Constant-temperature composite phase change cold storage agent and application thereof

Abstract

The invention discloses a constant-temperature composite phase change cold storage agent and application thereof. The constant-temperature composite phase change cold storage agent is prepared from the following components: water, NH4Cl, NaNO3, TiO2 and curdlan. The content of each component is as follows in percentage by mass: 15% of NH4Cl, 35%-9% of NaNO, 0.05%-0.15% of TiO2, 0.5%-1.5% of curdlan and the balance of water. The phase change latent heat of the constant-temperature composite phase change cold storage agent is 247.20 J / g, the phase change temperature is-25.08 DEG C, the supercooling degree is 0.4 DEG C, and no phase separation phenomenon is found after repeated freezing and thawing. The constant-temperature composite phase change cold storage agent is low in phase change temperature, high in phase change latent heat, small in supercooling degree and free of phase separation, and the constant-temperature process is achieved in the mode that the cold storage agent is combined with a fresh-keeping box.

Description

Technical Field

[0001] The invention specifically relates to a constant temperature composite phase change cold storage agent and application thereof, belonging to the field of composite cold storage agents. Background Art

[0002] Low-temperature freezing is the most commonly used preservation method for aquatic products. During the low-temperature freezing process, the growth of microorganisms and the activity of enzymes are inhibited, so the factors such as microorganisms and enzymes have little effect on the quality of frozen products. Among them, the quality degradation of frozen products caused by temperature fluctuations caused by frequent start-stop of cold storage compressors has become the most important influencing factor. The repeated freezing and thawing caused by temperature fluctuations will cause the ice crystals in the tissues of aquatic products to continue to grow, destroy the cell structure, and eventually lead to the degradation of shrimp quality, such as protein denaturation and juice loss. Therefore, it is of great significance to control and reduce temperature fluctuations to maintain the quality of aquatic products. At present, the main aquatic product preservation technologies include low-temperature preservation, gas conditioning preservation, ultra-high pressure preservation, irradiation preservation, chemical and biological preservation technology, but there are few studies on the changes in aquatic product quality from reducing temperature fluctuations, and there is no research on the preservation technology that combines refrigerants and fresh-keeping boxes to reduce temperature fluctuations. Phase change refrigerants can absorb and release cold energy according to the surrounding environment using their latent heat in the phase change process, and keep the system within a stable temperature range in this process. Phase change energy storage technology can use latent heat to store energy during the low electricity consumption period, and release cold energy during the peak electricity consumption period, that is, shifting the peak to fill the valley, thereby maintaining temperature stability.

[0003] Phase change cold storage materials can keep the system stable within a temperature range and are key materials for controlling and reducing temperature fluctuations. At present, there have been many studies on phase change cold storage materials at 0 to -18°C, but there are still few studies on phase change cold storage materials in the low temperature field, such as phase change cold storage materials in the temperature range of -20 to -25°C. However, this is exactly the preservation temperature required for frozen aquatic products, especially shrimps, which are prone to spoilage and require lower storage temperatures to ensure their quality. The cold storage agents currently studied are often difficult to have a higher phase change latent heat when the phase change temperature is low, and their phase change temperature is also higher when the phase change latent heat is high. Therefore, it is particularly important to develop a phase change cold storage material with high phase change latent heat, low phase change temperature, low supercooling, no phase separation phenomenon, and low cost. The present invention uses phase change cold storage materials as a starting point to control temperature fluctuations to a minimum to achieve a constant temperature process, thereby improving the frozen storage and preservation effect. Summary of the invention

[0004] In order to overcome the deficiencies of the prior art, the present invention provides a constant temperature composite phase change refrigerant and application thereof.

[0005] The technical solution adopted by the present invention to solve the technical problem is:

[0006] On the one hand, the present invention provides a constant temperature composite phase change refrigerant, comprising the following components: water, NH4Cl, NaNO3, TiO2 and curdlan; in terms of mass fraction, the content of each component is: NH4Cl 15%, NaNO3 5-9%, TiO2 0.05-0.15% and curdlan 0.5-1.5%, and the rest is water.

[0007] A constant temperature composite phase change refrigerant, specifically, in terms of mass fraction, the contents of the components are: 15% NH4Cl, 39% NaNO, 0.1% TiO2 and 1.0% curdlan, and the rest is water.

[0008] A constant temperature composite phase change refrigerant, specifically, in terms of mass fraction, the contents of the components are: 15% NH4Cl, 35% NaNO, 0.05% TiO2 and 0.5% curdlan, and the rest is water.

[0009] A constant temperature composite phase change refrigerant, specifically, in terms of mass fraction, the contents of the components are: 15% NH4Cl, 37% NaNO, 0.15% TiO2 and 1.5% curdlan, and the rest is water.

[0010] A constant temperature composite phase change refrigerant is disclosed. The preparation method of the constant temperature composite phase change refrigerant is as follows: NH4Cl, NaNO3, TiO2, curdlan and water are mixed in proportion to obtain the constant temperature composite phase change refrigerant.

[0011] A constant temperature composite phase change cold storage agent, wherein the TiO2 particle size is 60nm. When the TiO2 particle size is 60nm, the addition amount is less than that of the nucleating agent borax, and the TiO2 can play the role of a nucleating agent and produce a specific nano effect. Currently, there are many studies on borax as a nucleating agent, and considering that the addition amount of borax is more than that of TiO2 under the same effect, the present invention selects TiO2 as a nucleating agent.

[0012] A constant temperature composite phase change refrigerant, which is composed of 15% NH4Cl, 5-9% NaNO3 and the balance of water in terms of mass fraction, has a phase change latent heat of 290.61-264.44 J / g, and a phase change temperature of -22.09--26.75°C.

[0013] A constant temperature composite phase change refrigerant, which is composed of 15% NH4Cl, 9% NaNO3, 0.10% TiO2, 1.0% curdlan and the balance water, by mass fraction, has a phase change latent heat of 247.20 J / g, a phase change temperature of -25.08°C, a supercooling degree of 0.4°C, and has no significant changes in its phase change latent heat and phase change temperature after repeated freezing and thawing, and no phase separation phenomenon is found.

[0014] Compared with xanthan gum gel, sodium alginate and sodium carboxymethyl cellulose gel, the gel strength of xanthan gum in the composite phase change coolant changes the least and remains the most stable.

[0015] On the other hand, the present invention also provides an application of a constant temperature composite phase change cold storage agent. Specifically, the constant temperature composite phase change cold storage agent and a fresh-keeping box are combined and applied to the frozen storage of aquatic products.

[0016] An application of a constant temperature composite phase change cold storage agent, specifically, the constant temperature composite phase change cold storage agent is injected into the interlayer of a fresh-keeping box for constant temperature freezing.

[0017] An application of a constant temperature composite phase change coolant, specifically, the aquatic product is Chinese tube whip shrimp.

[0018] Beneficial effects:

[0019] (1) The present invention specifically relates to a constant temperature composite phase change cold storage agent and its application. From the perspective of controlling and reducing temperature fluctuations, the present invention develops a composite phase change cold storage material with low phase change temperature, high phase change latent heat, small supercooling and no phase separation phenomenon. The composite phase change cold storage agent is combined with the frozen storage and fresh-keeping method of the fresh-keeping box to effectively reduce temperature fluctuations, providing a theoretical basis for the frozen storage process technology.

[0020] (2) The composite phase-change refrigerant obtained by the present invention is composed of 15% NH4Cl, 9% NaNO3, 0.10% TiO2, 1.0% curdlan and the balance of water. Its phase change latent heat is 247.20 J / g, the phase change temperature is -25.08°C, the supercooling degree is 0.4°C, and no phase separation phenomenon is found after repeated freezing and thawing for 90 days. After being injected into the fresh-keeping box compartment, the temperature fluctuation inside the box was measured at -25°C, and the temperature fluctuation outside the box was about 10 times that of the temperature fluctuation inside the box. The temperature fluctuation is effectively reduced and controlled.

[0021] (3) By analyzing the physical and chemical properties of Chinese whip shrimp during constant temperature and conventional frozen storage, compared with conventional frozen storage, the constant temperature frozen storage method of the present invention, which combines a composite phase change cold storage agent and a fresh-keeping box, is more conducive to the storage and preservation of Chinese whip shrimp. The constant temperature frozen storage method of the present invention, which combines a composite phase change cold storage agent and a fresh-keeping box, effectively controls and reduces temperature fluctuations, and ensures the quality of Chinese whip shrimp during long-term frozen storage. The composite phase change cold storage agent of the present invention is suitable for low-temperature storage of food and has a high latent heat of phase change, which not only effectively improves the frozen storage and preservation effect, but also provides reference value for frozen storage process technology, cold chain logistics and other aspects. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 DSC melting curves of each substance in Examples 1-5 (A) and the relationship between its concentration and phase transition temperature and phase transition latent heat (B)

[0023] Figure 2 Cooling curves (A) and partial enlarged views (B) of Examples 5-8, Example 5 is a blank group

[0024] Figure 3 DSC curves of the composite phase-change refrigerant corresponding to Example 5 and Example 10

[0025] Figure 4 Temperature change diagram of the box inside and outside for 48 hours

[0026] Figure 5 Changes in head color of Chinese trombopsis cerana in Experimental Examples 1 and 2

[0027] Figure 6 Changes in color of abdominal segments of Chinese trombopsis cerana in Experimental Examples 1 and 2

[0028] Figure 7 Changes in the texture characteristics of Chinese prawns in Experimental Examples 1 and 2

[0029] Figure 8 PCA graph of Chinese shrimp in Experimental Example 1 (A) and Experimental Example 2 (B)

[0030] Fig. 9 Changes in pH value of Chinese shrimp in Experimental Examples 1 and 2

[0031] Fig.10 Changes in TVB-N values ​​of Chinese trout shrimp in Experimental Examples 1 and 2

[0032] Fig.11 Changes in PPO values ​​of Chinese trombopsis cerana in Experimental Examples 1 and 2

[0033] Fig.12 Changes in the salt-soluble protein content of Chinese prawns in Experimental Examples 1 and 2

[0034] Fig.13 Changes in the total number of colonies in the Chinese prawn meat (A) and the whole shrimp (B) in Experimental Examples 1 and 2 Figure 5-7 , Figure 9-13 Different lowercase letters indicate significant differences between different freezing conditions at different storage times (P < 0.05), and different capital letters indicate significant differences between different freezing conditions at the same freezing time (P < 0.05) DETAILED DESCRIPTION

[0035] The present invention is further explained below in conjunction with specific examples. It should be understood that these examples are only used to illustrate the present invention and are not used to limit the scope of the present invention. After reading the present invention, various equivalent modifications of the present invention by those skilled in the art all fall within the scope defined by the claims attached to this application.

[0036] Embodiment 1:

[0037] A constant temperature composite phase change refrigerant, comprising the following components: NH4Cl, NaNO3 and water, wherein the mass fractions of the above components are:

[0038] NH4Cl, 15%;

[0039] NaNO3, 1%;

[0040] Water, balance.

[0041] In the above embodiment, NH4Cl is the main energy storage agent and NaNO3 is the cooling agent.

[0042] Embodiment 2:

[0043] A constant temperature composite phase change refrigerant, comprising the following components: NH4Cl, NaNO3 and water, wherein the mass fractions of the above components are:

[0044] NH4Cl, 15%;

[0045] NaNO3, 3%;

[0046] Water, balance.

[0047] In the above embodiment, NH4Cl is the main energy storage agent and NaNO3 is the cooling agent.

[0048] Embodiment 3:

[0049] A constant temperature composite phase change refrigerant, comprising the following components: NH4Cl, NaNO3 and water, wherein the mass fractions of the above components are:

[0050] NH4Cl, 15%;

[0051] NaNO3, 5%;

[0052] Water, balance.

[0053] In the above embodiment, NH4Cl is the main energy storage agent and NaNO3 is the cooling agent.

[0054] Embodiment 4:

[0055] A constant temperature composite phase change refrigerant, comprising the following components: NH4Cl, NaNO3 and water, wherein the mass fractions of the above components are:

[0056] NH4Cl, 15%;

[0057] NaNO3, 7%;

[0058] Water, balance.

[0059] In the above embodiment, NH4Cl is the main energy storage agent and NaNO3 is the cooling agent.

[0060] Embodiment 5:

[0061] A constant temperature composite phase change refrigerant, comprising the following components: NH4Cl, NaNO3 and water, wherein the mass fractions of the above components are:

[0062] NH4Cl, 15%;

[0063] NaNO3, 9%;

[0064] Water, balance.

[0065] In the above embodiment, NH4Cl is the main energy storage agent and NaNO3 is the cooling agent.

[0066] Embodiment 6:

[0067] A constant temperature composite phase change refrigerant, comprising the following components: NH4Cl, NaNO3, TiO2 and water, wherein the mass fractions of the above components are:

[0068] NH4Cl, 15%;

[0069] NaNO3, 9%;

[0070] TiO2, 0.05%;

[0071] Water, balance.

[0072] In the above embodiment, NH4Cl is the main energy storage agent, NaNO3 is used as a cooling agent, and TiO2 is used as a nucleating agent to reduce supercooling.

[0073] Embodiment 7:

[0074] A constant temperature composite phase change refrigerant, comprising the following components: NH4Cl, NaNO3, TiO2 and water, wherein the mass fractions of the above components are:

[0075] NH4Cl, 15%;

[0076] NaNO3, 9%;

[0077] TiO2, 0.10%;

[0078] Water, balance.

[0079] In the above embodiment, NH4Cl is the main energy storage agent, NaNO3 is used as a cooling agent, and TiO2 is used as a nucleating agent to reduce supercooling.

[0080] Embodiment 8:

[0081] A constant temperature composite phase change refrigerant, comprising the following components: NH4Cl, NaNO3, TiO2 and water, wherein the mass fractions of the above components are:

[0082] NH4Cl, 15%;

[0083] NaNO3, 9%;

[0084] TiO2, 0.15%;

[0085] Water, balance.

[0086] In the above embodiment, NH4Cl is the main energy storage agent, NaNO3 is used as a cooling agent, and TiO2 is used as a nucleating agent to reduce supercooling.

[0087] Embodiment 9:

[0088] A constant temperature composite phase change refrigerant, comprising the following components: NH4Cl, NaNO3, TiO2, curdlan and water, wherein the mass fractions of the above components are:

[0089] NH4Cl, 15%;

[0090] NaNO3, 9%;

[0091] TiO2, 0.10%;

[0092] Curdlan, 0.5%;

[0093] Water, balance.

[0094] In the above embodiment, NH4Cl is the main energy storage agent, NaNO3 is used as a cooling agent, and TiO2 is used as a nucleating agent to reduce supercooling.

[0095] Embodiment 10:

[0096] A constant temperature composite phase change refrigerant, comprising the following components: NH4Cl, NaNO3, TiO2, curdlan and water, wherein the mass fractions of the above components are:

[0097] NH4Cl, 15%;

[0098] NaNO3, 9%;

[0099] TiO2, 0.10%;

[0100] Curdlan, 1.0%;

[0101] Water, balance.

[0102] In the above embodiment, NH4Cl is the main energy storage agent, NaNO3 is used as a cooling agent, and TiO2 is used as a nucleating agent to reduce supercooling.

[0103] Embodiment 11:

[0104] A constant temperature composite phase change refrigerant, comprising the following components: NH4Cl, NaNO3, TiO2, curdlan and water, wherein the mass fractions of the above components are:

[0105] NH4Cl, 15%;

[0106] NaNO3, 9%;

[0107] TiO2, 0.10%;

[0108] Curdlan, 1.5%;

[0109] Water, balance.

[0110] In the above embodiment, NH4Cl is the main energy storage agent, NaNO3 is used as a cooling agent, TiO2 is used as a nucleating agent to reduce supercooling, and curdlan is used as a thickener of the constant temperature composite phase change refrigerant.

[0111] The constant temperature composite phase change refrigerant of Examples 1-5 were subjected to DSC test respectively. Figure 1 It can be seen that by adding different concentrations of NaNO3 cooling agent to the 15% NH4Cl main energy storage agent, the two can form a good eutectic. As the concentration of NaNO3 increases, its phase change temperature becomes lower. When 5-9% NaNO3 is added, its phase change temperature is -22.09--26.75℃, which meets the refrigerant demand of the target temperature range, and the phase change latent heat is as high as 290.61-264.44J / g.

[0112] The supercooling degree of the constant temperature composite phase change refrigerant of Examples 5-9 was tested respectively. Figure 2 Without adding TiO2, the supercooling degree of the composite phase change refrigerant composed of 15% NH4Cl and 9% NaNO3 is 2.3℃. After adding 0.05%, 0.10% and 0.15% TiO2, the supercooling degree is reduced to 0.9℃, 0.4℃ and 0.5℃ respectively.

[0113] The composite phase-change refrigerants of Examples 9-11 were subjected to repeated freeze-thaw experiments and it was found that the best effect was achieved by adding 1.0% of curdlan, and no phase separation was found.

[0114] The composite phase change refrigerant of Example 5 and Example 10 was subjected to DSC test. Figure 3After adding nucleating agent and thickener, the latent heat of phase change was measured to decrease from 264.44 J / g to 247.20 J / g, and the phase change temperature was reduced from -26.75℃ to -25.08℃. The phase change temperature changed slightly, which met the requirements of the required temperature range. Although the latent heat of phase change decreased by 17.24 J / g, it remained above 240.00 J / g, and still had a high latent heat of phase change. No phase separation was found in the composite phase change refrigerant after repeated freezing and thawing. After repeated freezing and thawing, its latent heat of phase change and phase change temperature did not change significantly (P < 0.05).

[0115] Experimental Example 1:

[0116] A constant temperature composite phase change cold storage agent was prepared according to the component ratio of Example 10, and the constant temperature composite phase change cold storage agent was injected into the compartment of a fresh-keeping box to form a cold storage fresh-keeping box. The box was placed in a horizontal refrigeration and freezing conversion cabinet at -25°C, and the purchased Chinese tube whip shrimp was placed in the cold storage fresh-keeping box for frozen storage for 90 days (frozen storage in the box).

[0117] Experimental Example 2:

[0118] The purchased Chinese tube whip shrimp was placed in a freezer (i.e., in the horizontal refrigeration-freezing conversion cabinet in Experimental Example 1, outside the cold storage and fresh-keeping box) and frozen for 90 days (frozen outside the box).

[0119] Temperature changes inside the box: Place temperature recorders inside and outside the box and record every 10 seconds for a total of 48 hours without opening the freezer. Figure 4 The temperature inside the box fluctuates by about 0.2°C, and the temperature outside the box fluctuates by about 2°C, which is about 10 times that inside the box. The temperature inside the box is almost constant compared to the outside of the box. This shows that this cold storage and fresh-keeping box can better control temperature fluctuations.

[0120] Color: The brightness (L*), red-green (a*), and yellow-blue (b*) of the head and the second and third abdominal segments of the shelled Chinese whip shrimp in Experimental Example 1 and Experimental Example 2 were measured using a CR-400 colorimeter. Figure 5 and Figure 6, whether it is the shrimp head or the shrimp abdominal segment, the change trend of its brightness (L*), red-green (a*), and yellow-blue (b*) values ​​is consistent. Among them, the a* and b* values ​​of the shrimp head are larger than those of the abdominal segment surface, which may be because the enzyme activity contained in the shrimp head is the strongest, and the shrimp head is where the shrimp's internal organs are located. With the extension of the frozen storage time, the L* value has always been on a downward trend. It may be that the moisture of the shrimp meat is lost during the frozen storage process, and the brightness of the shrimp decreases, resulting in a decrease in the L* value. The color changes of the shrimp heads stored inside and outside the box showed significant changes with the extension of the frozen storage time (P < 0.05), but after 30 days, the color change values ​​of the shrimp heads and the abdominal segments in the box at the same frozen storage time were significantly smaller than those outside the box (P < 0.05), indicating that the constant temperature frozen storage in Experimental Example 1 is more conducive to delaying the change of shrimp color.

[0121] Texture properties: The muscles of the second and third abdominal segments of the Chinese whip shrimp in Experimental Examples 1 and 2 were placed on a texture analyzer to measure their hardness and elasticity. Figure 7 As the frozen storage time increased, the hardness of the shrimp muscle in the box changed significantly on the 60th day (P < 0.05), and changed significantly on the 40th day outside the box (P < 0.05), indicating that the hardness of the muscle in the box changed slowly. Under the same frozen storage time, the hardness and elasticity of the shrimp stored in the box and outside the box showed significant differences on the 45th day (P < 0.05), and the hardness and elasticity values ​​in the box decreased less than those outside the box, indicating that the constant temperature frozen storage in Experimental Example 1 helps to delay the changes in the texture characteristics of shrimp.

[0122] Odor characteristics: 1.0 g of shrimp meat from Experimental Example 1 and Experimental Example 2 were placed in a sealed headspace bottle with balanced gas for 20 minutes, and their odor characteristics were measured by electronic nose. Figure 8 , the first principal component and the second principal component contribution rates of the Chinese whip shrimp measured in constant temperature frozen storage of Experimental Example 1 were 99.27% ​​and 0.59% respectively, and the total contribution rate was 99.86%. The first principal component and the second principal component contribution rates of the Chinese whip shrimp measured in conventional frozen storage of Experimental Example 2 were 99.49% and 0.36% respectively, and the total contribution rate was 99.85%, indicating that principal component analysis can effectively distinguish the changes in the volatile odor of shrimp meat under the two frozen storage conditions. From the perspective of the first principal component and the second principal component, the odor of the two groups of shrimp meat has significant differences to varying degrees from the fresh group, indicating that different frozen storage conditions and different frozen storage times have a significant effect on the change in the freshness of the shrimp meat odor. The distance between the constant temperature frozen storage group of Experimental Example 1 and the fresh group after 45 days of storage is smaller than that of the conventional frozen storage group of Experimental Example 2, indicating that the constant temperature frozen storage preservation effect of Experimental Example 1 is better than that of the conventional frozen storage of Experimental Example 2.

[0123] pH: Accurately weigh 10 g of shrimp meat from the second and third abdominal segments in Experimental Examples 1 and 2, add ultrapure water to 100 mL, homogenize at 8000 rpm for 1 min, stir evenly, soak for 30 min, filter, and take the filtrate in a beaker to measure pH using an acidometer. Fig. 9 The pH value of Chinese whip shrimp under the two frozen storage conditions showed a trend of first decreasing and then increasing with the extension of time. Although the pH values ​​inside and outside the box increased significantly after 15 days (P < 0.05), the increase in pH value inside the box was significantly lower than that outside the box at the same frozen storage time (P < 0.05), indicating that the constant temperature frozen storage in Experimental Example 1 can delay the production of alkaline substances and is beneficial to the preservation of shrimp.

[0124] TVB-N: Accurately weigh 20g of shrimp meat from the second and third abdominal segments in Experimental Examples 1 and 2, add 100mL of water and homogenize at 8000rpm for 1min, place in a conical flask, shake continuously to disperse the sample evenly, and filter after soaking for 30min. The filtrate is placed at 4℃ for use. Add 10mL of boric acid solution and 5 drops of mixed indicator liquid to the receiving bottle, and insert the lower end of the condenser under the liquid surface. Accurately draw 10mL of filtrate and inject it into the reaction chamber from a small glass cup. Wash the small glass cup with 10mL of water and let it flow into the reaction chamber, then plug the rod-shaped glass stopper. Then inject 5mL of magnesium oxide suspension into the reaction chamber and immediately seal the glass stopper. After distilling for 5min, let the liquid level of the receiving bottle leave the lower end of the condenser and distill for another 1min. Titrate to the endpoint with 0.01mol / L hydrochloric acid standard titration solution. Use a mixed indicator solution, the end point color turns purple-red, and the TVB-N content is calculated based on the volume of hydrochloric acid consumed. See. Fig.10 The TVB-N value of Chinese whip shrimp under the two frozen storage conditions showed an upward trend with the extension of frozen storage time. The TVB-N value of the storage outside the box was 4.2 mg / 100g different from that of the storage inside the box on the 90th day, and the TVB-N value of the storage outside the box has been showing a significant upward trend (P < 0.05), and a significant difference appeared on the 60th day of storage inside the box (P < 0.05). There was a significant difference between the TVB-N value inside the box and the TVB-N value outside the box on the 30th day under the same frozen storage time (P < 0.05). The results showed that the constant temperature frozen storage of Experimental Example 1 helped to delay the rapid increase of TVB-N value.

[0125] PPO activity: Weigh 10g of shrimp heads from Experimental Example 1 and Experimental Example 2 at 4℃, grind them thoroughly, add 50mL of 0.067mol / L phosphate buffer (pH 7.2, precooled to 0℃), homogenize, centrifuge and take the supernatant as the enzyme extract, place at 0℃ for use. Prepare 0.05mol / L catechol solution with 0.10mol / L pH 6.0 phosphate buffer, and keep it at 30℃ in advance. Take 2.80mL of catechol solution and quickly add 0.20mL of enzyme solution to mix, measure the absorbance at 420nm wavelength, and the control group is 2.80mL of catechol solution plus 0.20mL of buffer. Enzyme activity is expressed as a change of 0.001 in absorbance per minute as one PPO activity unit. See Fig.11 Under both freezing conditions, the PPO activity showed a trend of first increasing and then decreasing with the extension of freezing time. Compared with the PPO activity of the head of fresh Chinese whip shrimp, the PPO activity increased significantly on the 15th day (P < 0.05). This may be due to the destruction of the cell structure by the continuous growth of ice crystals, which released and activated the PPO in the body at the beginning of freezing, resulting in a significant increase in PPO activity in the early stage of freezing. In the later stage of freezing, the PPO activity showed a downward trend but did not lose its activity, mainly because the activity of PPO was inhibited in a low temperature environment but still had activity, which would slowly occur. The PPO activity of frozen storage in the box was always lower than that outside the box (P < 0.05), indicating that the constant temperature freezing of Experimental Example 1 can better inhibit the PPO activity than conventional freezing, effectively slow down the blackening of shrimp, and have a better preservation effect.

[0126] Salt-soluble protein content: Take 2 portions of 2.0 g of the second and third abdominal segments of shrimp meat in Experimental Example 1 and Experimental Example 2, respectively, at 4 ° C, add 20.0 mL of high salt ion phosphate buffer (0.50 mol / L KCl-0.01 mol / L NaH2PO4-0.03 mol / L Na2HPO4) and 20.0 mL of low salt ion phosphate buffer (0.025 mol / L NaH2PO4-0.025 mol / L Na2HPO4), and fully homogenize at a speed of 8000 rpm for 4 min. The high and low salt homogenates are respectively allowed to stand for 3 h and 1 h at 4 ° C, centrifuged (10000 r / min, 4 ° C, 10 min), and the supernatant is added with 10 mL of 15% trichloroacetic acid to precipitate protein, centrifuged again (10000 r / min, 4 ° C, 10 min), and the supernatant is discarded. The precipitation is precipitated with 20 mL Dissolve 1.0 mol / L sodium hydroxide fully (it must be dissolved completely, and the dissolution time is determined according to the actual situation). After the solution is completely dissolved, dilute to 50 mL with high salt and low salt buffer respectively, and determine the protein content by the biuret method. The salt-soluble protein content is the difference between the protein content in the high salt solution and the protein content in the low salt solution. Fig.12At the beginning of frozen storage, the salt-soluble protein content of Chinese whip shrimp inside and outside the box decreased significantly due to air freezing (P < 0.05). After 30 days of frozen storage outside the box, the salt-soluble protein content decreased significantly (P < 0.05), and it decreased significantly only after 45 days of frozen storage in the box (P < 0.05). At the end of frozen storage, compared with the fresh group, the salt-soluble protein content in the box decreased by 32.87 mg / g, and the salt-soluble protein content outside the box decreased by 43.69 mg / g. The decline in storage in the box is always smaller than that outside the box (P < 0.05), which may be because the ice crystals formed by constant temperature frozen storage are smaller, which has less damage to the cell structure, has a certain inhibitory effect on protein denaturation activity, and delays the dissolution of salt-soluble protein. It can be seen that the constant temperature frozen storage of Experimental Example 1 is more conducive to the preservation of shrimp.

[0127] Total colony count: Weigh 25g of shrimp meat from the second and third abdominal segments of Experimental Example 1 and Experimental Example 2 respectively, place them in a sterile homogenizer cup containing 225mL of physiological saline, and homogenize at 8000rpm for 1min. Use a pipette to draw 1mL of the 1:10 sample homogenate, inject it into a sterile test tube containing 9mL of diluent along the tube wall, and shake it thoroughly to make a 1:100 sample homogenate. Repeat the above steps to prepare a 10-fold serial dilution of the sample homogenate. Select 2 to 3 sample homogenates with appropriate dilutions. When performing a 10-fold incremental dilution, draw 1mL of the sample homogenate into a sterile plate, and make two plates for each dilution. At the same time, use a blank dilution as a blank control. Pour the plate count agar medium cooled to 46°C into the plate in time, and incubate it at 30±1°C for 72±3h after the agar solidifies. See Reference Fig.13 The total number of colonies in fresh Chinese whip shrimp meat and whole shrimp was 2.90lg CFU / g and 4.93lg CFU / g, respectively. The total number of colonies in shrimp meat was much smaller than that in whole shrimp. The total number of colonies in whole shrimp was higher than that in shrimp meat, which might be due to the fact that the shrimp body surface carried more microorganisms and the shrimp thread in the shrimp body was not removed, resulting in more colonies than in shrimp meat. With the increase of frozen storage time, the total number of colonies also increased significantly (P<0.05). It can be seen from the figure that the total number of colonies in the frozen storage box was always smaller than that in the frozen storage box at the same frozen storage time (P<0.05), indicating that the constant temperature frozen storage in Experimental Example 1 is more conducive to delaying the growth and reproduction of microorganisms.

[0128] By analyzing the physical and chemical properties of Chinese whip shrimp during constant temperature storage in a box and conventional frozen storage outside a box, the results showed that under the two freezing conditions, as the freezing time increased, the L* value of the shrimp showed a downward trend, the a* and b* values ​​showed an upward trend, the texture characteristics (hardness, elasticity) and salt-soluble protein content of the shrimp showed a downward trend, the TVB-N value, PPO activity, and total colony count showed an upward trend, and the pH showed a trend of first decreasing and then increasing. Different freezing conditions and different freezing times had a significant effect on the change in the freshness of the shrimp meat odor, and all physical and chemical properties showed that there was a significant difference between constant temperature freezing and conventional freezing at the same freezing time after 45 days (P < 0.05), and the constant temperature process was more conducive to the storage and preservation of Chinese whip shrimp.

[0129] The applicant declares that the present invention illustrates the technical solution of the present invention through the above-mentioned embodiments, but the present invention is not limited to the above-mentioned embodiments, that is, it does not mean that the present invention must rely on the above-mentioned embodiments to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent measures for the raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

[0130] The preferred embodiments of the present invention are described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, a variety of simple modifications can be made to the technical solution of the present invention, and these simple modifications all belong to the protection scope of the present invention.

[0131] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

Claims

1. A constant temperature composite phase change refrigerant, characterized in that: The constant temperature composite phase change refrigerant comprises the following components: water, NH4Cl, NaNO3, TiO2 and curdlan; in terms of mass fraction, the content of each component is: NH4Cl 15%, NaNO3 5-9%, TiO2 0.05-0.15%, curdlan 0.5-1.5%, and the rest is water.

2. A constant temperature composite phase change refrigerant as claimed in claim 1, characterized in that: In terms of mass fraction, NaNO39%, TiO20.1%, and curdlan1.0%.

3. A constant temperature composite phase change refrigerant as claimed in claim 1, characterized in that: In terms of mass fraction, NaNO35%, TiO20.05%, and curdlan0.5%.

4. A constant temperature composite phase change refrigerant as claimed in claim 1, characterized in that: In terms of mass fraction, NaNO37%, TiO20.15%, and curdlan1.5%.

5. A constant temperature composite phase change refrigerant as claimed in any one of claims 1 to 4, characterized in that: The particle size of TiO2 is 60nm.

6. A constant temperature composite phase change refrigerant as claimed in any one of claims 1 to 4, characterized in that: The supercooling degree of the constant temperature composite phase change refrigerant is 0.4-0.9°C, and there is no phase separation phenomenon.

7. A constant temperature composite phase change refrigerant as claimed in any one of claim 2, characterized in that: The phase change latent heat of the constant temperature composite phase change refrigerant is 247.20 J / g, the phase change temperature is -25.08°C, the supercooling degree is 0.4°C, and there is no phase separation phenomenon.

8. An application of the constant temperature composite phase change refrigerant according to any one of claims 1 to 7, characterized in that: The constant temperature composite phase change cold storage agent and a fresh-keeping box are combined and applied to the frozen storage of aquatic products.

9. An application of the constant temperature composite phase change refrigerant as claimed in claim 8, characterized in that: The constant temperature composite phase change cold storage agent is injected into the compartment of the fresh-keeping box.

10. An application of the constant temperature composite phase change refrigerant as claimed in claim 8, characterized in that: The aquatic product is specifically Chinese tube whip shrimp.

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