Histamine is a naturally occurring compound present in many foods, often associated with allergic reactions. Whether sushi is high in histamine depends primarily on proper handling, not the inherent freshness of the fish. Certain species can rapidly accumulate high histamine levels if they are not correctly refrigerated after being caught. This accumulation is a food safety concern that can lead to a form of chemical poisoning.
The Histamine Connection: Scombroid Poisoning
Histamine is a chemical compound that acts as a neurotransmitter and plays a role in the immune system. In fish, high levels of histamine cause a foodborne illness known as Scombroid Poisoning, or histamine fish poisoning. This condition is a chemical intoxication resulting from consuming fish contaminated with high concentrations of histamine that form after the fish has died. Symptoms often mimic an allergic reaction, manifesting quickly (within minutes to a few hours), and can include facial flushing, sweating, headaches, nausea, and a rash. The poisoning usually resolves on its own, but treatment with antihistamines can alleviate the symptoms.
Factors That Increase Histamine Levels
Histamine accumulation begins when bacteria present on the fish’s skin and gills multiply rapidly after the fish dies. These bacteria possess the enzyme histidine decarboxylase, which converts the amino acid histidine, abundant in certain fish muscle tissue, into histamine. The primary driver for this conversion is temperature abuse and time, making cold chain maintenance important. If the fish is not chilled immediately and kept near melting ice after harvest, bacteria quickly generate significant histamine amounts.
The optimal temperature for rapid conversion is around 25°C (77°F), but production occurs even at moderate refrigeration temperatures. Once histamine forms in the tissue, it is thermostable, meaning it cannot be destroyed. Cooking, smoking, or freezing kills the bacteria but does not reduce the histamine level already present. Preventing histamine formation through strict time and temperature control is the only effective safety measure.
Identifying High-Risk Fish in Sushi
Certain fish species are more susceptible to histamine accumulation because their muscle tissue naturally contains high concentrations of the precursor amino acid, histidine. These are often migratory pelagic species with dark muscle, which provides the necessary material for bacteria to convert into histamine if mishandling occurs. The fish most frequently implicated in Scombroid Poisoning belong to the Scombridae family, including popular sushi choices like various types of tuna (bluefin and yellowfin), mackerel, and bonito. Other high-risk species include mahi-mahi, marlin, anchovies, sardines, and amberjack (hamachi). These histidine-rich species can develop toxic levels in the shortest amount of time when exposed to warm temperatures, requiring strict adherence to the cold chain.
Practical Steps for Mitigating Risk
Consumers can mitigate the risk of consuming high-histamine sushi by focusing on the establishment’s quality and handling practices. The most effective strategy is choosing restaurants with high volume and quick turnover, suggesting the fish is not sitting for long periods.
Consumer Mitigation Steps
- Ask staff about the sourcing and handling of high-risk fish, such as tuna and mackerel, to gauge their commitment to the cold chain.
- Pay attention to the taste of high-risk species; a tingling, sharp, or peppery sensation indicates elevated histamine levels.
- If this taste is noticed, stop eating immediately.
For those preparing fish at home, proper storage is paramount. The fish must be kept at refrigeration temperatures near or below 0°C (32°F) and consumed quickly. Promptly freezing the fish will stop bacterial growth and prevent further histamine production.