IntroductionThe main objective of aquaculture development is, first of all, sustainable and regular providing the population with fish products that are accessible to people with different income levels, as well as meeting the needs for high quality products. There is a tendency to replace consumption of seafood with aquaculture products. Carp fish provide the largest share of freshwater aquaculture production in the Russian Federation. However, due to the peculiarities of the anatomical structure and a large number of bones, carp is sold mainly in uncut form. Therefore, in order to maximize the use of carp meat, it is proposed to produce minced semi-finished products from it. This will open up new opportunities in the field of rational use of fish raw materials. Carp meat can be separated from the bones using a neopress, which will separate the fish meat from its unclaimed parts. As a result of the neopress, the minced meat is homogeneous, without scales and bones. One of the promising areas of the fish processing industry is producing semi-finished fish products. Nowadays, the assortment of semi-finished products is constantly changing and growing. The pace of life of a modern person increases the demand for products that require a minimum time spending. Preparation of semi-finished products allows improving the taste of the product and increasing the range of fish products. Semi-finished products prepared for frying are popular with the population since they are most convenient for both picnics and everyday use due to their ease of preparation and relatively low price.Fat is one of the most popular types of raw materi-als used in the production of meat products. Fat creates a unique pattern on the cut. The use of fat substitute, which includes a multifunctional mixture of MEATPRO M 750 based on sodium alginate and veg-etable oil, will allow to obtain a product of high and stable quality at the output, since it is resistant to heat, which is important when developing products for grill-ing [1].The purpose of the present work is to substantia-tion of the use of fat substitute in the production of semi- finished fish products.In conformity with the purpose set, the following research tasks have been assigned: – development of a score scale for quality assess-ment; – study of the effect of fat substitute on organoleptic, physico-chemical and structural-mechanical parameters;– substantiation of the shelf life of semi-finished fish products with fat substitute.Object and methods of research The objects of the research were samples of semi-finished fish products with fat substitute and those without fat substitute (control) for grilling. During the experiment, a batch of semi-finished products (grilled fish sausages) has been produced, where the main raw material has been common carp (Cyprinus carpio) according to GOST 814-2019 [2] and auxiliary com-ponents, such as dietary fiber (Kametsel FS 180) ob-tained by import, approved for use by the Office of Rospotrebnadzor and flavoring mixture RUTAFISH mixture 6, made according to TR 10.84.12-004-56746846-14. Vegetable (sunflower) oil according to GOST 1129-2013 [3] has been used as a fat-containing component in manufacturing of fat substitute. The fat structure is provided by the addition of MEATPRO M 750 with sodium alginate. To determine the shelf life, samples of semi-finished fish products have been prepared, which, after molding and sedimentation, have been boiled to a temperature of 71 ± 1°C in the center of the product and packed under vacuum. The expected shelf life is 10 days at 0-2°C. The product has been controlled at the background point, on the 6th, 10th and 13th days according to MG 4.2.2046-06 [4]. The organoleptic characteristics of semi-finished fish products were evaluated through-out the entire storage period, except for the stock point, according to the developed point scale. The yield point has been determined using a hand-held portable penetrometer according to GOST R 50814-95 [5]. The moisture content and moisture retaining power (MRP) have been established according to GOST 7636-85 [6]. Sanitary and microbiological studies have been carried out using the following methods: the number of mesophilic aerobic and facultative anaerobic microorganisms has been determined according to GOST 10444.15-94 [7], coli-form bacteria – according to GOST 31747-2012 [8], S. aureus – according to GOST 31746-2012 [9], sulfite-reducing clostridia – according to GOST 29185-2014 [10], Proteus bacteria – according to GOST 28560-90 [11], molds and yeasts – according to GOST 10444.12-2013 [12], Salmonella bacteria – according to GOST 31659-2012 (ISO 6579: 2002) [13], Listeria monocytogenes – according to GOST 32031-2012 [14].Results and discussionMoisture retaining power is one of the most impor-tant indicators of semi-finished products, which are further subjected to additional processing before use. As a result of heat treatment, part of the moisture and fat is separated, which can be expressed as weight loss or purge. Such organoleptic indicators as juiciness, tenderness and losses during heat treatment depend on the MRP. The values of water-holding capacity of samples of semi-finished fish products during stor-age are shown in Fig. 1. Fig. 1. Dynamic pattern of MRP: WHC – water holding capacity It can be seen from Fig. 1 that the value of the MRP decreases over time. Samples of semi-finished fish products, which contain fat substitute, have higher water-holding capacity than control ones. This is due to the fact that fat substitute contains sodium alginate, which binds water well, and an increase in the water-holding capacity of the sample is probably associated with this. As an objective indicator of consistency, the yield point value (YPV) is used, which has been calculated according to GOST R 50814-95. This indicator can be used to assess the quality of minced meat and finished products. Measurements were taken on an optical projection scale in degrees of penetration, where the degree of penetration is 0.1 mm. The results are pre-sented in Fig. 2. Fig. 2. Dynamic pattern of the yield point, Pa From the data presented in Fig. 2, it can be seen that over time, the YPV decreases. This is due not only to a decrease in MRP, but also to an increase in expo-sure time. A sample with the addition of fat substitute is less susceptible to the YPV changes compared to the control one.To assess the quality of samples of semi-finished fish products, a technique [15] has been used and a 5-point scale has been developed. The main principle of quality assessment is to highlight the features that characterize non-standard products. Deviations of se-mi-finished fish products that may result from the addition of fat substitute have been identified. Points have been set in the following order: 5 – full compliance with the requirements; 4 – single minor inconsistencies; 3 – numerous minor inconsistencies; 2 – significant inconsistencies; 1 – gross inconsisten-cies; 0 – not subject to evaluation. Samples with a score below 3 (inclusive) were not standard and should not be implemented. For identified inconsisten-cies, points have been reduced taking into account severity of the defect, options for reducing the score are given in Table 1. Table 15-point scale of organoleptic quality assessmentAppearance а5 – straight or slightly curved loaves, without damage to the shell, slips, spots, sagging minced fishIrregular shaped products432–Presence of bacon or minced fish on the surface of the shell432–A product with dirty surface–32–Slimming of the shell–––0Shell breaks–32––––––Sectional view b5 – Minced fish is evenly mixed, without voids; in the presence of fat - it does not separate from the minced fish and is well connected with muscle tissueMinced fish is not well mixed432–Fat in separated from minced fish432–Presence of foreign matter–32–Fat is unevenly distributed432–Indistinct cut pattern 432––––––Presence of voids in minced fish432––––––Color c5 – uniformly colored muscle tissue from gray to light pink; in the presence of fat – the color of the fat is white or with a pinky shadeHeterogeneous color432–Insufficiently expressed color43––Overly bright color432––––––The color is not typical for this type of product432––––––Taste and smell d5 – characteristic of this type of product, with the aroma of spices, without foreign taste and smell, the taste is moderately saltyPredominance of the taste of indi-vidual components in minced fish432–Prevalence of the smell of:– spices– other components43––Taste of oxidized fat––21No strong smell of:– species– other components43––Foreign flavor not characteristic of this product––21Acrid taste of smoke––21The taste of individual components in minced fish is not pronounced43––Putrid smell–––0Smell of mold or yeast–––0–––––Consistency e5 – dense Too dense consistency432–Rubber-like432–Soft, mealy432–Crumbly432–Spreadable432–––––– The overall score is calculated by the formula Fish semi-finished products tasting assessment results are shown in the Fig. 3. Fig. 3. Organoleptic evaluation of samples of semi-finished fish products in storage:а – background; b – 6th day; c – 10th day; d –13th day As can be seen from Fig. 3, both samples have got high marks. The presence of fat substitute did not cause negative assessments among the tasters, on the contrary, the sample with fat substitute turned out to be juicier and attractive.To determine the compliance of semi-finished fish products with microbiological safety indicators, the regulatory parameters provided for by TR TI 021/2011 and TR EAEU have been used [16, 17]. Microbiological tests have been carried out during the entire period of storage of samples, taking into account the reserve ratio. During the entire period of storage, sanitary indica-tive bacteria of the intestinal group (coliforms), oppor-tunistic (Staphylococcus aureus, Proteus bacteria) and pathogenic bacteria (Salmonella, Listeria monocytogenes bacteria) have not been detected in the control sample and in the sample with fat substitute, which confirms their sanitary security.The dynamic pattern of QMAFAnM indicator in the samples of semi-finished fish products during stor-age is shown in Table 2. Table 2Change of QMAFAnM indictor in samples of semi-finished fish productsControl dayRegulatory value, CFU/gControl sample, CFU/gSample with fat substitute, КОЕ/гBackground1 • 105Less than 106th dayLess than 1010th dayLess than 1013th day3,5 • 1025,9 • 103 During the entire storage period, both for the con-trol sample and for the sample with fat substitute, pathogenic microorganisms (Salmonella, L. monocyto-genes bacteria) have not been detected. Coliforms, S. aureus, Proteus bacteria have not also been detected in all samples of the product. The results presented in Table 2 show that the pro-totypes during storage have microbial contamination lower than the standard value. After 10 days of stor-age, growth of microflora has been observed. The mi-croflora of the samples is represented mainly by Bacil-lus bacteria, which formed large membranous colonies on fish-peptone agar. No significant difference has been found in the mi-crobial contamination of the control sample and the sample with fat substitute, which shows the possibility of its use. Based on the data obtained, the shelf life of semi-finished fish products has been established, which is 10 days at temperatures from 0 to 2°C.Conclusions 1. Influence of the fat substitute on the indicators of MRP and YPV has been studied. It has been shown that addition of fat substitute increases MRP and re-duces YPV, which indicates a juicier consistency and fewer losses during heat treatment.2. A 5-point scale for organoleptic quality assess-ment has been developed. The study of changes in organoleptic indicators bears evidence of a good stor-age capacity without signs of spoilage within the pre-scribed period. Study of changes in organoleptic pa-rameters indicates the storage capacity of fish semi-finished products without signs of spoilage at a stated time.3. Shelf life of semi-finished fish products has been established, which is 10 days at a temperature from 0 to 2°С.