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Hot smoked fish should fulfill the requirements set up for ready-to-eat foods. The total bacterial count on the raw material is 10(3) to 10(5) CFU per cm2 of skin and 10(2) to 10(9) CFU per gram of intestines. Contamination with pathogenic bacteria is very low, mainly with Clostridium botulinum, Listeria monocytogenes, Staphylococcus aureus, and Vibrio parahaemolyticus. In the premises of low hygiene, the contamination may increase due to unsanitary procedures, rotation of assigned duties of workers, and airborne microorganisms during packing of the product. Hot smoking in mild conditions at temperature in the fish not exceeding 65 degrees C and low concentration of salt does not inactivate all pathogens or inhibit bacteria during storage. Thus the required safety can be obtained only by using very fresh fish handled in hygienic conditions, controlling the processing and the plant hygiene in critical control points, and chilling of the product to about 2 degrees C. Most critical are the hygienic conditions in handling of the product after smoking. The use of preservatives for extending the shelf life of smoked fish is being investigated. High-quality shelf life of mild hot smoked mackerel at about 2 degrees C is at least 3 weeks.

Fish protein concentrates are mixtures of cross-linked and aggregated molecules of different muscle proteins. The final conformation of the components of the mixtures is formed as a result of procedures applied to convert the raw materials into a product of desirable and stable sensory properties, containing less than 0.1% of lipids. To achieve this end usually extraction with hot organic solvents, mainly isopropyl alcohol and 1,2-dichloroethene, followed by air drying are employed. These conditions bring about denaturation of many of the proteins followed by aggregation of the molecules due to the interaction of reactive functional groups in extended polypeptide chains. In the final product a large proportion of hydrophobic groups is exposed to the solvent and the proteins exhibit an extremely low water affinity. Such concentrates, although valuable as protein supplements, have only limited suitability as active components of various processed foods, as they have poor technological value. They are insoluble or have a very low water dispersibility and swelling ability, do not form gels after heating, or have any significant fat-emulsifying capacity. Changing the dissociation or number of ionic groups of the molecules prior to extraction, e.g., by acidifying or acylating, can partially reduce the denaturing effect of heat and organic solvents and thus improve the functional properties of the product. An upgrading of the quality of concentrates produced by hot extraction can be achieved by partial enzymatic or chemical deaggregation, hydrolysis followed by the plastein reaction, or formation of suitable derivatives. The best results have been obtained by partial hydrolysis of acylated proteins or precipitation of the aggregated products using sodium hexametaphosphate. The functional properties of such products are comparable to those of vegetable protein isolates used as meat extenders. Various proteins of high technological value can be also obtained by enzymatic hydrolysis of the raw material, followed by separation of the lipids without organic solvent extraction. Such products, however, have a distinct odor and flavor and must be stabilized because of residual lipids.