Disclosure of Invention
An object of the present invention is to solve at least the above problems and to provide at least the advantages described later.
The invention also aims to provide a method for improving the texture and color of the vacuum freeze-dried recombined apple crisp, which skillfully utilizes a spontaneous chemical interaction mechanism among natural food compounds, designs an anthocyanin spontaneous stabilization and fluidization process based on the interaction of cell wall pectin polysaccharide, p-hydroxybenzoic acid (4-hydroxybenzoic acid or derivatives thereof) and anthocyanin and based on the interaction of large molecules and small molecules, and simultaneously regulates the size of ice crystals and the pore characteristics of products by physical means such as texture recombination, air-charging pulping, freeze-thaw treatment and the like, thereby creating a brand new recombined red-meat apple crisp and effectively solving the problems of unstable storage period and low hardness and brittleness of the products of the anthocyanin.
To achieve these objects and other advantages in accordance with the present invention, there is provided a method for improving texture and color of vacuum freeze-dried reconstituted apple crisps, comprising the steps of:
step one, cleaning apples, peeling, removing kernels, crushing and pulping to obtain apple pulp;
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;
adding a leaven 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 leaven is obtained by mixing compound lactobacillus and lactobacillus plantarum in a ratio of 2: 1;
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.
Preferably, 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.
Preferably, the temperature for sterilization in the third step is 121 ℃, and the sterilization time is 15 min.
Preferably, the bacterial concentration of the leavening agent is 8.0-9.0 Log (CFU/ml).
Preferably, the mould tray is used to contain the apple pulp during freezing in step six.
Preferably, the apple crisp slices in the step eight are packaged in a dark and oxygen-insulated way.
Preferably, the crushing method in the first step is as follows: crushing in a low temperature nitrogen-filled crusher.
Preferably, the apple variety is red-fleshed apple.
Preferably, the organic acid is one or a combination of citric acid, malic acid and lactic acid.
Preferably, the compound lactobacillus is one or more of bifidobacterium longum, lactobacillus acidophilus, lactobacillus fermentum, lactobacillus helveticus, lactobacillus paracasei, lactobacillus rhamnosus and streptococcus thermophilus.
The invention at least comprises the following beneficial effects:
firstly, a spontaneous chemical interaction mechanism among natural food compounds is skillfully utilized, an anthocyanin spontaneous stabilization process based on the interaction of cell wall pectin polysaccharide, p-hydroxybenzoic acid (4-hydroxybenzoic acid or derivatives thereof) and anthocyanin based on large and small molecules is designed, and the size of ice crystals and the pore characteristics of products are regulated and controlled by physical means such as texture recombination, air inflation pulping, freeze-thaw treatment and the like, so that a brand new recombinant red-meat apple crisp chip is created, and the problems of unstable storage period and low hardness and brittleness of the products of the anthocyanin are effectively solved.
Secondly, stability of the anthocyanin during storage of the product is improved by elaborately designing a stabilization mechanism based on interaction of food size molecules and adding a physical oxygen barrier technology. Specifically, the proposal utilizes the mutual combination of the main electrostatic interaction and the auxiliary hydrogen bond and hydrophobic interaction by utilizing that rich carboxyl groups on pectin molecules with low methyl esterification degree are negatively charged above the isoelectric point and anthocyanin is positively charged below the isoelectric point; meanwhile, non-covalent bond n-n overlapping is generated between the benzene ring of the small-molecular p-hydroxybenzoic acid and the benzene ring of the anthocyanin, the chemical structure of the anthocyanin is limited stably from two dimensions, so that the B ring cannot move freely due to steric hindrance, the dissociation of the chemical bond of the anthocyanin is limited, and the chemical stability of the anthocyanin is greatly improved; aiming at the protection effect of cyanidin-3-glucoside which is a main color substance in red-pulp apples, the invention also tries the color protection effect of flavone and ferulic acid, which is not as obvious as the effect of p-hydroxybenzoic acid or derivatives thereof.
Thirdly, a layer of pectin coating film is formed on the periphery of the apple crisp through chitosan coating film treatment, the layer of pectin coating film can effectively prevent oxygen and water from permeating, the low-oxygen and low-water-activity environment of anthocyanin is maintained, the degradation of anthocyanin is further inhibited, and the degradation problem of anthocyanin during storage is also effectively solved.
Fourthly, the chitosan coating can also reduce the moisture absorption rate of the apple chips, relieve the problem of loss of crispness caused by rapid moisture absorption after the vacuum frozen apple chips are unpacked, and have obvious effect on maintaining the crisp texture of the product.
Fifthly, processing the pulp raw material by adopting an inflation pulping process, keeping a certain proportion of bubbles in the frozen result block, and then carrying out vacuum freeze drying on the bubbles, wherein the bubbles are quickly expanded and overflowed due to the improvement of the vacuum degree, and the left pore channels improve the drying rate; more importantly, the process can accurately regulate and control the porous network structure of the freeze-dried apple crisp chips to form a loose pore structure with larger pores and thicker pore walls, so that better crisp mouthfeel is obtained.
Sixthly, the sugar content of the red-pulp apples is as high as about 13 percent, so that the eutectic point of the red-pulp apples is very low, the solid structure of the product can be ensured to be maintained without collapse by reducing the temperature of materials during freeze-drying, and the freeze-drying time and the energy consumption of the apples are obviously higher than those of other low-sugar raw materials; on one hand, the invention reduces the content of small molecular sugar in the apple pulp through the fermentation process, and on the other hand, the invention also improves the high molecular weight dietary fiber of the product by adding the apple peel residue. The co-melting point and the glass transition temperature of the micromolecule sugar are low, the co-melting point and the glass transition temperature of the macromolecular dietary fiber are high, and based on the positive and negative effects, the co-melting point of the apple mixed slurry is greatly improved, so that a higher freeze-drying temperature can be used, the sublimation rate is obviously improved, and the drying time is shortened.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention.
Detailed Description
The present invention is further described in detail below with reference to the attached drawings so that those skilled in the art can implement the invention by referring to the description text.
It is to be noted that the experimental methods described in the following embodiments are all conventional methods unless otherwise specified, and the reagents and materials, if not otherwise specified, are commercially available; in the description of the present invention, the terms indicating orientation or positional relationship are based on the orientation or positional relationship shown in the drawings only for the convenience of description and simplification of description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus, should not be construed as limiting the present invention.
< example 1>
The method for improving the texture and color of the vacuum freeze-dried recombined apple crisp chips comprises the following steps:
pretreatment: selecting red-pulp apples with uniform maturity and no plant diseases and insect pests, cleaning the apples, peeling, removing kernels, and longitudinally cutting the apples into two halves;
crushing: crushing the apples in a low-temperature nitrogen-filled crusher;
pulping: pulping apple in a pulping machine to obtain apple pulp;
blending: adding low-ester pectin 50g/kg, calcium chloride 1.5mg/g, ethyl p-hydroxybenzoate 0.25g/kg and 3% dry powder of apple peel residue into apple pulp, mixing, and homogenizing to obtain mixed solution; the addition amount is based on the mass of the apple pulp;
adjusting the pH value: adding citric acid to adjust the pH value to 3.5;
and (3) sterilization: sterilizing apple pulp at 121 deg.C for 15min, cooling, and pouring into fermentation tank;
fermentation: adding a fermenting agent into a fermentation tank according to 15g/kg, wherein the bacterial concentration of the fermenting agent is 8.5Log (CFU/mL), the number of the compound lactobacillus and the lactobacillus plantarum is 2:1, and fermenting for 48 hours at 30 ℃ to obtain a fermentation liquid; the addition amount is based on the mass of the apple pulp;
and (3) inflating and pulping: pulping for 3min in sterile nitrogen-filled environment; clean nitrogen is continuously mixed below the container in the pulping process;
reshaping: pouring into a mould tray, and slowly freezing together with the mould tray at-18 ℃ to obtain apple pulp blocks, wherein the thickness of the apple pulp blocks is 5 mm; the frozen apple pulp blocks can be stored at the temperature of 18 ℃ below zero for a long time, the storage period can reach 12 months, and the production in the whole year can be realized;
coating: soaking the frozen apple pulp blocks in a chitosan aqueous solution with the mass fraction of 40% at the temperature of-1 ℃ for 3s, taking out the apple pulp blocks, spreading the apple pulp blocks on a stainless steel tray at the temperature of-40 ℃, and putting the apple pulp blocks back to a low-temperature freezer at the temperature of-18 ℃ for later use;
vacuum freeze drying: transferring the frozen apple pulp blocks to a vacuum freeze drying bin for vacuum freeze drying until the moisture content of the apple pulp blocks is below 7%, and stopping vacuum freeze drying to obtain apple crisp chips, wherein the cold trap temperature is set to be-50 ℃, and the tray temperature is set to be 50 ℃;
and (3) nitrogen filling and packaging: taking out the apple chips, selecting light-resistant and oxygen-insulating packages, filling nitrogen for packaging, and storing the nitrogen-filled and packaged products in a cool and dry place.
< example 2>
The method for improving the texture and color of the vacuum freeze-dried recombined apple crisp chips comprises the following steps:
pretreatment: selecting red-pulp apples with uniform maturity and no plant diseases and insect pests, cleaning the apples, peeling, removing kernels, and longitudinally cutting the apples into two halves;
crushing: crushing the apples in a low-temperature nitrogen-filled crusher;
pulping: pulping apple in a pulping machine to obtain apple pulp;
blending: adding low-ester pectin at a ratio of 10g/kg, calcium chloride at a ratio of 1mg/g, ethyl hydroxybenzoate sodium at a ratio of 0.012g/kg, and apple peel residue dry powder with a mass fraction of 2%, mixing well, and homogenizing to obtain a mixed solution; the addition amount is based on the mass of the apple pulp;
adjusting the pH value: adding malic acid to adjust the pH value to 3.0;
and (3) sterilization: sterilizing apple pulp at 121 deg.C for 15min, cooling, and pouring into fermentation tank;
fermentation: adding a fermenting agent into the fermentation tank according to the ratio of 10g/kg, wherein the bacterium concentration of the fermenting agent is 8.0Log (CFU/mL), the number of the compound lactobacillus and the lactobacillus plantarum is 1:1, and fermenting for 36h at the temperature of 30 ℃ to obtain a fermentation liquid; the addition amount is based on the mass of the apple pulp;
and (3) inflating and pulping: pulping for 2min in sterile nitrogen-filled environment; clean nitrogen is continuously mixed below the container in the pulping process;
reshaping: pouring into a mould tray, and slowly freezing together with the mould tray at-18 ℃ to obtain apple pulp blocks, wherein the thickness of the apple pulp blocks is 3 mm; the frozen apple pulp blocks can be stored at the temperature of 18 ℃ below zero for a long time, the storage period can reach 12 months, and the production in the whole year can be realized;
coating: soaking the frozen apple pulp blocks in 30% chitosan water solution at-1 deg.C for 2s, spreading on a stainless steel tray at-30 deg.C, and freezing at-18 deg.C;
vacuum freeze drying: transferring the frozen apple pulp blocks to a vacuum freeze drying bin for vacuum freeze drying until the moisture content of the apple pulp blocks is below 7%, and stopping vacuum freeze drying to obtain apple crisp chips, wherein the temperature of a cold trap is-50 ℃, and the temperature of a tray is 20 ℃;
and (3) nitrogen filling and packaging: taking out the apple chips, selecting light-resistant and oxygen-insulating packages, filling nitrogen for packaging, and storing the nitrogen-filled and packaged products in a cool and dry place.
< example 3>
The method for improving the texture and color of the vacuum freeze-dried recombined apple crisp chips comprises the following steps:
pretreatment: selecting red-pulp apples with uniform maturity and no plant diseases and insect pests, cleaning the apples, peeling, removing kernels, and longitudinally cutting the apples into two halves;
crushing: crushing the apples in a low-temperature nitrogen-filled crusher;
pulping: pulping apple in a pulping machine to obtain apple pulp;
blending: adding low-ester pectin and calcium chloride into apple pulp according to the proportion of 25g/kg, adding propyl p-hydroxybenzoate and 5% of apple peel residue dry powder into apple pulp according to the proportion of 2mg/g, and mixing uniformly and homogenizing to obtain a mixed solution; the addition amount is based on the mass of the apple pulp;
adjusting the pH value: adding lactic acid to adjust the pH to 3.8;
and (3) sterilization: sterilizing apple pulp at 121 deg.C for 15min, cooling, and pouring into fermentation tank;
fermentation: adding 20g/kg of a fermentation agent into the fermentation tank, wherein the bacteria concentration of the fermentation agent is 9.0Log (CFU/mL), the number of the compound lactobacillus and the lactobacillus plantarum is 3:1, and fermenting at 37 ℃ for 60 hours to obtain a fermentation liquid; the addition amount is based on the mass of the apple pulp;
and (3) inflating and pulping: pulping for 5min in sterile nitrogen-filled environment; clean nitrogen is continuously mixed below the container in the pulping process;
reshaping: pouring into a mould tray, and slowly freezing together with the mould tray at-18 ℃ to obtain apple pulp blocks, wherein the thickness of the apple pulp blocks is 8 mm; the frozen apple pulp blocks can be stored at the temperature of 18 ℃ below zero for a long time, the storage period can reach 12 months, and the production in the whole year can be realized;
coating: soaking the frozen apple pulp blocks in a chitosan aqueous solution with the mass fraction of 50% at 0 ℃ for 5s, taking out the apple pulp blocks, spreading the apple pulp blocks on a stainless steel tray at the temperature of minus 45 ℃, and putting the apple pulp blocks back to a low-temperature freezer at the temperature of minus 18 ℃ for later use;
vacuum freeze drying: transferring the frozen apple pulp blocks to a vacuum freeze drying bin for vacuum freeze drying until the moisture content of the apple pulp blocks is below 7%, and stopping vacuum freeze drying to obtain apple crisp chips, wherein the temperature of a cold trap is-50 ℃, and the temperature of a tray is 80 ℃;
and (3) nitrogen filling and packaging: taking out the apple chips, selecting light-resistant and oxygen-insulating packages, filling nitrogen for packaging, and storing the nitrogen-filled and packaged products in a cool and dry place.
< example 4>
The preparation method of the apple crisp chips is the same as that in example 1, except that sodium methylparaben is adopted to replace ethyl paraben in the preparation step, and the dosage is 0.25 g/kg.
< example 5>
The preparation method of the apple crisp chips is the same as that of example 1, wherein the difference is that p-hydroxybenzoic acid is adopted to replace ethyl p-hydroxybenzoate in the blending step, and the dosage is 0.25 g/kg.
< comparative example 1>
The preparation method of the apple crisp chips is the same as that in example 1, except that flavone is adopted to replace ethyl p-hydroxybenzoate in the blending step, and the dosage is 0.25 g/kg.
< comparative example 2>
The preparation method of the apple crisp chips is the same as that in example 1, except that ferulic acid is adopted to replace ethyl p-hydroxybenzoate in the blending step, and the dosage is 0.25 g/kg.
< comparative example 3>
The preparation method of the apple crisp chips is the same as that in example 1, except that water is used to replace ethyl p-hydroxybenzoate in the blending step, and the dosage is 0.25 g/kg.
< comparative example 4>
The preparation method of the apple crisp chips is the same as that in example 1, except that water is adopted to replace low-ester pectin in the blending step, and the dosage is 50 g/kg.
< comparative example 5>
The preparation method of the apple crisp chips is the same as that in example 1, except that high ester pectin is used instead of low ester pectin in the blending step, and the dosage is 50 g/kg.
< comparative example 6>
The preparation method of the apple crisp is the same as that of example 1, wherein, the difference is that the aeration treatment is not adopted in the aeration pulping step, and only pulping is carried out.
< comparative example 7>
The preparation method of the apple crisp chips comprises the following steps:
pretreatment: selecting red-pulp apples with uniform maturity and no plant diseases and insect pests, cleaning the apples, removing kernels, and longitudinally cutting the apples into two halves;
crushing: crushing the apples in a low-temperature nitrogen-filled crusher;
pulping: pulping apple in a pulping machine to obtain apple pulp;
and (3) sterilization: sterilizing the apple pulp at 121 deg.C for 15 min;
vacuum freeze drying: pouring into a mould tray, placing the mould tray and the mould tray in a vacuum freeze drying chamber for vacuum freeze drying, and stopping vacuum freeze drying until the moisture content of the apple pulp blocks is below 7% to obtain the apple crisp chips, wherein the temperature of a cold trap is-50 ℃, the temperature of the tray is 50 ℃, and the thickness of the apple pulp poured into the mould tray is 5 mm;
and (3) nitrogen filling and packaging: taking out the apple chips, selecting light-resistant and oxygen-insulating packages, filling nitrogen for packaging, and storing the nitrogen-filled and packaged products in a cool and dry place.
< quality detection of apple crisp >
1. Detection method
Determination of anthocyanin retention rate:
and (3) determining the total anthocyanin content in the sample by adopting an ultraviolet spectrophotometry. Anthocyanins in the sample were extracted using 2% methanol hydrochloride solution, filtered and assayed at 530 nm. The total anthocyanin content was calculated by a standard curve.
Determination of color difference value:
the color difference meter is adopted to measure the color of the fruit and vegetable crisp chips, and the values of delta L, delta a, delta b and delta E represent the color difference values of the measured samples (L, a and b) and the fresh samples (L, a and b). The Δ E calculation method is as follows:
wherein L, L denotes the lightness values of fresh fruit and dried crisp respectively; a. a is the red-green value of the fresh fruit and the dried crisp respectively; b and b are the yellow-blue values of the fresh fruit and the dried crisp respectively; Δ L is the total color difference value.
Measurement of eutectic point:
and measuring the material co-melting point by adopting a resistance method. The pulp was completely frozen at-40 ℃ and then the temperature was gradually raised. During the period, a resistance instrument is used for continuously detecting the resistance of the material, and the temperature when the resistance begins to show rapid reduction is the eutectic point of the material.
And (3) judging the shelf life:
storing the product at 25 ℃, tracking the quality of the product, and taking the degradation of anthocyanin of the product by more than 50 percent or the reduction of a value by more than 20 percent as the end point of shelf life.
Determination of hardness and brittleness:
measuring with TA-XT2i/50 type physical tester, and selecting brittle strips with similar shape and size for texture measurement. After the sample was quickly taken out from the package, a cutting test was performed with a physical property measuring instrument, and the cutting test was repeated 10 times, and finally an average value was taken. Brittleness is expressed in "number" as the number of peaks produced by the test. The test value is in positive correlation increase in a certain range, the more the number of peaks is, the better the crispness of the product is, and otherwise, the worse the crispness of the product is.
And (3) analyzing pore characteristics:
and (3) carrying out micro-CT scanning, and analyzing by using micro-CT self-contained analysis software to obtain the average pore diameter and the pore wall thickness in the material.
And (3) probiotic content determination:
the lactobacillus test is carried out by adopting the national standard GB 4789.35-2016 food safety national standard food microbiology test.
2. The result of the detection
The test results of examples 1 to 5 and comparative examples 1 to 7 are shown in tables 1 and 2, respectively.
TABLE 1 test results of examples 1 to 5
TABLE 2 test results of comparative examples 1 to 7
As can be seen from table 1, the anthocyanin retention rate of the recombinant apple crisp chips prepared by the methods of examples 1 to 5 is above 86%, which indicates that the anthocyanin is efficiently retained, the color change rate is below 1.53, and the color protection efficiency is excellent; the thicker the average pore diameter and the average wall thickness, the more units which are disintegrated in a single time in a texture compression test in the crisp chip are, the more peaks are reflected on the measurement of a texture instrument, namely the crispness is, the more crisp taste of a sample is represented in sensory experience, and the higher the quality of the product as the crisp chip is; the brittleness is all above 48, which shows that the brittleness is good. The recombined apple crisp chip product prepared by the common method (comparative example 7) has obviously reduced anthocyanin retention rate and obviously changed color change rate, and the brittleness is also obviously reduced.
As can be seen from the data in tables 1 and 2, compared with comparative examples 1, 2 and 3, the adoption of flavone or ferulic acid or water instead of ethyl p-hydroxybenzoate in example 1 significantly reduces the anthocyanin retention rate of the recombined apple crisp chips of the final product, increases the color change rate and reduces the brittleness, which indicates the irreplaceability of ethyl p-hydroxybenzoate.
Comparing example 1 with comparative example 4, it can be seen that the use of water instead of low-ester pectin also significantly reduces the anthocyanin retention rate, increases the color change rate and reduces the crispness of the recombined apple crisp chips of the final product, which indicates the irreplaceability of ethyl p-hydroxybenzoate.
As can be seen from the comparison between the example 1 and the comparative examples 1 to 4, the anthocyanin retention rate can be increased, the color change is reduced and the brittleness of the product is improved only by the synergistic effect of the ethyl p-hydroxybenzoate and the low-ester pectin.
As can be seen from a comparison of example 1 and comparative example 5, the high ester pectin also produced a positive synergistic effect with ethyl p-hydroxybenzoate, but the effect was not as good as the low ester pectin.
As can be seen from comparison between example 1 and comparative example 6, in the air-entraining beating step, aeration can significantly improve the brittleness of the product.
As shown in the product appearance diagram of fig. 1, the first row is the product appearance diagrams of six samples of examples 1 to 5 and comparative example 1 from left to right, and the anthocyanin retention rates are respectively 92%, 86%, 88%, 90%, 89% and 70%. The second row is the product appearance diagrams of six samples of comparative examples 2 to 7 in sequence, the anthocyanin retention rates are respectively 75%, 62%, 72%, 80%, 88% and 43%, the red color of example 1 and example 4 is the reddest, and the anthocyanin retention rate is just the highest.
While embodiments of the invention have been described above, it is not limited to the applications set forth in the description and the embodiments, which are fully applicable in various fields of endeavor to which the invention pertains, and further modifications may readily be made by those skilled in the art, it being understood that the invention is not limited to the details shown and described herein without departing from the general concept defined by the appended claims and their equivalents.