Low-temperature quick-freezing method for keeping fresh of black carp

Abstract

The application provides a low-temperature quick-freezing preservation method for grass carp, which comprises the following steps: soaking the treated grass carp in a solution containing sarcosine and dextran for 8 min, wherein the temperature of the solution is 9 DEG C; and then taking out the grass carp and performing low-temperature quick-freezing by spraying liquid nitrogen at-100 DEG C. The method can not only significantly improve the preservation ability of the grass carp and prolong the sales time of the grass carp, but also maximally ensure the taste, water retention, integrity, nutritional quality and edible value of the grass carp.

Description

Technical Field

[0001] This invention belongs to the field of aquatic product preservation technology, specifically, it relates to a method for low-temperature quick-freezing preservation of grass carp. Background Technology

[0002] Grass carp (Mylopharyngodon piceus), also known as black carp or blue carp, mainly grows and is distributed in areas south of the Yangtze River. It is unaffected by seasons and is available year-round, making it one of the four major freshwater aquaculture species in my country. Grass carp has thick, delicious flesh, rich in easily absorbed nutrients such as protein, nucleic acid, and fat. It also contains trace elements such as calcium, phosphorus, iron, selenium, and iodine, which can resist aging and prevent cancer. In particular, it contains eicosapentaenoic acid (EPA), which can regulate blood lipids and prevent blood clotting and blood vessel blockage, and docosahexaenoic acid (DHA), which can participate in promoting the growth and development of brain and nerve cells.

[0003] In 2017, the processing rate of freshwater products in my country reached 18.36%, with a total volume of 4.0819 million tons, which were 4.18 times and 5.78 times that of 2003, respectively. However, the development of grass carp farming in my country is still at a relatively low level, with many shortcomings in production, processing, and transportation methods. The processing and preservation technologies used for farming and sales in various regions mainly rely on drying, refrigeration, and freezing, with freezing remaining the most effective method for maintaining quality. Currently, grass carp is often sliced ​​and frozen at -18℃ before cold chain transportation. However, freezing the water in the fish meat leads to decreased water-holding capacity, juice loss, protein denaturation, and fat peroxidation, resulting in a deterioration in fish quality. There is a need to find and adopt new freezing methods to extend the sales time of grass carp and improve its economic benefits. Liquid nitrogen ultra-low temperature freezing of freshwater fish has become a new consumer trend and is an inevitable trend.

[0004] Liquid nitrogen is a product obtained by liquefying ammonia gas in the air using a special device. It is colorless, odorless, chemically stable, and does not react with food. Liquid nitrogen quick-freezing technology utilizes the property of liquid nitrogen (boiling point -195.8℃) to absorb a large amount of heat instantly upon vaporization. When it comes into contact with food to be frozen, it rapidly absorbs the food's latent and sensible heat, achieving almost simultaneous freezing from the inside out. This causes the formation of uniform, fine ice crystals within the food's cellular structure, resulting in minimal damage and preserving the food's original quality and flavor to a great extent. Liquid nitrogen quick-freezing technology is environmentally friendly and can achieve lower temperatures and better cooling rates. Its fast freezing speed, short freezing time, high-quality frozen food, high safety, and no pollution make it a new trend in the frozen food industry. Therefore, research and industrial application of liquid nitrogen quick-freezing technology for preserving herring meat has significant practical implications, helping to solve problems in industrial production and promoting the sustainable development of liquid nitrogen quick-freezing technology in the food industry.

[0005] However, there are currently no clear methods or measures for maximizing the freshness of grass carp and extending its sales period.

[0006] Therefore, there is an urgent need to find a low-temperature quick-freezing preservation method for grass carp, screen out suitable methods and temperatures, improve the preservation ability of grass carp through low-temperature quick-freezing, extend its sales time, and maintain the original quality of grass carp. Summary of the Invention

[0007] To address the problems existing in the prior art, this invention provides a method for low-temperature quick-freezing and preservation of grass carp. By immersing the treated grass carp in a solution containing sarcosine and dextran, and then removing the grass carp and quick-freezing it with liquid nitrogen at -100°C, the preservation ability of the grass carp is significantly improved, extending its sales time. Simultaneously, it maximizes the preservation of the grass carp's taste, water retention, integrity, nutritional quality, and edible value.

[0008] To achieve the above objectives, the present invention employs the following solution:

[0009] On the one hand, the present invention provides a method for low-temperature quick-freezing and preservation of grass carp, comprising the following steps:

[0010] 1) Soak the treated grass carp in a solution containing a certain composition;

[0011] 2) After removing the grass carp, quick-freeze it at different temperatures;

[0012] The composition comprises any combination of sarcosine, arginine, glycine or glutamic acid with sucrose or dextran.

[0013] Preferably, the composition includes sarcosine and dextran.

[0014] In some embodiments, the composition was screened, and the experimental results showed that when sarcosine and dextran were preferably combined, the quality of the resulting grass carp fillets was closest to that of fresh grass carp, with no significant difference (p>0.05). However, compared with the quality of grass carp fillets soaked in other single compounds, soaked in the composition solution, and unsoaked, the grass carp fillets soaked in the sarcosine and dextran composition solution showed significantly improved water-holding capacity, salt-soluble protein content, and textural properties, with significant differences (p<0.05).

[0015] Furthermore, in the composition, the mass ratio of sarcosine to dextran is 1:2.

[0016] In some embodiments, the mass ratio of sarcosine to dextran in the composition was screened. Experimental results showed that when the preferred mass ratio of sarcosine to dextran was 1:2, the quality of the grass carp fillets was closest to that of fresh grass carp, with no significant difference (p>0.05). However, compared to grass carp fillets soaked in solutions with other proportions, those soaked in a solution with a sarcosine to dextran mass ratio of 1:2 showed significantly improved water-holding capacity, salt-soluble protein content, and textural properties, with significant differences (p<0.05). Therefore, the preferred mass ratio of the composition for soaking grass carp is sarcosine:dextran = 1:2.

[0017] Furthermore, the solution contains 15 g / L of sarcosine and 20 g / L of dextran.

[0018] Furthermore, in step 1), the temperature of the solution is 6–12°C, and the soaking time is 6–10 min.

[0019] Preferably, in step 1), the temperature of the solution is 9°C and the soaking time is 8 minutes.

[0020] In some embodiments, the temperature of the soaking solution was screened. Experimental results showed that when the solution temperature was set at 6–12°C, the quality of the resulting grass carp fillets was closest to that of fresh grass carp, with no significant difference (p>0.05), and the grass carp fillets with the best quality were obtained at a solution temperature of 9°C. Compared with other groups of grass carp fillets soaked in solutions at different temperatures, the grass carp fillets with a solution temperature of 6–12°C showed significantly improved water-holding capacity, salt-soluble protein content, and textural properties, with significant differences (p<0.05). Therefore, the preferred soaking solution temperature is 6–12°C, and the grass carp fillets with the best quality are obtained at a solution temperature of 9°C.

[0021] In some implementations, the soaking time was selected. Experimental results showed that when the soaking time was set to 6–10 min, the quality of the grass carp fillets was closest to that of fresh grass carp, with no significant difference (p>0.05). Furthermore, the grass carp fillets had the best quality when soaked for 8 min. Compared with other groups of grass carp fillets soaked for different times, those soaked for 6–10 min showed significantly improved water-holding capacity, salt-soluble protein content, and textural properties, with significant differences (p<0.05). Therefore, a soaking time of 6–10 min is preferred, and the grass carp fillets have the best quality when soaked for 8 min.

[0022] Further, in step 2), the temperature includes one or more of -18℃, -30℃, -60℃, -80℃, -100℃, and -196℃; -100℃ is quick-freezing by spraying with liquid nitrogen; and -196℃ is quick-freezing by immersion in liquid nitrogen.

[0023] Preferably, in step 2), the temperature of liquid nitrogen cryogenic freezing is -100℃.

[0024] In some implementations, experiments were conducted to investigate the effects of different freezing temperatures on different freezing rates, as well as the effects of different freezing temperatures on the water-holding capacity, K value, salt-soluble protein content, and texture of grass carp. The experimental results showed that when the freezing temperature was -196℃ (i.e., the freezing rate was 3.05℃ / min), the quality of the grass carp fillets could be maintained to the maximum extent. However, considering factors such as cost, the most suitable method for quick-freezing grass carp fillets was liquid nitrogen spray quick-freezing at -100℃, with a freezing rate of 1.34℃ / min.

[0025] On the other hand, the present invention provides the use of a composition for preparing an agent that improves the freshness preservation ability of grass carp during low-temperature quick-freezing, said composition comprising sarcosine and dextran.

[0026] In some embodiments, the quality of grass carp fillets soaked in a solution of sarcosine and dextran was closest to that of fresh grass carp, with no significant difference (p>0.05). This may be because sarcosine ions are amphoteric, thus inhibiting pH changes in the solution during the low-temperature preservation and freeze-drying of biological products, thereby protecting the active components; dextran can inhibit the growth of ice crystals and provide freezing stability, thereby achieving low-temperature protection. When the two are combined, a liquid protective film can be formed on the surface of the grass carp, preventing moisture loss during freezing and storage, ensuring the tenderness of the grass carp meat after freezing, and improving the freezing preservation time and effect of grass carp.

[0027] In another aspect, the present invention provides the use of a composition for preparing an agent that improves the taste and nutritional value of frozen herring, characterized in that the composition comprises sarcosine and glucan.

[0028] The beneficial effects of this invention are as follows:

[0029] 1. This invention provides a method for quick-freezing and preserving grass carp at low temperature. The method involves immersing the treated grass carp in a solution containing a composition of sarcosine and dextran for 8 minutes at a temperature of 9°C. The grass carp is then removed and quick-frozen by spraying liquid nitrogen at -100°C. This method not only significantly improves the preservation ability of grass carp and extends its sales time, but also maximizes the preservation of the grass carp's taste, water retention, integrity, nutritional quality, and edible value. At the same time, it controls the overall cost, significantly reducing costs while maximizing the preservation ability of grass carp after freezing.

[0030] 2. The low-temperature quick-freezing preservation method for grass carp provided by this invention provides technical support and new ideas for maximizing the preservation of grass carp and extending its sales time, and has good application prospects. Attached Figure Description

[0031] Figure 1 These are the freezing curves at different freezing rates in this invention. Detailed Implementation

[0032] The present invention will be further described in detail below with reference to the embodiments. It should be noted that the embodiments described below are intended to facilitate the understanding of the present invention and do not limit it in any way.

[0033] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0034] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0035] Example 1: Low-temperature quick-freezing preservation method for grass carp

[0036] This embodiment provides the optimal operating procedure and conditions for the low-temperature quick-freezing preservation method of grass carp. The specific steps are as follows:

[0037] 1. Main raw materials and reagents

[0038] The grass carp were purchased from the West Lake District Aquatic Products Market in Hangzhou. Fresh grass carp with plump bellies, purplish-red gills, bulging eyes, shiny surface, intact scales, and no mucus were selected.

[0039] BCA kit, Shanghai Beyotime Biotechnology Co., Ltd.; KCl solid, ATP solid, NaOH solid, KHPO4 solid, HClO3, liquid nitrogen, CuSO4 solid and other chemical reagents are all analytical grade, Shanghai Guoyao Chemical Reagent Co., Ltd.

[0040] 2. Main Instruments and Equipment

[0041] BSA124S-CW Electronic Analytical Balance: SARTORIUS Group, Germany

[0042] TMS-Pro Texture Analyzer: FTC Instruments, Inc., USA

[0043] T-18 Homogenizer: IKA Instruments GmbH, Germany

[0044] Color Quest XE Colorimeter: Hunter Lab Instruments, Inc., USA

[0045] Sorvall LYNX 4000 High-Speed ​​Floor-Standing Centrifuge: Thermo Fisher Scientific, USA

[0046] Evolution 60s UV spectrophotometer: Thermo Fisher Scientific, USA

[0047] pH meter: Shanghai Mettler Toledo Instruments Co., Ltd.

[0048] Liquid nitrogen spraying equipment: Custom-made by Air Chemical Company

[0049] Ultra-low temperature freezers: Qingdao Haier Co., Ltd.

[0050] CRYOSTAR NX50 Cryostat Slicer: Thermo Fisher Scientific (China) Co., Ltd.

[0051] Water bath: Shanghai Yiheng Technology Co., Ltd.

[0052] 3. Sample processing

[0053] Fresh grass carp were brought back to the laboratory within 30 minutes in an ice box containing crushed ice. The head, tail, and internal organs were immediately removed, and the fish were then rinsed with ultrapure water at low temperature. The grass carp samples were then soaked in a solution containing a combination of sarcosine and dextran, with a mass ratio of sarcosine to dextran of 1:2. The solution temperature was 9°C, and the soaking time was 8 minutes. The solution contained 15 g / L of sarcosine and 20 g / L of dextran.

[0054] After soaking, the grass carp fillet samples were removed and quick-frozen by spraying with liquid nitrogen at -100°C. The temperature was measured using a center thermometer (Funa Technology (Beijing) Co., Ltd., TP101). When the center temperature of the sample reached -100°C, the freezing was considered complete. The frozen samples were then stored in a -100°C cold storage.

[0055] This embodiment provides an optimal method for low-temperature quick-freezing and preservation of grass carp. The method involves immersing the treated grass carp in a solution containing a composition of sarcosine and dextran at a mass ratio of 1:2 for 8 minutes at a solution temperature of 9°C. The grass carp is then removed and quick-frozen by liquid nitrogen spraying at -100°C. This significantly improves the preservation ability of grass carp, extends its sales time, and maximizes the preservation of its taste, water retention, integrity, nutritional quality, and edible value while controlling costs.

[0056] Example 2: Effect of different freezing temperatures on the quality of herring fillets

[0057] To obtain the optimal freezing temperature in Example 1, experiments were conducted in this example to investigate the effects of different freezing temperatures on different freezing rates and the effects of different freezing temperatures on the water-holding capacity, K value, salt-soluble protein content, and texture of grass carp (the main raw materials, reagents, instruments, and equipment were as described in Example 1; all the above experiments were conducted after being frozen in a cold storage for 3 months).

[0058] 1. Experimental Methods

[0059] 1.1 Sample preparation

[0060] Fresh grass carp were brought back to the laboratory within 30 minutes in an ice box containing crushed ice. The head, tail, and internal organs were immediately removed, and the samples were then cleaned with ultrapure water at low temperature. The grass carp samples were divided into 7 groups: (1) fresh samples (control); (2) samples quick-frozen at -18℃; (3) samples quick-frozen at -30℃; (4) samples quick-frozen at -60℃; (5) samples quick-frozen at -80℃; (6) samples quick-frozen by spraying liquid nitrogen at -100℃; and (7) samples immersed in liquid nitrogen at -196℃. The temperature of each group of samples was then measured using a central thermometer. When the central temperature of each group of samples reached the target temperature, the freezing was considered complete. The frozen samples were placed in cold storage at the corresponding temperature for freezing (groups 2 to 5 were directly placed in a quick-freezing cabinet for quick freezing; group 6 was quick-frozen at -100℃ by spraying liquid nitrogen and controlling the amount of liquid nitrogen spray; group 7 was immersed in liquid nitrogen at -196℃).

[0061] 1.2 Freezing curves and rate determination methods at different freezing temperatures

[0062] The temperature during the sample freezing process was measured using a temperature sensor, and the temperature was recorded every 2 seconds. The curve showing the temperature change over time is the sample freezing curve. The time required for the sample to pass through the maximum ice crystal formation zone (-1 to -5℃) is the sample phase transition time.

[0063] Freezing rate (°C / min) = (T2-T1) / (t2-t1) × 60

[0064] Where T2 = -1℃, T1 = -5℃, and t2 - t1 represents the phase transition time (s).

[0065] 1.3 Methods for determining water retention

[0066] Thawing loss (TL) is calculated by measuring the weight change of meat before and after thawing.

[0067] TL=(W1-W2) / W1

[0068] Where: W1: weight of fish meat before thawing, g; W2: weight of fish meat after thawing, g.

[0069] The loss rate during steaming is approximately 5.0g (W) when cut from the back of the fish. a The fish fillets were placed in a beaker and weighed, and the weight was recorded as W. b Place the beaker in an 80°C water bath and heat for 30 minutes. After cooling to room temperature, wipe off the surface moisture and weigh the sample (W). c ).

[0070] Cooking loss rate (%) = (W b -W c ) / W a ×100

[0071] 1.4 Methods for determining textural properties

[0072] Take a sample of the fish's back muscle, thaw it at room temperature, and cut it into 2×2×1cm pieces. 3 For small pieces, a texture analyzer with a cylindrical probe was used. During the measurement, the probe entered the sample at a speed of 1 mm / s, the deformation was 50%, the holding time was 5 s, the triggering force was 0.1 g, the return speed was 2 mm / s, and the measurement was performed twice.

[0073] 1.5 Determination of Salt-Soluble Proteins

[0074] Accurately weigh 2g of fish meat and add 20mL each of low-ion phosphate buffer (0.025mol / L NaH2PO4-0.025mol / L Na2HPO4) and high-ion phosphate buffer (0.5mol / L KCl-0.01mol / L NaH2PO4-0.03mol / L Na2HPO4), homogenize for 5min to mix thoroughly, and centrifuge at 4000r / min for 10min after 1h and 3h, respectively. Take the supernatant, add 15% trichloroacetic acid to precipitate the protein, dissolve the fish meat protein with 1M NaOH, and make up to 50mL with low- and high-phosphate buffers, respectively. All the above operations were performed at 4℃.

[0075] Salt-soluble protein content was determined using a BCA kit.

[0076] 1.6 Data Analysis

[0077] All experiments were repeated at least three times. Data are expressed as mean ± standard deviation. Excel 2010, SPSS 25 software, and ANOVA were used for data processing and significance analysis. Note: p < 0.05 indicates a significant difference.

[0078] 2. Experimental Results

[0079] 2.1 Effects of different freezing temperatures on freezing time and freezing rate of grass carp

[0080] The freezing rate, which is adjusted by controlling the operating temperature of the blast freezer, is shown in Table 1. It can be seen that the freezing rate gradually increases as the temperature decreases.

[0081] Table 1 Freezing rates of liquid nitrogen quick-freezing cabinets at different operating temperatures

[0082]

[0083] The freezing curve is divided into three stages: the first stage is the initial stage, from the initial temperature at the start of freezing to the freezing point, the sample temperature drops rapidly, releasing sensible heat. At this point, the sample reaches the crystallization temperature, and ice crystals begin to form. The second stage is the phase transition stage, where most of the water in the sample transforms into ice crystals. In this stage, the sample temperature drops relatively slowly, the freezing curve tends to be flat, and the duration is relatively long. The phase transition stage is called the maximum ice crystal formation zone and is a critical stage in the food freezing process, which can greatly affect the quality of the food. (Refer to Table 1 and...) Figure 1 As shown, under the freezing rate condition, the phase transition time of the frozen sample decreases significantly with increasing freezing rate. This may be due to the limitations of the sample's own heat transfer characteristics; when the temperature decreases to a certain level, the phase transition time no longer changes significantly. The third stage is the supercooling stage, in which the remaining water continues to freeze, and ice crystals continue to crystallize. Figure 1 As can be seen, due to the higher thermal conductivity of ice than water, the temperature in this stage shows a sharp downward trend. Because the freezing rate is too fast, the freezing curves at -100℃ and -196℃ are almost linear, while the characteristics of the remaining stages are not obvious.

[0084] 2.2 Effects of different freezing temperatures on the water-holding capacity of grass carp

[0085] The moisture content of muscle tissue in aquatic products is closely related to their quality and texture. Therefore, the water-holding capacity of aquatic products is usually used to reflect changes in the meat quality of frozen aquatic products. Excessive water loss leads to the loss of flavor substances and soluble nutrients, resulting in a dry and tough texture, decreased sensory quality, and microbial growth.

[0086] In this study, the water-holding capacity of the samples was measured by thawing loss rate and cooking loss rate.

[0087] Table 2 shows that as the freezing rate increases, the thawing loss rate of the samples gradually decreases, exhibiting a significant downward trend. Furthermore, the samples can retain moisture to the maximum extent at a freezing temperature of -196℃ (i.e., a freezing rate of 3.05℃ / min). Table 3 shows that the cooking loss rate exhibits the same trend as the thawing loss rate; when the freezing rate increases to 3.05℃ / min, the cooking loss rate of the samples reaches its minimum.

[0088] Furthermore, because the samples produced finer ice crystals at freezing rates of 0.81℃ / min (-80℃) and 1.34℃ / min (-100℃), the damage to muscle tissue was less, and the muscle tissue maintained better water retention compared to other freezing rates. The faster supercooling rate leads to a higher deheating rate, resulting in the formation of numerous small ice crystals. These small ice crystals maintain the integrity of the intracellular and extracellular spaces, thus minimizing the thawing loss rate of the frozen samples. While a freezing rate of 1.34℃ / min (-196℃) can produce even finer ice crystals, it requires a larger amount of liquid nitrogen, thus increasing costs.

[0089] Therefore, it can be seen that when the grass carp sample is frozen at a temperature of -196℃ (i.e., freezing rate of 3.05℃ / min), the thawing loss rate and cooking loss rate are the lowest, and the water retention is also higher; the next best freezing effect is achieved at -100℃ (i.e., freezing rate of 1.34℃ / min); therefore, in this experiment, liquid nitrogen spraying at -100℃ is preferred for quick-freezing grass carp.

[0090] Table 2 Thawing loss rate of grass carp fillets at different freezing rates

[0091] Freezing temperature -18℃ -30℃ -60℃ -80℃ -100℃ -196℃ loss rate 1.13±0.15 0.94±0.10 0.74±0.05 0.44±0.05 0.17±0.02 0.04±0.01

[0092] Table 3. Cooking loss rate of grass carp fillets at different freezing rates

[0093] Freezing temperature -18℃ -30℃ -60℃ -80℃ -100℃ -196℃ Comparison loss rate 32.8±4 30.3±3.1 27.2±3.1 25.5±2.1 23.3±2.5 22.1±1.2 21.1±0.7

[0094] 2.3 Different salt-soluble proteins

[0095] The content of salt-soluble proteins (i.e., myofibrillar proteins) significantly affects the nutritional value, processing characteristics, sensory characteristics, and commercial value of aquatic products. During freezing, proteins undergo a series of physical and chemical processes, altering the internal spatial structure of the molecules, but without destroying the primary structure. There are many studies on myofibrillar proteins, and the main conclusions regarding their freeze denaturation mechanism can be summarized as follows: (1) The theory of bound water separation. During freezing and storage, the formation of ice crystals leads to the redistribution of water molecules, but the water cannot return to its original position upon thawing, thus reducing the rehydration capacity of myofibrillar proteins; (2) The theory of cell fluid concentration. Under freezing conditions, free water and bound water in myofibrillar proteins crystallize sequentially, causing changes in the three-dimensional structure of the protein; (3) The theory of hydration. The chemical bonds of protein molecules are reconstructed or destroyed by ice crystals, thereby changing the binding state between bound water and protein, altering the internal structure of myofibrillar proteins, and leading to their freeze denaturation. The effects of different freezing temperatures (rates) on the content of salt-soluble proteins are shown in Table 4.

[0096] Table 4. Changes in salt-soluble protein content of grass carp fillets at different freezing temperatures (rates).

[0097]

[0098] As shown in Table 4, compared with the control group, the content of salt-soluble protein in the grass carp samples was significantly reduced (p<0.05), but the difference among the six experimental groups was not significant (p>0.05). Based on the mechanism of protein denaturation during freezing, it is speculated that this is because the formation of ice crystals during freezing alters the internal spatial structure of the protein molecules, reducing the rehydration capacity of myofibril proteins and thus causing a decrease in the content of salt-soluble proteins. However, due to the short freezing storage time, no significant differences were observed among the denatured proteins.

[0099] 2.4 Different textures

[0100] Texture is an important quality indicator affecting the sensory and functional characteristics of fish. In this study, we used hardness, chewiness, and resilience to evaluate the textural properties of grass carp samples.

[0101] Table 5 shows that the differences in grass carp samples treated at different freezing temperatures, as revealed by texture analysis, are not as intuitive and obvious as those revealed by sensory evaluation. However, it is still evident that the hardness, chewiness, and elasticity of the liquid nitrogen group samples (-100℃ and -196℃) are significantly higher than other groups, and are closest to fresh samples. This indicates that liquid nitrogen quick-freezing has a certain protective effect on the tissue state, myofibril structure, and cell morphology of grass carp muscle. TPA (Total Texture Test: Grass carp pieces cut into 10×10×15mm pieces were tested using a TMS-Pro texture analyzer with a spherical probe. The puncture speed was 1mm / s, the deformation was 50%, the return speed was 1mm / s, and compression was performed twice with a 1s interval. Three parallel tests were conducted, and the average value was taken; equipment: TMS-Pro texture analyzer, FTC Instruments, USA) analysis and sensory evaluation together demonstrate that liquid nitrogen quick-freezing can significantly improve the edible value and nutritional quality of frozen grass carp. Deterioration in fish meat texture is related to various internal and external factors, including muscle dehydration and tissue degradation. In this study, the differences in hardness, chewiness, and resilience of the liquid nitrogen group samples compared to the control group of fresh grass carp may be due to reduced water-holding capacity and damage to muscle tissue.

[0102] Therefore, although the hardness, chewiness, and resilience of the liquid nitrogen group samples were slightly different from those of the fresh grass carp control group, the hardness, chewiness, and elasticity of the liquid nitrogen group samples (-100℃, -196℃) were significantly higher than those of other frozen groups. Therefore, this freezing temperature (freezing rate) is preferred.

[0103] Table 5. Changes in the texture of herring fillets at different freezing rates.

[0104] sample hardness chewing elasticity -18℃ 397.54 2.79±0.22 2.18±0.34 -30℃ 403.54 2.99±0.41 2.21±0.24 -60℃ 440.75 3.12±0.33 2.56±0.44 -80℃ 435.68 3.77±0.35 2.87±0.34 -100℃ 454.59±11.15 3.87±0.57 2.9±0.31 -196℃ 460.52±8.44 4.10±0.40 3.02±0.47 Comparison 477.25±8.99 4.13±0.51 3.17±0.56

[0105] As can be seen from the above experiments, this embodiment uses a liquid nitrogen quick-freezing cabinet to investigate the effect of different freezing rates on the quality of herring fillets. Six freezing rates were obtained by adjusting the operating temperature of the quick-freezing cabinet: 0.18℃ / min, 0.2℃ / min, 0.37℃ / min, 0.81℃ / min, 1.34℃ / min, and 3.05℃ / min. As the freezing rate increased, the phase transition time of each group decreased significantly. Regarding the microstructure and ice crystal morphology, the faster the freezing rate, the less damage to the sample's structure. The area, equivalent diameter, and perimeter of the ice crystals reached their minimum values ​​when the freezing rate increased to 1.34℃ / min and 3.05℃ / min, respectively. At this point, the ice crystals were evenly distributed and small in size. However, different freezing rates had almost no effect on the roundness and stretchability of the ice crystals. When the freezing rate was increased to 3.05℃ / min, the water-holding capacity of the grass carp fillets was the best, and there was no significant difference between them and the control group. The salt-soluble protein content of the samples decreased significantly after quick-freezing, but there was no significant difference between the 0.37, 0.81, 1.34, and 3.05 (℃ / min) treatment groups. Although the hardness, chewiness, and resilience of the liquid nitrogen group samples were slightly different from those of the fresh grass carp control group, the hardness, chewiness, and elasticity of the liquid nitrogen group samples (-100℃, -196℃) were significantly higher than those of other frozen groups (p<0.05).

[0106] Based on the correlation results between freezing rate and ice crystals and physicochemical indicators, freezing rate was significantly correlated with the water-holding capacity of grass carp fillets, and the area, equivalent diameter, and circumference of ice crystals. It did not show a significant correlation with the roundness, stretchability, and salt-soluble protein content of ice crystals, but it was significantly correlated with the texture of the grass carp. In conclusion, a freezing rate of 3.05℃ / min can maximize the preservation of grass carp fillet quality. However, considering factors such as cost, the most suitable method for quick-freezing grass carp fillets is liquid nitrogen spray freezing at -100℃, with a freezing rate of 1.34℃ / min.

[0107] Example 3: Effect of soaking in different compositions on the quality of grass carp

[0108] To obtain the optimal low-temperature quick-freezing preservation method in Example 1, this example screened the composition for soaking grass carp, using the following methods (the other materials, cultivation processes, and conditions not mentioned are the optimal conditions in Examples 1 and 2, and are all the same, with a freezing rate of 1.34℃ / min; after treating different groups of grass carp separately, the water-holding capacity, salt-soluble protein content, and texture of the grass carp pieces were finally tested, and the testing process was as described in Example 2):

[0109] 1. Control group: Fresh grass carp chunks;

[0110] 2. Blank group: Immersed in a solution without the added composition, and then quick-frozen by liquid nitrogen spraying at -100℃. The solution temperature and immersion time are the same, which is the optimal condition.

[0111] 3. Creatine: Soak in a solution containing only creatine, then quick-freeze by liquid nitrogen spray at -100℃. The optimal conditions are the same solution temperature and soaking time.

[0112] 4. Arginine: Soak in a solution containing only arginine, then quick-freeze by liquid nitrogen spray at -100℃. The optimal conditions are the same solution temperature and soaking time.

[0113] 5. Glycine: Soak in a solution containing only glycine, then quick-freeze by liquid nitrogen spray at -100℃. The optimal conditions are the same solution temperature and soaking time.

[0114] 6. Glutamic acid: Soak in a solution containing only glutamic acid, then quick-freeze by liquid nitrogen spray at -100℃. The optimal conditions are the same solution temperature and soaking time.

[0115] 7. Dextran: Soak in a solution containing only dextran, then quick-freeze by liquid nitrogen spray at -100℃. The optimal conditions are the same solution temperature and soaking time.

[0116] 8. Sucrose: Soak in a solution containing only sucrose, then quick-freeze by liquid nitrogen spraying at -100℃. The solution temperature and soaking time are the same, which is the optimal condition.

[0117] 9. Sarcosine + Dextran: Soak in a solution with a composition of sarcosine:dextran = 1:2, and then quick-freeze by liquid nitrogen spraying at -100℃. The solution temperature and soaking time are the same, which is the optimal condition.

[0118] 10. Creatine + Sucrose: Soak in a solution with a composition of creatine:sucrose = 1:2, and then quick-freeze by liquid nitrogen spraying at -100℃. The solution temperature and soaking time are the same, which is the optimal condition.

[0119] 11. Arginine + Dextran: Soak in a solution with an arginine:dextran ratio of 1:2, then quick-freeze by liquid nitrogen spraying at -100°C. The optimal conditions are the same solution temperature and soaking time.

[0120] 12. Arginine + Sucrose: Soak in a solution with an arginine:sucrose ratio of 1:2, then quick-freeze by liquid nitrogen spraying at -100°C. The optimal conditions are the same solution temperature and soaking time.

[0121] 13. Glycine + Dextran: Soak in a solution with a glycine:dextran ratio of 1:2, then quick-freeze by liquid nitrogen spraying at -100°C. The optimal conditions are the same for both solution temperature and soaking time.

[0122] 14. Glycine + Sucrose: Soak in a solution with a glycine:sucrose ratio of 1:2, then quick-freeze by liquid nitrogen spraying at -100°C. The optimal conditions are the same solution temperature and soaking time.

[0123] 15. Glutamic acid + dextran: Soak in a solution with a composition of glutamic acid: dextran = 1:2, and then quick-freeze by liquid nitrogen spraying at -100℃. The solution temperature and soaking time are the same, which is the optimal condition.

[0124] 16. Glutamic acid + sucrose: Soak in a solution with a composition of glutamic acid: sucrose = 1:2, and then quick-freeze by liquid nitrogen spraying at -100℃. The solution temperature and soaking time are the same, which is the optimal condition.

[0125] The specific results are shown in Table 6:

[0126] Table 6. Effects of soaking in different composite solutions on the quality of grass carp fillets.

[0127]

[0128]

[0129] As shown in Table 6, under liquid nitrogen spray quick-freezing conditions at -100℃, the water-holding capacity, salt-soluble protein content, and textural properties of grass carp soaked in a solution containing only sarcosine were significantly improved compared to solutions containing only arginine, glycine, or glutamic acid (p<0.05). Similarly, the water-holding capacity, salt-soluble protein content, and textural properties of grass carp soaked in a solution containing only dextran were significantly improved compared to solutions containing only sucrose (p<0.05). When sarcosine and dextran were combined, the quality of grass carp fillets soaked in a sarcosine and dextran combined solution was closest to that of fresh grass carp, with no significant difference (p>0.05). However, compared to grass carp fillets soaked in other single-compound solutions, combined solutions, or unsoaked fillets, the water-holding capacity, salt-soluble protein content, and textural properties of grass carp soaked in a sarcosine and dextran combined solution were significantly improved (p<0.05). This may be because sarcosine ions are amphoteric, meaning they can inhibit pH changes in solutions during the low-temperature preservation and freeze-drying of biological products, thus protecting the active components. Glucan can inhibit ice crystal growth and provide freeze stability, thereby achieving low-temperature protection. When sarcosine and glucan work together, they can form a liquid protective film on the surface of the grass carp, exerting a synergistic effect and significantly enhancing freeze protection. This prevents moisture loss during freezing and storage, ensuring the tenderness of the grass carp meat after freezing and improving the freeze preservation time and effect.

[0130] Therefore, in this embodiment, the preferred composition for soaking the grass carp is sarcosine and glucan.

[0131] Example 4: Effect of different ratios of sarcosine and dextran in the composition on the quality of grass carp

[0132] To obtain the optimal low-temperature quick-freezing preservation method in Example 1, this example screened different ratios of sarcosine and dextran in the composition, using the following methods (the other materials, cultivation processes, and conditions not mentioned are the optimal conditions in Examples 1 and 2, and are all the same, with a freezing rate of 1.34℃ / min. After treating different groups of grass carp, the water-holding capacity, salt-soluble protein content, and texture of the grass carp pieces were finally tested, and the testing process was as described in Example 2):

[0133] 1. Control group: Fresh grass carp chunks;

[0134] 2. The optimal conditions are to soak the sarcosine and dextran in a 1:1 ratio solution and then quick-freeze it by liquid nitrogen spraying at -100°C, with the solution temperature and soaking time being the same.

[0135] 3. sarcosine:glucan = 1:2: Soak in a sarcosine:glucan = 1:2 composition solution, and then quick-freeze by liquid nitrogen spray at -100℃. The solution temperature and soaking time are the same, which is the optimal condition.

[0136] 4. The optimal conditions are to soak the sarcosine:glucan = 2:1 mixture in a solution of sarcosine:glucan = 2:1 and then quick-freeze it by liquid nitrogen spraying at -100℃, with the solution temperature and soaking time being the same.

[0137] The specific results are shown in Table 7:

[0138] Table 7. Effects of soaking in solutions of different proportions of sarcosine and dextran on the quality of herring fillets.

[0139]

[0140] As shown in Table 7, under liquid nitrogen spray quick-freezing conditions at -100℃, the quality of grass carp fillets soaked in a 1:2 mass ratio of sarcosine and dextran was closest to that of fresh grass carp, with no significant difference (p>0.05). However, compared with grass carp fillets soaked in other proportions of the sarcosine and dextran solution, the water-holding capacity, salt-soluble protein content, and textural properties of grass carp fillets soaked in the 1:2 mass ratio of sarcosine and dextran solution were significantly improved, showing significant differences (p<0.05).

[0141] Therefore, in this embodiment, the preferred mass ratio of the composition for soaking grass carp is sarcosine:glucan = 1:2.

[0142] Example 5: Effect of different soaking times on the quality of grass carp

[0143] To obtain the optimal low-temperature quick-freezing preservation method in Example 1, this example screened the soaking time of grass carp fillets in a 1:2 mass ratio of sarcosine and dextran. Several methods were used (the materials, culture process, and conditions not mentioned were the optimal conditions in Examples 1 and 2, and were all the same; the freezing rate was 1.34℃ / min; different groups of grass carp were treated separately, and finally, the water-holding capacity, salt-soluble protein content, and texture of the grass carp fillets were tested, and the testing process was as described in Example 2):

[0144] 1. Control group: Fresh grass carp chunks;

[0145] 2. Soaking time is 5 min: Soak in a sarcosine:glucan = 1:2 composition solution for 5 min, and then quick-freeze by liquid nitrogen spray at -100℃. The solution temperature is the same for all cases, which is the optimal condition.

[0146] 3. Soaking time is 6 minutes: Soak in a sarcosine:glucan = 1:2 composition solution for 6 minutes, and then quick-freeze by liquid nitrogen spray at -100℃. The solution temperature is the same, which is the optimal condition.

[0147] 4. Soaking time is 8 minutes: Soak in a sarcosine:glucan = 1:2 composition solution for 8 minutes, and then quick-freeze by liquid nitrogen spray at -100℃. The solution temperature is the same, which is the optimal condition.

[0148] 5. Soaking time is 10 min: Soak in a sarcosine:glucan = 1:2 composition solution for 10 min, and then quick-freeze by liquid nitrogen spray at -100℃. The solution temperature is the same, which is the optimal condition.

[0149] 6. Soaking time is 11 min: Soak in a sarcosine:glucan = 1:2 composition solution for 11 min, and then quick-freeze by liquid nitrogen spray at -100℃. The solution temperature is the same for all cases, which is the optimal condition.

[0150] The specific results are shown in Table 8:

[0151] Table 8. Effects of soaking in different composite solutions on the quality of grass carp fillets.

[0152]

[0153] As shown in Table 8, under the condition of liquid nitrogen spray quick-freezing at -100℃, the quality of grass carp fillets soaked in a solution of sarcosine and dextran for 6-10 min was closest to that of fresh grass carp, with no significant difference (p>0.05), and the grass carp fillets soaked for 8 min had the best quality. Compared with the grass carp fillets soaked for different times in other groups, the water-holding capacity, salt-soluble protein content and textural properties of grass carp fillets soaked for 6-10 min were significantly improved, and there were significant differences (p<0.05).

[0154] Therefore, in this embodiment, the preferred soaking time is 6 to 10 minutes, and the quality of the grass carp slices is best when the soaking time is 8 minutes.

[0155] Example 6: Effect of different soaking solution temperatures on the quality of grass carp

[0156] To obtain the optimal low-temperature quick-freezing preservation method in Example 1, this example screened the temperature of the solution used to soak the grass carp fillets. Several methods were used (the materials, culture process, and conditions not mentioned were all the optimal conditions in Examples 1 and 2, and were all the same; the freezing rate was 1.34℃ / min; different groups of grass carp were treated separately, and finally, the water-holding capacity, salt-soluble protein content, and texture of the grass carp fillets were tested, and the testing process was as described in Example 2):

[0157] 1. Control group: Fresh grass carp chunks;

[0158] 2. The temperature of the soaking solution is 5℃: Soaking in the composition solution at 5℃, followed by quick freezing by liquid nitrogen spraying at -100℃, with the soaking time being the same, is the optimal condition;

[0159] 3. The temperature of the soaking solution is 6℃: Soaking in the composition solution at 6℃, followed by quick freezing by liquid nitrogen spraying at -100℃, with the soaking time being the same, is the optimal condition;

[0160] 4. The temperature of the soaking solution is 9℃: Soaking in the composition solution at 9℃ and then quick-freezing by liquid nitrogen spraying at -100℃, with the soaking time being the same, is the optimal condition;

[0161] 5. The temperature of the soaking solution is 12℃: Soaking in the composition solution at 12℃, followed by quick freezing by liquid nitrogen spraying at -100℃, with the soaking time being the same, is the optimal condition;

[0162] 6. The temperature of the soaking solution is 13℃: Soaking in the composition solution at 13℃, followed by quick freezing by liquid nitrogen spraying at -100℃, with the soaking time being the same, is the optimal condition;

[0163] The specific results are shown in Table 9:

[0164] Table 9. Effects of soaking in different composite solutions on the quality of grass carp fillets.

[0165]

[0166] As shown in Table 9, under the condition of liquid nitrogen spray quick-freezing at -100℃, the quality of grass carp fillets soaked in solutions at temperatures of 6–12℃ was closest to that of fresh grass carp, with no significant difference (p>0.05), and the grass carp fillets with the best quality were those with a solution temperature of 9℃. Compared with the grass carp fillets soaked in solutions at different temperatures in other groups, the water-holding capacity, salt-soluble protein content, and textural properties of grass carp fillets soaked in solutions at temperatures of 6–12℃ were significantly improved, and there were significant differences (p<0.05).

[0167] Therefore, in this embodiment, the preferred soaking solution temperature is 6-12°C, and the quality of the grass carp slices is best when the solution temperature is 9°C.

[0168] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Anyone skilled in the art can make various modifications and alterations without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be determined by the claims.

Claims

1. A low-temperature quick-freezing preservation method for black carp, characterized in that, The method comprises the following steps: 1) soaking the treated grass carp in a solution containing a composition; 2) taking out the grass carp and then rapidly freezing at different temperatures; The composition comprises sarcosine and dextran; the mass ratio of sarcosine to dextran in the composition is 1:2; in the step 1), the temperature of the solution is 6-12℃, and the soaking time is 6-10 min.

2. The method of claim 1, wherein, In the step 1), the temperature of the solution is 9℃, and the soaking time is 8 min.

3. The method of claim 1, wherein, In the step 2), the temperature comprises one or more of -18℃, -30℃, -60℃, -80℃, -100℃ and -196℃; the -100℃ is spray freezing using liquid nitrogen; and the -196℃ is immersion freezing using liquid nitrogen.

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