NL2026475B1

NL2026475B1 - Phase change cold storage agent for strawberry preservation and method for preparing the same

Info

Publication number: NL2026475B1
Application number: NL2026475A
Authority: NL
Inventors: Luo Zisheng; Xu Yanqun; Li Li; Ying Tiejin
Original assignee: Univ Zhejiang
Priority date: 2020-09-15
Filing date: 2020-09-15
Publication date: 2021-05-25
Also published as: NL2026475A

Abstract

The present invention discloses a phase change cold storage agent for strawberry preservation and a method for preparing the same, and belongs to the technical ﬁeld of cold 5 storage agents. The optimal formula of the phase change cold storage agent consisted the following components: maltitol 1.72%, nano titanium dioxide 0.05%, sodium carboxymethyl cellulose 0.10%, super absorbent resin 0.50%, and the rest was deionized water. Its phase change temperature was 0.11 °C, and its latent heat was 299.61J/g. The source of the raw materials involved in the present invention was convenient, the preparation process was simpler, 10 and the production cost was lower. And the prepared cold storage agent had a larger latent heat, and its phase change temperature was compatible with the storage temperature range and freezing point of strawberries. It had no supercooling and phase separation, and no obvious change in the latent heat after repeated cycles. It was non-toxic and tasteless, safe and environmentally friendly. Compared with other cold storage agents with lower phase change 15 temperature, it was more suitable for strawberry preservation and cold chain transportation.

Description

1 001652P-NL

PHASE CHANGE COLD STORAGE AGENT FOR STRAWBERRY PRESERVATION

AND METHOD FOR PREPARING THE SAME Technical Field The present invention relates to the technical field of cold storage agent preparation, in particular to a phase change cold storage agent for strawberry preservation and a method for preparing the same. Background At present, the global cold chain is expanding uninterruptedly, especially in developing countries. The expanded cold chain may promote changes in global diets, food production and distribution, and shopping habits. With the growth of population and demand, food safety has become an increasingly important issue in recent years. In order to extend and ensure the shelf life of food, it is very important to keep the temperature during storage and transportation within a given range. Every year, a large amount of food around the world deteriorates and rots due to transportation and sales without cold chain protection, causing serious economic losses. Therefore, with the support of logistics fresh-keeping facilities and technology, establishing a sound logistics fresh-keeping system and reducing food losses in the process of logistics fresh-keeping is the only way for the sustainable development of the global food industry.

Cold storage technology is a process of using various physical, chemical, mechanical and other effective means to store cold energy in a cold storage agent, and then release the stored cold energy when needed. The special materials produced by this technology that can store cold energy efficiently and meet various physical and chemical requirements are called cold storage agents. As a new type of functional material, the cold storage agent plays an important role in cold chain logistics with its advantages of economy, safety and convenience, and is the core technology to realize cold chain transportation.

Strawberry, known as the "queen of fruits", is soft, juicy, sweet and sour, and has a strong aroma, and is loved by consumers around the world. Strawberry has high nutritional value. It is not only rich in nutrients such as vitamin A, vitamin C, calcium, iron and dietary fiber, but also rich in natural antioxidants such as anthocyanins, which can help improve vision, reduce night blindness, protect liver and promote gastrointestinal motility, etc. At present, the total global strawberry production is about 9.2 million tons, and the market scale is growing strongly.

2 001652P-NL However, due to the thin skin and fragile tissues of strawberries, mechanical damage is prone to occur, which further leads to bacterial infections and is not resistant to storage; at the same time, strawberries have high post-harvest respiration strength, high water activity, and active post-harvest physiological metabolic processes, leading to nutrient loss, reducing their eating quality and commodity value, and causing serious economic losses. Therefore, the post-harvest storage, transportation and preservation of strawberries is a key issue that needs to be resolved in the strawberry industry. Different foods have different transportation and storage temperatures. The temperature range of the cold storage agent should be compatible with the actual storage and transportation temperature range and freezing point of the food. Data show that the optimum storage temperature for strawberries is 0°C, and the freezing temperature is -0.8°C. Too low temperature can cause freezing damage to strawberries.

However, the currently disclosed cold storage agents are generally low or high in temperature, which can not meet the requirements of strawberry storage and transportation; for example, the invention patent application with publication number CN104232024A discloses a cold storage agent which is composed of sodium chloride, glycerol and water, and has a phase change temperature of -30.3°C~-29.57C; the invention patent application with publication number CN105601819A discloses a cold storage agent, which is composed of a graft copolymer of konjac glucomannan-acrylic acid-acrylamide, ammonium chloride, potassium nitrate and water, and has a phase change temperature of -18~-15°C; their phase change temperatures are too low for strawberries, which may cause damage such as freezing damage to strawberries. However, the invention patent application with application number CN90109434.X discloses a cold storage agent composed of potassium chloride and water, which has a phase separation problem, resulting in a higher decay rate.

Therefore, in view of the storage characteristics of strawberries, it is of great significance to design and develop a cold storage agent with suitable phase change temperature, economy, safety and convenience for storage, transportation and preservation of strawberries.

Summary The invention provides a phase change cold storage agent for strawberry preservation and a method for preparing the same. The phase change cold storage agent not only has a phase change temperature (-1~1°C) suitable for strawberry storage and transportation, but also has a higher phase change latent heat (>280J/g), and no supercooling and phase separation, especially

3 001652P-NL suitable for strawberry storage and transportation.

The specific technical solutions are as follows: The present invention provides a phase change cold storage agent for strawberry preservation, consisting of the following components by mass percentage: maltitol 1.38-2.07%; nano titanium dioxide 0.03~0.06%; sodium carboxymethyl cellulose 0.09~0.11%; super absorbent resin 0.40~0.60%; and the rest being deionized water.

Among the above-mentioned phase change cold storage agents, the phase change temperature and latent heat of maltitol are relatively stable, and are suitable as the main cold storage material; the nanometer effect of nano titanium dioxide can have antibacterial and sterilization effects, and can increase the latent heat value of the cold storage agent system; as a thickening agent, sodium carboxymethyl cellulose can prevent phase separation without affecting the phase change process, super absorbent resin with its good water retention performance and gel strength can effectively extend the low-temperature freezing time, avoid the leakage of melted water, and also effectively alleviate the phase separation of the cold storage agent.

Preferably, it consists of the following components by mass percentage: maltitol 1.55-1.89%; nano titanium dioxide 0.04~0.055%; sodium carboxymethyl cellulose 0.095-0. 105%; super absorbent resin 0.45-0.55%; and the rest being deionized water. More preferably, it consists of the following components by mass percentage: maltitol 1.72%; nano titanium dioxide 0.05%; sodium carboxymethyl cellulose 0.10%, super absorbent resin 0.50%; and the rest being deionized water.

Further, the particle size of the nano titanium dioxide is 5~10 nm. The nano titanium dioxide used is hydrophilic anatase with a uniform and small particle size, large specific surface area, and strong nanomaterial effects.

Further, the viscosity of the sodium carboxymethyl cellulose is 800~1200 mpa.s.

4 001652P-NL Viscosity is one of the most important technical indicators of sodium carboxymethyl cellulose. The sodium carboxymethyl cellulose used has a moderate viscosity and can be basically completely dissolved in water.

The super absorbent resin is a functional polymer material that contains strong hydrophilic groups and has a certain degree of cross-linking. The main component is sodium polyacrylate with fine particles and the full gel after absorbing water, which can effectively enhance the cold storage time.

Further, the phase change temperature of the phase change cold storage agent is 0.1~1°C, and the latent heat of phase change is 280.30~300.00 J/g.

Data show that the best storage temperature for strawberries 1s 0°C, and some researchers have measured the freezing point of strawberries is -0.8°C; therefore, the above phase change cold storage agent is particularly suitable for strawberry storage and transportation.

The present invention also provides a method for preparing the phase change cold storage agent for strawberry preservation, comprising the following steps: (1) adding maltitol and sodium carboxymethyl cellulose to deionized water and mixing well to obtain solution I; (2) adding nano titanium dioxide to the solution I and mixing well to obtain solution II; (3) adding super absorbent resin to the solution II and mixing well to obtain the phase change cold storage agent. Further, in steps (1)~(3), the mixing temperature is 20~25°C. Compared with the prior art, the present invention has the following beneficial effects: (1) the present invention combines maltitol, nano titanium dioxide, sodium carboxymethyl cellulose and super absorbent resin to obtain the phase change cold storage agent with a phase change temperature of 0.117-0.62°C, and latent heat of 285.30~299.61J /g, which is suitable for strawberry preservation and cold chain transportation to avoid freezing damage due to too low phase change temperature of the cold storage agent.

(2) The raw material sources involved in the phase change cold storage agent of the present invention are universal, the production cost is lower, the preparation process is simple. And the prepared cold storage agent has larger latent heat, no supercooling and phase separation, and no obvious change in the latent heat after repeated cycles. It 1s non-toxic and tasteless, safe and environmentally friendly. Compared with other cold storage agents with lower phase change temperature, it is more suitable for strawberry preservation and cold chain transportation.

001652P-NL Brief Description Of Drawings Fig. 1 is the relationship curve between the concentration of the maltitol aqueous solution and the phase change temperature in example 1.

Fig. 2 is the relationship curve between the concentration of the maltitol aqueous 5 solution and the latent heat in example 1.

Fig. 3 is the DSC curve diagram of the phase change cold storage agent prepared in example 2.

Fig. 4 1s the DSC curve diagram of the phase change cold storage agent prepared in example 3.

Fig. 5 is the DSC curve diagram of the phase change cold storage agent prepared in example 4.

Fig. 6 is the DSC curve diagram of the phase change cold storage agent prepared in example 5. Fig. 7 is the T-t curve of the phase change cold storage agent prepared in example 5.

Detailed Description The present invention will be further described below in conjunction with specific embodiments. The following are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto.

The maltitol (product number M 113279), sodium carboxymethyl cellulose (product number C 104985), and nano titanium dioxide (product number T104949) used in the following examples were all purchased from Aladdin Reagent Network, and the super absorbent resin was purchased from Changzhou Suyu Packaging Co., Ltd.

Example 1 In this example, maltitol was prepared into aqueous solutions with corresponding concentration gradients respectively, which were prepared for immediate use, and the phase change temperature and latent heat of each solution were measured by the DSC method.

The specific steps were as follows: A. maltitol was formulated into an aqueous solution according to the following concentration gradient: maltitol: 0.01, 0.02, 0.05, 0.08, 0.1, 0.2, 0.4 mol/L; B. the phase change temperature and latent heat of each solution were measured by the DSC method.

6 001652P-NL The results were shown in Fig. 1. The phase change temperature of the maltitol aqueous solution remained between -3.7 and -3.5°C with the increase in concentration, which was relatively stable and was a better monomer cold storage material for compound phase change cold storage agents.

As shown in Fig. 2, the latent heat of the maltitol aqueous solution was above 270J/g with the increase in concentration, which met the requirements of the main cold storage substance selected as the phase change cold storage agent.

Therefore, maltitol was selected as the main cold storage substance of the phase change cold storage agent, but it could not be used alone. Its phase change temperature did not meet the requirements of -1~17C in this patent, and its latent heat need to be further increased to above 280J/ g, therefore it was chosen to compound with other substances.

Example 2 The maltitol selected according to example 1 was used as the main cold storage material, and 0.05mol/L maltitol (mass percentage was 1.72%) aqueous solution with the largest latent heat (289.24]/g), nanoparticles (nano titanium dioxide, the mass percentage was 0.01%) and sodium carboxymethyl cellulose (mass percentage was 0.10%) were compounded. The phase change temperature and latent heat of the compound solution were measured by the DSC method.

Wherein the steps of compounding maltitol, nano titanium dioxide and sodium carboxymethyl cellulose were as follows: A. at room temperature, adding the maltitol and sodium carboxymethyl cellulose to deionized water according to the concentration requirements, mixing and stirring well to obtain a clear solution I; B. adding the weighed nano titanium dioxide to the solution I according to the mass percentage (0.01%), and stirring to make it evenly dispersed to obtain the required compound solution, namely solution II; C. the phase change temperature and the latent heat of the compound solution obtained in step B were measured by the DSC method.

As shown in Fig. 3, the phase change temperature of the obtained compound solution was 0.56°C, and the latent heat was 271.11 J/g.

In addition, judging from the state of the cold storage agent compound solution, the compound solution added with 0.50% super absorbent resin (by mass percentage) was evenly dispersed and had enhanced its gel properties.

7 001652P-NL Example 3 The maltitol selected according to example 1 was used as the main cold storage material, and maltitol (mass percentage was 1.72%) aqueous solution, nanoparticles (nano titanium dioxide, the mass percentage was 0.03%) and sodium carboxymethyl cellulose (mass percentage was 0.10%) were compounded. The phase change temperature and latent heat of the compound solution were measured by the DSC method.

The steps of compounding maltitol, nano titanium dioxide and sodium carboxymethyl cellulose were as follows: A. at room temperature, adding the maltitol and sodium carboxymethyl cellulose to deionized water according to the concentration requirements, mixing and stirring well to obtain a clear solution I; B. adding the weighed nano titanium dioxide to the solution I according to the mass percentage (0.03%), and stirring to make it evenly dispersed to obtain the required compound solution, namely solution II; C. the phase change temperature and the latent heat of the compound solution obtained in step B were measured by the DSC method.

As shown in Fig. 4, the phase change temperature of the obtained compound solution was 0.46°C, and the latent heat was 292.45J/g.

Embodiment 4 The maltitol selected according to example 1 was used as the main cold storage material, and maltitol (mass percentage was 1.72%) aqueous solution, nanoparticles (nano titanium dioxide, the mass percentage was 0.05%) and sodium carboxymethyl cellulose (mass percentage was 0.10%) were compounded. The phase change temperature and latent heat of the compound solution were measured by the DSC method.

The steps of compounding maltitol, nano titanium dioxide and sodium carboxymethyl cellulose were as follows: A. at room temperature, adding the maltitol and sodium carboxymethyl cellulose to deionized water according to the concentration requirements, mixing and stirring well to obtain a clear solution I;

8 001652P-NL B. adding the weighed nano titanium dioxide to the solution I according to the mass percentage (0.05%), and stirring to make it evenly dispersed to obtain the required compound solution; C. the phase change temperature and the latent heat of the compound solution obtained in step B were measured by the DSC method.

As shown in Fig. 5, the phase change temperature of the obtained compound solution was 0.04637°C, and the latent heat was 296.56]/g.

Example 5 The phase change temperature and the latent heat of the compound solution in example 4 met the expected requirements, and compared to examples 2 and 3, its phase change temperature was lower and the latent heat of phase change was higher.

However, it was still water-like and had poor gel properties, which may cause leakage of melted water and phase separation during transportation.

In order to improve the state of the cold storage agent, 0.50% (by mass percentage) super absorbent resin was added to the compound solution of example 4 for compounding to prepare a phase change cold storage agent.

This kind of phase change cold storage agent consisted the following component ratios: maltitol 1.72% (by mass percentage); nano titanium dioxide 0.05% (by mass percentage); sodium carboxymethyl cellulose 0.10% (by mass percentage); super absorbent resin 0.50% (by mass percentage), and the rest was deionized water.

The method for preparing the phase change cold storage agent, comprising the following steps: A. at room temperature, adding the maltitol and sodium carboxymethyl cellulose to deionized water, mixing and stirring well to obtain a clear solution; B. adding the weighed nano titanium dioxide to the solution obtained in step A according to the mass percentage, and stirring to make it evenly dispersed; C.

Adding the weighed super absorbent resin to the liquid obtained in step B according to the mass percentage, and stirring to make it evenly dispersed to obtain the phase change cold

9 001652P-NL storage agent.

As shown in Fig. 6, the phase change temperature of the phase change cold storage agent was 0. 11°C, and the latent heat was 299.61J/g. Its phase change temperature met the phase change temperature range (-1~1°C) of the cold storage agent to be developed, and the latent heat also exceeded 280J/g. And its dispersion was uniform, and the gel state was good, therefore it met the requirements of the phase change cold storage agent to be developed.

The following tested the supercooling, phase separation and the changes in phase change temperature and latent heat after repeated freezing and thawing.

The method for testing the supercooling was as follows: 150mL of the cold storage agent formula was put into a 400 mL beaker, which was put in the refrigerator at -20°C. The probe of the thermal resistance thermometer was fixed at the center of the solution, and the temperature was measured and recorded every | minute to obtain the temperature-time (T-t) curve of the cold storage agent.

Fig. 7 was the T-t curve of this example. It could be seen from the figure that the cold storage agent of this example had no supercooling, and a phase change temperature of 0.10°C, which was in good agreement with the result measured by DSC.

The method for testing the phase separation and phase change temperature and latent heat curve after repeated freezing and thawing was as follows: 150 mL of the cold storage agent formula was put into a 400 mL beaker which was put in the refrigerator at -20°C.

Repeated freezing and thawing (every 7 days) were performed to observe whether there was a phase separation, and the melted cold storage agent was tested by DSC to determine the phase change temperature and latent heat after repeated freezing and thawing.

After repeated freezing and thawing, it was observed that the phase change cold storage agent of this example had no phase separation, and had good gel properties and good dispersion uniformity.

Table 1 Changes in phase change temperature and latent heat over time in example 3 of the present invention after repeated freezing and thawing Ce we

10 001652P-NL It could be seen from Table 1 that the phase change temperature after repeated freezing and thawing only showed a slight change, and could basically maintain stability; the latent heat after repeated freezing and thawing only showed a slight change, and could be stable greater than 280J/g.

It could be seen that the cold storage agent of this example had the characteristics that the latent heat after repeated freezing and thawing cycles did not change significantly, and it could always remain in a higher range for a long time.

Claims

11 001652P-EN Conclusions

1. A phase-change cold storage agent for preserving strawberries, which consists of the following components by mass percentage: maltitol 1.38~2.07%; nano titanium dioxide 0.03~0.06%; sodium carboxymethyl cellulose 0.09~0.11%; super absorbent resin 0.40~0.60%; and the rest is deionized water.

The phase change cold storage agent for preserving strawberries according to claim 1, which consists of the following components by mass percentage: maltitol 1.55-1.89%; nano titanium dioxide 0.04~0.055%; sodium carboxymethyl cellulose 0.095-0. 105%; super absorbent resin 0.45-0.55%; and the rest is deionized water.

The phase change cold storage agent for preserving strawberries according to claim 1, which consists of the following components by mass percentage: maltitol 1.72%; nano titanium dioxide 0.05%; sodium carboxymethyl cellulose 0.10%; super absorbent resin 0.50%; and the rest is deionized water.

The phase change cold storage agent for preserving strawberries according to claim 1, wherein the particle size of the nanotitanium dioxide is 5-10 nm.

The phase change cold storage agent for preserving strawberries according to claim 1, wherein the particle size of the nano titanium dioxide is 800-1200 nm.

The phase-change cold storage means for preserving strawberries according to any one of claims 1-5, wherein the phase-change temperature of the

12 001652P-EN cold storage phase change medium is 0.1~1°C and the latent heat is 280.30~300.00 Jig.

A process for preparing the cold storage phase change agent 5S for preserving strawberries according to any one of claims 1 to 5, comprising the steps of: (1) adding maltitol and sodium carboxymethyl cellulose to deionized water and mixing well to obtain solution I; (2) adding nano titanium dioxide to solution I and mixing well to obtain solution II; (3) adding superabsorbent resin to solution II and mixing well to obtain the phase change cold storage agent.

The process for preparing the cold storage phase change agent according to claim 7, wherein in the steps (1) to (3) the mixing temperature is 20-25°C.