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

Abstract

The invention 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 of the composite phase change cold storage agent in fruit and vegetable preservation. According to the invention, xylitol is used as a main energy storage agent, and the influence of xylitol compounded with different phase change regulators, nucleating agents, preservatives and thickeners on the supercooling degree, cooling curve, phase change latent heat, Onset temperature and other performance indexes is explored. Results show that the xylitol, the potassium chloride, the silicon dioxide, the potassium sorbate, the sodium alginate and the water are compounded according to a certain proportion to achieve the best cold storage effect, the relative potential is larger than 290 J / g, the phase change temperature is kept between-5 DEG C and 0 DEG C, the lowest Onset temperature can reach-3 DEG C, the degree of supercooling is lower than 3 DEG C, and good cycle stability is shown in a low-temperature environment for 12 h; the fresh-keeping agent has excellent cold insulation performance, is suitable for cold storage and fresh keeping of fruits and vegetables, especially brassicaceous vegetables including common head cabbages in long-distance transportation, and makes up for the deficiency of existing fresh-keeping conditions for storage and transportation of fresh fruits and vegetables.

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 characteristic 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, 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. The mass-volume percentage content of xylitol in the composite phase change cold storage agent is 0.5-4%. The mass-volume percentage content of potassium chloride in the composite phase change cold storage agent is 0.25-0.5%. The mass-volume percentage content of silicon dioxide in the composite phase change cold storage agent is 0.001-0.02%. The mass-volume percentage content of potassium sorbate in the composite phase change cold storage agent is 0.05-0.3%. The mass-volume percentage content of sodium alginate in the composite phase change cold storage agent is 0.9-1.5%.

[0005] Preferably, the mass-volume percentage of xylitol in the composite phase change cold storage agent is 1-2%.

[0006] Preferably, the mass-volume percentage of silicon dioxide in the composite phase change cold storage agent is 0.005%.

[0007] Preferably, the mass-volume percentage of potassium sorbate in the composite phase change cold storage agent is 0.1-0.2%.

[0008] Preferably, the mass-volume percentage of sodium alginate in the composite phase change cold storage agent is 1.2%.

[0009] The application also provides a preparation method of the composite phase change cold storage agent, comprising the following steps: 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.

[0010] Preferably, the freezing and solidification temperature is-20℃, and the time is 24-48 h.

[0011] 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 or the composite phase change cold storage agent prepared by the preparation method.

[0012] The application also 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.

[0013] Preferably, the fruits and vegetables comprise cruciferous vegetables, and the cruciferous vegetables comprise cabbage.

[0014] Beneficial effects: 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 the 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 best cold storage effect is obtained by compounding xylitol, potassium chloride, silicon dioxide, potassium sorbate, sodium alginate and water in a certain proportion, 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 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, which makes up for the deficiency of the existing fresh fruit and vegetable storage and preservation conditions. BRIEF DESCRIPTION OF DRAWINGS

[0015] 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.

[0016] 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; Figure 2 The supercooling degrees of different concentrations of candidate main energy storage agents; Figure 3 The differential scanning calorimetry (DSC) curve of 2% xylitol aqueous solution; Figure 4 The cooling curves of 2% xylitol aqueous solution and different concentrations of candidate phase change modifiers; wherein, (A) is 2% xylitol aqueous solution compounded with KCl, (B) is 2% xylitol aqueous solution compounded with NaCl, and (C) is 2% xylitol aqueous solution compounded with NH4Cl; Figure 5 The supercooling degrees of 2% xylitol aqueous solution and different concentrations of candidate phase change modifiers; Figure 6 The DSC curves of 2% xylitol aqueous solution and candidate phase change modifiers at 0.25% concentration; 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; Figure 8 Supercooling degree of 2% xylitol aqueous solution, 0.25% candidate phase change modifier and different concentrations of candidate nucleating agent; Figure 9 DSC curve of 2% xylitol aqueous solution, 0.25% candidate phase change modifier and 0.005% SiO2; Figure 10 Cooling curve of 2% xylitol aqueous solution, 0.25% KCl, 0.005% SiO2 and different concentrations of potassium sorbate; Figure 11 Supercooling degree of 2% xylitol aqueous solution, 0.25% KCl, 0.005% SiO2 and different concentrations of potassium sorbate; Figure 12 DSC curve of 2% xylitol aqueous solution, 0.25% KCl, 0.005% SiO2 and different concentrations of potassium sorbate; 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; 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; 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; Figure 16 Cooling curve of 2% xylitol aqueous solution, 0.25% KCl, 0.005% SiO2, 0.1% potassium sorbate and different concentrations of sodium alginate; 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 repeated freezing and thawing for 20 times; Figure 18 Effect of different treatments on the weight loss rate of cabbage during storage and transportation; Figure 19 Effect of different treatments on the L value (A), a value (B) and b The effect of the value (C); Figure 20 The effect of different treatments on the firmness of head cabbage during storage and transportation; Figure 21 The effects of different treatments on the soluble solids content of head cabbage during storage and transportation; 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

[0017] This invention provides a composite phase change cold storage agent, comprising 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%.

[0018] The mass / volume percentage content of xylitol in the composite phase change cold accumulator is 0.5-4%. As an embodiment, the mass / volume percentage content of xylitol in the composite phase change cold accumulator is 1-2%. In the specific implementation process of the present application, the value can be taken randomly 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%. The present application compares the performance of erythritol, isomaltulose, D-sorbitol and xylitol, and finds that xylitol has stable cooling characteristics and lower supercooling degree (≤1℃).

[0019] The mass / volume percentage content of potassium chloride in the composite phase change cold accumulator is 0.25-0.5%. In the specific implementation process of the present application, the value can be taken randomly 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%.

[0020] The mass / volume percentage content of silicon dioxide in the composite phase change cold accumulator is 0.001-0.02%. As an embodiment, the mass / volume percentage content of silicon dioxide in the composite phase change cold accumulator is 0.005%. In the specific implementation process of the present application, the value can be taken randomly 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%.

[0021] The present application compares the effect of xylitol compounded with different concentrations of phase change adjusting agents (potassium chloride, ammonium chloride, sodium chloride) and different nucleating agents (silicon dioxide, sodium tetraborate), and finds that potassium chloride, ammonium chloride and sodium chloride compounded with xylitol meet the screening standards for transportation and storage. However, when nucleating agents are added, the supercooling degree, the highest relative latent heat and the Onset temperature show significant differences. The cold storage effect of potassium chloride is the most significant, and when the nucleating agent is silicon dioxide, the cold storage effect is more significant.

[0022] The mass / volume percentage content of potassium sorbate in the composite phase change cold accumulator is 0.05-0.3%. As an embodiment, the mass / volume percentage content of potassium sorbate in the composite phase change cold accumulator is 0.1-0.2%. In the specific implementation process of the present application, the value can be taken randomly within the range of 0.05-0.3%, for example, 0.05%, 0.08%, 0.1%, 0.15%, 0.18%, 0.2%, 0.25%, 0.26% or 0.3%. The present application limits the concentration of potassium sorbate, which has the optimal cold storage effect.

[0023] 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 present application can be arbitrarily selected 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 present application limits the concentration of sodium alginate, which has the optimal cold storage effect.

[0024] As an embodiment, the composite phase change cold storage agent according to the present application comprises 2% xylitol, 0.25% potassium chloride, 0.005% silicon dioxide, 0.1% potassium sorbate, 1.2% sodium alginate and the balance of 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 balance of water has the most significant cold storage effect, exhibits higher phase change latent heat (≥ 290 J / g), suitable Onset temperature (-3℃), lower supercooling degree (1.77℃) and good cycle stability, and can effectively maintain a stable 12 h low-temperature environment.

[0025] The present application also provides a preparation method of the composite phase change cold storage agent according to the above technical solution, comprising the following steps: Mixing xylitol, potassium chloride, silicon dioxide, potassium sorbate, sodium alginate and water, and then freezing and solidifying after packaging to obtain the composite phase change cold storage agent.

[0026] As an embodiment, the freezing and solidification temperature according to the present application is -20℃. As an embodiment, the freezing and solidification time according to the present application is 24-48 h; as another embodiment, the freezing and solidification time according to the present application is 30-45 h; as another embodiment, the freezing and solidification time according to the present application is 340 h.

[0027] The present 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.

[0028] As an embodiment, the bag body according to the present application is a 14# thick self-sealing bag.

[0029] The present application also provides the application of 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 or the ice bag according to the above technical solution in fruit and vegetable preservation.

[0030] As an embodiment, the fruits and vegetables according to the present application comprise cruciferous vegetables. As an embodiment, the cruciferous vegetables according to the present application comprise cabbage.

[0031] In order to further illustrate the present application, a composite phase change cold storage agent, a preparation method thereof and application thereof in fruit and vegetable preservation are described in detail below in combination with the accompanying drawings and examples, but they should not be understood as limiting the scope of protection of the present application.

[0032] The percentage (%) mentioned in the present application is mass percentage.

[0033] Example 1 Screening of main energy storage agent 1. Solution preparation: four candidate main energy storage agents, isomalt, D-sorbitol, xylitol and erythritol, were prepared into 0.25%, 0.5%, 1%, 2% and 4% aqueous solutions, which were used immediately after preparation.

[0034] 2. Cooling curve preparation: 25 mL of solution with different concentrations was measured and placed in a 50 mL centrifuge tube, the K / J thermocouple probe was fixed in the center of the solution to avoid the probe touching the centrifuge tube wall, and was placed in a constant temperature water bath, and the temperature in the tube was stabilized 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, and the time-temperature curve of the solution cooling process was obtained, as shown in Figure 1 The results showed that the erythritol, isomalt, D-sorbitol and xylitol aqueous solutions with the same concentration rapidly cooled from 0 min to 20 min, and dropped to about 0℃ at 40 min, and maintained at about 0℃ from 40 min to 100 min. At the end of 2 h cooling, the lowest temperature of the xylitol solution showed no significant difference at different concentrations, showing stable cooling characteristics. In contrast, the lowest temperature of the erythritol, isomalt and D-sorbitol solutions changed significantly with the concentration.

[0035] 2. Supercooling degree determination: 25 mL of solution with different concentrations was measured and placed in a 50 mL centrifuge tube, the K / J thermocouple probe was fixed in the center of the solution to avoid the probe touching the centrifuge tube wall, and was placed in a constant temperature water bath, and the temperature in the tube was stabilized at about 26℃. Then the device was placed in a-20℃ environment for 1 h, and the temperature was measured and recorded every 1 min. Each group of samples was repeated 3 times, and the average value was taken, and the difference between the actual crystallization temperature and the theoretical crystallization temperature on the cooling curve was observed, which was the supercooling degree, as shown in Figure 2As shown in the figure, the results indicate that there are significant differences in supercooling at different concentrations of the materials. Erythritol exhibited good stability with supercooling less than 1°C at concentrations of 0.5%, 1%, and 2%. Isomaltitol showed supercooling less than 1°C at concentrations of 1%, 2%, and 4%. D-sorbitol showed supercooling less than 1°C at all concentrations (0.25%, 0.5%, 1%, 2%, and 4%), with the lowest supercooling at 1% concentration, demonstrating excellent stability. Xylitol showed highly stable characteristics with supercooling less than 1°C at concentrations of 0.5%, 1%, 2%, and 4%. Furthermore, the supercooling of the 2% xylitol solution was significantly lower than that of other substances and concentrations.

[0036] 4. Relative potential and onset temperature determination: Differential scanning calorimetry (DSC) was used. 7–10 mg (accurate to 0.01 mg) of 2% xylitol solution was weighed into an aluminum crucible. An identical empty crucible was placed on the reference side. The solution was cooled from 10 °C to -30 °C at a rate of 20 °C / min, then heated back to 10 °C at a rate of 20 °C / min, repeated three times to eliminate thermal history. The temperature was held at 10 °C for 2 min to stabilize the heat flow, then cooled to -30 °C at a rate of 5 °C / min, then heated back to 15 °C at a rate of 5 °C / min, and held for 2 min. The results are as follows: Figure 3 As shown in the figure. The relative heat of phase change and onset temperature were then obtained using TA analysis software. The results showed that the latent heat of phase change of the 2% xylitol aqueous solution was 303.4 J / g, and the onset temperature was -2.48℃, meeting the screening criteria for the transportation and storage of head cabbage.

[0037] Example 2 Screening of phase change modifiers Potassium chloride (KCl), ammonium chloride (NH4Cl), and sodium chloride (NaCl), three safe and non-toxic phase change temperature regulators, were used as candidate phase change modifiers and were added to a 2% xylitol aqueous solution to a final concentration of 0.25%, 0.5%, 1%, 2%, and 4%, respectively. Following the steps of Example 1, cooling curves were plotted, and the supercooling, relative potential, and onset temperature were measured. The results are as follows: Figures 4-6 As shown.

[0038] 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 compound 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 compound solution of the three substances shows high stability during the cooling process. The supercooling degree measurement results show that the supercooling degree of the compound solution of NaCl, KCl and NH4Cl increases with the increase of the concentration. The supercooling degree of the compound 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 compound 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 temperature is -2.91℃, -2.75℃ and -2.91℃, respectively. When the concentrations of NaCl, KCl and NH4Cl are all 0.25%, the compound solution and the 2% xylitol solution both meet the screening standards for transportation and storage.

[0039] Example 3 A composite energy storage agent is obtained by adding 0.25% KCl to a 2% xylitol aqueous solution.

[0040] Example 4 A composite energy storage agent is obtained by adding 0.25% NH4Cl to a 2% xylitol aqueous solution.

[0041] Example 5 A composite energy storage agent is obtained by adding 0.25% NaCl to a 2% xylitol aqueous solution.

[0042] Example 6 Screening of nucleating agent Silicon dioxide (SiO2) and sodium tetraborate (Na2B4O7) were added to the composite energy storage agents (labeled as KCl, NH4Cl and NaCl, respectively) obtained in Examples 4-6 to a final concentration of 0.002%, 0.005% and 0.01%, respectively. According to the steps of Example 1, the cooling curve was drawn, and the supercooling degree, relative latent heat and Onset temperature were measured, and the results are shown in Table 1. Figures 7-9

[0043] ​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 exhibits 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.

[0044] Example 7 Screening of preservative concentration 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. The results are shown in Table 3. Figures 10-12

[0045] 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 exhibits the lowest supercooling degree and the highest phase change potential, with a phase change potential of 343.43 J / g.

[0046] Example 8 Screening of thickening agent concentration 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. The results are shown in Table 4. Figures 13-15

[0047] 2 h cooling curve results show that the cooling trends of different concentrations of sodium alginate at -20℃ are basically consistent. The supercooling degree of the complex solution 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 complex solution, the relative potential of the five different concentrations of sodium alginate complex solution 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, transportation and preservation. ​​

[0048] Example 9 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 water, in terms of mass volume percentage.

[0049] Comparative Example 1 A commercially available phase change cold storage agent, consisting of a high polymer compound.

[0050] Test Example 1 1. Empty box time-temperature curve 250 g of the composite phase change cold storage agent of Example 1 (CL) and 250 g of the commercially available phase change cold storage agent of Comparative Example 1 (CA) 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 in 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 3 times, and the average value was taken. The treatment group without the addition of the phase change cold storage agent was taken as the blank control (CK), and the treatment group with ice was taken as the positive control (ICE). The time-temperature curve of the foam box warming process was obtained, and the results are shown in Figure 16 .

[0051] According to Figure 16 It can be seen that, except for the blank control (CK), the other three groups all showed a rapid cooling trend within the first 3 h, among which the composite phase change cold storage agent provided by Example 9 of the present application had the lowest temperature, 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 present application showed significant advantages in cooling speed and cold preservation time, and could better meet the needs of maintaining a low temperature environment during the storage process of fruits and vegetables, and provided reliable technical support for the quality preservation of fresh products.

[0052] 2. Circulation performance determination 250 g of the composite phase change cold storage agent of Example 9 was placed in a 14# thick packaging bag, sealed, frozen at -20℃ for 24 h, and then placed at room temperature (25℃) for 6 h to completely melt for the first freeze-thaw cycle. After 20 repeated freeze-thaw cycles, the cooling curve was drawn according to the steps of Example 1, and the supercooling degree, relative potential, and Onset temperature were determined. The results are shown in Figure 17 . Comparing the non-repeated freeze-thaw (C0) with the repeated freeze-thaw 20 times (C 20The 2 h cooling curve, supercooling degree, relative latent heat and Onset temperature of the composite phase change cold storage agent after 20 freeze-thaw cycles can be found that the temperature of the cold storage agent at 2 h after 20 freeze-thaw cycles is slightly decreased, the relative latent heat is slightly decreased, and the absolute value of the Onset temperature and the supercooling degree are slightly increased. These changes show that the freeze-thaw cycle has a certain influence on the cold storage and cold preservation capacity of the cold storage agent. Further analysis shows that the cooling process of the composite phase change cold storage agent of the application after 20 freeze-thaw cycles is basically similar to that of the first freeze-thaw cycle, which is rapid cooling first, then slow cooling, and maintaining at about 0℃ for a period of time. In addition, the supercooling degree of the composite phase change cold storage agent after 20 freeze-thaw cycles does not increase significantly, and no crystal precipitation or obvious phase separation phenomenon is observed. It shows that the composite phase change cold storage agent of the application can still maintain good cycle performance in the repeated freeze-thaw process, and has excellent cold storage and cold release capacity.

[0053] Example 10 Fresh cabbages were divided into 4 groups and stored in different foam boxes. The CK group was the control group, and no cold storage agent was placed in the foam box. The ICE group placed ordinary ice in the foam box. The CA group used the commercial cold storage agent of Comparative Example 1. The CL group used the composite phase change cold storage agent of Example 9. Before the test, 250 g of water, commercial cold storage agent and composite phase change cold storage agent of Example 9 were measured and placed in the same size 14# thick packaging bags, which were sealed and frozen at-20℃ for 48 h to completely freeze. After complete freezing, 12 cold storage agent ice bags were placed in each foam box. The treated foam boxes were sealed and stored at room temperature.

[0054] Test Example 2 The samples of Example 10 were taken at 0, 1, 3, 5, 7 days of storage, and various indicators were measured.

[0055] 1. Weight loss rate determination The weight loss rate was calculated according to the following formula: weight loss rate (%) = (M2-M1) / M1x100%; wherein M1 represents the weight of cabbages recorded on day 0 g, and M2 represents the weight of cabbages recorded at each sampling point g, and each group of treatment was measured 3 times (n = 3), and the results are shown in Table 1. Figure 18 The results show that after the end of the storage period, the weight loss rate of cabbages in the ice treatment group and the composite phase change cold storage agent treatment group (CL) of the application (6.93%) is significantly lower than that of the control group (CK group). The weight loss rate value of the CL group at the end of storage is the smallest (1.49%), and the loss is the smallest, 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 application can maintain a high sensory quality of cabbages during transportation and storage.

[0056] 2. Color index determination The color difference meter was used to measure the L , a , b values were determined, each group was determined in triplicate, and the results are shown in Figure 19 . The results show that the L values of the broccoli heads of each group all showed an upward trend during the entire storage period, among which the L value of the ice treatment group (ICE) was the highest at the end of the storage period (76.73), while the L value of the composite phase change cold storage agent treatment group (CL) was the lowest (73.22). The a values of all groups of broccoli 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 broccoli heads showed an upward trend during the entire storage period, and the b values of the ICE group (35.5) and the CK group (35.32) were higher at the end of the storage. These results show that all broccoli samples experienced a color change from green to yellow during storage, reflecting the phenomenon of leaf senescence as the storage time increased.

[0057] 3. Texture index determination 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 speeds were 60 mm / min, the compression degree was 50%, the interval time was 1 s, and the trigger value was 5 g. Each treatment was repeated three times (n = 3), and the results are shown in Figure 20 . The results show that at the beginning of the storage, the hardness values of the broccoli heads of the CK group and the ICE group decreased rapidly, among which the hardness of the broccoli heads of the CK group decreased significantly from 92.08 N at 0 d to 65.8 N at 7 d, with the largest change. In contrast, the hardness of the broccoli heads of the CA group and the CL group changed less, indicating that their tissue structure was more complete. The composite phase change cold storage agent of the application can effectively inhibit the water loss of broccoli during transportation and storage, thereby maintaining the integrity of the leaf cell wall and the stability of the tissue structure.

[0058] 4. Soluble solids determination The soluble solids were determined using a portable digital refractometer. The broccoli samples of each treatment group were mixed and juiced, then filtered with gauze to determine the soluble solids content. After calibrating the refractometer with distilled water, the refractometer lens was carefully wiped dry, and then measured. The data was recorded and expressed as a percentage (%) of the weight of fresh broccoli, and the results are shown in Figure 21The results showed that the soluble solid content of all groups of Brussels sprouts showed a downward trend during storage, but the soluble solid content of the CL and CA treatment groups was significantly higher than that of the control group (CK) at the later stage of storage. Among them, the soluble solid contents of the CL group, the CA group, the ice treatment group (ICE group) and the CK group were 5.53%, 5.38%, 5.28% and 4.98% respectively at 7 d. This result showed that the composite phase change cold accumulator treatment of the application could effectively inhibit the oxidation reaction of polyphenolic substances of Brussels sprouts during transportation and storage by maintaining a low-temperature storage environment for a long time, reduce the respiration rate, thereby reducing the consumption of nutrients and delaying the aging process.

[0059] Comparative Example 2 A composite phase change cold accumulator similar to Example 9, except that xylitol is replaced by isomalt.

[0060] Comparative Example 3 A composite phase change cold accumulator similar to Example 9, except that xylitol is replaced by D-sorbitol.

[0061] Comparative Example 4 A composite phase change cold accumulator similar to Example 9, except that xylitol is replaced by erythritol.

[0062] Comparative Example 5 A composite phase change cold accumulator similar to Example 9, except that potassium chloride is replaced by ammonium chloride.

[0063] Comparative Example 6 A composite phase change cold accumulator similar to Example 9, except that potassium chloride is replaced by sodium chloride.

[0064] Comparative Example 7 A composite phase change cold accumulator similar to Example 9, except that silicon dioxide is replaced by sodium tetraborate.

[0065] Example 11 Fresh Brussels sprouts were divided into 7 groups and placed in different foam boxes for storage test. Among them, the first treatment group used the composite phase change cold accumulator of Example 9, and the second to seventh treatment groups used the composite phase change cold accumulators of Comparative Examples 2 to 7, respectively. Before the test, 250 g of water, commercially available cold accumulators and the composite phase change cold accumulator of Example 9 were measured and placed in 14# thick packaging bags of the same size, sealed and frozen in a-20℃ refrigerator for 48 h to completely freeze. After complete freezing, 12 cold accumulator ice bags were placed in each foam box. The treated foam boxes were sealed and stored at room temperature.

[0066] Test Example 3 The hardness and soluble solid content of the cabbage were determined according to the method of Test Example 2, and the results are shown in Table 1.

[0067] Table 1: Results of hardness and soluble solid content determination of cabbage under different storage

[0068] Note: indicates compared with the first treatment group, P <0.05, indicates compared with the first treatment group, P <0.01.

[0069] According to Table 1, it can be seen that the composition of different composite phase change cold accumulators has a significant difference on the hardness and soluble solid content of the cabbage after storage.

[0070] According to the above, it can be seen that the composite phase change cold accumulator 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 cabbage.

[0071] Although the above embodiment has made a detailed description of the present application, it is only a part of the embodiments of the present application, but not all the embodiments, and other embodiments can be obtained according to the present embodiment without creativity, which all belong to the protection scope of the present application.

Claims

1. A composite phase change cold accumulator, characterized in that, Xylitol, potassium chloride, silicon dioxide, potassium sorbate, sodium alginate and water; The mass-volume percentage of xylitol in the composite phase change cold storage agent is 0.5-4%. 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 silicon dioxide 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 energy accumulator according to claim 1, characterized in that, The mass-volume percentage of xylitol in the composite phase change cold storage agent is 1-2%.

3. The composite phase change thermal energy storage agent of claim 1, wherein, The mass-volume percentage of silicon dioxide in the composite phase change cold storage agent is 0.005%.

4. The composite phase change thermal energy storage agent of claim 1, wherein, 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 thermal energy storage agent of claim 1, wherein, The mass-volume percentage of sodium alginate in the composite phase change cold storage agent is 1.2%.

6. The method of producing a composite phase change cold accumulator according to any one of claims 1 to 5, characterized in that, The method comprises the following steps: Xylitol, potassium chloride, silicon dioxide, potassium sorbate, sodium alginate and water are mixed, and then the mixture is frozen and solidified after being packaged to obtain the composite phase change cold storage agent.

7. The preparation method according to claim 6, characterized in that, The freezing and solidification is performed at a temperature of-20℃ for 24-48 h.

8. An ice pack comprising a bag, characterised in that The bag contains the composite phase change cold storage agent of any one of claims 1-5 or the composite phase change cold storage agent obtained by the method of claim 6 or 7. 9.The composite phase change cold storage agent of any one of claims 1-5 or the composite phase change cold storage agent obtained by the method of claim 6 or 7 or the ice bag of claim 8 is applied to the preservation of fruits and vegetables.

10. Use according to claim 9, characterized in that, The fruits and vegetables comprise cruciferous vegetables; the cruciferous vegetables comprise cabbage. The fruits and vegetables comprise cruciferous vegetables; the cruciferous vegetables comprise cabbage.

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