The article presents the results of the assessment of quality and safety of frozen fish of different species (mackerel, pollack, hake) on organoleptic, chemical and microbiological criteria.

Evaluation of the quality of frozen fish, which figures significantly change during the long period of refrigeration storage, has always been important. The biochemical processes that occur in frozen fish, mostly affecting the quality of its manufactured finished products. Since quality is a complex combination of many properties and characteristics of the product, the main difficulty evaluating the state of frozen fish is an objective combination and analysis of all parameters, ie its comprehensive assessment.

The aim of fish processing refrigeration is to preserve its quality indicators for a long time. The basis of preserving fish cold is inhibiting the processes of microorganisms and activity of tissue enzymes. The most valuable is the fish nitrogenous compounds, which in turn are protein and non-protein components. Fish is an important source of protein for human nutrition because its proteins contain all the essential amino acids. More than half of all proteins make up proteins myofibrils of muscle fibers - myosin, actin, actomyosin. The structure of the connective tissue is deficient protein collagen. For breach of refrigeration storage of fish (non temperature, repeated freezing etc.) is hydrolytic breakdown of proteins with the formation of amino acids, nitrogenous substances. This in turn causes a disturbance of tissue turgor, impaired sensory indicators, and processes for deepening decay – deterioration of the product. The high nutritional value of fish has fat because it contains nonsaturated fatty acids, including those that are not in the fat of land animals. In particular fatty acids such as linoleic, linolenic, arachidonic have high biological activity. However, fish oil with high content of unsaturated fatty acids is unstable and easily oxidized.

Failure to comply with the storage conditions, sudden fluctuations in temperature, crash, re-freeze the fish cause deterioration of sensory, chemical and microbiological indexes of product. These changes of products can make a negative impact on human health.

For organoleptic evaluation of quality frozen fish we used the method of sensory analysis (tasting) in combination with descriptive -profile method, which was proposed by american scientists to illustrate the results of sensory perception research. Significant changes during freezing occur with such quality indicators as appearance, texture and glaze. The highest overall assessment of samples in scores received mackerel. Comprehensive assessment of organoleptic characteristics of hake was at 0.07 points, pollock – 0.2 points lower compared with the mackerel. Total profilohrama all studied samples frozen pollock shows a slight deviation of descriptors, mackerel – three and hake – four descriptors.

Glazing surface allows fish extend its storage and protects the product from the negative impact of external factors. Number of glaze on the surface of mackerel was in the normal range and averaged 3.8 %. Number of glaze on the surface of pollock was 4.2 %, hake – 4.5 %, which exceeded the norm by 0.2 % and 0.5 % respectively.

Assessment fish only for organoleptic characteristics is insufficient for a final opinion on its quality, must also identify biochemical indicators. The results of biochemical studies of frozen fish agreement with the data of sensory evaluation. During the study, tests on fresh fish from deviations from organoleptic properties (appearance, smell, texture) were appreciated as doubtful freshness in qualitative reactions to hydrogen sulfide and peroxidase. Number of amino-ammonia nitrogen in samples of fish had uncertain organoleptic – more than 0.7 mg of NaOH, which is a measure of questionable freshness of the product.

Scientists have established installed gradual shift of pH from acidic to neutral rate over a long storage refrigeration, freezing fish at the beginning of a pH within 5.2–5.8, indicating that active hydrolysis of ATP and glycogen accumulation in muscle and lactic acid. After 60 days of storage – 6.7–6.9, a sign of accumulation alkali products as a result of proteolytic changes in proteins. The filtrate from the samples we have studied of questionable freshness of fish was slightly turbid and had a pH of 6.9 and above.

In any sample of frozen fish is not found pathogens. Number of mesophilic aerobic and facultative anaerobic microorganisms in fish ranged from 4,2x10² cells/cm³ to 9,8x10⁴ cells/cm³, which does not exceed the maximum permissible level. The level of total microbial contamination of samples of questionable freshness fish was slightly higher compared to fish without deviations of organoleptic and biochemical parameters. Such raw fish is allowed to be used for technological processing.

We had control in fish the content of certain contaminants (heavy metals, radionuclides, pesticides). These residual amounts were much lower than the maximum permitted levels. Mass fraction of Lead in frozen fish was 0.02±0.006 mg/kg, Cadmium – 0.011±0.009, Arsenic – 0.16±0.071, Silver – 0.023±0.003 mg/kg, which was within regulated standards. Number of Cesium-137 was 7.17±1.507 Bq/kg, Strontium-90 – 10.87±1.586 Bq/kg.

For an objective assessment of the changes that occur in frozen fish, it is necessary to monitor a set of indicators of quality and safety throughout the all term of refrigeration storage.

Key words: frozen fish, safety, quality, sensory evaluation, biochemical parameters, microbiological parameters, toxic elements, radionuclides.