Composite phase change cold storage agent, preparation method thereof and application thereof in fruit and vegetable preservation

Abstract

The present application belongs to the technical field of cold storage, and particularly relates to a composite phase change cold storage agent, a preparation method thereof and application thereof in fruit and vegetable preservation. The present application takes xylitol as a main energy storage agent, and explores the influence of the xylitol compounded with different phase change adjusting agents, nucleating agents, preservatives and thickening agents on the supercooling degree, cooling curve, phase change latent heat and onset temperature and other performance indicators. The results show that the xylitol, potassium chloride, silicon dioxide, potassium sorbate, sodium alginate and water are compounded in a certain proportion to obtain the best cold storage effect, the relative potential is greater than 290 J / g, the phase change temperature is kept between -5 DEG C and 0 DEG C, the onset temperature can be as low as -3 DEG C, the supercooling degree is lower than 3 DEG C, and the composite phase change cold storage agent shows good cycle stability in a 12-hour low-temperature environment, has excellent cold storage performance, and is suitable for fruit and vegetable, especially cruciferous vegetables including cabbage, long-distance transportation and cold storage and preservation, and makes up for the deficiency of the existing fresh fruit and vegetable storage and preservation conditions.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of cold storage, and particularly relates to a composite phase change cold storage agent, a preparation method thereof and application thereof in fruit and vegetable preservation. BACKGROUND

[0002] Phase change materials (PCM) are a kind of functional materials that can absorb or release a large amount of latent heat through a phase change process to achieve temperature regulation and energy storage. Compared with traditional cold storage agents, phase change cold storage agents have stronger cold storage capacity, are more convenient to use, and are easy to apply and manage. By taking advantage of the feature that the temperature of a substance hardly changes during a phase change process, the temperature slip of a phase change cold storage agent is very small during the release of cold energy, so that the phase change cold storage agent can provide higher energy storage density while effectively ensuring the stability of the system. At present, phase change cold storage agents are widely used in postharvest storage and preservation of fresh fruits and vegetables, can reduce the energy consumption of equipment, and have a green and environmentally friendly market competitive advantage. However, the latent heat of general cold storage ice bags on the market exceeds 290 J / g, and the lowest onset temperature is only -2.5℃. The latent heat of an ice bag product with the lowest onset temperature of -2.9℃ does not reach 290 J / g, and the phase change temperature is not adjustable. For example, Chinese patent CN106433566A discloses a food-grade cold storage agent, which comprises water, sodium chloride, sodium carboxymethyl cellulose and fructose syrup, and is non-toxic, harmless and non-polluting, but has a short duration at low temperature and an uncontrollable phase change temperature. SUMMARY

[0003] The present application aims to make up for the many deficiencies of existing phase change cold storage agents in terms of onset temperature, supercooling degree and cycle stability, and to provide a composite phase change cold storage agent, a preparation method thereof and application thereof in fruit and vegetable preservation, which has excellent cold preservation performance and improves the application effect in the field of fruit and vegetable storage and preservation.

[0004] The present application provides a composite phase change cold storage agent, which comprises xylitol, potassium chloride, silicon dioxide, potassium sorbate, sodium alginate and water.

[0005] The mass-volume percentage content of xylitol in the composite phase change cold storage agent is 0.5-4%.

[0006] The mass-volume percentage content of potassium chloride in the composite phase change cold storage agent is 0.25-0.5%.

[0007] The mass-volume percentage content of silicon dioxide in the composite phase change cold storage agent is 0.001-0.02%.

[0008] The mass-volume percentage content of potassium sorbate in the composite phase change cold storage agent is 0.05-0.3%.

[0009] The mass-volume percentage of sodium alginate in the composite phase change cold storage agent is 0.9-1.5%.

[0010] Preferably, the mass-volume percentage of xylitol in the composite phase change cold storage agent is 1-2%.

[0011] Preferably, the mass-volume percentage of silicon dioxide in the composite phase change cold storage agent is 0.005%.

[0012] Preferably, the mass-volume percentage of potassium sorbate in the composite phase change cold storage agent is 0.1-0.2%.

[0013] Preferably, the mass-volume percentage of sodium alginate in the composite phase change cold storage agent is 1.2%.

[0014] The application further provides a preparation method of the composite phase change cold storage agent, comprising the following steps:

[0015] The xylitol, potassium chloride, silicon dioxide, potassium sorbate, sodium alginate and water are mixed, and then frozen and solidified after packaging to obtain the composite phase change cold storage agent.

[0016] Preferably, the freezing and solidification temperature is-20 DEG C, and the time is 24-48 h.

[0017] The application further provides an ice bag comprising a bag body, wherein the bag body is packaged with the composite phase change cold storage agent or the composite phase change cold storage agent prepared by the preparation method.

[0018] The application further provides an application of the composite phase change cold storage agent or the composite phase change cold storage agent prepared by the preparation method or the ice bag in fruit and vegetable preservation.

[0019] Preferably, the fruit and vegetable comprises cruciferous vegetables, and the cruciferous vegetables comprise cabbage.

[0020] Beneficial effects:

[0021] The system compares the performance of erythritol, isomalt, D-sorbitol and xylitol, and finds that xylitol has stable cooling characteristics and low supercooling degree (≤1℃). On this basis, the application takes xylitol as a main energy storage agent, and explores the influence of the compound of xylitol and different phase change modifiers, nucleating agents, preservatives and thickening agents on the supercooling degree, cooling curve, phase change latent heat and onset temperature and other performance indicators. The results show that the compound of xylitol, potassium chloride, silicon dioxide, potassium sorbate, sodium alginate and water has the best cold storage effect, the relative potential is greater than 290 J / g, the phase change temperature is kept between-5℃ and 0℃, the onset temperature can be as low as-3℃, the supercooling degree is less than 3℃, and good cycle stability is shown in a 12 h low-temperature environment, which has excellent cold preservation performance and is suitable for cold storage and preservation in long-distance transportation, especially for cruciferous vegetables including cabbage, and makes up for the deficiency of the existing fresh fruit and vegetable storage and preservation conditions. BRIEF DESCRIPTION OF DRAWINGS

[0022] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments.

[0023] Figure 1 The cooling curves of different concentrations of candidate main energy storage agents, wherein (A) is maltitol, (B) is erythritol, (C) is D-sorbitol, and (D) is xylitol;

[0024] Figure 2 The supercooling degrees of different concentrations of candidate main energy storage agents;

[0025] Figure 3 The differential scanning calorimetry (DSC) curve of 2% xylitol aqueous solution;

[0026] Figure 4 The cooling curves of the compound of 2% xylitol aqueous solution and different concentrations of candidate phase change modifiers, wherein (A) is the compound of 2% xylitol aqueous solution and KCl, (B) is the compound of 2% xylitol aqueous solution and NaCl, and (C) is the compound of 2% xylitol aqueous solution and NH4Cl;

[0027] Figure 5 The supercooling degrees of the compound of 2% xylitol aqueous solution and different concentrations of candidate phase change modifiers;

[0028] Figure 6 The DSC curves of the compound of 2% xylitol aqueous solution and candidate phase change modifiers at a concentration of 0.25%;

[0029] Figure 7Cooling curve of 2% xylitol aqueous solution, 0.25% candidate phase change modifier and different concentrations of candidate nucleating agent; wherein (A) 2% xylitol aqueous solution, 0.25% concentration candidate phase change modifier and SiO2 are compounded, (B) 2% xylitol aqueous solution, 0.25% concentration candidate phase change modifier and Na2B4O7 are compounded;

[0030] Figure 8 Supercooling degree of 2% xylitol aqueous solution, 0.25% candidate phase change modifier and different concentrations of candidate nucleating agent;

[0031] Figure 9 DSC curve of 2% xylitol aqueous solution, 0.25% candidate phase change modifier and 0.005% SiO2;

[0032] Figure 10 Cooling curve of 2% xylitol aqueous solution, 0.25% KCl, 0.005% SiO2 and different concentrations of potassium sorbate;

[0033] Figure 11 Supercooling degree of 2% xylitol aqueous solution, 0.25% KCl, 0.005% SiO2 and different concentrations of potassium sorbate;

[0034] Figure 12 DSC curve of 2% xylitol aqueous solution, 0.25% KCl, 0.005% SiO2 and different concentrations of potassium sorbate;

[0035] Figure 13 Cooling curve of 2% xylitol aqueous solution, 0.25% KCl, 0.005% SiO2, 0.1% potassium sorbate and different concentrations of sodium alginate;

[0036] Figure 14 Supercooling degree of 2% xylitol aqueous solution, 0.25% KCl, 0.005% SiO2, 0.1% potassium sorbate and different concentrations of sodium alginate;

[0037] Figure 15 DSC curve of 2% xylitol aqueous solution, 0.25% KCl, 0.005% SiO2, 0.1% potassium sorbate and different concentrations of sodium alginate;

[0038] Figure 16 Time-temperature curve of empty box of different treatment groups of test example 1;

[0039] Figure 17 Cooling curve (A), supercooling degree (B), relative potential (C) and onset temperature (D) of the composite phase change cold storage agent of the application after not repeated freeze-thaw and repeated freeze-thaw for 20 times;

[0040] Figure 18 The effects of different treatments on the weight loss rate of head cabbage during storage and transportation;

[0041] Figure 19 Different treatments for head cabbage during storage and transportation value (A), a Value (B) and b The effect of the value (C);

[0042] Figure 20 The effect of different treatments on the firmness of head cabbage during storage and transportation;

[0043] Figure 21 The effects of different treatments on the soluble solids content of head cabbage during storage and transportation;

[0044] In this context, different uppercase letters indicate significant differences between different substances, and different lowercase letters indicate significant differences between different concentrations. P <0.05, P <0.01, P <0.001, P <0.0001, compared to the CK group; # P <0.05, ## P <0.01, ### P <0.001, #### P <0.0001, compared with the CK group, CA group; Δ P <0.05, ΔΔ P <0.01, ΔΔΔ P <0.001, ΔΔΔΔ P <0.0001, compared to the CK group in the CL group. Detailed Implementation

[0045] This invention provides a composite phase change cold storage agent, comprising xylitol, potassium chloride, silicon dioxide, potassium sorbate, sodium alginate and water;

[0046] The xylitol content in the composite phase change cold storage agent is 0.5-4% by mass and volume.

[0047] The mass-volume percentage of potassium chloride in the composite phase change cold storage agent is 0.25~0.5%;

[0048] The mass-volume percentage of silica in the composite phase change cold storage agent is 0.001~0.02%;

[0049] The mass-volume percentage of potassium sorbate in the composite phase change cold storage agent is 0.05~0.3%;

[0050] The mass-volume percentage of sodium alginate in the composite phase change cold storage agent is 0.9~1.5%.

[0051] The xylitol content in the composite phase change cold storage agent of this invention is 0.5-4% by mass and volume. As one embodiment, the xylitol content in the composite phase change cold storage agent of this invention is 1-2% by mass and volume. In specific implementations of this invention, the xylitol content can be arbitrarily selected within the range of 0.5-4%, for example, 0.5%, 0.6%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.5%, 3%, 3.5%, 3.8%, or 4%. This invention systematically compares the performance of four sugar alcohols: erythritol, isomaltitol, D-sorbitol, and xylitol, and finds that xylitol has stable cooling characteristics and a low supercooling degree (≤1℃).

[0052] The mass-volume percentage of potassium chloride in the composite phase change cold storage agent of the present invention is 0.25~0.5%. In specific implementation, the content can be arbitrarily selected within the range of 0.25~0.5%, for example, 0.25%, 0.3%, 0.32%, 0.36%, 0.44%, 0.45%, 0.48% or 0.5%.

[0053] The composite phase change refrigerant of this invention contains 0.001-0.02% silica by mass volume. As one embodiment, the composite phase change refrigerant of this invention contains 0.005% silica by mass volume. In specific implementations, the silica content can be arbitrarily selected within the range of 0.001-0.02%, for example, 0.001%, 0.002%, 0.005%, 0.008%, 0.01%, 0.015%, or 0.02%.

[0054] This invention systematically compares the effects of xylitol combined with different concentrations of phase change modifiers (potassium chloride, ammonium chloride, sodium chloride) and different nucleating agents (silica, sodium tetraborate). It was found that the combination of potassium chloride, ammonium chloride, sodium chloride and xylitol met the screening criteria for transportation and storage. However, when nucleating agents were added, there were significant differences in supercooling, maximum relative potential and onset temperature. Potassium chloride had the most significant cold storage effect, and when silica was chosen as the nucleating agent, the cold storage effect was more significant.

[0055] The mass / volume percentage of potassium sorbate in the composite phase change cold storage agent is 0.05-0.3%. As an embodiment, the mass / volume percentage of potassium sorbate in the composite phase change cold storage agent is 0.1-0.2%. The application can take any value within the range of 0.05-0.3% in the specific implementation process, for example, 0.05%, 0.08%, 0.1%, 0.15%, 0.18%, 0.2%, 0.25%, 0.26% or 0.3%. The application limits the concentration of potassium sorbate, which has the optimal cold storage effect.

[0056] The mass / volume percentage of sodium alginate in the composite phase change cold storage agent is 0.9-1.5%. As an embodiment, the mass / volume percentage of sodium alginate in the composite phase change cold storage agent is 1.2%. The application can take any value within the range of 0.9-1.5% in the specific implementation process, for example, 0.9%, 1.0%, 1.2%, 1.4% or 1.5%. The application limits the concentration of sodium alginate, which has the optimal cold storage effect.

[0057] As an embodiment, the composite phase change cold storage agent according to the application comprises 2% xylitol, 0.25% potassium chloride, 0.005% silicon dioxide, 0.1% potassium sorbate, 1.2% sodium alginate and the rest water in terms of mass / volume percentage. The composite phase change cold storage agent configured according to 2% xylitol, 0.25% potassium chloride, 0.005% silicon dioxide, 0.1% potassium sorbate, 1.2% sodium alginate and the rest water has the most significant cold storage effect, shows a higher phase change latent heat (≥ 290 J / g), a suitable Onset temperature (-3℃), a lower supercooling degree (1.77℃) and good cycle stability, and can effectively maintain a stable 12 h low-temperature environment.

[0058] The application also provides a preparation method of the composite phase change cold storage agent.

[0059] The xylitol, potassium chloride, silicon dioxide, potassium sorbate, sodium alginate and water are mixed, and then frozen and solidified after packaging to obtain the composite phase change cold storage agent.

[0060] As an embodiment, the freezing and solidification temperature is -20℃. As an embodiment, the freezing and solidification time is 24-48 h; as another embodiment, the freezing and solidification time is 30-45 h; as another embodiment, the freezing and solidification time is 340 h.

[0061] The application also provides an ice bag comprising a bag body, wherein the bag body is packaged with the composite phase change cold storage agent according to the above technical solution or the composite phase change cold storage agent obtained by the preparation method according to the above technical solution.

[0062] As an implementation form, the bag body is a 14# thickened self-sealing bag.

[0063] The application also provides the application of the composite phase change cold storage agent in fruit and vegetable preservation.

[0064] As an implementation form, the fruit and vegetable includes cruciferous vegetables. As an implementation form, the cruciferous vegetables include cabbage.

[0065] In order to further illustrate the application, the composite phase change cold storage agent, the preparation method thereof and the application thereof in fruit and vegetable preservation provided by the application are described in detail below in combination with the drawings and examples, but they should not be understood as the limitation of the protection scope of the application.

[0066] The percentage (%) mentioned in the application is mass percentage.

[0067] Example 1

[0068] Screening of main energy storage agents

[0069] 1. Solution preparation: four candidate main energy storage agents, isomalt, D-sorbitol, xylitol and erythritol, were respectively prepared into 0.25%, 0.5%, 1%, 2% and 4% aqueous solutions, which were used immediately after preparation.

[0070] 2. Cooling curve preparation: 25 mL of solution with different concentrations was measured and placed in a 50 mL centrifuge tube, and the K / J thermocouple probe was fixed in the center of the solution to avoid the probe touching the centrifuge tube wall. The device was placed in a constant temperature water bath at about 26℃. Then the device was placed in a-20℃ environment for 2 h, and the temperature of the solution was measured and recorded every 20 min to obtain the time-temperature curve of the solution cooling process, as shown in Figure 1 The results show that the aqueous solutions of erythritol, isomalt, D-sorbitol and xylitol with the same concentration rapidly cool from 0 min to 20 min, and drop to about 0℃ at 40 min, and maintain about 0℃ from 40 min to 100 min. At the end of 2 h cooling, there is no obvious difference in the lowest temperature of the xylitol solution at different concentrations, which shows stable cooling characteristics. In contrast, the lowest temperature of the erythritol, isomalt and D-sorbitol solutions changes significantly with the concentration.

[0071] 2. Supercooling degree determination: 25 mL of different concentration solutions were measured and placed in a 50 mL centrifuge tube. The K / J thermocouple thermometer probe was fixed in the center of the solution to avoid the probe touching the centrifuge tube wall. The device was placed in a constant temperature water bath and the temperature in the tube was stabilized at about 26°C. Then the device was placed in a-20°C environment for 1 h. The temperature was measured and recorded every 1 min. Each group of samples was repeated 3 times, and the average value was taken. The difference between the actual crystallization temperature and the theoretical crystallization temperature on the cooling curve was observed, which was the supercooling degree. The results are shown in Table 1. The results show that there is a significant difference in the supercooling degree of different concentrations of materials. The supercooling degree of erythritol at 0.5%, 1% and 2% is less than 1°C, showing good stability. The supercooling degree of isomalt at 1%, 2% and 4% is less than 1°C. The supercooling degree of D-sorbitol at all concentrations (0.25%, 0.5%, 1%, 2% and 4%) is less than 1°C, and the supercooling degree at 1% is the lowest, showing excellent stability. The supercooling degree of xylitol at 0.5%, 1%, 2% and 4% is less than 1°C, showing high stability. Moreover, the supercooling degree of 2% xylitol solution is significantly lower than that of other substances and concentrations. Figure 2

[0072] 4. Relative potential and onset temperature determination: Differential scanning calorimetry (DSC) was used for determination. 7-10 mg (accurate to 0.01 mg) of 2% xylitol solution was weighed into an aluminum crucible, and the same empty crucible was placed on the reference side. The temperature was decreased from 10°C to-30°C at a rate of 20°C / min, then increased to 10°C at a rate of 20°C / min, repeated 3 times to eliminate thermal history. The heat flow was stabilized at 10°C for 2 min, then decreased to-30°C at a rate of 5°C / min, and then increased to 15°C at a rate of 5°C / min, and the results are shown in Table 2. Then the relative potential and onset temperature were obtained by TA analysis software. The results show that the phase change latent heat of 2% xylitol aqueous solution is 303.4 J / g, and the onset temperature is-2.48°C, which meets the selection criteria for transporting and storing of ball cabbage. Figure 3

[0073] Example 2

[0074] Screening of phase change adjuster

[0075] Potassium chloride (KCl), ammonium chloride (NH4Cl) and sodium chloride (NaCl) were used as candidate phase change adjusters. They were added to 2% xylitol aqueous solution to a final concentration of 0.25%, 0.5%, 1%, 2% and 4%. According to the steps of Example 1, the cooling curve was drawn, the supercooling degree, the relative potential and the onset temperature were measured, and the results are shown in Table 3. Figures 4-6

[0076] ​​​2 h cooling curve results show that with the increase of the concentration of the solution, the final temperature shows a downward trend, and the solution with a concentration of 4% reaches the lowest temperature. In particular, when the concentrations of NaCl, KCl and NH4Cl are all 0.25%, the cooling rate of the compounded solution is similar to that of 2% xylitol solution, and the temperatures of the two are both stable at about -2℃ at 2 h. At a concentration of 0.25%, the compounded solution of the three substances shows high stability during the cooling process. The supercooling degree measurement results show that the supercooling degree of the compounded solution of NaCl, KCl and NH4Cl increases with the increase of the concentration. The supercooling degree of the compounded solution of NaCl, KCl and NH4Cl at a concentration of 0.25% is significantly lower than that at other concentrations. By measuring the phase change latent heat of the compounded solution of NaCl, KCl and NH4Cl at a concentration of 0.25%, it is 341.57 J / g, 331.72 J / g and 346.56 J / g, respectively, and the Onset temperatures are -2.91℃, -2.75℃ and -2.91℃, respectively. When the concentrations of NaCl, KCl and NH4Cl are all 0.25%, the compounded solution and the 2% xylitol solution both meet the screening standards for transportation and storage.

[0077] Example 3

[0078] A composite energy storage agent is obtained by adding 0.25% KCl to a 2% xylitol aqueous solution.

[0079] Example 4

[0080] A composite energy storage agent is obtained by adding 0.25% NH4Cl to a 2% xylitol aqueous solution.

[0081] Example 5

[0082] A composite energy storage agent is obtained by adding 0.25% NaCl to a 2% xylitol aqueous solution.

[0083] Example 6

[0084] Screening of nucleating agent screening

[0085] Silicon dioxide (SiO2) and sodium tetraborate (Na2B4O7) are used as candidate nucleating agents and are added to the composite energy storage agents obtained in Examples 4-6 (labeled as KCl, NH4Cl and NaCl, respectively) to a final concentration of 0.002%, 0.005% and 0.01%, respectively. According to the steps of Example 1, the cooling curve is drawn, the supercooling degree, the relative latent heat and the Onset temperature are measured, and the results are shown in Table 2. Figures 7-9

[0086] ​2 h cooling curve results show that the solution presents a significant phenomenon of first cooling and then heating during the cooling process, and the supercooling degree of SiO2 is significantly lower than that of Na2B4O7. SiO2 at a concentration of 0.005% is lower than other concentrations, so 0.005% SiO2 is selected as the nucleating agent. According to the differential scanning calorimetry (DSC) results, the complex solution composed of 0.005% SiO2, 0.25% KCl and 2% xylitol shows the highest relative potential and absolute value of Onset temperature, which is 344.75 J / g and -2.81℃, respectively. Based on the above analysis, the complex solution composed of 0.005% SiO2, 0.25% KCl and 2% xylitol is selected for subsequent experiments.

[0087] Example 7

[0088] Screening of preservative concentration

[0089] To ensure that the cold storage agent does not easily breed bacteria during long-term use and prolong its service life, potassium sorbate is selected as a preservative. 0.005% SiO2 is added to the composite energy storage agent obtained in Example 3, and potassium sorbate is added to a final concentration of 0.05%, 0.1%, 0.2% and 0.3%. According to the steps of Example 1, the cooling curve is drawn, and the supercooling degree, relative potential and Onset temperature are measured, and the results are shown in Table 3. Figures 10-12

[0090] 2 h cooling curve results show that different concentrations of potassium sorbate have little effect on the cooling curve. The complex solution with 0.1% potassium sorbate shows the lowest supercooling degree and the highest phase change potential, with a phase change potential of 343.43 J / g.

[0091] Example 8

[0092] Screening of thickener concentration

[0093] To improve the stability and practicability of the cold storage agent, sodium alginate is selected as a thickening agent. 0.005% SiO2 and 0.1% potassium sorbate are added to the composite energy storage agent obtained in Example 3, and sodium alginate is added to a final concentration of 0.3%, 0.6%, 0.9%, 1.2% and 1.5%. According to the steps of Example 1, the cooling curve is drawn, and the supercooling degree, relative potential and Onset temperature are measured, and the results are shown in Table 4. Figures 13-15

[0094] ​​2 h cooling curve results show that the cooling trend of different concentrations of sodium alginate at-20℃ is basically the same, and the supercooling degree of the compound solution added with 1.2% sodium alginate is significantly lower than that of other concentrations. Although the addition of sodium alginate reduces the relative potential and phase change temperature of the compound solution, the relative potential of the compound solution with five different concentrations of sodium alginate is greater than 290 J / g, and the phase change temperature is maintained between-5℃ and 0℃, which fully meets the requirements of fruit and vegetable storage and transportation preservation.

[0095] Example 9

[0096] A composite phase change cold storage agent, consisting of 2% xylitol, 0.25% potassium chloride, 0.005% silicon dioxide, 0.1% potassium sorbate, 1.2% sodium alginate, and the balance of water.

[0097] Comparative Example 1

[0098] A commercially available phase change cold storage agent, consisting of a high polymer compound.

[0099] Test Example 1

[0100] 1. Empty box time-temperature curve

[0101] 250 g of the composite phase change cold storage agent (CL) of Example 1 and the commercially available phase change cold storage agent (CA) of Comparative Example 1 were respectively measured and placed in 14# thick self-sealing bags, sealed with a sealing machine, and placed in a-20℃ refrigerator for 48 h until completely frozen. A thermometer was inserted from the center of the foam box cover, and the tip of the thermometer was placed at the center of the foam box. Twelve phase change cold storage agents were placed in each foam box, and the temperature was recorded every 3 h after sealing. Each sample was repeated three times, and the average value was taken. The treatment group without adding phase change cold storage agent was used as a blank control (CK), and the treatment group with ice was used as a positive control (ICE). The time-temperature curve of the foam box warming process was obtained, and the results are shown in Figure 16 .

[0102] According to Figure 16 It can be seen that, in addition to the blank control (CK), the other three groups all showed a rapid cooling trend within the first 3 h, among which the temperature of the composite phase change cold storage agent provided by Example 9 of the application was the lowest, reaching 3.4℃. After 3 h, the temperature of each group showed a slow rising trend, and the temperature in each group rose to above 10℃ at 12 h. Compared with the ice group and the commercially available cold storage agent group, the composite phase change cold storage agent provided by Example 9 showed more excellent cooling capacity and could more effectively maintain a low temperature environment in the box, and the cold preservation effect was significantly better than that of the other groups. In summary, the composite phase change cold storage agent provided by Example 9 of the application showed significant advantages in cooling speed and cold preservation time, and could better meet the demand for maintaining a low temperature environment during the fruit and vegetable logistics storage process, providing reliable technical support for the quality preservation of fresh products.

[0103] 2. Cyclic performance testing

[0104] 250 g of the composite phase change refrigerant from Example 9 was placed in a No. 14 thickened packaging bag, sealed, and frozen at -20°C for 24 h. It was then left at room temperature (25°C) for 6 h until completely thawed, constituting one freeze-thaw cycle. After repeating this freeze-thaw cycle 20 times, the cooling curve was plotted following the steps in Example 1, and the supercooling, relative potential, and onset temperature were measured. The results are as follows: Figure 17 As shown. A comparison is made between no repeated freeze-thaw cycles (C0) and 20 repeated freeze-thaw cycles (C...). 20 The 2-hour cooling curves, supercooling, relative potential, and onset temperature of the composite phase change refrigerant after 20 freeze-thaw cycles revealed a slight decrease in temperature and relative potential at 2 hours, while the absolute value of the onset temperature and supercooling increased slightly. These changes indicate that repeated freeze-thaw cycles have a certain impact on the refrigerant's cold storage and preservation capabilities. Further analysis shows that the cooling process of the composite phase change refrigerant after 20 freeze-thaw cycles is basically similar to that during the initial freeze-thaw cycle, exhibiting a rapid initial cooling followed by a gradual decrease, maintaining a temperature near 0°C for a period of time. Furthermore, the supercooling of the composite phase change refrigerant did not increase significantly after 20 freeze-thaw cycles, and no crystal precipitation or obvious phase separation was observed. This indicates that the composite phase change refrigerant of this invention maintains good cycling performance and possesses excellent cold storage and release capabilities during repeated freeze-thaw cycles.

[0105] Example 10

[0106] Fresh head cabbage was divided into four groups and placed in different foam boxes for storage experiments. The CK group served as the control group, with no cold storage agent in the foam box; the ICE group had ordinary ice in the foam box; the CA group used the commercially available cold storage agent from Comparative Example 1; and the CL group used the composite phase change cold storage agent from Example 9 of this application. Before the experiment, 250 g of water, the commercially available cold storage agent, and the composite phase change cold storage agent from Example 9 were measured and placed into identical 14# thickened packaging bags, sealed, and frozen at -20°C for 48 h until completely frozen. After complete freezing, each foam box was filled with 12 ice packs containing the cold storage agent. The treated foam boxes were then sealed and stored at room temperature.

[0107] Test Example 2

[0108] Example 10: Samples were taken on days 0, 1, 3, 5, and 7 of storage, and various indicators were measured.

[0109] 1. Weight loss rate determination

[0110] The weight loss rate was calculated according to the following formula: weight loss rate (%) = (M2-M1) / M1x100%; wherein M1 represents the weight of the cabbage head recorded on day 0 g, and M2 represents the weight of the cabbage head recorded at each sampling point g, and each group of treatments was measured three times (n = 3), and the results are shown in Table 2. Figure 18 The results show that, after the end of the storage period, the cabbage heads of the ice treatment group and the composite phase change cold storage agent treatment group (CL) of Example 9 of the present application are significantly lower than the weight loss rate of the cabbage heads of the control group (CK group) (6.93%). Among them, the weight loss rate value of the CL group at the end of the storage is the smallest (1.49%), with the smallest loss, which is 4.65 times lower than the weight loss rate value of the CK group. Therefore, the composite phase change cold storage agent treatment of Example 9 of the present application can make the cabbage heads maintain a higher sensory quality during transportation and storage.

[0111] 2. Color index determination

[0112] The L , a , and b values of the cabbage heads were measured by a color difference meter, and each group was measured three times, and the results are shown in Table 3. Figure 19 The results show that, during the entire storage period, the L values of the cabbage heads of each group showed an upward trend, among which the L value of the ice treatment group (ICE) was the highest at the end of the storage period (76.73), and the L value of the composite phase change cold storage agent treatment group (CL) of the present application was the lowest (73.22). The a values of all groups of cabbage heads showed a downward trend first and then an upward trend, reaching the lowest value at 5 d, and then began to rise, among which the a values of the CK group and the ICE group changed most significantly. The b values of all groups of cabbage heads showed an upward trend during the entire storage period, and at the end of the storage, the b values of the ICE group (35.5) and the CK group (35.32) were higher. These results show that all cabbage head samples experienced a color change from green to yellow during storage, reflecting the phenomenon of leaf senescence with the extension of storage time.

[0113] 3. Texture index determination

[0114] The hardness was determined using a food texture analyzer. A flat-bottomed cylindrical probe P / 0.5 N was used, and the pre-test, in-test, and post-test rates were 60 mm / min, the compression degree was 50%, the interval time was 1 s, and the trigger value was 5 g. Each group of treatments was repeated three times (n = 3), and the results are shown in Table 4. Figure 20The results show that at the initial stage of storage, the hardness of the cabbages in the CK group and the ICE group decreased rapidly, and the hardness of the cabbages in the CK group decreased from 92.08 N at 0 d to 65.8 N at 7 d, with the largest change. In contrast, the hardness of the cabbages in the CA group and the CL group changed less, indicating that the tissue structure of the cabbages was more complete. The composite phase change cold storage agent of the application can effectively inhibit the water loss of the cabbages during transportation and storage, thereby maintaining the integrity of the leaf cell wall and the stability of the tissue structure of the cabbages.

[0115] 4. Soluble solids determination

[0116] The soluble solids were determined by using a portable digital refractometer. The cabbage samples in each treatment group were mixed and squeezed to juice, and then filtered with gauze to determine the soluble solids content. After calibrating the refractometer with distilled water, the lens of the refractometer was carefully wiped dry, and then the determination was performed. The data were recorded and expressed as a percentage (%) of the fresh cabbage weight, and the results are shown in Table 4. Figure 21 The results show that the soluble solids content of the cabbages in all groups showed a downward trend during storage, but the soluble solids content of the cabbages in the CL and CA treatment groups was significantly higher than that in the control group (CK) at the later stage of storage. Among them, the soluble solids content of the cabbages in the CL group, the CA group, the ice treatment group (ICE group) and the CK group was 5.53%, 5.38%, 5.28% and 4.98% respectively at 7 d. This result shows that the composite phase change cold storage agent of the application can effectively inhibit the oxidation reaction of polyphenolic substances in the cabbages during transportation and storage by maintaining a low-temperature storage environment for a long time, reduce the respiration rate of the cabbages, thereby reducing the consumption of nutrients and delaying the aging process.

[0117] Comparative Example 2

[0118] A composite phase change cold storage agent similar to Example 9, except that the xylitol is replaced by isomalt.

[0119] Comparative Example 3

[0120] A composite phase change cold storage agent similar to Example 9, except that the xylitol is replaced by D-sorbitol.

[0121] Comparative Example 4

[0122] A composite phase change cold storage agent similar to Example 9, except that the xylitol is replaced by erythritol.

[0123] Comparative Example 5

[0124] A composite phase change cold storage agent similar to Example 9, except that the potassium chloride is replaced by ammonium chloride.

[0125] Comparative Example 6

[0126] A composite phase change cold storage agent similar to Example 9, except that potassium chloride is replaced by sodium chloride.

[0127] Comparative Example 7

[0128] A composite phase change cold storage agent similar to Example 9, except that silicon dioxide is replaced by sodium tetraborate.

[0129] Example 11

[0130] Fresh cabbages were divided into 7 groups and stored in different foam boxes. The first treatment group used the composite phase change cold storage agent of Example 9, and the second to seventh treatment groups used the composite phase change cold storage agents of Comparative Examples 2 to 7, respectively. Before the test, 250 g of water, commercially available cold storage agent and the composite phase change cold storage agent of Example 9 were measured and placed in 14# thick packaging bags of the same size, and then sealed and frozen at -20℃ in a refrigerator for 48 h to completely freeze. After complete freezing, 12 cold storage ice bags were placed in each foam box. The treated foam boxes were sealed and stored at room temperature.

[0131] Test Example 3

[0132] The hardness and soluble solids content of cabbages were measured according to the method of Test Example 2, and the results are shown in Table 1.

[0133] Table 1. Test results of hardness and soluble solids content of cabbages under different storage

[0134]

[0135] Note: indicates the comparison with the first treatment group, P <0.05, indicates the comparison with the first treatment group, P <0.01.

[0136] As can be seen from Table 1, the composition of different composite phase change cold storage agents has a significant difference on the hardness and soluble solids content of cabbages after storage.

[0137] As can be seen from the above, the composite phase change cold storage agent provided by the present application has excellent cold storage performance and can meet the needs of fruit and vegetable storage and preservation, especially cruciferous vegetables including cabbages.

[0138] Although the above examples have made a detailed description of the present application, it is only a part of the embodiments of the present application, not all the embodiments, and other embodiments can be obtained according to the present embodiments without creativity, which are within the protection scope of the present application.

Claims

1. A composite phase change refrigerant, characterized in that, It includes xylitol, potassium chloride, silicon dioxide, potassium sorbate, sodium alginate, and water; The xylitol content in the composite phase change cold storage agent is 0.5-4% by mass and volume. The mass-volume percentage of potassium chloride in the composite phase change cold storage agent is 0.25~0.5%; The mass-volume percentage of silica in the composite phase change cold storage agent is 0.001~0.02%; The mass-volume percentage of potassium sorbate in the composite phase change cold storage agent is 0.05~0.3%; The mass-volume percentage of sodium alginate in the composite phase change cold storage agent is 0.9~1.5%.

2. The composite phase change cold storage agent according to claim 1, characterized in that, The xylitol content in the composite phase change cold storage agent is 1-2% by mass and volume.

3. The composite phase change cold storage agent according to claim 1, characterized in that, The mass-volume percentage of silicon dioxide in the composite phase change cold storage agent is 0.005%.

4. The composite phase change refrigerant according to claim 1, characterized in that, The mass-volume percentage of potassium sorbate in the composite phase change cold storage agent is 0.1~0.2%.

5. The composite phase change cold storage agent according to claim 1, characterized in that, The sodium alginate content in the composite phase change cold storage agent is 1.2% by mass and volume.

6. The method for preparing the composite phase change refrigerant according to any one of claims 1 to 5, characterized in that, Includes the following steps: Xylitol, potassium chloride, silicon dioxide, potassium sorbate, sodium alginate, and water were mixed, encapsulated, and then frozen to obtain the composite phase change cold storage agent.

7. The preparation method according to claim 6, characterized in that, The freeze-curing temperature is -20℃ and the time is 24~48 h.

8. An ice pack, comprising a bag body, characterized in that, The bag contains the composite phase change cold storage agent as described in any one of claims 1 to 5, or the composite phase change cold storage agent obtained by the preparation method described in claim 6 or 7.

9. The application of the composite phase change cold storage agent according to any one of claims 1 to 5, or the composite phase change cold storage agent obtained by the preparation method according to claim 6 or 7, or the ice pack according to claim 8, in the preservation of fruits and vegetables.

10. The application according to claim 9, characterized in that, The fruits and vegetables mentioned include cruciferous vegetables; the cruciferous vegetables include head cabbage.

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