the formation of histamine.  Interestingly, histamine can also be found in cheeses (such as Swiss cheese) that rely on the action of bacteria to form the product.  The distribution of histamine within an individual fish fillet is not necessarily consistent.  One portion of the fish may cause poisoning, while another causes no reaction.  It follows then that cans of processed product can have inconsistent histamine levels even within the same case lot (FDA, 1998).

Histamine poisoning manifests as an allergic reaction. Onset of the reaction can be immediate to within one hour.  Symptoms may include tingling/burning mouth and lips, rash, headache, or nausea and vomiting.  The symptoms may last for several hours and recovery is generally rapid.  Antihistamine drugs are an effective treatment, however sensitive individuals may need further medical treatment. The suspect food is analyzed within a few hours to confirm the presence of histamine.  A good indicator of undesirable fish is a sharp, metallic or peppery taste.  Also, fish with an "off-smell" should be avoided (FDA, 1998).

Scombroid poisoning knows no geographic boundaries.  The network for harvesting, processing and distributing fisheries products is worldwide.  Finished seafood products are sold fresh, frozen or processed to homes, restaurants or various institutions.  That adds up to a lot of opportunities for spoilage to occur.  The FDA monitors fresh, frozen and canned seafood for decomposition through organoleptic analysis.  Products that might form histamine can be subjected to further chemical testing.  Aside from the results of organoleptic analysis, product is also considered decomposed if it contains at least 50 ppm of histamine.  However, regulatory action is considered on a case by case basis (CPG 7108.24).

B. Exercise

The student should familiarize him/herself with the analytical guidance for histamine analysis: AOAC fluorometric method 977.13; CPGM 7303.842 and 7303.844; and the local laboratory’s SOP for histamine analysis. The student will analyze either canned or fresh/frozen tuna.  Both may be analyzed if time and resources permit. The trainer spikes duplicate samples at 50 ppm histamine [spiking done after the trainee has measured out an aliquot of the sample composite].  Alternatively, previously prepared canned tuna packs of known histamine concentration can be used.  Analyze duplicate samples using the AOAC method, and following any additional analytical directives in the CPGM and SOP.

C. Questions

  1. How many sub-samples are needed for histamine analysis when no odors of decomposition are present?  When is it optional to do histamine analysis on product found by organoleptic analysis to be decomposed?
  2. Why does histamine analysis need to be performed immediately following organoleptic analysis? If that is not possible, how should the sample be handled?
  3. For fresh/frozen fish, why is the anterior portion preferred for histamine analysis?
  4. What is the purpose of the ion-exchange column?  What chemistry is involved?
  5. What is the purpose of the OPT reagent?  What chemistry is involved?
  6. Why is it important to "read" derivatized samples in a timely fashion?
  7. Why does the slit width of the xenon lamp need to be less than 6 nm? 

D. References

  1. AOAC official methods of analysis (current ed.). Method 977.13 Histamine in seafood, Fluorometric Method. Gaithersburg, MD: AOAC International.
  2. U.S. Food & Drug Administration. Compliance program guidance manual. Compliance Programs 7303.842 Domestic fish & fishery products, and 7303.844 Imported seafood products. Washington DC: U.S. Government Printing Office. Available via Internet at: http://www.cfsan.fda.gov/~comm/cp-toc.html.
  3. Staruszkiewicz, W., Jr., Waldron, E. and. Bond, J. (1977).  Fluorometric determination of histamine in tuna: development of method. Journal of Association of Official Analytical Chemists, 60, 1125-1130.
  4. Local laboratory’s SOP for Histamine Analysis.

9.2.2 Indole

A. Background

The presence of indole may serve as a chemical indicator for the evaluation of incipient spoilage of shellfish and other fisheries products.   Indole analysis can be used to enhance and reinforce sensory data.  Indole is formed in shrimp, crabmeat, oysters, clams, lobsters, salted anchovies, and other fisheries products by bacterial decomposition of fish proteins.

B. Exercise

The student should familiarize him/herself with the analytical guidance for indole analysis: AOAC LC-fluorometric method 981.07; CPGM 7303.842 and 7303.844; and the local laboratory’s SOP for indole analysis. The student will analyze either canned or fresh/frozen shrimp, or canned crabmeat.  Multiple sample types may be analyzed if time and resources permit.  The trainer spikes duplicate samples at 10 ug indole /100 g tissue (= 0.1 ug/g = 0.1 ppm) [spiking done after the trainee has measured out an aliquot of the sample composite].  Alternatively, previously prepared canned shrimp or crabmeat packs of known indole concentration can be used.  Analyze duplicate samples using the AOAC method, and following any additional analytical directives in the CPGM and SOP.

C. Questions

  1. What is the purpose of spiking samples with 2-methylindole?
  2. What is the logic behind making standard solutions A, B and C first, instead of making calibrations solutions directly?
  3. How does the detector type influence the extent of the extraction chemistry?
  4. If a matrix is too "dirty" to allow baseline separation of the indole peak, what other options might the analyst have?  Hint:  see LIB#4016.

D. References

  1. AOAC official methods of analysis (current ed.) Method 981.07 Indole in seafood, liquid chromatographic fluorometric method. Gaithersburg, MD: AOAC International.
  2. U.S. Food and Drug Administration.  Compliance program guidance manual. Compliance Programs 7303.842 Domestic fish and fishery products, and 7303.844 Imported seafood products. Washington DC: U.S. Government Printing Office. Available via Internet at: http://www.fda.gov/ICECI/ComplianceManuals/default.htm.
  3. Berg, R. and Carley, C. Modification of HPLC method for indole in shrimp. FDA  Laboratory Information Bulletin, No. 4016.
  4. Local laboratory’s SOP for Indole Analysis.