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UDC 641.1:[637.56:639.231		DOI: https://doi.org/10.31617/tr.knute.2019(29)07
Olena ROMANENKO, E-mail: Ця електронна адреса захищена від спам-ботів. вам потрібно увімкнути JavaScript, щоб побачити її. ORCID: 0000-0003-1804-1225		PhD in Technical Sciences, Associate Professor, Associate Professor at the Department of Commodity Science, Safety and Quality Management, Kyiv National University of Trade and Economics 19, Kyoto str., Kyiv, 02156, Ukraine
Olena SYDORENKO, E-mail: Ця електронна адреса захищена від спам-ботів. вам потрібно увімкнути JavaScript, щоб побачити її. ORCID: 0000-0001-5919-4370		Doctor of Sciences (Technical), Professor, Professor at the Department of Commodity Science, Safety and Quality Management, Kyiv National University of Trade and Economics 19, Kyoto str., Kyiv, 02156, Ukraine
Svitlana SHAPOVAL,   E-mail: Ця електронна адреса захищена від спам-ботів. вам потрібно увімкнути JavaScript, щоб побачити її. ORCID: 0000-0001-7650-8597		Vice rector on scientific and pedagogical work, PhD in Technical Sciences, Associate Professor, Associate Professor at the Department of Engineering and Technical Disciplines, Kyiv National University of Trade and Economics 19, Kyoto str., Kyiv, 02156, Ukraine

STRUCTURAL-MECHANICAL PROPERTIES
OF FISH PRESERVES DURING STORAGE

Background. Structural-mechanical properties, along with the organoleptic and physical-chemical, are an essential criterion for choosing products by consumers. However, structural, mechanical, physical-chemical and organoleptic properties do not remain stable throughout the shelf life, in particular for fish preserves.
The dynamics of the rheological properties of fish preserves depends on chemical changes, and indirectly indicates their intensity, what can be used in developing new express methods for analyzing individual fish quality parameters through the establishment of rheological characteristics and correlation dependencies.
The aim of researches – determination of the dynamics of structural and mechanical parameters of preserves from freshwater (grass carp and silver carp) and sea (herring) fish during storage and determination of influence of their general chemical composition, fractions of fish preserves fat on structural and mechanical properties.
Materials and methods. Research objects – fish preserves are made according to technological instructions: sample 1 – from herring; sample 2 – from grass carp (ctenopharyngodon idella) with barberry; sample 3 – from the silver carp (hypophthalmichthys) with vegetables. Each sample is selected for 40 pieces of fillet. The shelf life of preserves is 5–45 days.
The structural-mechanical properties are determined on the multifunctional measuring complex MIG-1.4 by the Reology module. The fractional composition of lipids of fish preserves was carried out by thin-layer chromatography; moisture content was determined by drying method, fat by the Soxhlet method, protein content (total nitrogen) by Kjeldahl method, mineral elements by X-ray fluorescence analysis on ElvaX-Med.
Results. The protein content of preservative samples ranges from 11.9 to 10.9 %. After 45 days of storage, it decreases, as there is partial denaturation of proteins and the appearance of amino acids. The moisture content is increased somewhat in finished preserves. These changes affect the structural and mechanical properties, in particular, the consistency that becomes softer during the shelf life of preserves.
The dynamics of reducing the strength of the surface of preserves is established. The reduction in the structure's strength in herring preserves is faster by 28.3 % than in grass carp preserves and 31.6 % faster than in silver carp preserves.
After storage, there were slight changes in the index of active acidity in all samples of preserves. The pH of samples studied with berries and vegetables after 45 days of storage increased only by 0.28–0.33, and the pH of the sample with herring was 0.5, indicating the stability of preserves for storage.
The correlation coefficient between the indicator of active acidity and the strength limit of the sample surface of herring preserves is –0.72; for preserves from the silver carp –0.65; from the grass carp –0.68. Relatively small values of the relaxation effort for preserves from freshwater fish indicate the expediency of their storage only in solid containers.
Conclusion. According to the analysis of the general chemical composition of fish preserves, it has been established that decreasing the protein content and increasing the moisture content during storage affects the consistency, which becomes softer. Changes in the fatty acid composition of preserves during storage are negligible and due to the hydrolysis of lipids.
According to the results of research of structural and mechanical parameters of fish preserves, it was established that the surface strength of samples of preserves from grass carp and silver carp decreases by 17.6 and 18.3 % faster than the strength of preserves from herring.
The inverse correlation dependence between the structural-mechanical properties and the active acidity of the preserves is observed.
It is established that the dynamics of structural and mechanical properties of preserves from freshwater fish is significantly different from the change in the relaxation force of preserves from herring. Therefore, preserves from freshwater fish are best kept in solid containers.
 
Keywords: preserves, silver carp, herring, structural and mechanical properties, fractional fat composition, relaxation effort, penetration.

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