CN112544919B - Method for improving color and texture quality of vacuum freeze-dried recombined strawberry crisp chips - Google Patents

Abstract

The invention discloses a method for improving the color and texture quality of vacuum freeze-dried recombined strawberry crisps, which comprises the following steps: crushing strawberries to obtain strawberry pulp, uniformly mixing the strawberry pulp with pectin and protocatechuic acid, and adjusting the pH value to 3.0-3.8 to obtain a material A; wherein the mass ratio of the strawberry pulp to the pectin is 1: 0.02-0.08, and the mass concentration of protocatechuic acid in the material A is 0.1-1.0 g/kg; step two, pouring the material A into a mould tray, and placing the mould tray in a refrigeration house at the temperature of-18 ℃ for freeze thawing treatment to obtain a blocky material B; coating a layer of chitosan on the surface of the material B to obtain a material C; and step four, drying the material C in a vacuum freeze drying box, and then filling nitrogen for packaging to obtain the strawberry crisp chips. The invention creates a brand-new recombinant strawberry crisp chip, and effectively solves the problems that the product pelargonidin-3-glucoside is unstable in storage period and low in hardness and brittleness.

Description

Method for improving the color and texture quality of vacuum freeze-dried recombinant strawberry chips

technical field

The invention relates to the technical field of food processing. More specifically, the present invention relates to a method for improving the color and texture quality of vacuum freeze-dried reconstituted strawberry chips.

Background technique

In recent years, the market of vacuum-frozen fruit and vegetable chips has developed rapidly. It is favored by consumers because of its advantages of being convenient to eat, nutritious and healthy, and easy to carry. Vacuum freeze-drying has gradually become a green and high-quality drying method for preparing strawberry chips.

Strawberry is the largest berry in my country. Strawberry is rich in natural pigments, of which pelargonidin-3-glucoside accounts for 80-90%, which is the main coloring substance of strawberry red. Pelargonium-3-glucoside has strong antioxidant properties, and has various health effects such as preventing aging, improving immunity, and reducing blood lipids. Pelargonium-3-glucoside is easily degraded by external factors such as light and oxygen, especially because the vacuum freeze-dried red heart apple chips have a crisp porous network structure and a relatively large area, which makes oxygen, moisture and light more accessible. Pelargonium-3-glucoside, so the color fade and functional weakening caused by the degradation of pelargonin-3-glucoside become a quality defect that is difficult to solve during the storage process of pelargonin-3-glucoside-rich fruit and vegetable chips. For a long time, how to improve the stability of pelargonidin-3-glucoside in fruit and vegetable food has troubled the food industry, especially the fruit and vegetable chip processing industry.

On the other hand, vacuum freeze-dried natural fruit and vegetable chips have the problems of low hardness and brittleness and soft texture. One of the reasons is the heterogeneity of the tissue structure of the fruit and vegetable raw materials, and the second is that the dry matter content of the fruit and vegetable cell wall is less, and it is difficult to support the rigidity of the porous network structure of the fruit and vegetable chips after drying.

SUMMARY OF THE INVENTION

An object of the present invention is to solve at least the above-mentioned problems and to provide at least the advantages which will be explained later.

Another object of the present invention is to provide a method for improving the color and texture quality of vacuum freeze-dried recombinant strawberry chips. Spontaneous stabilization process of pelargonidin-3-glucoside by the interaction of large and small molecules of catechin (3,4-dihydroxybenzoic acid) and pelargonidin-3-glucoside, using texture reorganization, aeration, freezing and thawing at the same time The size of ice crystals and the pore characteristics of the product are precisely controlled by physical means such as treatment, and a new recombinant strawberry chip is created, which effectively solves the problems of unstable storage period and low hardness and brittleness of the product pelargonidin-3-glucoside.

In order to achieve these objects and other advantages according to the present invention, there is provided a method for improving the color and texture quality of vacuum freeze-dried reconstituted strawberry chips, comprising the following steps:

Step 1: Crush the strawberries to obtain strawberry pulp, mix the strawberry pulp with pectin and protocatechuic acid uniformly, and adjust the pH to 3.0～3.8 to obtain material A; wherein, the mass ratio of strawberry pulp to pectin is 1:0.02～0.08 , the mass concentration of protocatechuic acid in material A is 0.1 to 1.0 g/kg;

Step 2: Pour material A into the mold tray, and place it in a cold storage at -18°C for freeze-thaw treatment to obtain block material B;

Step 3, coating a layer of chitosan on the surface of material B to obtain material C;

Step 4: The material C is placed in a vacuum freeze-drying box to dry, and then packed with nitrogen to obtain strawberry chips.

Preferably, in the method for improving the color and texture quality of vacuum freeze-drying and reconstituting strawberry chips, in step 1, crushing the strawberries to obtain strawberry pulp is specifically as follows: selecting strawberries with uniform maturity and no pests and diseases, washing them, and passing through The vibrating screen is drained and mixed with apple peel residue, and then placed in a beating machine to be beaten to obtain strawberry pulp. The mass fraction of apple peel residue in the strawberry pulp is 5-10%.

Preferably, in the method for improving the color and texture quality of vacuum freeze-drying and reconstituted strawberry chips, in step 1, the strawberries are crushed to obtain strawberry pulp, the strawberry pulp is uniformly mixed with pectin and protocatechuic acid, and citric acid is used for mixing. Adjust pH to 3.0～3.8 to obtain material A.

Preferably, in the method for improving the color and texture quality of vacuum freeze-drying and reconstituting strawberry chips, the second step is specifically: pour the material A into the mold groove of the mold tray after homogenizing, and place it in a temperature of -18°C. In the cold storage, after the material A is frozen, adjust the temperature of the cold storage: increase the temperature of the cold storage by 1 °C every 1 hour until the temperature of the cold storage is adjusted to -4 °C, and then adjust the temperature of the cold storage to -18 °C again after holding for 3 to 6 hours. The temperature adjustment method is to adjust the cycle for 1 to 5 times, then keep the temperature for 1 hour, take out the mold tray, and take out the block from the mold groove to obtain material B.

Preferably, in the method for improving the color and texture quality of vacuum freeze-drying and reconstituted strawberry chips, the third step is specifically: placing material B at -1～0°C with a volume fraction of 30～50% chitosan Soak it in the solution, take it out after 2 to 5 seconds, put it on a tray at -40°C, put it back in a freezer at -18°C, and take it out to get material C.

Preferably, in the method for improving the color and texture quality of vacuum freeze-drying and reconstituted strawberry chips, the fourth step is specifically: placing material C in a vacuum freeze-drying oven, wherein the cold trap temperature of the vacuum drying oven is -50°C , the temperature of the storage tray of the freeze-drying box is 0-70°C; when the water content of the material C drops below 7%, the material C is taken out from the vacuum freeze-drying box and packed with nitrogen to obtain strawberry chips.

The present invention includes at least the following beneficial effects:

1. The present invention announces for the first time the color protection process of pelargonidin-3-glucoside based on the spontaneous chemical stabilization of pectin combined with protocatechuic acid; Oxygen barrier technology significantly improves the stability of pelargonidin-3-glucoside during product storage. Specifically, this scheme utilizes that the abundant carboxyl groups on the pectin molecule with low methyl esterification degree are negatively charged above its isoelectric point, and pelargonidin-3-glucoside is positively charged below the isoelectric point, thus resulting in electrostatic interaction. At the same time, the non-covalent bond "Π-Π overlap" between the small molecule protocatechuic acid benzene ring and the pelargonidin-3-glucoside benzene ring is used to form the Both sides stabilize the chemical structure that restricts pelargonidin-3-glucoside, so that the B ring cannot move freely due to steric hindrance, and at the same time limits the dissociation of chemical bonds, greatly improving the chemical stability of pelargonidin-3-glucoside; Both gum and protocatechuic acid are widely present in natural fruits and vegetables. The present invention utilizes protocatechuic acid that can be extracted in large quantities from raw materials such as tea leaves and coffee scraps as color-protecting substances, and the prepared food does not contain artificial synthetic food additives. The product is green and natural;

2. In the present invention, a layer of pectin coating is formed on the periphery of the strawberry chips by chitosan coating treatment on the strawberry pieces. The low oxygen and low water activity environment around the glycoside molecule further inhibits the degradation of pelargonidin-3-glucoside and effectively improves the degradation of pelargonidin-3-glucoside during storage; the chitosan coating can also reduce the degradation of strawberry. The moisture absorption rate of crisps can alleviate the problem of crispness loss caused by rapid moisture absorption after vacuum-frozen strawberry crisps are opened;

3. The present invention adopts a slow freezing combined with a freeze-thaw treatment process, so that the ice crystals in the strawberry pulp block continue to grow after freezing, and finally large ice crystals are formed; in the freeze-drying process, the large ice crystals around the frozen fruit block can be formed after sublimation. Larger porosity, these pores can further improve the drying rate; more importantly, this process of adjusting the size of ice crystals through physical action can precisely control the porous network structure of freeze-dried fruit and vegetable chips to obtain larger pores and Loose pore structure with thicker pore walls, resulting in a better crispy mouthfeel;

4. The present invention improves the fusion point of the product by adding the dietary fiber of apple peel residue, so that the product can be sublimated at a higher temperature, and the larger pore structure formed by the freeze-thaw treatment is conducive to the dispersion of water vapor, and the comprehensive effect Significant savings in drying time and production energy.

Other advantages, objects, and features of the present invention will appear in part from the description that follows, and in part will be appreciated by those skilled in the art from the study and practice of the invention.

Detailed ways

The present invention will be further described in detail below with reference to the embodiments, so that those skilled in the art can implement according to the description.

It should be understood that terms such as "having", "comprising" and "including" as used herein do not exclude the presence or addition of one or more other elements or combinations thereof.

It should be noted that the experimental methods described in the following embodiments are conventional methods unless otherwise specified, and the reagents and materials can be obtained from commercial sources unless otherwise specified.

<Example 1>

A method for improving the color and texture quality of vacuum freeze-dried recombinant strawberry chips, comprising the following steps:

Pretreatment: Wash strawberries with uniform maturity and no pests and diseases, and drain the water through a vibrating screen;

Mixing and beating: mixing strawberries and apple peel residues, and then placing them in a beating machine to obtain strawberry pulp, and the mass fraction of apple peel residues in the strawberry pulp is 5%;

Preparation: add low-ester pectin and protocatechuic acid (3,4-dihydroxybenzoic acid) to strawberry pulp, and add citric acid to adjust pH to 3.0 to obtain material A, wherein the mass ratio of strawberry pulp to pectin is 1:0.02, the mass concentration of protocatechuic acid in material A is 0.1g/kg;

Homogenization: Homogenize material A;

Remodeling: Pour the homogenized material A into the mold groove of the mold tray;

Freezing: place the mold tray in a cold storage at -18°C and freeze slowly;

Freeze-thaw treatment: adjust the temperature of the cold storage: increase the temperature of the cold storage by 1 °C every 1h until the temperature of the cold storage is adjusted to -4 °C, and then adjust the temperature of the cold storage to -18 °C again after holding for 3 to 6 hours. The block is taken out in the groove to obtain material B; the purpose of this step is to make the ice crystals in the frozen strawberry blocks grow continuously to form larger ice crystals;

Coating: Soak material B in a chitosan solution with a volume fraction of 30% at -1°C, take it out after 2s, put it on a tray at -40°C, put it back in a freezer at -18°C, and then take it out. get material C;

Vacuum freeze-drying: place material C in a vacuum freeze-drying box, wherein the temperature of the cold trap of the vacuum drying box is -50°C, and the temperature of the storage tray of the freeze-drying box is 0°C;

Nitrogen-filling packaging: When the moisture content of material C drops below 7%, material C is taken out of the vacuum freeze-drying box, and nitrogen-filled packaging is carried out to obtain strawberry chips. The product packed with nitrogen should be stored in a cool and dry place.

<Example 2>

A method for improving the color and texture quality of vacuum freeze-dried recombinant strawberry chips, comprising the following steps:

Pretreatment: Wash strawberries with uniform maturity and no pests and diseases, and drain the water through a vibrating screen;

Mixing and beating: mixing strawberries and apple peel residues, then placing them in a beating machine to obtain strawberry pulp, and the mass fraction of apple peel residues in the strawberry pulp is 10%;

Preparation: adding low-ester pectin and protocatechuic acid (3,4-dihydroxybenzoic acid) to strawberry pulp, and adding citric acid to adjust pH to 3.8 to obtain material A, wherein the mass ratio of strawberry pulp and pectin is 1:0.08, the mass concentration of protocatechuic acid in material A is 1.0g/kg;

Homogenization: Homogenize material A;

Remodeling: Pour the homogenized material A into the mold groove of the mold tray;

Freezing: place the mold tray in a cold storage at -18°C and freeze slowly;

Freeze-thaw treatment: Adjust the temperature of the cold storage: increase the temperature of the cold storage by 1 °C every 1h until the temperature of the cold storage is adjusted to -4 °C, and then adjust the temperature of the cold storage to -18 °C again after 6 hours of heat preservation. 5 times (make the frozen strawberry pieces fluctuate at -18°C to -4°C for 5 cycles, and stay for 6h when the temperature of the cold storage reaches -4°C in each cycle), then keep it for 1h, take out the mold tray, and take out the block from the mold groove material B; the purpose of this step is to make ice crystals grow continuously in the frozen strawberry pieces to form larger ice crystals;

Coating: Soak material B in a chitosan solution with a volume fraction of 50% at 0°C, take it out after 5s, put it on a tray at -40°C, put it back in a freezer at -18°C, and take it out. material C;

Vacuum freeze-drying: place material C in a vacuum freeze-drying box, wherein the temperature of the cold trap of the vacuum drying box is -50°C, and the temperature of the storage tray of the freeze-drying box is 70°C;

Nitrogen-filling packaging: When the moisture content of material C drops below 7%, material C is taken out of the vacuum freeze-drying box, and nitrogen-filled packaging is carried out to obtain strawberry chips. The product packed with nitrogen should be stored in a cool and dry place.

<Example 3>

A method for improving the color and texture quality of vacuum freeze-dried recombinant strawberry chips, comprising the following steps:

Pretreatment: Wash strawberries with uniform maturity and no pests and diseases, and drain the water through a vibrating screen;

Mixing and beating: mixing strawberries and apple peel residues, and then placing them in a beating machine to obtain strawberry pulp. The mass fraction of apple peel residues in the strawberry pulp is 8%;

Preparation: adding low-ester pectin and protocatechuic acid (3,4-dihydroxybenzoic acid) to strawberry pulp, and adding citric acid to adjust pH to 3.4 to obtain material A, wherein the mass ratio of strawberry pulp and pectin is 1:0.05, the mass concentration of protocatechuic acid in material A is 0.5g/kg;

Homogenization: Homogenize material A;

Remodeling: Pour the homogenized material A into the mold groove of the mold tray;

Freezing: place the mold tray in a cold storage at -18°C and freeze slowly;

Freeze-thaw treatment: Adjust the temperature of the cold storage: increase the temperature of the cold storage by 1°C every 1 hour until the temperature of the cold storage is adjusted to -4 °C, and then adjust the temperature of the cold storage to -18 °C again after 5 hours of heat preservation. 3 times (make the frozen strawberry pieces fluctuate from -18°C to -4°C for 3 cycles, and stay for 5h when the temperature of the cold storage reaches -4°C in each cycle), then keep it for 1h, take out the mold tray, and take out the block from the mold groove material B; the purpose of this step is to make ice crystals grow continuously in the frozen strawberry pieces to form larger ice crystals;

Coating: Soak material B in a chitosan solution with a volume fraction of 40% at -0.5°C, take it out after 4s, put it on a tray at -40°C, put it back in a freezer at -18°C, and then take it out. get material C;

Vacuum freeze-drying: Place material C in a vacuum freeze-drying box, where the temperature of the cold trap of the vacuum-drying box is -50°C, and the temperature of the storage tray of the freeze-drying box is 35°C;

Nitrogen-filling packaging: When the moisture content of material C drops below 7%, material C is taken out of the vacuum freeze-drying box, and nitrogen-filled packaging is carried out to obtain strawberry chips. The product packed with nitrogen should be stored in a cool and dry place.

<Comparative Example 1>

A method for improving the color and texture quality of vacuum freeze-dried reconstituted strawberry chips, which is different from Example 3 in that in the blending step, citric acid is added to the strawberry pulp to adjust the pH to 3.4 to obtain material A; that is, no fruit is added to material A. Gum and protocatechuic acid, other conditions and parameters are the same as in Example 3.

<Comparative Example 2>

A method for improving the color and texture quality of vacuum freeze-dried reconstituted strawberry chips is different from Example 3 in that no pectin is added to material A in the compounding step, and other conditions and parameters are the same as those of Example 3.

<Comparative Example 3>

A method for improving the color and texture quality of vacuum freeze-dried reconstituted strawberry chips is different from Example 3 in that no protocatechuic acid is added to material A in the compounding step, and other conditions and parameters are the same as those of Example 3.

<Comparative Example 4>

A method for improving the color and texture quality of vacuum freeze-dried recombinant strawberry chips, which is different from Example 3 in that flavonoids are used to replace protocatechuic acid in the compounding step, and the mass concentration of flavonoids in material A is 0.1-1.0 g/ kg, and other conditions and parameters are the same as in Example 3.

<Comparative Example 5>

A method for improving the color and texture quality of vacuum freeze-dried reconstituted strawberry chips, which is different from Example 3 in that caffeic acid is used instead of protocatechuic acid in the compounding step, and the mass concentration of caffeic acid in material A is 0.1-1.0 g/kg, and other conditions and parameters are the same as in Example 3.

<Comparative Example 6>

A method for improving the color and texture quality of vacuum freeze-dried and reconstituted strawberry chips is different from Example 3 in that material A is slowly frozen after the freezing step, and directly enters the film coating step, that is, there is no freeze-thaw treatment step; other conditions and parameters are the same as in Example 3.

<Comparative Example 7>

A method for improving the color and texture quality of the reconstituted strawberry chips by vacuum freeze-drying is different from Example 3 in that material B is directly placed in a vacuum freeze-drying box for vacuum freeze-drying, that is, without the coating step; Conditions and parameters are the same as in Example 3.

<Comparative Example 8>

A method for improving the color and texture quality of vacuum freeze-drying and reconstituted strawberry chips is different from Example 3 in that in the steps of mixing and beating, the strawberries are directly placed in a beating machine to be beaten to obtain strawberry pulp, that is, without adding Apple peel residue, other conditions and parameters are the same as Example 3.

<Comparative Example 9>

A method for improving the color and texture quality of vacuum freeze-dried recombinant strawberry chips, comprising the following steps:

Pretreatment: Wash strawberries with uniform maturity and no pests and diseases, and drain the water through a vibrating screen;

Beating: put the strawberries in a beater to beat and homogenize to obtain material A;

Vacuum freeze-drying: place material A in a vacuum freeze-drying box, wherein the temperature of the cold trap of the vacuum drying box is -50°C, and the temperature of the storage tray of the freeze-drying box is 35°C;

Nitrogen-filled packaging: When the moisture content of material A drops below 7%, take out material A from the vacuum freeze-drying box, and carry out nitrogen-filled packaging to obtain strawberry chips. The product packed with nitrogen should be stored in a cool and dry place.

<Test example>

1. Detect the quality of the strawberry chips prepared in Examples 1-3 of the present invention and Comparative Examples 1-9:

1.1. Determination of retention rate of pelargonidin-3-glucoside in strawberry chips

The content of total anthocyanins in the samples was determined by high performance liquid chromatography-mass spectrometry coupled with HPLC-MS. The pelargonidin-3-glucoside in the sample was extracted with 2% hydrochloric acid methanol solution, filtered and determined by liquid phase method. Pelargonium-3-glucoside content and retention were calculated from the standard curve obtained from the standard.

1.2. Determination of color difference value of strawberry chips

The color of the fruit and vegetable chips was measured by a colorimeter. In this experiment, the △L, △a, △b, and △E values were used to represent the color (L, a, b) of the tested sample and the fresh sample (L*, a*, b*) color difference value. The calculation method of △E is as follows:

In the formula, L and L* are the brightness values of fresh fruit and dried chips, respectively; a, a* are the red and green values of fresh fruit and dried chips, respectively; b and b* are the yellowness of fresh fruit and dried chips, respectively. Blue value; ΔL is the total color difference value.

1.3. Determination of dietary fiber content in strawberry chips

The content of dietary fiber was determined by the weighing method in "GB/T 5009.88-2008 Determination of Dietary Fiber in Foods".

1.4. Determination of the fusion point

The material eutectic point was determined by resistance method. Freeze the pulp completely at -40°C, then gradually increase the temperature. During the period, the resistance meter is used to continuously detect the resistance of the material. When the resistance begins to decrease rapidly, the temperature is the eutectic point of the material.

1.5. Analysis of Pore Characteristics

The micro-CT scan was used, and the internal average pore diameter and pore wall thickness of the strawberry chips obtained after analysis by the micro-CT self-contained analysis software.

1.6. Determination of hardness and brittleness

Measured with TA-XT2i/50 type physical property analyzer, selected strawberry chips with similar shape and size for texture determination. After quickly taking out the sample from the package, use the physical property analyzer to do the cutting test, repeat 10 times, and finally take the average value. The brittleness is expressed by the number of peaks produced by the test, and the unit is "pieces". The test value increases in a positive correlation within a certain range. The more peaks, the better the crispness of the product, and vice versa, the worse the crispness of the product.

1.7. Determination of shelf life

The packaged strawberry chips were stored at 25°C, the product quality was tracked, and the product pelargonidin-3-glucoside was degraded by more than 50%, or the a value decreased by more than 20% as the end of the shelf life.

2. Analysis of test results

The detection results of Examples 1 to 3 of the present invention and Comparative Examples 1 to 9 are shown in Table 1:

Table 1 Test results

As can be seen from Table 1, compared with the conventional technology Comparative Example 9, the retention rates of pelargonidin-3-glucoside of the strawberry chips obtained in Examples 1 to 3 of the present invention are all as high as more than 90%, the color difference is small, and the dietary fiber content is small. The content is high, the average pore diameter and the evaluation wall thickness are relatively high, the brittleness has reached more than 45, and the shelf life is as long as 18 months. It solves the problems of unstable storage period of the product pelargonidin-3-glucoside and low hardness and brittleness of the product.

Comparing the data of Example 3 and Comparative Examples 1 to 5, it can be seen that the present invention adds pectin and protocatechuic acid to strawberry pulp, and based on pectin combined with protocatechuic acid, the spontaneous chemical stabilization of pelargonidin-3-glucoside Color protection process; The stability of pelargonidin-3-glucoside during product storage is significantly improved through careful design of the homeostasis mechanism based on the interaction of large and small molecules in food, coupled with physical oxygen barrier technology.

Comparing the data of Example 3 and Comparative Example 6, it can be seen that the present invention adopts the slow freezing combined with the freeze-thaw treatment process, so that the ice crystals in the frozen strawberry pulp continue to grow, and finally large ice crystals are formed; As a result, larger porosity can be formed after the sublimation of large ice crystals on the periphery of the block. These pores can further improve the drying rate. More importantly, this process of adjusting the size of ice crystals through physical action can precisely control the freeze-dried fruit and vegetable chips. Porous network structure to obtain a loose pore structure with larger pores and thicker pore walls, thereby obtaining a better crispy taste;

Comparing the data of Example 3 and Comparative Example 7, it can be seen that the present invention forms a layer of pectin coating on the periphery of the strawberry chips by carrying out the chitosan coating treatment on the strawberry pieces, which can effectively block oxygen and moisture. The infiltration of pelargonidin-3-glucoside maintains a low oxygen and low water activity environment around the pelargonidin-3-glucoside molecule, further inhibits the degradation of pelargonidin-3-glucoside, and effectively improves the degradation of pelargonidin-3-glucoside during storage; Chitosan coating can also reduce the moisture absorption rate of strawberry chips and alleviate the problem of crispness loss caused by rapid moisture absorption after vacuum-frozen strawberry chips are opened;

Comparing the data of Example 3 and Comparative Example 8, it can be seen that the present invention improves the fusion point of the product by adding the dietary fiber of apple peel residue, so that the product can be sublimated at a higher temperature, and the larger pores formed by the freeze-thaw treatment are added. The structure is conducive to the dissipation of water vapor, and the comprehensive effect can greatly save drying time and production energy consumption.

The number of apparatuses and processing scales described here are intended to simplify the description of the present invention. Applications, modifications and variations to the present invention will be apparent to those skilled in the art.

Although the embodiment of the present invention has been disclosed as above, it is not limited to the application listed in the description and the embodiment, and it can be applied to various fields suitable for the present invention. For those skilled in the art, it can be easily Therefore, the invention is not limited to the specific details without departing from the general concept defined by the appended claims and the scope of equivalents.

Claims (5)

1. The method for improving the color and texture quality of the vacuum freeze-dried recombined strawberry crisp is characterized by comprising the following steps of:

crushing strawberries to obtain strawberry pulp, uniformly mixing the strawberry pulp with pectin and protocatechuic acid, and adjusting the pH value to 3.0-3.8 to obtain a material A; wherein the mass ratio of the strawberry pulp to the pectin is 1: 0.02-0.08, and the mass concentration of protocatechuic acid in the material A is 0.1-1.0 g/kg;

step two, pouring the material A into a mould tray, and placing the mould tray in a refrigeration house at the temperature of-18 ℃ for freeze thawing treatment to obtain a blocky material B;

coating a layer of chitosan on the surface of the material B to obtain a material C;

fourthly, drying the material C in a vacuum freeze drying box, and then filling nitrogen for packaging to obtain the strawberry crisp chips;

wherein, in the step one, the crushing of the strawberries to obtain the strawberry pulp specifically comprises the following steps: selecting and cleaning strawberries with uniform maturity and no plant diseases and insect pests, draining water through a vibrating screen, mixing the strawberries with the apple peel residues, and then placing the strawberries into a beating machine for beating to obtain strawberry pulp, wherein the mass fraction of the apple peel residues in the strawberry pulp is 5-10%.

2. The method for improving color and texture quality of vacuum freeze-dried recombined strawberry crisps according to claim 1, wherein in the first step, the strawberries are crushed to obtain strawberry pulp, the strawberry pulp is uniformly mixed with pectin and protocatechuic acid, and the pH is adjusted to 3.0-3.8 by using citric acid to obtain a material A.

3. The method for improving the color and texture quality of the vacuum freeze-dried recombined strawberry crisp according to claim 2, wherein the second step is specifically as follows: after homogenizing the material A, pouring the material A into a mold groove of a mold tray, placing the mold tray in a refrigeration house at-18 ℃, and after the material A is frozen, adjusting the temperature of the refrigeration house: and (3) adjusting the temperature of the cold storage by 1 ℃ every 1 hour until the temperature of the cold storage is adjusted to-4 ℃, keeping the temperature for 3-6 hours, adjusting the temperature of the cold storage to-18 ℃ again, circularly adjusting the temperature of the cold storage for 1-5 times according to the adjusting mode of the temperature of the cold storage, keeping the temperature for 1 hour, taking out the mold tray, and taking out the blocks from the mold grooves to obtain the material B.

4. The method for improving the color and texture quality of the vacuum freeze-dried reconstituted strawberry crisp according to claim 3, wherein the third step is specifically: and (3) soaking the material B in a chitosan solution with the volume fraction of 30-50% at the temperature of-1-0 ℃, taking out after 2-5 seconds, placing on a tray at the temperature of-40 ℃, putting back to a refrigeration house at the temperature of-18 ℃ again, freezing and taking out to obtain a material C.

5. The method for improving the color and texture quality of the vacuum freeze-dried reconstituted strawberry crisp according to claim 4, wherein the step four is specifically as follows: placing the material C in a vacuum freeze drying oven, wherein the temperature of a cold trap of the vacuum freeze drying oven is-50 ℃, and the temperature of a storage disc of the freeze drying oven is 0-70 ℃; and when the water content of the material C is reduced to below 7%, taking the material C out of the vacuum freeze drying oven, and filling nitrogen for packaging to obtain the strawberry crisp chips.