Method for recovering alkali liquor in preserved kiwi fruit processing process

Abstract

The invention relates to the technical field of comprehensive utilization of waste resources and environmental protection, in particular to a method for recovering alkali liquor in the processing process of preserved kiwi fruits. The method for recovering the alkali liquor in the preserved kiwi fruit processing process comprises the following steps: carrying out primary filtration on the alkali liquor obtained after peeling kiwi fruits, then adding maltodextrin into filtrate, stirring, then adding calcium citrate suspension liquid, carrying out reaction, standing the reaction liquid, carrying out secondary filtration on the supernatant obtained after standing, and carrying out secondary filtration on the supernatant obtained after secondary filtration so as to obtain the preserved kiwi fruit. Finally, alkali liquor with the pH value and the concentration meeting the use requirements is added into the kiwi fruit peeling procedure; according to the method, through the synergistic effect of the two substances of maltodextrin and calcium citrate, the problems of colloid residues, equipment blockage, safety risks and the like in a traditional recovery method are solved, and direct circulation of the alkali liquor is achieved.

Description

Technical Field

[0001] This invention relates to the field of waste resource comprehensive utilization and environmental protection technology, specifically to a method for recovering alkali solution during the processing of dried kiwifruit. Background Technology

[0002] In the processing of kiwifruit preserves, alkaline peeling is the mainstream technology in the industry due to its ease of operation and high peeling efficiency, aiming to achieve efficient separation of pulp and peel. Its core principle is to use a 2.5–4% sodium hydroxide (NaOH) solution at 60–70°C to decompose the cell wall structure of the peel, achieving rapid peeling. However, the alkaline solution after peeling contains a large amount of pectin, pulp particles, and peel fragments, with a solid content of 1.2–2.5%. Direct discharge not only results in a serious waste of NaOH resources but also causes water pollution due to high pH and organic impurities, failing to meet environmental protection requirements. Direct recycling, on the other hand, leads to increased alkaline solution viscosity and decreased peeling efficiency due to residual colloidal impurities, and can easily clog subsequent equipment. Therefore, the purification and recycling of alkaline solution has become a critical issue that kiwifruit processing enterprises urgently need to address.

[0003] To achieve alkali recovery, the commonly used process is membrane separation technology: food-grade ultrafiltration or nanofiltration membranes are used to remove colloids and particles from the alkali solution. However, while this technology can purify the alkali solution to a certain extent, it has significant drawbacks: the initial investment cost of membrane modules is extremely high, and colloids easily deposit on the membrane surface during operation, forming fouling, requiring frequent cleaning or replacement of membrane elements, resulting in poor long-term economic efficiency; at the same time, membrane separation is sensitive to feed viscosity, and when the viscosity of the alkali solution increases, the flux will drop significantly, making it difficult to adapt to the high solids content of kiwifruit peeling alkali solution.

[0004] Therefore, there is an urgent need for a method for recovering alkali solution with low pectin residue and good purification effect. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a method for recovering alkali solution during the processing of dried kiwifruit. This method utilizes the synergistic effect of maltodextrin and calcium citrate to construct a safe, efficient, and low-cost kiwifruit alkali solution recovery system. This system not only solves the problems of colloidal residue, equipment blockage, and safety risks associated with traditional recovery methods, but also achieves direct recycling of the alkali solution.

[0006] Therefore, the present invention provides the following technical solution:

[0007] In an optional embodiment, the present invention provides a method for recovering alkali solution during the processing of dried kiwifruit, comprising the following steps:

[0008] The alkaline solution after peeling kiwifruit is initially filtered. Maltodextrin is then added to the filtrate and stirred. After stirring, calcium citrate suspension is added and reacted. After the reaction is complete, the reaction solution is allowed to stand. The supernatant is then filtered a second time. If the pH and concentration of the filtrate do not meet the requirements after the second filtration, the concentration or pH of the filtrate is adjusted. Finally, the alkaline solution with the required pH and concentration is added to the kiwifruit peeling process.

[0009] The mass ratio of the alkaline solution, maltodextrin, and calcium citrate suspension after peeling the kiwifruit is 1t: 0.5-0.7kg: 0.3-0.5kg.

[0010] In this invention, maltodextrin forms a three-dimensional network structure after hydration. The hydroxyl groups (-OH) on its molecular chains can bind with a small amount of incompletely dissociated carboxyl groups (-COOH) in pectin through hydrogen bonds. At the same time, the hydrophobic regions of the network structure encapsulate the pulp particles through hydrophobic interactions. Furthermore, in an alkaline environment, the maltodextrin molecular chains, due to the weak dissociation of hydroxyl groups, exhibit a weak negative charge, which can adsorb the -COOH generated by the dissociation of pectin through electrostatic attraction. - This forms 'maltodextrin + colloid' adsorption units, preventing colloid redispersibility. Calcium citrate dissolves slowly in alkaline solutions, releasing Ca... 2+ Preferred to be the -COO of pectin - Combined to form chelates, reducing -COO - OH in alkaline solution - The system exhibits 'competitive adsorption'; simultaneously, unreacted citrate ions can react with a small amount of organic acids released from fruit peel fragments in the system, inhibiting a sudden drop in pH due to the intervention of organic acids, and indirectly maintaining the system pH at 11-12, thus preventing the colloid from redispersing due to pH fluctuations.

[0011] Preferably, the calcium citrate suspension has a mass concentration of 3-6%; and / or, the maltodextrin has a DE value of 10-15. The reaction temperature is 55-60°C, and the time is 8-12 min; and / or, the reaction speed is 50-60 rpm. A 120-mesh food-grade nylon filter is used for the initial filtration; and / or, a food-grade precision filter is used for the secondary filtration, and the filter element of the food-grade precision filter is a 200-mesh nylon filter element.

[0012] Preferably, the temperature of the alkaline solution after peeling the kiwifruit is 60–70°C, the sodium hydroxide concentration is 2.5–4%, and the solid content is 1.2–2.5%. The stirring speed is 35–45 rpm; and / or the stirring time is 3–5 min. The settling time is 1.5–2 h.

[0013] Preferably, if the pH of the filtrate is less than 11, NaOH solution is added to adjust the pH to 11.5–12. If the concentration of the filtrate is less than 2.5%, NaOH solution is added to adjust the concentration to 3–3.5%.

[0014] Preferably, the precipitate after settling is mixed with kiwi fruit peel, the pH is adjusted to neutral, and then the mixture is dehydrated by pressure filtration to prepare an organic feed additive.

[0015] Compared with the prior art, the present invention has one of the following beneficial effects:

[0016] 1. The alkali recovery method provided by this invention constructs a "safe, efficient, and low-cost" kiwi alkali recovery system through the synergistic effect of "maltodextrin + calcium citrate". It not only solves the problems of colloidal residue, equipment blockage, and safety risks of traditional recovery methods, but also realizes the direct recycling of alkali.

[0017] 2. The maltodextrin provided by this invention forms a three-dimensional network structure after hydration. The hydroxyl groups (-OH) on its molecular chains can bind with a small amount of incompletely dissociated carboxyl groups (-COOH) in pectin through hydrogen bonds. At the same time, the hydrophobic regions of the network structure encapsulate the pulp particles through hydrophobic interactions. Furthermore, in an alkaline environment, the maltodextrin molecular chains, due to the weak dissociation of hydroxyl groups, exhibit a weak negative charge and can adsorb the -COOH generated by the dissociation of pectin through electrostatic attraction. - This forms 'maltodextrin + colloid' adsorption units, preventing colloid redispersibility; calcium citrate dissolves slowly in alkaline solution, releasing Ca... 2+ Preferred to be the -COO of pectin - Combined to form chelates, reducing -COO - OH in alkaline solution - The system employs a competitive adsorption mechanism. Simultaneously, unreacted citrate ions can react with a small amount of organic acids released from fruit peel fragments in the system, inhibiting a sudden drop in pH due to the intervention of organic acids. This indirectly maintains the system's pH at a stable level of 11-12, preventing the colloids from redispersing due to pH fluctuations. This achieves efficient recycling of kiwifruit alkali solution, directly reducing kiwifruit processing costs. It is economical and practical, and has good application prospects in the field of kiwifruit processing. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1This is a flowchart illustrating the method for alkali recovery during the processing of kiwifruit preserves, as described in Embodiment 1 of this application. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0021] The technical solution of the present invention will be described below with reference to the embodiments. The embodiments and comparative examples were conducted at a company in Songbai Town, Yongshun County, Hunan Province from 2024 to 2025.

[0022] Example 1

[0023] See Figure 1 This embodiment provides a method for recovering alkali solution during the processing of dried kiwifruit, including the following steps:

[0024] (1) The alkaline solution (temperature 63℃, sodium hydroxide concentration 3.2%, solid content 1.8%) after peeling kiwifruit was passed through a 120-mesh food-grade nylon filter to remove peel fragments and pulp pieces with a diameter >125μm.

[0025] (2) The pretreated alkaline solution was sprayed at 1m 3 The solution is fed into the reaction vessel at a flow rate of / h. Maltodextrin (DE value of 12) is added at a rate of 0.6 kg maltodextrin per ton of alkali solution. Stirring is started, and the mixture is first stirred at 90 rpm for 1 minute. Then the speed is reduced to 40 rpm and stirred for 3 minutes to ensure that the maltodextrin is evenly dispersed.

[0026] (3) Add calcium citrate suspension with a mass concentration of 5% to the reaction vessel. The amount added is 0.4 kg of calcium citrate suspension for every 1 t of alkaline solution. Increase the stirring speed to 55 rpm, control the temperature at 55℃, and react for 10 min.

[0027] (4) After the reaction is completed, the solution after the reaction is transferred to the sedimentation tank and left to stand for 10 minutes. Then, the supernatant in the sedimentation tank is passed through a food-grade precision filter (the filter element is a 200-mesh nylon filter element) to intercept the small flocs that have not settled.

[0028] (5) The filtrate after secondary filtration enters the circulation adjustment tank. The concentration and pH value of the filtrate are monitored. If the pH value of the filtrate is less than 11, NaOH solution is added to adjust the pH to 11.5-12. If the concentration of the filtrate is less than 2.5%, NaOH solution is added to adjust the concentration to 3-3.5%. Finally, the alkaline solution with the tested pH value and concentration meeting the usage requirements is added to the kiwi peeling process for recycling.

[0029] Comparative Example 1

[0030] This comparative example provides a method for alkali recovery during the processing of dried kiwifruit, including the following steps:

[0031] (1) The alkaline solution (temperature 63℃, sodium hydroxide concentration 3.2%, solid content 1.8%) after peeling kiwifruit was passed through a 120-mesh food-grade nylon filter to remove peel fragments and pulp pieces with a diameter >125μm.

[0032] (2) The pretreated alkaline solution was sprayed at 1m 3 The solution is fed into the reaction vessel at a flow rate of / h. Maltodextrin (DE value of 12) is added at a rate of 0.6 kg maltodextrin per ton of alkali solution. Stirring is started, and the mixture is first stirred at 90 rpm for 1 minute. Then the speed is reduced to 40 rpm and stirred for 3 minutes to ensure that the maltodextrin is evenly dispersed.

[0033] (3) After stirring, the stirred solution is transferred to the sedimentation tank and left to stand for 10 minutes. Then, the supernatant in the sedimentation tank is passed through a food-grade precision filter (the filter element is a 200-mesh nylon filter element) to trap the small flocs that have not settled.

[0034] (4) The filtrate after secondary filtration enters the circulation adjustment tank. The concentration and pH value of the filtrate are monitored. If the pH value of the filtrate is less than 11, NaOH solution is added to adjust the pH to 11.5-12. If the concentration of the filtrate is less than 2.5%, NaOH solution is added to adjust the concentration to 3-3.5%. Finally, the alkaline solution with the tested pH value and concentration meeting the usage requirements is added to the kiwi peeling process for recycling.

[0035] Comparative Example 2

[0036] This comparative example provides a method for alkali recovery during the processing of dried kiwifruit, including the following steps:

[0037] (1) The alkaline solution (temperature 63℃, sodium hydroxide concentration 3.2%, solid content 1.8%) after peeling kiwifruit was passed through a 120-mesh food-grade nylon filter to remove peel fragments and pulp pieces with a diameter >125μm.

[0038] (2) The pretreated alkaline solution was sprayed at 1m 3 The solution is fed into the reaction vessel at a flow rate of / h. A calcium citrate suspension with a mass concentration of 5% is added to the reaction vessel. The amount added is 0.4 kg of calcium citrate suspension for every 1 t of alkali solution. The stirring speed is increased to 55 rpm, the temperature is controlled at 55℃, and the reaction is carried out for 10 min.

[0039] (3) After the reaction is completed, the solution after the reaction is transferred to the sedimentation tank and left to stand for 10 minutes. Then, the supernatant in the sedimentation tank is passed through a food-grade precision filter (the filter element is a 200-mesh nylon filter element) to intercept the small flocs that have not settled.

[0040] (4) The filtrate after secondary filtration enters the circulation adjustment tank. The concentration and pH value of the filtrate are monitored. If the pH value of the filtrate is less than 11, NaOH solution is added to adjust the pH to 11.5-12. If the concentration of the filtrate is less than 2.5%, NaOH solution is added to adjust the concentration to 3-3.5%. Finally, the alkaline solution with the tested pH value and concentration meeting the usage requirements is added to the kiwi peeling process for recycling.

[0041] Comparative Example 3

[0042] This comparative example provides a method for alkali recovery during the processing of dried kiwifruit, including the following steps:

[0043] (1) The alkaline solution (temperature 63℃, sodium hydroxide concentration 3.2%, solid content 1.8%) after peeling kiwifruit was passed through a 120-mesh food-grade nylon filter to remove peel fragments and pulp pieces with a diameter >125μm.

[0044] (2) The filtered solution is transferred to a sedimentation tank and left to stand for 10 minutes. Then the supernatant in the sedimentation tank is passed through a food-grade precision filter (the filter element is a 200-mesh nylon filter element) to trap the small flocs that have not settled.

[0045] (3) The filtrate after secondary filtration enters the circulation adjustment tank. The concentration and pH value of the filtrate are monitored. If the pH value of the filtrate is less than 11, NaOH solution is added to adjust the pH to 11.5-12. If the concentration of the filtrate is less than 2.5%, NaOH solution is added to adjust the concentration to 3-3.5%. Finally, the alkaline solution with the tested pH value and concentration meeting the usage requirements is added to the kiwi peeling process for recycling.

[0046] Comparative Example 4

[0047] This comparative example provides a method for alkali recovery during the processing of dried kiwifruit, including the following steps:

[0048] (1) The alkaline solution (temperature 63℃, sodium hydroxide concentration 3.2%, solid content 1.8%) after peeling kiwifruit was passed through a 120-mesh food-grade nylon filter to remove peel fragments and pulp pieces with a diameter >125μm.

[0049] (2) The pretreated alkaline solution was sprayed at 1m 3The solution is fed into the reaction vessel at a flow rate of / h. Maltodextrin (DE value of 20) is added at a rate of 0.6 kg of maltodextrin per ton of alkali solution. Stirring is started, and the mixture is first stirred at 90 rpm for 1 minute. Then the speed is reduced to 40 rpm and stirred for 3 minutes to ensure that the maltodextrin is evenly dispersed.

[0050] (3) Add calcium citrate suspension with a mass concentration of 5% to the reaction vessel. The amount added is 0.4 kg of calcium citrate suspension for every 1 t of alkaline solution. Increase the stirring speed to 55 rpm, control the temperature at 55℃, and react for 10 min.

[0051] (4) After the reaction is completed, the solution after the reaction is transferred to the sedimentation tank and left to stand for 10 minutes. Then, the supernatant in the sedimentation tank is passed through a food-grade precision filter (the filter element is a 200-mesh nylon filter element) to intercept the small flocs that have not settled.

[0052] (5) The filtrate after secondary filtration enters the circulation adjustment tank. The concentration and pH value of the filtrate are monitored. If the pH value of the filtrate is less than 11, NaOH solution is added to adjust the pH to 11.5-12. If the concentration of the filtrate is less than 2.5%, NaOH solution is added to adjust the concentration to 3-3.5%. Finally, the alkaline solution with the tested pH value and concentration meeting the usage requirements is added to the kiwi peeling process for recycling.

[0053] Comparative Example 5

[0054] This comparative example provides a method for alkali recovery during the processing of dried kiwifruit, including the following steps:

[0055] (1) The alkaline solution (temperature 63℃, sodium hydroxide concentration 3.2%, solid content 1.8%) after peeling kiwifruit was passed through a 120-mesh food-grade nylon filter to remove peel fragments and pulp pieces with a diameter >125μm.

[0056] (2) The pretreated alkaline solution was sprayed at 1m 3 The solution is fed into the reaction vessel at a flow rate of / h. Maltodextrin (DE value of 5) is added at a rate of 0.6 kg of maltodextrin per ton of alkali solution. Stirring is started, and the mixture is first stirred at 90 rpm for 1 minute. Then the speed is reduced to 40 rpm and stirred for 3 minutes to ensure that the maltodextrin is evenly dispersed.

[0057] (3) Add calcium citrate suspension with a mass concentration of 5% to the reaction vessel. The amount added is 0.4 kg of calcium citrate suspension for every 1 t of alkaline solution. Increase the stirring speed to 55 rpm, control the temperature at 55℃, and react for 10 min.

[0058] (4) After the reaction is completed, the solution after the reaction is transferred to the sedimentation tank and left to stand for 10 minutes. Then, the supernatant in the sedimentation tank is passed through a food-grade precision filter (the filter element is a 200-mesh nylon filter element) to intercept the small flocs that have not settled.

[0059] (5) The filtrate after secondary filtration enters the circulation adjustment tank. The concentration and pH value of the filtrate are monitored. If the pH value of the filtrate is less than 11, NaOH solution is added to adjust the pH to 11.5-12. If the concentration of the filtrate is less than 2.5%, NaOH solution is added to adjust the concentration to 3-3.5%. Finally, the alkaline solution with the tested pH value and concentration meeting the usage requirements is added to the kiwi peeling process for recycling.

[0060] The differences between the methods for alkali recovery during the processing of kiwifruit preserves provided in Example 1 and Comparative Examples 1-5 are shown in Table 1:

[0061] Example 1 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Should maltodextrin be added? yes yes no no yes yes Should calcium citrate be added? yes no yes no yes yes DE value of added maltodextrin 12 12 0 0 20 5

[0062] Example 2

[0063] This embodiment provides a method for alkali recovery during the processing of dried kiwifruit, including the following steps:

[0064] (1) The alkaline solution (temperature 63℃, sodium hydroxide concentration 3.2%, solid content 1.8%) after peeling kiwifruit was passed through a 120-mesh food-grade nylon filter to remove peel fragments and pulp pieces with a diameter >125μm.

[0065] (2) The pretreated alkaline solution was sprayed at 1m 3 The solution is fed into the reaction vessel at a flow rate of / h. Maltodextrin (DE value of 12) is added at a rate of 0.7 kg maltodextrin per ton of alkali solution. Stirring is started, and the mixture is first stirred at 90 rpm for 1 minute. Then the speed is reduced to 40 rpm and stirred for 3 minutes to ensure that the maltodextrin is evenly dispersed.

[0066] (3) Add calcium citrate suspension with a mass concentration of 5% to the reaction vessel. The amount added is 0.3 kg of calcium citrate suspension for every 1 t of alkaline solution. Increase the stirring speed to 55 rpm, control the temperature at 55℃, and react for 10 min.

[0067] (4) After the reaction is completed, the solution after the reaction is transferred to the sedimentation tank and left to stand for 10 minutes. Then, the supernatant in the sedimentation tank is passed through a food-grade precision filter (the filter element is a 200-mesh nylon filter element) to intercept the small flocs that have not settled.

[0068] (5) The filtrate after secondary filtration enters the circulation adjustment tank. The concentration and pH value of the filtrate are monitored. If the pH value of the filtrate is less than 11, NaOH solution is added to adjust the pH to 11.5-12. If the concentration of the filtrate is less than 2.5%, NaOH solution is added to adjust the concentration to 3-3.5%. Finally, the alkaline solution with the tested pH value and concentration meeting the usage requirements is added to the kiwi peeling process for recycling.

[0069] Example 3

[0070] This embodiment provides a method for alkali recovery during the processing of dried kiwifruit, including the following steps:

[0071] (1) The alkaline solution (temperature 63℃, sodium hydroxide concentration 3.2%, solid content 1.8%) after peeling kiwifruit was passed through a 120-mesh food-grade nylon filter to remove peel fragments and pulp pieces with a diameter >125μm.

[0072] (2) The pretreated alkaline solution was sprayed at 1m 3 The solution is fed into the reaction vessel at a flow rate of / h. Maltodextrin (DE value of 12) is added at a rate of 0.5 kg maltodextrin per ton of alkali solution. Stirring is started, and the mixture is first stirred at 90 rpm for 1 minute. Then the speed is reduced to 40 rpm and stirred for 3 minutes to ensure that the maltodextrin is evenly dispersed.

[0073] (3) Add calcium citrate suspension with a mass concentration of 5% to the reaction vessel. The amount added is 0.5 kg of calcium citrate suspension for every 1 t of alkaline solution. Increase the stirring speed to 55 rpm and control the temperature at 55℃. React for 10 min.

[0074] (4) After the reaction is completed, the solution after the reaction is transferred to the sedimentation tank and left to stand for 10 minutes. Then, the supernatant in the sedimentation tank is passed through a food-grade precision filter (the filter element is a 200-mesh nylon filter element) to intercept the small flocs that have not settled.

[0075] (5) The filtrate after secondary filtration enters the circulation adjustment tank. The concentration and pH value of the filtrate are monitored. If the pH value of the filtrate is less than 11, NaOH solution is added to adjust the pH to 11.5-12. If the concentration of the filtrate is less than 2.5%, NaOH solution is added to adjust the concentration to 3-3.5%. Finally, the alkaline solution with the tested pH value and concentration meeting the usage requirements is added to the kiwi peeling process for recycling.

[0076] Example 4

[0077] This embodiment provides a method for alkali recovery during the processing of dried kiwifruit, including the following steps:

[0078] (1) The alkaline solution (temperature 63℃, sodium hydroxide concentration 3.2%, solid content 1.8%) after peeling kiwifruit was passed through a 120-mesh food-grade nylon filter to remove peel fragments and pulp pieces with a diameter >125μm.

[0079] (2) The pretreated alkaline solution was sprayed at 1m 3 The solution is fed into the reaction vessel at a flow rate of / h. Maltodextrin (DE value of 15) is added at a rate of 0.6 kg of maltodextrin per ton of alkali solution. Stirring is started, and the mixture is first stirred at 90 rpm for 1 minute. Then the speed is reduced to 40 rpm and stirred for 3 minutes to ensure that the maltodextrin is evenly dispersed.

[0080] (3) Add calcium citrate suspension with a mass concentration of 3% to the reaction vessel. The amount added is 0.4 kg of calcium citrate suspension for every 1 t of alkaline solution. Increase the stirring speed to 55 rpm, control the temperature at 55℃, and react for 10 min.

[0081] (4) After the reaction is completed, the solution after the reaction is transferred to the sedimentation tank and left to stand for 10 minutes. Then, the supernatant in the sedimentation tank is passed through a food-grade precision filter (the filter element is a 200-mesh nylon filter element) to intercept the small flocs that have not settled.

[0082] (5) The filtrate after secondary filtration enters the circulation adjustment tank. The concentration and pH value of the filtrate are monitored. If the pH value of the filtrate is less than 11, NaOH solution is added to adjust the pH to 11.5-12. If the concentration of the filtrate is less than 2.5%, NaOH solution is added to adjust the concentration to 3-3.5%. Finally, the alkaline solution with the tested pH value and concentration meeting the usage requirements is added to the kiwi peeling process for recycling.

[0083] Example 5

[0084] This embodiment provides a method for alkali recovery during the processing of dried kiwifruit, including the following steps:

[0085] (1) The alkaline solution (temperature 63℃, sodium hydroxide concentration 3.2%, solid content 1.8%) after peeling kiwifruit was passed through a 120-mesh food-grade nylon filter to remove peel fragments and pulp pieces with a diameter >125μm.

[0086] (2) The pretreated alkaline solution was sprayed at 1m 3 The solution is fed into the reaction vessel at a flow rate of / h. Maltodextrin (DE value of 10) is added at a rate of 0.6 kg of maltodextrin per ton of alkali solution. Stirring is started, and the mixture is first stirred at 90 rpm for 1 minute. Then the speed is reduced to 40 rpm and stirred for 3 minutes to ensure that the maltodextrin is evenly dispersed.

[0087] (3) Add a 6% calcium citrate suspension to the reaction vessel. The amount of calcium citrate suspension added to 1t of alkaline solution is 0.4kg. Increase the stirring speed to 55rpm, control the temperature at 55℃, and react for 10min.

[0088] (4) After the reaction is completed, the solution after the reaction is transferred to the sedimentation tank and left to stand for 10 minutes. Then, the supernatant in the sedimentation tank is passed through a food-grade precision filter (the filter element is a 200-mesh nylon filter element) to intercept the small flocs that have not settled.

[0089] (5) The filtrate after secondary filtration enters the circulation adjustment tank. The concentration and pH value of the filtrate are monitored. If the pH value of the filtrate is less than 11, NaOH solution is added to adjust the pH to 11.5-12. If the concentration of the filtrate is less than 2.5%, NaOH solution is added to adjust the concentration to 3-3.5%. Finally, the alkaline solution with the tested pH value and concentration meeting the usage requirements is added to the kiwi peeling process for recycling.

[0090] Experimental Example

[0091] Alkali recovery effect experiment

[0092] The alkaline solution (temperature 63℃, sodium hydroxide concentration 3.2%, solid content 1.8%, pectin content 0.7 g / mL) obtained after peeling kiwifruit was recovered using the alkaline solution recovery methods described in Examples 1-5 and Comparative Examples 1-5. The pectin residue and solid content of the alkaline solution were then tested using the following methods:

[0093] Pectin residue: The carbazole colorimetric method was used. 5 mL of recovered alkali solution was taken, and 3 mL of 0.15% carbazole-anhydrous ethanol solution and 12 mL of concentrated sulfuric acid were added. After boiling in a water bath for 20 min, the absorbance was measured at a wavelength of 530 nm. The residue was calculated using a standard curve (unit: g / 100 mL). The detection limit was 0.01 g / 100 mL.

[0094] Solid content: Take 10 mL of alkaline solution in a constant weight evaporating dish, dry it at 105 °C to constant weight, and calculate the percentage of solids (unit: %).

[0095] The results are shown in Table 1:

[0096] Table 1. Results of alkali recovery in Examples 1-5 and Comparative Examples 1-5

[0097] Pectin residue (g / 100mL) Solid content (%) Example 1 0.03 0.31 Example 2 0.04 0.35 Example 3 0.04 0.34 Example 4 0.05 0.36 Example 5 0.04 0.33 Comparative Example 1 0.18 0.68 Comparative Example 2 0.15 0.62 Comparative Example 3 0.25 0.92 Comparative Example 4 0.12 0.51 Comparative Example 5 0.10 0.49

[0098] Alkali recovery stability test

[0099] The recovered alkali solutions from Examples 1-5 and Comparative Examples 1-5 were recycled 22 times, and the pectin residue was measured after the 1st, 11th, and 22nd recycling cycles. The method for detecting pectin residue is described in the alkali recovery effect experiment. The results are shown in Table 2.

[0100] Table 2. Stability results of alkali recovery in Examples 1-5 and Comparative Examples 1-5

[0101]

[0102]

[0103] As shown in Tables 1 and 2, the alkali recovery effect and stability of Comparative Examples 1 and 2 are significantly worse than those of Examples 1-5. Using only maltodextrin or calcium citrate cannot solve the problems of alkali recovery effect and stability. Examples 1-5, using "maltodextrin + calcium citrate," can synergistically improve both alkali recovery effect and stability. Comparative Example 3, which does not use maltodextrin and calcium citrate and only employs a two-step filtration method, has the worst alkali recovery effect and stability. Comparative Example 4 uses maltodextrin with an excessively high DE value. Maltodextrin with a high DE value has a high degree of hydrolysis and short molecular chains, making it unable to form a stable network structure, resulting in poor alkali recovery effect and stability. Comparative Example 5 uses maltodextrin with an excessively low DE value. Maltodextrin with a low DE value has poor water solubility and is prone to agglomeration and uneven dispersion, also leading to poor alkali recovery effect and stability.

[0104] Although the principles of the present invention have been described in detail above with reference to preferred embodiments, those skilled in the art should understand that the above embodiments are merely illustrative explanations of the implementation of the present invention and are not intended to limit the scope of the present invention. The details in the embodiments do not constitute a limitation on the scope of the present invention. Any obvious changes, such as equivalent transformations or simple substitutions, based on the technical solutions of the present invention without departing from the spirit and scope of the present invention fall within the protection scope of the present invention.

Claims

1. A method for recovering lye in a kiwifruit preserving process, characterized by, The method comprises the following steps: The alkali solution after kiwi peeling is first filtered, then malt dextrin is added into the filtrate and stirred, after the stirring, calcium citrate suspension is added into the reaction, after the reaction, the reaction liquid is left to stand, the supernatant after standing is second filtered, after the second filtering, if the pH value and concentration of the filtrate do not meet the use requirements, the filtrate is adjusted in concentration or pH value, finally, the alkali solution with pH value and concentration meeting the use requirements is added into the kiwi peeling process. The mass ratio of the alkali solution after kiwi peeling, malt dextrin and calcium citrate suspension is 1t:0.5-0.7kg:0.3-0.5kg.

2. The method of recovering lye during kiwifruit processing according to claim 1, characterized in that, The mass concentration of the calcium citrate suspension is 3-6%; and / or, The DE value of the malt dextrin is 10-15.

3. The method of recovering lye during kiwifruit processing according to claim 1, characterized in that, The temperature of the reaction is 55-60℃, and the time is 8-12min; and / or, The rotation speed of the reaction is 50-60rpm.

4. The method of recovering lye during kiwifruit processing according to claim 1, characterized in that, The 120 mesh food-grade nylon filter screen is used in the first filtering; and / or, The food-grade precision filter is used in the second filtering, and the filter core of the food-grade precision filter is 200 mesh nylon filter core.

5. The method of recovering lye during kiwifruit processing according to claim 1, characterized in that, The temperature of the alkali solution after kiwi peeling is 60-70℃, the concentration of sodium hydroxide is 2.5-4%, and the solid content is 1.2-2.5%.

6. The method of recovering lye during kiwifruit processing according to claim 1, wherein, The stirring mode is: first, high-speed stirring at 80-100rpm for 1min, then reducing to 35-45rpm for 2-4min.

7. The method of recovering lye during kiwifruit processing according to claim 1, characterized in that, The standing time is 1.5-2h.

8. The method of recovering lye during kiwifruit processing according to claim 1, characterized in that, If the pH value of the filtrate is less than 11, NaOH solution is added to adjust the pH value to 11.5-12.

9. The method of recovering lye during kiwifruit processing according to claim 1, wherein, If the concentration of the filtrate is less than 2.5%, NaOH solution is added to adjust the concentration to 3-3.5%.

10. The method of recovering lye during kiwifruit processing according to claim 1, characterized in that, After the precipitate after standing and the kiwi peel are mixed, the pH value is adjusted to neutral, pressure filtration and dehydration are carried out, and the organic feed additive is prepared.

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