CN112568395B - Method for improving the texture and color of vacuum freeze-dried reconstituted apple crisps - Google Patents

Abstract

The invention discloses a method for improving the texture and color of vacuum freeze-dried recombined apple crisp chips, which comprises the following steps: step one, cleaning apples, peeling, removing kernels, crushing and pulping to obtain apple pulp; step two, adding low-ester pectin, calcium chloride, p-hydroxybenzoic acid or derivatives thereof and dry apple peel residue powder into the apple pulp, uniformly mixing, and homogenizing to obtain a mixed solution; adding organic acid to adjust the pH value, sterilizing and cooling; adding a fermentation agent, and fermenting to obtain a fermentation liquid; fifthly, pulping in a sterile environment, and filling nitrogen into the fermentation liquor in the pulping process; step six, freezing to obtain apple pulp blocks; step seven, soaking in chitosan water solution, spreading on a tray, and freezing; and step eight, after freezing, carrying out vacuum freeze drying to obtain the recombined apple crisp chips. The method can effectively solve the problems of unstable storage period and low hardness and brittleness of the recombinant apple crisp chip anthocyanin.

Description

Method for improving the texture and color of vacuum freeze-dried reconstituted apple crisps

technical field

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

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 convenient consumption, nutrition and health, and easy portability. Vacuum freeze-drying has gradually become a green and high-quality drying method for preparing apple chips.

Apple is the largest fruit in my country. Red-fleshed apples are rich in anthocyanins and are a high antioxidant product. Anthocyanins are easily degraded by external factors such as light and oxygen, especially because the vacuum freeze-dried red meat apple crisps have a crisp porous network structure and a large specific surface area, which makes it easier for oxygen, moisture and light to contact anthocyanins , the color fading and functional weakening caused by the degradation of anthocyanins become the quality defects that are difficult to solve during the processing and storage of anthocyanin-rich fruit and vegetable chips. For a long time, how to improve the stability of anthocyanins in fruit and vegetable foods has plagued the food industry, especially the fruit and vegetable chips 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 inhomogeneity 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 texture and color of reconstituted apple crisps by vacuum freeze-drying, cleverly utilizing the spontaneous chemical interaction mechanism between natural food compounds, and designing a method based on cell wall pectin polysaccharide, p-hydroxyl Spontaneous stabilization process of anthocyanins based on the interaction of large and small molecules between benzoic acid (4-hydroxybenzoic acid or its derivatives) and anthocyanins, and at the same time using physical means such as texture reorganization, aeration beating, freeze-thaw treatment, etc. By adjusting the size of ice crystals and the pore characteristics of the product, a brand-new reconstituted red-meat apple crisp was created, which effectively solved the problems of unstable storage period of anthocyanins and low hardness and brittleness of the product.

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

Step 1. Wash, peel, core, crush and beat the apples to obtain apple pulp;

Step 2: Add low-ester pectin at 10-50 g/kg, add calcium chloride at 1-2 mg/g, add p-hydroxybenzoic acid or its derivative at 0.012-0.5 g/kg, and add a mass fraction of 2- 5% dry powder of apple peel residue, mixed evenly and homogenized to obtain a mixed solution;

Step 3, adding organic acid to adjust the pH of the mixed solution in step 2 to 3.0-3.8, sterilizing and cooling;

Step 4, adding a starter at 10-20g/kg, and fermenting at 30°C for 48h to obtain a fermented liquid, wherein the starter is obtained by mixing compound lactic acid bacteria and Lactobacillus plantarum at a ratio of 2:1;

Step 5, beating in a sterile environment for 2 to 5 minutes, and filling the fermentation broth with nitrogen during the beating process;

Step 6, freezing at -18°C to obtain apple pulp blocks, wherein the thickness of the apple pulp blocks is 3-8 mm;

Step 7. Immerse the chitosan aqueous solution with a mass fraction of 30 to 50% at -1 to 0 °C for 2 to 5 s, spread it on a tray at -40 °C, and freeze at -18 °C;

Step 8. After freezing, vacuum freeze-drying to obtain apple crisps;

Wherein, the addition amount of step 2 and step 4 is based on the quality of apple pulp.

Preferably, the p-hydroxybenzoic acid derivatives include: any one or a combination of ethyl p-hydroxybenzoate, sodium ethyl p-hydroxybenzoate, propyl p-hydroxybenzoate and sodium methyl p-hydroxybenzoate.

Preferably, the temperature of the sterilization in step 3 is 121° C., and the sterilization time is 15 minutes.

Preferably, the bacterial concentration of the starter is 8.0 to 9.0 Log (CFU/ml).

Preferably, a mold tray is used to hold the apple pulp during freezing in step 6.

Preferably, the apple crisps in step 8 are packaged in a light and oxygen barrier.

Preferably, the crushing method in step 1 is: placing in a low-temperature nitrogen-filled crusher and crushing.

Preferably, the apple variety is a red-fleshed apple.

Preferably, the organic acid is one or a combination of citric acid, malic acid and lactic acid.

Preferably, the compound lactic acid bacteria is one or a combination of Bifidobacterium longum, Lactobacillus acidophilus, Lactobacillus fermentum, Lactobacillus helveticus, Lactobacillus paracasei, Lactobacillus rhamnosus, and Streptococcus thermophilus.

The present invention includes at least the following beneficial effects:

First, by cleverly exploiting the spontaneous chemical interaction mechanism between food natural compounds, a size-based size-based cell wall pectin polysaccharide, p-hydroxybenzoic acid (4-hydroxybenzoic acid or its derivatives) and anthocyanin were designed. The spontaneous stabilization process of anthocyanins through molecular interaction, and at the same time using physical means such as texture reorganization, aeration beating, freeze-thaw treatment and other physical means to control the ice crystal size and product pore characteristics, has created a brand-new reconstituted red meat apple crisp, which is effective The problem of unstable storage period of anthocyanins and low hardness and brittleness of products is solved.

Second, the stability of anthocyanins during product storage has been 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. Specifically, this scheme utilizes the abundant carboxyl groups on the pectin molecule with low methyl esterification degree to be negatively charged above its isoelectric point, and the anthocyanin to be positively charged below the isoelectric point, which is mainly caused by electrostatic interaction and secondary At the same time, the non-covalent bond "Π-Π overlap" between the small molecule p-hydroxybenzoic acid benzene ring and the anthocyanin benzene ring is used to stabilize the restricted cyanine from two dimensions. The chemical structure of anthocyanin makes the B ring unable to move freely due to steric hindrance, which limits the dissociation of anthocyanin chemical bonds and greatly improves the chemical stability of anthocyanin. The protection effect of -3-glucoside, the present invention also tried the color protection effect of flavonoids and ferulic acid, both of which are not as obvious as p-hydroxybenzoic acid or its derivatives.

Third, through the chitosan coating treatment, a layer of pectin coating is formed on the periphery of the apple chips, which can effectively block the infiltration of oxygen and water, and maintain the low oxygen and low water activity of anthocyanins. The temperature environment further inhibits the degradation of anthocyanins, which is also effective in the degradation of anthocyanins during storage.

Fourth, the chitosan coating can also reduce the moisture absorption rate of apple crisps, alleviate the problem of the loss of crispness caused by rapid moisture absorption after the vacuum-frozen apple crisps are opened, and maintain the crisp texture of the product. Effect.

Fifth, use the aeration beating process to treat the pulp raw materials, so that a certain proportion of air bubbles remain in the frozen block. These air bubbles will expand and overflow rapidly due to the increase of vacuum degree at the beginning of vacuum freeze-drying. More importantly, this process can precisely control the porous network structure of freeze-dried apple chips to form a loose pore structure with larger pores and thicker pore walls, thereby obtaining a better crispy taste.

Sixth, the sugar content of red-fleshed apples is as high as about 13%, resulting in a very low melting point. Therefore, it is necessary to reduce the material temperature during freeze-drying to ensure that the product maintains a solid structure and does not collapse, which leads to the freeze-drying time and energy of apples. The consumption is significantly higher than other low-sugar raw materials; on the one hand, the present invention reduces the content of small molecular sugar in the apple pulp through the fermentation process, and on the other hand, the high molecular weight dietary fiber of the product is increased by adding apple peel residue. The melting point and glass transition temperature of small molecular sugar are low, and the melting point and glass transition temperature of macromolecular dietary fiber are high. Based on the above-mentioned positive and negative effects, the eutectic point of apple mixed slurry is greatly improved, so it can be used Higher freeze-drying temperature significantly increases the sublimation rate and shortens the drying time.

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.

Description of drawings

Fig. 1 is the appearance diagram of the product prepared by each embodiment of the present invention and the comparative example.

Detailed ways

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

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; in the description of the present invention, The orientation or positional relationship indicated by the terms is based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the referred device or element must have a specific orientation or a specific orientation. The orientation configuration and operation are therefore not to be construed as limitations of the present invention.

<Example 1>

A method for improving the texture and color of vacuum freeze-dried reconstituted apple crisps, comprising the following steps:

Pretreatment: Select red-fleshed apples with uniform maturity and no pests and diseases, clean the apples, peel and core, and cut them in half lengthwise;

Crushing: The apples are crushed in a low-temperature nitrogen-filled crusher;

Beating: put apples in a beater and beat to get apple pulp;

Preparation: add low-ester pectin, 1.5mg/g calcium chloride, 0.25g/kg ethylparaben, and 3% dry powder of apple peel residue to apple pulp at a rate of 50g/kg, mix well After homogenization, a mixed liquid is obtained; the addition amount is based on the quality of apple pulp;

Adjust pH: add citric acid to adjust pH to 3.5;

Sterilization: Sterilize the apple pulp at 121°C for 15min, and pour it into the fermentation tank after cooling;

Fermentation: add a starter at 15g/kg to the fermenter, the bacterial concentration of the starter is 8.5Log (CFU/mL), wherein the number of compound lactic acid bacteria and Lactobacillus plantarum is 2:1, fermented at 30°C for 48h, The fermentation broth was obtained; the addition amount was based on the quality of apple pulp;

Air-filled beating: beating for 3 minutes in a sterile, nitrogen-filled environment; clean nitrogen is continuously mixed under the container during the beating process;

Remodeling: pour it into the mold tray, and slowly freeze it at -18°C together with the mold tray to obtain apple pulp blocks, wherein the thickness of the apple pulp blocks is 5mm; the frozen apple pulp blocks can be stored at -18°C for a long time. The storage period can be up to 12 months, and the year-round production can be realized;

Coating: Immerse the frozen apple pulp block in a chitosan aqueous solution with a mass fraction of 40% at -1°C for 3s, take it out and flatten it on a stainless steel tray at -40°C, and put it back at -18°C Low temperature freezer for backup;

Vacuum freeze-drying: transfer the frozen apple pulp block to a vacuum freeze-drying chamber for vacuum freeze-drying until the moisture content of the apple pulp block is below 7%, stop the vacuum freeze-drying, and obtain apple chips, wherein the temperature of the cold trap is set is -50°C, and the tray temperature is 50°C;

Nitrogen-filled packaging: Take out the apple chips, choose a light-proof and oxygen-isolated packaging, carry out nitrogen-filled packaging, and store the nitrogen-filled products in a cool, dry place.

<Example 2>

A method for improving the texture and color of vacuum freeze-dried reconstituted apple crisps, comprising the following steps:

Pretreatment: Select red-fleshed apples with uniform maturity and no pests and diseases, clean the apples, peel and core, and cut them in half lengthwise;

Crushing: The apples are crushed in a low-temperature nitrogen-filled crusher;

Beating: put apples in a beater and beat to get apple pulp;

Preparation: Add 10g/kg of low-ester pectin, 1mg/g of calcium chloride, 0.012g/kg of sodium ethyl hydroxybenzoate, and 2% dry powder of apple peel residue to apple pulp, and mix them evenly. Homogenize to obtain a mixed solution; the amount of addition is based on the quality of apple pulp;

Adjust pH: add malic acid to adjust pH to 3.0;

Sterilization: Sterilize the apple pulp at 121°C for 15min, and pour it into the fermentation tank after cooling;

Fermentation: add a starter at 10g/kg to the fermenter, the bacterial concentration of the starter is 8.0Log (CFU/mL), and the number of compound lactic acid bacteria and Lactobacillus plantarum is 1:1, fermented at 30°C for 36h, The fermentation broth was obtained; the addition amount was based on the quality of apple pulp;

Air-filled beating: beating in a sterile, nitrogen-filled environment for 2 minutes; clean nitrogen is continuously mixed under the container during the beating process;

Remodeling: pour it into the mold tray, and slowly freeze it at -18°C together with the mold tray to obtain apple pulp blocks, of which the thickness of the apple pulp blocks is 3mm; the frozen apple pulp blocks can be stored at -18°C for a long time. The storage period can be up to 12 months, and the year-round production can be realized;

Coating: Immerse the frozen apple pulp block in a chitosan aqueous solution with a mass fraction of 30% at -1°C for 2s, take it out and flatten it on a stainless steel tray at -30°C, and put it back at -18°C Low temperature freezer for backup;

Vacuum freeze-drying: transfer the frozen apple pulp block to a vacuum freeze-drying bin for vacuum freeze-drying until the moisture content of the apple pulp block is below 7%, stop the vacuum freeze-drying, and obtain apple chips, wherein the cold trap temperature is -50℃, the tray temperature is 20℃;

Nitrogen-filled packaging: Take out the apple chips, choose a light-proof and oxygen-isolated packaging, carry out nitrogen-filled packaging, and store the nitrogen-filled products in a cool, dry place.

<Example 3>

A method for improving the texture and color of vacuum freeze-dried reconstituted apple crisps, comprising the following steps:

Pretreatment: Select red-fleshed apples with uniform maturity and no pests and diseases, clean the apples, peel and core, and cut them in half lengthwise;

Crushing: The apples are crushed in a low-temperature nitrogen-filled crusher;

Beating: put apples in a beater and beat to get apple pulp;

Preparation: add low-ester pectin at 25g/kg, add calcium chloride at 2mg/g, add propylparaben at 0.5g/kg, add 5% dry powder of apple peel residue to apple pulp, and mix evenly. Homogenize to obtain a mixed solution; the amount of addition is based on the quality of apple pulp;

Adjust pH: add lactic acid to adjust pH to 3.8;

Sterilization: Sterilize the apple pulp at 121°C for 15min, and pour it into the fermentation tank after cooling;

Fermentation: add a starter at 20g/kg to the fermenter, the bacterial concentration of the starter is 9.0Log (CFU/mL), wherein the number of compound lactic acid bacteria and Lactobacillus plantarum is 3:1, fermented at 37°C for 60h, The fermentation broth was obtained; the addition amount was based on the quality of apple pulp;

Air-filled beating: beating for 5 minutes in a sterile, nitrogen-filled environment; clean nitrogen is continuously mixed under the container during the beating process;

Remodeling: pour it into the mold tray, and slowly freeze it at -18°C together with the mold tray to obtain apple pulp blocks, of which the thickness of the apple pulp blocks is 8mm; the frozen apple pulp blocks can be stored at -18°C for a long time. The storage period can be up to 12 months, and the year-round production can be realized;

Coating: Immerse the frozen apple pulp block in a 50% chitosan aqueous solution at 0°C for 5s, take it out and flatten it on a stainless steel tray at -45°C, and put it back to -18°C low temperature Freezer spare;

Vacuum freeze-drying: transfer the frozen apple pulp block to a vacuum freeze-drying bin for vacuum freeze-drying until the moisture content of the apple pulp block is below 7%, stop the vacuum freeze-drying, and obtain apple chips, wherein the cold trap temperature is -50℃, the tray temperature is 80℃;

Nitrogen-filled packaging: Take out the apple chips, choose a light-proof and oxygen-isolated packaging, carry out nitrogen-filled packaging, and store the nitrogen-filled products in a cool, dry place.

<Example 4>

The preparation method of apple crisps is the same as that of Example 1, and the difference is that in the preparation step, sodium methyl parahydroxybenzoate is used instead of ethyl parahydroxybenzoate, and the amount is 0.25 g/kg.

<Example 5>

The preparation method of apple crisps is the same as that of Example 1, and the difference is that in the preparation step, p-hydroxybenzoic acid is used instead of ethyl p-hydroxybenzoate, and the dosage is 0.25 g/kg.

<Comparative Example 1>

The preparation method of apple crisps is the same as that of Example 1, and the difference is that flavonoids are used instead of ethyl p-hydroxybenzoate in the preparation step, and the dosage is 0.25 g/kg.

<Comparative Example 2>

The preparation method of apple crisps is the same as that of Example 1, and the difference is that ferulic acid is used instead of ethyl p-hydroxybenzoate in the preparation step, and the dosage is 0.25g/kg.

<Comparative Example 3>

The preparation method of apple chips is the same as that of Example 1, and the difference is that in the preparation step, water is used instead of ethyl p-hydroxybenzoate, and the amount is 0.25 g/kg.

<Comparative Example 4>

The preparation method of apple crisps is the same as that in Example 1, and the difference is that in the preparation step, water is used instead of low-ester pectin, and the dosage is 50 g/kg.

<Comparative Example 5>

The preparation method of apple crisps is the same as that of Example 1, and the difference is that high-ester pectin is used instead of low-ester pectin in the compounding step, and the dosage is 50 g/kg.

<Comparative Example 6>

The preparation method of apple crisps is the same as that in Example 1, except that the aeration treatment is not adopted in the aeration beating step, and only beating is performed.

<Comparative Example 7>

The preparation method of apple crisps includes the following steps:

Pretreatment: Select red-fleshed apples with uniform maturity and no pests and diseases, clean the apples, remove the core, and cut them in half lengthwise;

Crushing: The apples are crushed in a low-temperature nitrogen-filled crusher;

Beating: put apples in a beater and beat to get apple pulp;

Sterilization: Sterilize apple pulp at 121°C for 15min;

Vacuum freeze-drying: pour into the mold tray, and carry out vacuum freeze-drying in the vacuum freeze-drying chamber together with the mold tray. When the moisture content of the apple pulp block is below 7%, the vacuum freeze-drying is stopped to obtain apple crisps. The temperature is -50°C, the tray temperature is 50°C, and the thickness of the apple pulp into the mold tray is 5mm;

Nitrogen-filled packaging: Take out the apple chips, choose a light-proof and oxygen-isolated packaging, carry out nitrogen-filled packaging, and store the nitrogen-filled products in a cool, dry place.

<Quality Inspection of Apple Chips>

1. Detection method

Determination of anthocyanin retention rate:

The total anthocyanin content in the samples was determined by UV spectrophotometry. The anthocyanins in the samples were extracted with 2% hydrochloric acid methanol solution, filtered and measured at 530 nm. Total anthocyanin content was calculated by standard curve.

Determination of color difference value:

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.

Fusion point determination:

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.

Shelf life determination:

Store the product at 25°C, track the quality of the product, and take the product anthocyanin degraded by more than 50% or the a value of more than 20% as the end of the shelf life.

Determination of hardness and brittleness:

Measure with TA-XT2i/50 type physical property analyzer, and select brittle strips 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.

Pore Feature Analysis:

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

Determination of probiotic content:

Adopt the national standard GB 4789.35-2016 food safety national standard food microbiology inspection lactic acid bacteria inspection.

2. Test results

The detection results of Examples 1 to 5 and Comparative Examples 1 to 7 are shown in Table 1 and Table 2, respectively.

The detection results of Table 1 Examples 1-5

Table 2 Test results of comparative examples 1 to 7

It can be seen from Table 1 that the anthocyanin retention rates of the recombinant apple crisps prepared by the methods of Examples 1 to 5 are all above 86%, indicating that the anthocyanins are efficiently retained, and the color change rates are all below 1.53, indicating that The color protection efficiency is excellent; the thicker the average pore diameter and the average wall thickness, the more units in the crisp tablet have single disintegration in the texture compression test, which is reflected in the texture analyzer measurement, that is, the peak number of brittleness The higher the number, the stronger the crispy taste of the sample in the sensory experience, and the higher the quality of the product as a crisp; the crispness is above 48, indicating that the crispness is good. However, in the reconstituted apple crisp product prepared by the common method (Comparative Example 7), the anthocyanin retention rate is significantly reduced, the color change rate is significantly changed, and the crispness is also significantly reduced.

From the data in Table 1 and Table 2, it can be seen that compared with Comparative Example 1, Comparative Example 2, and Comparative Example 3, the use of flavone or ferulic acid or water instead of ethyl p-hydroxybenzoate significantly reduces the final result. The anthocyanin retention rate and color change rate of the product reconstituted apple crisps increased, and the brittleness decreased, indicating the irreplaceability of ethyl paraben.

It can be seen from the comparison of Example 1 and Comparative Example 4 that the use of water instead of low-ester pectin also significantly reduces the anthocyanin retention rate of the final product reconstituted apple crisps, the color change rate increases, and the brittleness decreases, indicating that p-hydroxybenzoic acid The irreplaceability of ethyl esters.

From the comparison of Example 1 and Comparative Examples 1 to 4, it can be seen that the synergistic effect of ethyl p-hydroxybenzoate and low-ester pectin can increase the anthocyanin retention rate, reduce the color change, and at the same time improve the brittleness of the product. Spend.

It can be seen from the comparison between Example 1 and Comparative Example 5 that high-ester pectin can also produce a positive synergistic effect with ethyl p-hydroxybenzoate, but the effect is not as good as that of low-ester pectin.

It can be seen from the comparison between Example 1 and Comparative Example 6 that in the aeration beating step, aeration can significantly improve the brittleness of the product.

As shown in Figure 1, from left to right, the first row is the product appearance of the six samples from Examples 1 to 5 and Comparative Example 1. The anthocyanin retention rates are 92% and 86%, respectively. , 88%, 90%, 89%, 70%. The second row is the product appearance diagram of the six samples of Comparative Examples 2 to 7. The anthocyanin retention rates are 75%, 62%, 72%, 80%, 88%, and 43%, respectively. Example 1 and Example The red color of 4 is the reddest, and the anthocyanin retention rate is also the highest.

Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the description and the embodiments, and can be applied to various fields suitable for the present invention. For those skilled in the art, they can easily Therefore, the invention is not limited to the specific details and illustrations shown and described herein without departing from the general concept defined by the appended claims and the scope of equivalents.

Claims (8)

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

step one, cleaning apples, peeling, removing kernels, crushing and pulping to obtain apple pulp; the crushing method comprises the following steps: crushing in a low-temperature nitrogen-filled crusher;

step two, adding low-ester pectin in an amount of 10-50 g/kg, calcium chloride in an amount of 1-2 mg/g, p-hydroxybenzoic acid or a derivative thereof in an amount of 0.012-0.5g/kg, and apple peel residue dry powder in an amount of 2-5% by mass into the apple pulp, uniformly mixing, and homogenizing to obtain a mixed solution;

step three, adding organic acid to adjust the pH of the mixed solution in the step two to 3.0-3.8, sterilizing and cooling;

step four, adding a leavening agent according to the ratio of 10-20 g/kg, and fermenting for 48 hours at the temperature of 30 ℃ to obtain a fermentation liquid, wherein the leavening agent is obtained by mixing the compound lactobacillus and the lactobacillus plantarum in a ratio of 2:1, and the bacterial concentration of the leavening agent is 8.0-9.0 Log (CFU/ml);

fifthly, pulping for 2-5 min in an aseptic environment, and filling nitrogen into the fermentation liquor in the pulping process;

sixthly, freezing at-18 ℃ to obtain apple pulp blocks, wherein the thickness of the apple pulp blocks is 3-8 mm;

seventhly, soaking the mixture in a chitosan water solution with the mass fraction of 30-50% at the temperature of-1-0 ℃ for 2-5 seconds, spreading the soaked mixture on a tray at the temperature of-40 ℃, and freezing the spread mixture at the temperature of-18 ℃;

step eight, after freezing, carrying out vacuum freeze drying to obtain apple chips;

wherein, the addition amount of the second step and the fourth step is based on the mass of the apple pulp.

2. The method for improving the texture and color of vacuum freeze-dried reconstituted apple crisps as claimed in claim 1, wherein the parahydroxybenzoic acid derivative comprises: any one or combination of more of ethyl p-hydroxybenzoate, sodium ethyl hydroxybenzoate, propyl p-hydroxybenzoate and sodium methyl p-hydroxybenzoate.

3. The method for improving the texture and color of vacuum freeze-dried reconstituted apple crisps as claimed in claim 1, wherein the sterilization temperature in the third step is 121 ℃ and the sterilization time is 15 min.

4. The method for improving the texture and color of vacuum freeze-dried reconstituted apple crisps as claimed in claim 1, wherein in step six the mold tray is used to hold the apple pulp during freezing.

5. The method for improving the texture and color of the vacuum freeze-dried reconstituted apple crisps as claimed in claim 1, wherein the apple crisps in the step eight are packaged in the dark and oxygen-isolated manner.

6. The method for improving the texture and color of vacuum freeze-dried reconstituted apple crisps according to claim 1, wherein the apple variety is red-fleshed apple.

7. The method for improving the texture and color of the vacuum freeze-dried reconstituted apple crisps as claimed in claim 1, wherein the organic acid is one or a combination of citric acid, malic acid and lactic acid.

8. The method for improving the texture and color of the vacuum freeze-dried reconstituted apple crisp according to claim 1, wherein the compound lactic acid bacteria is one or a combination of bifidobacterium longum, lactobacillus acidophilus, lactobacillus fermentum, lactobacillus helveticus, lactobacillus paracasei, lactobacillus rhamnosus, and streptococcus thermophilus.

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