A composite method for improving the quality of frozen pickled apple slices

Abstract

A composite method for improving the quality of frozen pickled apple slices includes (1) raw material selection; (2) pretreatment; (3) impregnation with a composite color-protecting and crisp-preserving agent; (4) pickling; (5) CO2 microbubble injection; (6) immersion in an antifreeze liquid; (7) impregnation coating; (8) high-voltage electric field (HVEF) treatment; (9) static magnetic field-assisted quick-freezing; and (10) packaging. This invention provides an effective color-protecting method for improving the quality of frozen pickled apple slices. The combination of color-protecting agent immersion and impregnation coating with HVEF treatment effectively prevents the frozen pickled apple slices from browning for an extended period after thawing. The color-protecting method used is non-thermal treatment and does not damage the flavor, nutrition, texture, or other qualities of the frozen apples. HVEF treatment also has antibacterial and enzyme-inhibiting effects, which helps reduce the microbial content of the frozen pickled apple slices.

Description

Technical Field

[0001] This invention belongs to the field of food freezing processing technology, and specifically relates to a composite method for improving the quality of frozen pickled apple slices. Background Technology

[0002] Pickled apples are a processed apple product that caters to diverse consumer needs. Both fresh and pickled apples have high water content, making them prone to spoilage during transportation and storage. In recent years, the processing of frozen fruits and vegetables has developed. Frozen apples not only better preserve their flavor and nutrients, allowing for direct consumption, but also serve as a raw material in processed foods such as fruit-flavored drinks and fruit jellies. However, during freezing, the cell membrane proteins undergo denaturation, altering the cell membrane structure and affecting product quality. Ice crystals formed during freezing can also disrupt cell pressure, leading to structural damage and further deterioration in quality, such as decreased texture, color, flavor, and nutritional content. Frozen apples often experience significant changes in color during processing and long-term storage and transportation, significantly impacting their commercial acceptability. Therefore, this patent addresses the browning and quality degradation problems caused by freezing in processed apples, developing a novel freezing processing technology to improve the color stability and overall quality of frozen pickled apples and extend their shelf life. Summary of the Invention

[0003] Technical problem to be solved: In order to overcome the problem that frozen pickled apples are very prone to browning after thawing, resulting in a serious decline in quality, and that traditional color-protecting agents and quality improvement methods are not effective, this invention develops a complete set of composite methods for improving the quality of frozen pickled apple slices.

[0004] Technical Solution: A composite method for improving the quality of frozen pickled apple slices, comprising the following steps: (1) Raw material selection: selecting fresh apples as raw materials; (2) Pretreatment: washing the apples and then slicing them; (3) Impregnation with a composite color-protecting and crispness-preserving agent: immersing the pretreated apple slices in a composite color-protecting and crispness-preserving agent at 1-4℃ for 20-30 minutes, wherein the composite color-protecting and crispness-preserving agent comprises 1wt.%-2wt.% citric acid, 1wt.%-2wt.% ascorbic acid, and 0.5wt.%... ~1wt.% ferulic acid and 1wt.%~2wt.% calcium chloride, the remainder being water; (4) Pickling: The apple slices treated with color protection and crispness preservation are immersed in the pickling material at 0~5℃ at a material-liquid mass ratio of 1:(2~4) for 1~2 hours, and then drained; The pickling material consists of 3~5g of millet pepper, 150~300g of rice vinegar, 800~1000g of saturated carbonated water, and 10~20g of honey; (5) CO2 microbubble injection: The pickled apple slices are placed in a CO2 pressurization device. Pressurization treatment is performed, and CO2 microbubbles are injected into the apple tissue; the pressurization temperature is 1-4℃ and the pressure is 0.5-1.5MPa; (6) Antifreeze liquid immersion: the pickled apple slices containing CO2 microbubbles are transferred into the antifreeze liquid and immersed for 30-60 minutes, so that the antifreeze liquid penetrates into the apple tissue, and then the water is drained; the antifreeze substance is a mixture of apple pectin, trehalose, isomaltulose and glycerol; (7) Impregnation coating: the treated apple slices are impregnated at a material-to-liquid mass ratio of 1:(5-7). Immerse the apple slices in the coating solution, then take them out and air dry them to coat the surface of the apple slices with a protective layer; (8) High voltage electric field (HVEF) treatment: lay the coated apple slices flat in the high voltage electric field equipment and subject them to a high voltage electrostatic field treatment of ≥40kV for no less than 4 hours; (9) Static magnetic field assisted quick freezing: place the treated sample in the static magnetic field assisted quick freezing equipment for quick freezing, and use the static magnetic field to control the formation of apple ice crystals during the quick freezing process; (10) Packaging: take out the frozen apple slices, package them and store them in a -20℃ freezer.

[0005] Preferably, the composite color-protecting and brittle-preserving agent in step (3) is a compound of color-protecting agent and brittle-preserving agent, and its components are 2 wt.% citric acid, 2 wt.% ascorbic acid, 0.5 wt.% ferulic acid and 1 wt.% calcium chloride, with the remaining components being water.

[0006] Preferably, the marinade and apple slices in the above step (4) marinating method consist of 3g of millet pepper, 150g of rice vinegar, 800g of saturated carbonated water, 10g of honey, and 500g of apple slices.

[0007] Preferably, the process of step (5) above is as follows: adjust the temperature to 4°C, put the sample into the pressure tank, tighten the cover, evacuate, introduce CO2, turn on the pressure pump to 0.5MPa, maintain pressure for 30min, depressurize, and take out the sample.

[0008] Preferably, the antifreeze substance in step (6) consists of apple pectin, trehalose, isomaltulose and glycerol in a mass ratio of 5:1:1:0.1; the mixed antifreeze substance is then mixed with water in a mass ratio of 1:10 to obtain an antifreeze solution.

[0009] Preferably, the above-mentioned antifreeze liquid immersion is performed simultaneously with vacuum ultrasonic assistance, using a vacuum degree of 0.2-0.5MPa, an ultrasonic frequency of 28kHz, and a power of 400W.

[0010] Preferably, the composition of the impregnation coating solution in step (7) is 1 wt.% to 5 wt.% chitosan, 0.5 wt.% to 1 wt.% sodium isoascorbate, 0.5 wt.% to 1 wt.% calcium chloride, 0.5 wt.% to 1 wt.% edible salt, 0.1 wt.% to 0.5 wt.% sodium citrate, 0.05 wt.% to 0.1 wt.% phytic acid, and the remainder is water.

[0011] Preferably, the above-mentioned coating method is a two-stage coating. The apple slices are first immersed for 5 seconds and then drained. Then, they are immersed for 10 seconds and then drained.

[0012] Preferably, the high-voltage electric field (HVEF) is a high-voltage electrostatic field, which outputs the high-voltage electric field upward and downward through the barbed electrode plate; the apple slices are laid flat on the polytetrafluoroethylene plate, the sample is 10cm away from the barbed electrode plate, the electrostatic field strength is set to 40kV, the field strength acting on the apple sample is 4kV / cm, the high-voltage electrostatic field treatment time is 4h, and the high-voltage electric field treatment temperature is 4℃.

[0013] Preferably, the above-mentioned static magnetic field assisted quick-freezing is carried out using a static magnetic field assisted quick-freezing device. The static magnetic field is provided by a pair of Helmholtz coils placed on both sides of the quick-freezing cabinet. The static magnetic field is used to regulate the formation of apple ice crystals during the freezing process. The static magnetic field strength is 10mT, and the operating temperature range is 0 to -5℃. The quick-freezing temperature is -40℃.

[0014] Beneficial effects: 1. This invention provides an effective method for color protection to improve the quality of frozen pickled apple slices. The combination of immersion in a color-protecting agent and impregnation coating with HVEF treatment effectively prevents browning of frozen pickled apple slices for an extended period after thawing. The color protection method used is non-thermal treatment and does not damage the flavor, nutrition, or texture of the frozen apples. HVEF treatment also has antibacterial and enzyme-inhibiting effects, which helps reduce the microbial content of the frozen pickled apple slices.

[0015] 2. This invention provides an effective method for improving the crispness of frozen pickled apple slices. The color-protecting and crispness-preserving agent used not only protects the color but also enhances the crispness of the frozen pickled apple slices after thawing, resulting in a significant improvement in the texture of the frozen apples. The developed pickled apple composite color-protecting and crispness-preserving agent is green, safe, and efficient.

[0016] 3. The CO2 microbubble injection provided by this invention can effectively promote the penetration of antifreeze liquid. The CO2 pressurization technology combined with antifreeze liquid can reduce the damage of freezing to apple tissue cells.

[0017] 4. The static magnetic field assisted quick-freezing technology of this invention can further reduce the size of ice crystals formed during the freezing process on the basis of quick-freezing. The injection of CO2 microbubbles before freezing can further enhance the static magnetic field assisted freezing effect. Combined with antifreezing liquid, the frozen pickled apple slices are less damaged by ice crystals, thereby effectively improving the quality of frozen apple slices.

[0018] 5. The composite method for improving the quality of frozen pickled apple slices provided by this invention is not only applicable to improving the quality of frozen pickled apple slices, but also applicable to the processing of frozen fruits for other purposes. After thawing, the frozen products obtained by this method maintain good physicochemical and nutritional indicators, and the overall quality of the materials is improved.

[0019] 6. The freezing method of this invention for freezing fruits has a gentle electromagnetic field effect, is convenient to use, and has high feasibility in practical applications. Attached Figure Description

[0020] Figure 1 The color changes of control samples (1-4) in Experiment 1 and the samples in Example 1 of this invention after freezing and thawing;

[0021] Figure 2 The hardness changes of control samples (1-4) in Experiment 1 and the samples in Example 1 of this invention after freezing and thawing;

[0022] Figure 3 The changes in juice loss after freezing and thawing of control samples (1-4) in Experiment 1 and the samples in Example 1 of this invention were compared.

[0023] Figure 4 The color changes of control samples (1-4) in Experiment 2 and the samples in Example 2 of this invention after freezing and thawing;

[0024] Figure 5 The hardness changes of control samples (1-4) in Experiment 2 and samples in Example 2 of this invention after freezing and thawing;

[0025] Figure 6 The changes in juice loss after freezing and thawing of control samples (1-4) in Experiment 2 and samples in Example 2 of this invention;

[0026] Figure 7The color changes of control samples (1-4) in Experiment 3 and the samples in Example 3 of this invention after freezing and thawing;

[0027] Figure 8 Compare the hardness changes of control samples (1-4) in Experiment 3 with those in Example 3 of this invention after freezing and thawing;

[0028] Figure 9 The changes in juice loss after freezing and thawing of control samples (1-4) in Experiment 3 and the sample in Example 3 of this invention were compared. Detailed Implementation

[0029] The technical solution of the present invention will be described in detail below with reference to the embodiments:

[0030] Example 1

[0031] A complex method for improving the quality of frozen marinated Fuji apple slices, comprising the following steps:

[0032] (1) Raw material selection: Select fresh Fuji apples that are uniform in size, free from pests and diseases, mechanical damage, rot and spoilage, normal in color, moderately ripe, and suitable for freezing processing as raw materials.

[0033] (2) Pre-treatment: Wash the selected apple raw materials and then slice them (with skin). Each apple slice is 5mm thick and weighs about 5g.

[0034] (3) Impregnation with composite color-protecting and crispness-preserving agent: The pretreated apple slices are impregnated with a composite color-protecting and crispness-preserving agent at 4°C for 20 minutes. The color-protecting and crispness-preserving agent consists of 2% citric acid, 2% ascorbic acid, 0.5% ferulic acid and 1% calcium chloride.

[0035] (4) Marinating: Immerse the apple slices, which have been treated to protect color and crispness, in a marinade at 0-5℃ for 1 hour at a ratio of 1:2 (material to liquid by weight). Remove and drain. The marinade and apple slices consist of 3g of small red chili peppers, 150g of rice vinegar, 800g of Sprite, 10g of honey, and 500g of apple slices.

[0036] (5) CO2 microbubble injection: The pickled apple slices were placed in a CO2 pressurization device for pressurization treatment, and CO2 microbubbles were injected into the apple tissue. The CO2 microbubble injection method was carried out using a dedicated CO2 micro-pressurization device. The pressurization process was as follows: adjusting the temperature, placing the sample into the pressurization tank, tightening the lid, evacuating the vacuum, introducing CO2, turning on the pressurization pump to the required pressure, maintaining the pressure for 30 minutes, depressurizing, and removing the sample. The pressurization temperature used was 4℃, and the pressure was 0.5MPa.

[0037] (6) Immersion in antifreeze liquid: The pickled apple slices containing CO2 microbubbles were immersed in the antifreeze liquid for 30 minutes to allow the liquid to penetrate the apple tissue, and then drained. The antifreeze substance consisted of apple pectin, trehalose, isomaltulose, and glycerol in a mass ratio of 5 (apple pectin): 1 (trehalose): 1 (isomaltulose): 0.1 (glycerol). The mixed antifreeze substance was then mixed with water at a mass ratio of 1:10. Vacuum ultrasound was used to enhance the immersion effect. The vacuum level used was 0.3 MPa, the ultrasonic frequency was 28 kHz, and the power was 400 W.

[0038] (7) Immersion Coating: Immerse the treated apple slices in the coating solution at a material-to-liquid ratio of 1:5 for 30 seconds, then remove and air dry to coat the apple slices with a protective layer. The immersion coating solution consists of 2.5 wt.% chitosan, 0.5 wt.% sodium isoascorbate, 0.5 wt.% calcium chloride, 0.5 wt.% edible salt, 0.2 wt.% sodium citrate, and 0.1 wt.% phytic acid. The coating method is a two-stage coating: first, immerse the apple samples for 5 seconds and drain; then immerse them for 10 seconds and drain.

[0039] (8) High voltage electric field (HVEF) treatment: Apple samples are laid flat on a polytetrafluoroethylene plate in the sample chamber of the high voltage electrostatic field equipment. The sample is 10cm away from the barbed electrode plate. The electrostatic field strength is set to 40kV, the field strength acting on the apple sample is 4kV / cm, the high voltage electrostatic field treatment time is 4h, and the high voltage electric field treatment temperature is 4℃.

[0040] (9) Static magnetic field assisted quick freezing: The treated sample is placed in a static magnetic field assisted quick freezing device for quick freezing. The static magnetic field strength is 10mT, the operating temperature range is 0 to -5℃, and the quick freezing temperature is -40℃.

[0041] (10) Packaging: Take out the frozen apple slices, package them and store them in a freezer at -20℃.

[0042] Comparative Experiment 1

[0043] The following control experiment was set up to verify the effect of the composite method of the present invention in improving the quality of frozen marinated Fuji apple slices; and the effect of the present invention was compared with that of a single application of a certain technology in the present invention to demonstrate the application effect of the combination of various technologies in the present invention.

[0044] Control 1: Red Fuji apples that were not subjected to any of the treatments of this invention, but were simply quick-frozen at -40℃, were used as Control 1;

[0045] Control 2: Red Fuji apples that were quick-frozen with magnetic field assistance but without undergoing the pre-freezing treatment of this invention were used as Control 2;

[0046] Control 3: Red Fuji apples that were quick-frozen after only undergoing color protection and crispness preservation treatment without the HVEF treatment of this invention were used as Control 3;

[0047] Control 4: Red Fuji apples that were quick-frozen using other techniques of the present invention but without CO2 microbubble injection were used as Control 4.

[0048] Then, control samples 1-4 and the pickled Fuji apples frozen using the method of this invention were thawed under the same room temperature conditions. After thawing for 24 hours, the color, firmness, and juice loss indices of different Fuji apple samples were measured to compare the beneficial effects of this invention. The experimental results are as follows: Figures 1-3 As shown, compared to control samples 1-4, the frozen pickled Fuji apple slices of this invention significantly inhibited color changes, significantly improved hardness, and significantly reduced juice loss after thawing, with significant differences (P<0.05). This indicates that the combined method of this invention can significantly improve the quality of frozen pickled apple slices, with effects significantly superior to ordinary freezing methods and single-technology inventions. Furthermore, observation... Figure 3 It can be observed that the techniques used in controls 1, 2, 3, and 4 did not effectively control the juice loss of frozen apples (no significant difference), but the combined method of the present invention had a significant effect on the juice loss of the sample, with a significant difference compared to the controls (P<0.05). This indicates that using any one of the techniques in the present invention alone would not be effective, but the combination of them produced an organic synergistic effect, rather than the sum of the effects of individual techniques in the invention.

[0049] Example 2

[0050] A complex method for improving the quality of frozen pickled Luochuan apple slices includes the following steps:

[0051] (1) Raw material selection: Select fresh Luochuan apples that are uniform in size, free from pests and diseases and mechanical damage, free from rot and spoilage, normal in color, moderately ripe, and suitable for freezing processing as raw materials.

[0052] (2) Pre-treatment: Wash the selected apple raw materials and then slice them (with skin). Each apple slice is 5mm thick and weighs about 5g.

[0053] (3) Impregnation with composite color-protecting and crispness-preserving agent: The pretreated apple slices were impregnated with a composite color-protecting and crispness-preserving agent at 4°C for 20 minutes. The color-protecting and crispness-preserving agent consists of 2 wt.% citric acid, 2 wt.% ascorbic acid, 0.5 wt.% ferulic acid and 1 wt.% calcium chloride.

[0054] (4) Marinating: Immerse the apple slices, which have been treated to protect color and crispness, in a marinade at 0-5℃ for 1 hour at a ratio of 1:2. Remove and drain. The marinade and apple slices consist of 3g of millet chili, 150g of rice vinegar, 800g of Sprite, 10g of honey, and 500g of apple slices.

[0055] (5) CO2 microbubble injection: The pickled apple slices were placed in a CO2 pressurization device for pressurization treatment, and CO2 microbubbles were injected into the apple tissue. The CO2 microbubble injection method was carried out using a dedicated CO2 micro-pressurization device. The pressurization process was as follows: adjusting the temperature, placing the sample into the pressurization tank, tightening the lid, evacuating the vacuum, introducing CO2, turning on the pressurization pump to the required pressure, maintaining the pressure for 30 minutes, depressurizing, and removing the sample. The pressurization temperature used was 4℃, and the pressure was 0.5MPa.

[0056] (6) Immersion in antifreeze liquid: The pickled apple slices containing CO2 microbubbles were immersed in the antifreeze liquid for 30 minutes to allow the liquid to penetrate the apple tissue, and then drained. The antifreeze substance consisted of apple pectin, trehalose, isomaltulose, and glycerol in a mass ratio of 5 (apple pectin): 1 (trehalose): 1 (isomaltulose): 0.1 (glycerol). The mixed antifreeze substance was then mixed with water at a mass ratio of 1:10. Vacuum ultrasound was used to enhance the immersion effect. The vacuum level used was 0.3 MPa, the ultrasonic frequency was 28 kHz, and the power was 400 W.

[0057] (7) Immersion Coating: Immerse the treated apple slices in the coating solution at a material-to-liquid ratio of 1:5 for 30 seconds, then remove and air dry to coat the apple slices with a protective layer. The immersion coating solution consists of 2.5 wt.% chitosan, 0.5 wt.% sodium isoascorbate, 0.5 wt.% calcium chloride, 0.5 wt.% edible salt, 0.2 wt.% sodium citrate, and 0.1 wt.% phytic acid. The coating method is a two-stage coating: first, immerse the apple samples for 5 seconds and drain; then immerse them for 10 seconds and drain.

[0058] (8) High voltage electric field (HVEF) treatment: Apple samples are laid flat on a polytetrafluoroethylene plate in the sample chamber of the high voltage electrostatic field equipment. The sample is 10cm away from the barbed electrode plate. The electrostatic field strength is set to 40kV, the field strength acting on the apple sample is 4kV / cm, the high voltage electrostatic field treatment time is 4h, and the high voltage electric field treatment temperature is 4℃.

[0059] (9) Static magnetic field assisted quick freezing: The treated sample is placed in a static magnetic field assisted quick freezing device for quick freezing. The static magnetic field strength is 10mT, the operating temperature range is 0 to -5℃, and the quick freezing temperature is -40℃.

[0060] (10) Packaging: Take out the frozen apple slices, package them and store them in a freezer at -20℃.

[0061] Comparative Experiment 2

[0062] The following control experiment was set up to verify the effect of the composite method of the present invention on improving the quality of frozen pickled Luochuan apple slices; and the effect of the present invention was compared with that of a single application of a certain technology in the present invention to demonstrate the application effect of the combination of various technologies in the present invention.

[0063] Control 1: Luochuan apples that were ordinary quick-frozen at -40℃ without any treatment according to the present invention were used as Control 1;

[0064] Control 2: Luochuan apples that were quick-frozen with magnetic field assistance but without the pre-freezing treatment of the present invention were used as Control 2;

[0065] Control 3: Luochuan apples that were quick-frozen after only undergoing color protection and crispness preservation treatment without the HVEF treatment of this invention were used as Control 3;

[0066] Control 4: Luochuan apples quick-frozen using other techniques of the present invention but without CO2 microbubble injection as described in this invention were used as Control 4.

[0067] Then, control samples 1-4 and pickled Luochuan apples frozen using the method of this invention were thawed under the same room temperature conditions. After thawing for 24 hours, the color, firmness, and juice loss indices of different Luochuan apple samples were measured to compare the beneficial effects of this invention. The experimental results are as follows: Figures 4-6 As shown in the figure, compared with control samples 1-4, the frozen pickled Luochuan apple slices of the present invention significantly inhibited color changes, significantly improved hardness, and significantly reduced juice loss after thawing, with significant differences (P<0.05). This indicates that the composite method of the present invention can significantly improve the quality of frozen pickled apple slices, and its effect is significantly better than ordinary freezing methods and single invention technologies.

[0068] Example 3

[0069] A complex method for improving the quality of frozen marinated African apple slices includes the following steps:

[0070] (1) Raw material selection: Select fresh fresh cow apples that are uniform in size, free from pests and diseases and mechanical damage, free from rot and deterioration, normal in color, moderately ripe, and suitable for freezing processing as raw materials.

[0071] (2) Pre-treatment: Wash the selected apple raw materials and then slice them (with skin). Each apple slice is 5mm thick and weighs about 5g.

[0072] (3) Impregnation with composite color-protecting and crispness-preserving agent: The pretreated apple slices were impregnated with a composite color-protecting and crispness-preserving agent at 4°C for 20 minutes. The color-protecting and crispness-preserving agent consists of 2 wt.% citric acid, 2 wt.% ascorbic acid, 0.5 wt.% ferulic acid and 1 wt.% calcium chloride.

[0073] (4) Marinating: Immerse the apple slices, which have been treated to protect color and crispness, in a marinade at 0-5℃ for 1 hour at a ratio of 1:2. Remove and drain. The marinade and apple slices consist of 3g of millet chili, 150g of rice vinegar, 800g of Sprite, 10g of honey, and 500g of apple slices.

[0074] (5) CO2 microbubble injection: The pickled apple slices were placed in a CO2 pressurization device for pressurization treatment, and CO2 microbubbles were injected into the apple tissue. The CO2 microbubble injection method was carried out using a dedicated CO2 micro-pressurization device. The pressurization process was as follows: adjusting the temperature, placing the sample into the pressurization tank, tightening the lid, evacuating the vacuum, introducing CO2, turning on the pressurization pump to the required pressure, maintaining the pressure for 30 minutes, depressurizing, and removing the sample. The pressurization temperature used was 4℃, and the pressure was 0.5MPa.

[0075] (6) Immersion in antifreeze liquid: The pickled apple slices containing CO2 microbubbles were immersed in the antifreeze liquid for 30 minutes to allow the liquid to penetrate the apple tissue, and then drained. The antifreeze substance consisted of apple pectin, trehalose, isomaltulose, and glycerol in a mass ratio of 5 (apple pectin): 1 (trehalose): 1 (isomaltulose): 0.1 (glycerol). The mixed antifreeze substance was then mixed with water at a mass ratio of 1:10. Vacuum ultrasound was used to enhance the immersion effect. The vacuum level used was 0.3 MPa, the ultrasonic frequency was 28 kHz, and the power was 400 W.

[0076] (7) Immersion Coating: Immerse the treated apple slices in the coating solution at a material-to-liquid ratio of 1:5 for 30 seconds, then remove and air dry to coat the apple slices with a protective layer. The immersion coating solution consists of 2.5 wt.% chitosan, 0.5 wt.% sodium isoascorbate, 0.5 wt.% calcium chloride, 0.5 wt.% edible salt, 0.2 wt.% sodium citrate, and 0.1 wt.% phytic acid. The coating method is a two-stage coating: first, immerse the apple samples for 5 seconds and drain; then immerse them for 10 seconds and drain.

[0077] (8) High voltage electric field (HVEF) treatment: Apple samples are laid flat on a polytetrafluoroethylene plate in the sample chamber of the high voltage electrostatic field equipment. The sample is 10cm away from the barbed electrode plate. The electrostatic field strength is set to 40kV, the field strength acting on the apple sample is 4kV / cm, the high voltage electrostatic field treatment time is 4h, and the high voltage electric field treatment temperature is 4℃.

[0078] (9) Static magnetic field assisted quick freezing: The treated sample is placed in a static magnetic field assisted quick freezing device for quick freezing. The static magnetic field strength is 10mT, the operating temperature range is 0 to -5℃, and the quick freezing temperature is -40℃.

[0079] (10) Packaging: Take out the frozen apple slices, package them and store them in a freezer at -20℃.

[0080] Comparative Experiment 3

[0081] The following control experiment was set up to verify the effect of the composite method of the present invention on improving the quality of frozen marinated Huaniu apple slices; and the effect of the present invention was compared with that of a single application of a certain technology in the present invention to demonstrate the application effect of the combination of various technologies in the present invention.

[0082] Control 1: Huaniu apples that were not subjected to any of the treatments of this invention, but were simply quick-frozen at -40℃, were used as Control 1;

[0083] Control 2: Huaniu apples that were quick-frozen with magnetic field assistance but without the pre-freezing treatment of this invention were used as Control 2;

[0084] Control 3: Huaniu apples that were quick-frozen after only undergoing color protection and crispness preservation treatment without the HVEF treatment of this invention were used as Control 3;

[0085] Control 4: Huaniu apples that were quick-frozen using other techniques of the present invention but without CO2 microbubble injection were used as Control 4.

[0086] Then, control samples 1-4 and the pickled Huaniu apples frozen using the method of this invention were thawed under the same room temperature conditions. After thawing for 24 hours, the color, firmness, and juice loss indices of different Huaniu apple samples were measured to compare the beneficial effects of this invention. The experimental results are as follows: Figures 7-9 As shown in the figure, compared with control samples 1-4, the frozen pickled apple slices of this invention significantly inhibited color changes, significantly improved hardness, and significantly reduced juice loss after thawing, with significant differences (P<0.05). This indicates that the composite method of this invention can significantly improve the quality of frozen pickled apple slices, and its effect is significantly better than ordinary freezing methods and single invention technologies.

[0087] The foregoing illustrative description of the invention and its embodiments is not restrictive. Therefore, if those skilled in the art are inspired by it and design similar structural methods and embodiments without departing from the spirit of the invention, they should all fall within the protection scope of the invention.

Claims

1. A composite method for improving the quality of frozen pickled apple slices, characterized in that, The process includes the following steps: (1) Raw material selection: Select fresh apples as raw materials; (2) Pretreatment: Wash the apples and then slice them; (3) Impregnation with a compound color-protecting and crisp-preserving agent: Immerse the pretreated apple slices in a compound color-protecting and crisp-preserving agent at 1-4℃ for 20-30 minutes. The compound color-protecting and crisp-preserving agent consists of 1wt.%-2wt.% citric acid, 1wt.%-2wt.% ascorbic acid, 0.5wt.%-1wt.% ferulic acid and 1wt.%-2wt.% calcium chloride, with the remainder being water; (4) Pickling: Immerse the color-protecting and crisp-preserving apple slices in a pickling solution at 0-5℃ at a material-liquid mass ratio of 1:(2-4) for 1-2 hours, then remove and drain the water. The pickling solution consists of 3-5g of millet peppers, 150-300g of rice vinegar, and 800-1000g of saturated carbonated water. 1000 g, honey 10 ~ 20 g; (5) CO2 microbubble injection: Place the pickled apple slices in a CO2 pressurizing device for pressurization treatment, and inject CO2 microbubbles into the apple tissue; the pressurization temperature is 1 ~ 4℃, and the pressure is 0.5 ~ 1.5 MPa; (6) Antifreeze liquid immersion: Transfer the pickled apple slices containing CO2 microbubbles into the antifreeze liquid for immersion for 30 ~ 60 minutes. min, so that the antifreeze liquid penetrates into the apple tissue, and then drain the water; the antifreeze substance is a mixture of apple pectin, trehalose, isomaltulose and glycerol, with a mass ratio of 5:1:1:0.1; the mixed antifreeze substance is then mixed with water at a mass ratio of 1:10 to obtain the antifreeze liquid; (7) Immersion coating: the treated apple slices are immersed in the coating liquid at a mass ratio of 1:(5~7), and then taken out and dried, so that the surface of the apple slices is covered with a protective layer; (8) High voltage electric field (HVEF) treatment: the coated apple slices are laid flat in the high voltage electric field equipment and subjected to a high voltage electrostatic field treatment of ≥40 kV for no less than 4 h; (9) Static magnetic field assisted quick freezing: the treated sample is placed in the static magnetic field assisted quick freezing equipment for quick freezing, and the formation of apple ice crystals during the quick freezing process is controlled by the static magnetic field; (10) Packaging: the frozen apple slices are taken out, packaged and stored in the -20℃ freezer.

2. The composite method for improving the quality of frozen pickled apple slices according to claim 1, characterized in that, The composite color-protecting and brittle-preserving agent in step (3) is a compound of color-protecting agent and brittle-preserving agent. Its components are 2 wt.% citric acid, 2 wt.% ascorbic acid, 0.5 wt.% ferulic acid and 1 wt.% calcium chloride, with the remainder being water.

3. The composite method for improving the quality of frozen pickled apple slices according to claim 1, characterized in that, The pickling ingredients and apple slices in step (4) consist of 3 g of millet peppers, 150 g of rice vinegar, 800 g of saturated carbonated water, 10 g of honey, and 500 g of apple slices.

4. The composite method for improving the quality of frozen pickled apple slices according to claim 1, characterized in that, The process of step (5) is as follows: adjust the temperature to 4℃, put the sample into the pressure tank, tighten the cover, draw a vacuum, introduce CO2, turn on the pressure pump to 0.5 MPa, maintain the pressure for 30 min, release the pressure, and take out the sample.

5. The composite method for improving the quality of frozen pickled apple slices according to claim 1, characterized in that, The process involves immersion in an antifreeze liquid while simultaneously using vacuum ultrasound assistance, employing a vacuum level of 0.2~0.5 MPa, an ultrasonic frequency of 28 kHz, and a power of 400 W.

6. The composite method for improving the quality of frozen pickled apple slices according to claim 1, characterized in that, The impregnation coating solution in step (7) consists of 1 wt.%~5 wt.% chitosan, 0.5 wt.%~1 wt.% sodium isoascorbate, 0.5 wt.%~1 wt.% calcium chloride, 0.5 wt.%~1 wt.% edible salt, 0.1 wt.%~0.5 wt.% sodium citrate, 0.05 wt.%~0.1 wt.% phytic acid, and the remainder is water.

7. The composite method for improving the quality of frozen pickled apple slices according to claim 1, characterized in that, The dipping and coating method in step (7) is a two-stage coating process. The apple slices are first immersed for 5 seconds and then taken out and drained. Then, they are immersed for 10 seconds and then taken out and drained.

8. The composite method for improving the quality of frozen pickled apple slices according to claim 1, characterized in that, The high-voltage electric field (HVEF) is a high-voltage electrostatic field that outputs high-voltage electric fields upward and downward through the barbed electrode plate. Apple slices are laid flat on a polytetrafluoroethylene plate, with the sample 10 cm away from the barbed electrode plate. The electrostatic field strength is set to 40 kV, the field strength acting on the apple sample is 4 kV / cm, the high-voltage electrostatic field treatment time is 4 h, and the high-voltage electric field treatment temperature is 4℃.

9. The composite method for improving the quality of frozen pickled apple slices according to claim 1, characterized in that, The static magnetic field-assisted quick-freezing is carried out using a static magnetic field-assisted quick-freezing device. The static magnetic field is provided by a pair of Helmholtz coils placed on both sides of the quick-freezing cabinet. The static magnetic field is used to regulate the formation of apple ice crystals during the freezing process. The static magnetic field strength is 10 mT, and the operating temperature range is 0~-5℃. The quick-freezing temperature is -40℃.

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