Contents Index

Handling and Processing Mackerel













Accompanying Notes
Table of Contents


J. N. KEAY

MINISTRY OF AGRICULTURE, FISHERIES AND FOOD
TORRY RESEARCH STATION

TORRY ADVISORY NOTE No. 66 (REVISED)

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Accompanying Notes


Provides general notes on mackerel, including common and scientific names, distinguishing features, life history, length, weight, distribution and the fishery. The UK mackerel fishery has fluctuated considerably. As the herring catch declined, UK pelagic supplies were maintained by diversion of the fleet to mackerel in the 1970s. In 1970, the total UK catch was 4,600 tonnes; it peaked at about 300,000 tonnes in 1987 and declined to about 54,100 tonnes in 1998, valued at 21.6 million. The Note gives information on handling at sea and onshore, signs of stale fish, chilling, freezing, cold storage, cold and hot smoking, production of pt, canning, salting, shelf life, and chemical composition. Plastic laminate bags with a discontinuous, rough, outer layer can be used for freezing blocks of whole fish in the vertical plate freezer. The rough outer layer increases the friction between blocks and helps to prevent stacks of blocks slipping due to movement of the ship or when stacked on a pallet. In addition to Note 48 referenced in the text, the following Notes are relevant, 22, 73, 75, 79, 82 and 96.

Depending on feeding conditions and the ambient temperature, mackerel may rapidly develop burst bellies after catching as a result of intense enzyme activity in the gut. Rapid chilling to 0C is essential to help control this problem. Fish with burst bellies should not enter the food chain and should be discarded. A condition called 'blackberry mackerel' has been described. The fish have a sulphide odour and flavour due to the presence of dimethyl sulphide, produced when feeding on the pteropod mollusc, Spiratella retroversa.

The Note refers briefly to mackerel and poisoning. From time to time consumers become mildly ill after eating mackerel products with what has been described as histamine poisoning. This type of illness has been associated with a variety of scombroid fish, including tuna, as well as other non-scombroid, dark fleshed , fatty fish species, such as sardines and anchovies, and is often referred to as scombroid fish poisoning. It is thought to be the most common form of seafood poisoning world-wide. Generally, it has been associated with high levels of histamine in the flesh (greater than 50 mg/100 g) produced by bacteria in the spoiling fish which decarboxylate the naturally high levels of histidine in the flesh of these fish. Illness has also occurred when the histamine levels have been very much lower (less 5 mg/100 g). The real cause of this illness has not been clearly established and other, but so far unproven, suggestions about the causative factor(s) have been made. However, since the spoilage flora is implicated in the problem, rapid chilling after catching, and effective chilling below 5C during subsequent handling, before and after smoking, and during processing and distribution is strongly recommended. Controls on histamine concentrations vary in different countries, and the relevant food legislation should be consulted.

Hot smoked mackerel products are intended for eating without any further heating. More recent advice about the safety of smoked products that can be eaten without further cooking recommends a minimum salt concentration of 3.5% (weight by weight) in the water phase and keeping the product chilled below 5C throughout the distribution chain. Particular attention should be given to the control of the botulinum risk if the product is to be vacuum packed because C. botulinum can grow in the absence of oxygen (anaerobic conditions) and because of the inhibition of competing spoilage organisms. . Further information about the important distinction between salt content of the flesh and salt concentration in the water phase can be found in Notes 22, 66, 74 and 82. The following practices should always be part of process control:

The current food legislation should be consulted with respect to the use of colours or dyes and the labelling of products.

(FAO in partnership with Support unit for International Fisheries and Aquatic Research, SIFAR, 2001).


Table of Contents


Introduction
Scientific name
Common name
Distinguishing features
Life history
Length and weight
Distribution
The fishery
Composition of mackerel
Chilled and frozen storage
Smoked mackerel
Mackerel pate
Canned mackerel
Salted mackerel
Mackerel and poisoning

Contents Index