CN114304251B - Method for controlling discoloration of freeze-dried fruits and vegetables during normal-temperature storage - Google Patents
Method for controlling discoloration of freeze-dried fruits and vegetables during normal-temperature storage Download PDFInfo
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Abstract
The invention discloses a method for controlling discoloration of freeze-dried fruits and vegetables during normal-temperature storage, and belongs to the technical field of fruit and vegetable processing. The invention takes fresh fruits and vegetables as raw materials and adopts high-pressure CO 2 After the pretreatment and enzyme deactivation of fruits and vegetables are carried out at a lower temperature by combining a physical mode of radio frequency, an edible film with an antioxidant function is coated on the surfaces of the fruits and vegetables, and then the fruits and vegetables are freeze-dried and are filled with nitrogen and stored at normal temperature in a dark manner, so that the fading time of the freeze-dried fruits and vegetables during normal-temperature storage can be prolonged. The method mainly comprises the following steps: cleaning, trimming, cutting and high-pressure CO of fresh fruits and vegetables without disease spots and with uniform color 2 Treating, radio frequency pretreatment, dipping and coating, air drying and pre-freezing, freeze drying, inert atmosphere packaging, light-shielding normal-temperature storage and the like. The color of the freeze-dried fruit and vegetable product treated by the method is effectively protected, the loss degree of pigment substances is reduced, the final water content of the product is less than 5%, and the fading time can be prolonged under the normal-temperature storage condition.
Description
Technical Field
The invention belongs to the technical field of fruit and vegetable processing, and particularly relates to a method for controlling discoloration of freeze-dried fruits and vegetables during normal-temperature storage.
Background
The fruits and vegetables have high moisture content, so that the fruits and vegetables are easy to be subjected to microbial action after harvesting to cause tissue decay, and the nutritional value and sensory quality of the fruits and vegetables are affected. In order to keep the nutritional ingredients and physical properties of fruits and vegetables to the greatest extent, the vacuum freeze-drying technology can be used in the field of fruit and vegetable drying, and can keep the heat-sensitive ingredients to a great extent while removing the moisture of materials, thereby being beneficial to transportation and preservation.
The color of the freeze-dried fruit and vegetable product is lighter than that of fresh fruit and vegetable, and the color of the freeze-dried fruit and vegetable product is easy to fade under the normal-temperature preservation condition, thereby influencing the sensory quality and shortening the preservation period. The apparent color of the fruits and vegetables has a great relationship with pigments in the fruits and vegetables, and is easily influenced by various factors such as illumination, oxygen, temperature, enzyme and the like.
Zhang, fang Zhongxiang, du Weihua, sun Jincai (patent application number 200510039031.9) discloses a blanching pretreatment method for preventing discoloration of waxberry juice during storage, which is mainly aimed at stabilizing the stability of pigments such as anthocyanin in the waxberry juice during storage. Soaking fructus Myricae Rubrae in hot water (90-100deg.C) for 3-5 min or single layer spreading, steaming (120-130deg.C) for 30-90 s, cooling, and processing juice. The blanching pretreatment method can ensure that the waxberry juice is not discolored when being stored for about one year at normal temperature, but the blanching effect is carried out by taking water as a medium, so that pigment substances are inevitably lost along with the water, and the fragrance components of the waxberry juice are also influenced. The invention is characterized in that after the fruits and vegetables are cut into small pieces, the enzyme activity of enzymes related to the colors of the fruits and vegetables is inactivated by adopting a radio frequency method, air is used as a heat transfer medium, the influence on the pigment content by contact with water is avoided, and high-pressure CO is combined 2 The treatment can achieve the effect of synergistic enzyme deactivation. The fruit and vegetable are subjected to film coating treatment after enzyme deactivation by a physical method without taking water as a medium, the oxidation degree of pigment is further reduced during storage, and finally, the heat-sensitive components such as pigment and the like can be protected to a greater extent by freeze drying, so that the color of the freeze-dried fruit and vegetable product is stable.
Zhang, liu Peng (patent application No. 201010572755.0) disclose a recombined mixed purple sweet potato microwave spouted drying productIs a uniform color protection method. The patent mainly comprises the steps of cutting purple sweet potatoes, spraying citric acid color protection liquid with pH less than or equal to 3, steaming, curing, pulping, mixing with other potatoes, granulating, performing secondary color protection (coating a layer of cured purple sweet potato powder on the surface), and finally performing microwave spouted drying. The citric acid color protection liquid, steaming and curing operation and cured purple sweet potato powder can protect the color of the purple sweet potato mixture. The invention is characterized in that high-pressure CO is adopted 2 And radio frequency physical methods deactivate enzymes at lower temperatures. The radio frequency has high frequency effect on molecules in the material in the form of electromagnetic wave, has stronger penetrability in agricultural products, ensures that the whole volume of the material can be heated, and uses air as a heat transfer medium, so that more pigment can not be lost compared with steam. The grapefruit peel extract with the antioxidation function is used as a microcapsule solution core material, gelatin with gas and water isolation is used as a wall material, and the grapefruit peel extract can continuously play a role in color protection compared with citric acid aqueous solution during normal-temperature storage after being coated on the surfaces of fruit and vegetable blocks, so that pigment substances can be better stabilized.
The color protection process of dehydrated cabbage is disclosed by army, kang Mengli, ling Jiangang, jiang Jianke, guanjin, lin Xudong, chen Xueling, mei Xin, shi Jian and Cai Sha (patent application number 201610012814.6), the cabbage with holes punched on the surface is cleaned and sterilized (96-98 ℃,100mg/L sodium carbonate solution is oscillated for 30 seconds to stabilize chlorophyll), then frozen to a surface at-15 ℃ to form a layer of ice, then soaked in 5% -10% glucose solution for 3-5 minutes for quality guarantee, transferred into a blast drying box for water removal, and finally kept in a vacuum drying box at 50-60 ℃ for 7 hours for water removal. The invention has the difference that a single acid-base solution is not used for stabilizing pigment, and the alkali solution can stabilize chlorophyll, but can shrink fruits and vegetables, damage nutrient substances and influence taste. The microcapsule solution adopted by the patent plays an antioxidant role in the storage period under the action of water vapor and air, and has small influence on the flavor of fruit and vegetable products.
Zhang, ran Xinli and Wang Bin (patent application number 201910156380.0) disclose a method for improving natural color stability of red rose during drying and storage, wherein the trimmed and shaped red rose is soaked in a compound soaking solution containing 0.5% of roselle pigment, 0.3% of calcium chloride and 0.5% of sodium ascorbate for 30 minutes, pre-frozen and dried, and finally coated and dried for the second time. The invention firstly adopts the low-temperature enzyme-inactivating treatment to the fruits and vegetables to prevent enzymatic browning and non-enzymatic browning possibly occurring at high temperature, and coats the color protection film capable of playing the antioxidant function for a long time, thereby avoiding pigment loss caused by soaking the fruits and vegetables for a long time on one hand, and protecting pigment in the initial stage and the storage period on the other hand.
Malia, charpy Hang Dela, luo Jiasi, gelao and Rake Wu Luxi, charpy (patent application No. 201480074231. X) disclose an edible fresh-keeping film for fruit pieces, and methods for making and using the same, wherein the edible film comprises an aqueous carboxymethyl cellulose solution, and citric acid or a combination of citric acid and sodium ascorbate is used as an antioxidant. The invention adopts microcapsule solution to coat fruits and vegetables, the antioxidant component is derived from the grapefruit peel extract, and the antioxidant component can play an antioxidant role on pigment during long-term storage while waste is utilized.
The technology mainly uses the water medium blanching and film coating technology and proper package to achieve the purpose of color protection during storage, and the patent adopts the radio frequency combined high-pressure CO with the volume heating characteristic 2 The physical field destroys the enzyme structure at a lower temperature to inactivate enzyme, then combines the microcapsule solution embedded with natural antioxidant components to protect the color of the freeze-dried product, and packs the sample in cooperation with a light-proof aluminum foil bag filled with nitrogen atmosphere, thus playing the roles of protecting pigment and inactivating enzyme on the premise of not damaging the shape of the freeze-dried fruits and vegetables, and ensuring that the color and luster of the freeze-dried fruits and vegetables are not obviously changed when being preserved for 12 months at normal temperature.
Disclosure of Invention
The invention aims to provide a method for controlling the discoloration of freeze-dried fruits and vegetables during normal-temperature storage, which can relieve the degradation degree of pigments of freeze-dried fruits and vegetables products during normal-temperature storage, prolong the discoloration time of the freeze-dried fruits and vegetables products, and utilize nitrogen inert gas to cooperate with radio frequency and high-pressure CO 2 Physical field enzyme deactivation and film coating pretreatment technology, and can be preserved in a normal temperature light-proof environment for 12 months after freeze drying.
The technical scheme of the invention is as follows:
a method for controlling the discoloration of freeze-dried fruits and vegetables during normal-temperature storage mainly comprises the following steps:
(1) Selecting materials: fresh fruits and vegetables with no disease spots on the surface and uniform color are selected as raw materials, so that the color of the finally freeze-dried fruits and vegetables is prevented from being adversely affected by the color of the raw materials;
(2) Cleaning and finishing: cleaning the surface stains of the selected fruit and vegetable raw materials with clear water, and removing unnecessary parts of the fruits and vegetables;
(3) Cutting: slicing the trimmed fruits and vegetables into fruit and vegetable blocks with certain specification by using a slicing machine according to the shape and the texture;
(4) High pressure CO 2 Pretreatment: placing the segmented fruit and vegetable blocks into a glass plate, and placing the glass plate into high-pressure CO 2 The reaction kettle is arranged, after the set pressure is reached, the reaction kettle is treated for a period of time, and after the pressure is released, the treated fruit and vegetable blocks are subjected to ice bath cooling;
(5) Radio frequency pretreatment: placing the fruit and vegetable blocks pretreated in the step (4) in a glass container, stacking a certain thickness on a dielectric block for radio frequency treatment, and then placing in an ice bath for cooling;
(6) Preparing microcapsule solution: preparing microcapsule emulsion by taking gelatin as a wall material and a grapefruit peel extract as a core material, performing microcapsule by adopting a freeze drying mode, and then dissolving microcapsule powder into distilled water to form a solution;
(7) Dipping and coating: mixing the fruit and vegetable blocks according to a feed liquid ratio of 1: immersing the microcapsule solution in the step (6) for a period of time, fishing out, and placing the microcapsule solution on a sieve plate for draining;
(8) And (3) airing and performing intervention freezing: the fruit and vegetable blocks subjected to the dip coating treatment in the step (7) are placed at room temperature for airing, then are spread in a plastic culture dish, and are pre-frozen for about 10 hours in a refrigerator at the temperature of minus 80 ℃ overnight;
(9) And (3) freeze drying: freeze-drying the fruit and vegetable blocks treated in the step (8) for 10 hours until the final moisture content is lower than 5%, wherein the freeze-drying conditions are as follows: the temperature of the heating plate is 50 ℃, the cold trap temperature is minus 40 ℃, and the vacuum condition is kept at 80pa;
(10) And (3) inert atmosphere packaging: subpackaging the freeze-dried fruit and vegetable blocks obtained in the step (9) into light-proof aluminum foil bags, and filling nitrogen to extrude air components in the packaging bags for 10s;
(11) And (3) sealing: sealing the aluminum foil bag by a heat sealing machine immediately after filling nitrogen, wherein the sealing conditions are as follows: 3s at 180 ℃;
(12) And (5) light-shielding preservation: and sealing the freeze-dried fruit and vegetable products in an aluminum foil bag filled with nitrogen atmosphere, and then storing the freeze-dried fruit and vegetable products in a dark place under the normal temperature condition.
The high-pressure CO in the step (4) 2 The pretreatment process comprises treating fruit and vegetable block at 40deg.C under 30Mpa for 30min, relieving pressure, taking out, and cooling in ice bath for 3min.
The radio frequency pretreatment in the step (5) is carried out at the frequency of 27.12MHz and the power of 1600W, fruits and vegetables are placed in a glass container to be stacked to the height of 6-7cm, the treatment is carried out for 10-15min, the center temperature is about 60-70 ℃, and the ice bath cooling is carried out after the treatment is finished.
In the step (6), the microcapsule solution wall material is prepared by dissolving 3% (w/v) gelatin serving as the wall material in distilled water, and magnetically stirring for 2 hours at 40 ℃ and 600 rpm.
The preparation of the microcapsule solution core material in the step (6) takes grapefruit peel as a raw material, the grapefruit peel is placed in a plastic tray to be frozen completely at the temperature of minus 80 ℃, freeze-drying is carried out, powder is obtained by grinding, 1.5g of freeze-dried powder is mixed with 25ml of 70% ethanol solution to prepare the microcapsule solution core material, stirring is continued for 15 minutes, centrifugation is carried out to obtain supernatant, finally ethanol is evaporated under vacuum, and residual solvent is removed by flushing with nitrogen.
The microcapsule solution in the step (6) is prepared according to the following steps: gelatin solution = 1: 6. The mixture was prepared at 40℃for 30min using a magnetic stirrer at 200rpm, freeze-dried to a solid powder and rehydrated to give a microcapsule solution.
The invention has the beneficial effects that:
(1) Compared with the common hot water scalding and enzyme inactivating method, the method has the advantages of radio frequency and high-pressure CO 2 The pretreatment does not use liquid as a heat transfer medium, so that the loss caused by the contact of pigment and liquid is effectively avoided, each part of the material can be heated by a volume heating mode of radio frequency, and high-pressure CO (carbon monoxide) 2 As a non-heat treatment mode, the thermosensitive components in fruits and vegetables can be reserved to a great extent.
(2) Compared with the common hot air drying in the field of fruit and vegetable drying, the freeze drying can remove water from the materials under high vacuum and lower temperature, and can relieve the degree of oxidation pigment and high-temperature degradation pigment of oxygen in the drying process.
(3) The fruit and vegetable is subjected to film coating pretreatment before being dried, pigment content is reserved to a large extent in the initial processing stage, and compared with the film coating after being dried, the film coating method can reduce the drying cost; the microcapsule prepared from the grapefruit peel extract with the antioxidation function serving as a core material by taking gelatin as a wall material can protect pigment from oxidization for a long time under normal-temperature storage conditions, and has the function of isolating gas and moisture.
Detailed Description
The present invention will be described in further detail with reference to the following examples in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.
The technical scheme of the invention will be further described with reference to specific embodiments.
Example 1 Process for controlling discoloration of lyophilized Allium fistulosum during storage at Normal temperature
Cleaning fresh green onion, cutting into segments with length of 5mm, and treating under high pressure CO 2 The green onion sections are transferred to a dielectric block for processing for 10min under 1600w power after being cooled to room temperature in an ice bath in a reaction kettle of the equipment under 30Mpa, and the stacking thickness is 6cm. After the treatment is completed, the mixture is placed in an ice bath and cooled to room temperature. Placing the onion sections in dark places and keeping away from light until the surface is free of water, immersing the onion sections in the prepared microcapsule solution for coating pretreatment for 2min, placing the onion sections on a sieve plate for leaching redundant film solution, removing the redundant film solution on the surface of the onion sections after the coating treatment by adopting water absorption paper, uniformly spreading the onion sections in a plastic tray, and airing at room temperature. And (3) placing the dried onion sections in a plastic tray, pre-freezing for 10 hours in a refrigerator at the temperature of minus 80 ℃, and then performing vacuum freeze drying for 10 hours under the conditions that the vacuum condition is 80pa, the cold trap temperature is minus 40 ℃ and the heating plate is 50 ℃ so that the water content at the drying end point of the onion sections is below 5%.
Samples of the green onion which were pre-frozen directly without any pretreatment after the cutting and freeze-dried under the same conditions for the same time were set as control groups, and all were stored at normal temperature using an aluminum foil bag filled with nitrogen after the completion of the cutting.
Example 2 Process for controlling discoloration of lyophilized carrots during storage at ambient temperature
Washing fresh radix Dauci Sativae, cutting into pieces with diameter of 25mm and thickness of 5mm, placing in glass tray under high pressure CO 2 The carrot slices were then transferred to a dielectric block and treated at 1600w for 15min in a reactor at 30Mpa for a build-up thickness of 7cm. And (5) after the treatment is finished, placing the mixture in an ice bath for cooling. Absorbing surface water with absorbent paper, immersing carrot slices in prepared microcapsule solution, coating, pretreating for 2min, draining, uniformly spreading in a tray, and airing at room temperature for 1h. And (3) placing the dried carrot slices in a plastic tray, pre-freezing for 10 hours in a refrigerator at the temperature of minus 80 ℃, and then performing vacuum freeze drying for 11 hours under the conditions of 80pa of vacuum condition, cold trap temperature of minus 40 ℃ and heating plate temperature of 50 ℃ to ensure that the water content at the end point of carrot drying is below 5%.
The carrot control group is not pretreated and freeze-dried under the same condition, and is packaged in an aluminum foil bag filled with nitrogen gas at normal temperature for storage.
Example 3 Process for controlling discoloration of lyophilized grapefruit upon storage at ambient temperature
Cleaning fresh grapefruit, removing grapefruit peel, cutting into pieces with diameter of 70mm and thickness of 5mm, standing in glass tray under high pressure of CO 2 The reaction kettle of the equipment is treated for 30min under 30Mpa, the grapefruit pieces are transferred onto a dielectric block and treated for 10min under 1600w power, and the stacking thickness is 6cm. Cooling in ice bath, absorbing excessive water on surface with water absorbing paper, immersing grapefruit pieces in prepared microcapsule solution, coating, pretreating for 2min, draining, spreading in tray, and air drying at room temperature for about 1 hr. And (3) placing the dried grapefruit slices in a plastic tray, pre-freezing for 10 hours in a refrigerator at the temperature of minus 80 ℃, and then performing vacuum freeze drying for 11 hours under the conditions of 80pa of vacuum condition, cold trap temperature of minus 40 ℃ and heating plate temperature of 50 ℃ to ensure that the final drying end water content of the dried grapefruit is below 5%.
The control group was prepared from grapefruit pieces which had not been subjected to any pretreatment and had been freeze-dried under the same conditions, and after the completion, the control group was packed in an aluminum foil bag filled with nitrogen gas and stored at room temperature.
Table 1 below shows the L, a, b values of the lyophilized green onion, carrot, grapefruit and the control group without any pretreatment, treated by the method of the invention, stored for 0 and 12 months at ambient temperature; table 2 shows the pigment content of lyophilized green onion, carrot, grapefruit and control groups treated by the method of the invention, stored for 0 and 12 months at ambient temperature. As can be seen from tables 1 and 2, for the green onion, the values of the pre-treated freeze-dried green onion at the initial stage of storage are not significantly different from each other, the brightness value (L) of the pre-treated freeze-dried green onion is lower than that of the control group after 12 months of storage, the redness value (a) and the yellowness value (b) are lower, which means that the green color of the green onion of the treatment group is deeper than that of the control group after freeze-drying, and the higher chlorophyll content of the green onion is combined with the storage for 12 months.
For carrots, the values of L, a and b of the treated carrot and the control group after lyophilization are not greatly different, when the two lyophilized products are stored for 12 months at normal temperature and light, the brightness value (L) of the pretreated lyophilized carrot is lower than that of the control group, the redness value (a) is higher than that of the control group, the yellowness value (b) is slightly lower than that of the control group sample, which indicates that the red degree of the treated carrot is deeper than that of the control group after lyophilization, and the total carotenoid content of the treated carrot and the treated carrot is higher than that of the control group when the treated carrot is stored for 12 months.
For grapefruits, there was a visually significant difference in the values of L, a, b after lyophilization between the grapefruit treated and control groups, the brightness value (L) of the grapefruit pretreated at the initial stage of storage was lower than that of the control group, the redness value (a) was higher than that of the control group, and the yellowness value (b) was lower than that of the control group.
When the two lyophilized products were stored at room temperature in the dark for 12 months, the brightness value (L) of the pre-treated lyophilized grapefruit was lower than that of the control, the redness value (a) was higher than that of the control, and the yellowness value (b) was lower than that of the control sample. When two groups of freeze-dried grapefruits are stored for 12 months under the normal temperature and light-shielding conditions, the L, a and b values of the two groups still keep the same conclusion, which indicates that the color of the freeze-dried grapefruits of the treatment group is darker than that of the control group, and the color of the freeze-dried grapefruits of the treatment group can still be effectively kept after being stored for 12 months under the same conditions, and the high anthocyanin content of the freeze-dried grapefruits of the treatment group and the control group can be combined with the high anthocyanin content of the freeze-dried grapefruits of the treatment group under the normal temperature storage, so that the pre-treatment method can be considered to be effective in relieving the fading degree of the freeze-dried grapefruits under the normal temperature.
Table 1 lyophilized green onion, carrot, grapefruit stored for 0 and 12 months at ambient temperature L, a, b
TABLE 2 colorant content of lyophilized Allium fistulosum, carrot and grapefruit stored at ambient temperature for 0 and 12 months
Claims (3)
1. The method for controlling the discoloration of the freeze-dried fruits and vegetables during normal-temperature storage is characterized by mainly comprising the following steps:
(1) Selecting materials: fresh fruits and vegetables with no disease spots on the surface and uniform color are selected as raw materials, so that the color of the finally freeze-dried fruits and vegetables is prevented from being adversely affected by the color of the raw materials;
(2) Cleaning and finishing: cleaning the surface stains of the selected fruit and vegetable raw materials with clear water, and removing unnecessary parts of the fruits and vegetables;
(3) Cutting: slicing the trimmed fruits and vegetables into fruit and vegetable blocks with certain specification by using a slicing machine according to the shape and the texture;
(4) High pressure CO 2 Pretreatment: placing the segmented fruit and vegetable blocks into a glass plate, and placing the glass plate into high-pressure CO 2 In the reaction kettle of the device, the device is treated at 40 ℃ under the pressure of 30Mpa for 30min, then is decompressed and taken out, and is cooled in an ice bath for 3min;
(5) Radio frequency pretreatment: placing the fruit and vegetable blocks pretreated in the step (4) in a glass container, stacking the fruit and vegetable blocks on a dielectric block with a certain thickness for carrying out radio frequency treatment, wherein the radio frequency is 27.12MHz, the power is 1600W, the stacking height of the fruit and vegetable blocks placed in the glass container is 6-7cm, the treatment is carried out for 10-15min, the central temperature is 60-70 ℃, and ice bath cooling is carried out after the treatment is finished;
(6) Preparing microcapsule solution: preparing microcapsule emulsion by taking gelatin as a wall material and a grapefruit peel extract as a core material, performing microcapsule by adopting a freeze drying mode, and then dissolving microcapsule powder into distilled water to form a solution; the preparation of the core material takes grapefruit peel as a raw material, the grapefruit peel is placed in a plastic tray to be frozen completely at the temperature of minus 80 ℃, then freeze-dried and ground to obtain powder, 1.5g freeze-dried powder is mixed with 25ml of 70% ethanol solution to prepare the core material, the mixture is continuously stirred for 15 minutes and centrifuged to obtain supernatant, finally ethanol is evaporated under the vacuum condition, and residual solvent is removed by flushing with nitrogen;
(7) Dipping and coating: mixing the fruit and vegetable blocks according to a feed liquid ratio of 1: immersing the microcapsule solution in the step (6) for a period of time, fishing out, and placing the microcapsule solution on a sieve plate for draining;
(8) And (3) airing and performing intervention freezing: the fruit and vegetable blocks subjected to the dip coating treatment in the step (7) are placed at room temperature for airing, then are spread in a plastic culture dish, and are pre-frozen in a refrigerator at-80 ℃ for 10 hours overnight;
(9) And (3) freeze drying: freeze-drying the fruit and vegetable blocks treated in the step (8) for 10 hours until the final moisture content is lower than 5%, wherein the freeze-drying conditions are as follows: the temperature of the heating plate is 50 ℃, the cold trap temperature is minus 40 ℃, and the vacuum condition is kept at 80pa;
(10) And (3) inert atmosphere packaging: subpackaging the freeze-dried fruit and vegetable blocks obtained in the step (9) into light-proof aluminum foil bags, and filling nitrogen to extrude air components in the packaging bags for 10s;
(11) And (3) sealing: immediately sealing the aluminum foil bag by a heat sealing machine after filling nitrogen, wherein the sealing conditions are as follows: 3s at 180 ℃;
(12) And (5) light-shielding preservation: and sealing the freeze-dried fruit and vegetable products in an aluminum foil bag filled with nitrogen atmosphere, and then placing the freeze-dried fruit and vegetable products in a normal-temperature environment to realize light-proof storage.
2. The method for controlling discoloration of freeze-dried fruits and vegetables stored at normal temperature according to claim 1, wherein the microcapsule solution wall material in the step (6) is prepared by dissolving 3% w/v gelatin as a wall material in distilled water, and magnetically stirring for 2 hours at 40 ℃ and 600 rpm.
3. The method for controlling discoloration of freeze-dried fruits and vegetables stored at normal temperature according to claim 1, wherein the microcapsule solution prepared in the step (6) is prepared by the following steps: gelatin solution = 1: 6. The mixture was prepared at 40℃for 30min using a magnetic stirrer at 200rpm, freeze-dried to a solid powder and rehydrated to give a microcapsule solution.
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