A method for improving the quality of chlorophyll-containing heat-sensitive fruit and vegetable juice

Abstract

The application discloses a method for improving the quality of chlorophyll-containing heat-sensitive fruit and vegetable juice. The method comprises the following steps: providing an alternating magnetic field, the strength of the alternating magnetic field is 0.5-1 T, the excitation voltage for generating the alternating magnetic field is 1000-1200 V, the frequency is 30-50 kHz, and the duty cycle is 45%; and making the heat-sensitive fruit and vegetable juice enter the alternating magnetic field and flow in the alternating magnetic field to generate an induced electric field, so as to at least realize sterilization treatment on the heat-sensitive fruit and vegetable juice, wherein the strength of the induced electric field is 20-24 V / cm, and the density of the corresponding induced current is 0.50-0.62 A / cm 2 The heat-sensitive fruit and vegetable juice comprises kale compound fruit and vegetable juice. The method provided by the application can effectively sterilize at a lower temperature, significantly reduce the loss of heat-sensitive nutrients such as chlorophyll, maintain the natural green color and fresh flavor of the chlorophyll-containing heat-sensitive fruit and vegetable juice, and improve the sensory quality of the product.

Description

Technical Field

[0001] This invention belongs to the field of food processing technology, and specifically relates to a method for improving the quality of heat-sensitive fruit and vegetable juices containing chlorophyll. Background Technology

[0002] Kale is highly nutritious and often referred to as a "superfood," rich in essential minerals, vitamins, dietary fiber, and bioactive substances such as polyphenols and chlorophyll, giving it significant commercial value. Kale blended fruit and vegetable juice is one product form that combines nutritional value with high added value. Its commercialization requires sterilization to extend shelf life and ensure quality. Kale juice is a heat-sensitive fruit and vegetable juice beverage; its key nutrients and natural color are extremely sensitive to processing conditions.

[0003] Traditional heat sterilization methods, such as pasteurization and ultra-high temperature (UHT) sterilization, while effectively killing microorganisms, often negatively impact the heat effects on heat-sensitive substances that impart high nutritional value and natural color and flavor to fruit and vegetable juices. For example, chlorophyll, which gives kale juice its green color and nutritional benefits, is easily degraded into pheophytin and pyropheophytin under the combined effects of high temperature and acidity, causing its color to turn an undesirable olive green. Simultaneously, heat-sensitive nutrients such as ascorbic acid and polyphenols are also lost in large quantities, severely affecting the product's nutritional value and flavor. These problems make traditional heat treatment methods insufficient to meet the processing requirements of kale juice products for high nutrient retention and preservation of natural color.

[0004] To meet consumer demand for more natural and healthier fruit and vegetable juice products, various novel electric field processing technologies have emerged, such as Ohmic Electric Field Heating (OH), Pulsed Electric Field (PEF), and Inductive Electric Field (IEF). Among these, OH technology directly applies an electric field to a conductive sample, utilizing the sample's resistance to generate Joule heating during conduction, achieving a sterilization effect with high heating efficiency. However, this technology requires direct contact between the electrodes and the food; acidic fruit juices are prone to electrochemical reactions with metal electrodes during long-term processing, leading to metal ion leakage from the food and equipment corrosion. PEF technology relies on instantaneous high-intensity pulsed electric fields to disrupt microbial cell membranes, achieving sterilization at low temperatures. However, it also relies on electrode contact, facing similar corrosion and contamination problems as OH, and is accompanied by high energy consumption.

[0005] Existing technologies have proposed a dual-physical-field coupling processing method using ultrasound and magnetic induction electric fields. This method leverages the cavitation effect of ultrasound and the magnetic field excitation effect of magnetic induction electric fields to achieve, to some extent, the pectin hydrolysis and sterilization requirements of fruit juice. However, for the unique system of kale juice, ultrasound processing generates localized high temperatures and high shear stress within the system, potentially leading to cell breakage and the exposure and degradation of heat- and mechanosensitive components such as intracellular chlorophyll, resulting in color loss and offsetting some of the advantages of non-thermal effects. Furthermore, while the synergistic effect of ultrasound and magnetic induction electric fields can enhance sterilization at low temperatures, it suffers from complex energy input methods, high equipment costs, and high energy consumption. All of these factors make it difficult to achieve the goal of processing high-quality products.

[0006] Therefore, the problems with existing technologies are as follows: traditional heat treatments such as UHT will severely damage the color and nutrition of kale juice, making it difficult to meet consumers' demand for high-quality fruit and vegetable juices; although emerging electric field technologies such as OH can reduce the processing temperature, the electrochemical reactions and food safety hazards caused by direct contact between the electrodes and the food medium limit their application in acidic fruit and vegetable juices; the research on the dual-field coupling process of ultrasound and magnetic induction electric field focuses on the sterilization and enzyme inactivation effects on juice, but its additional cavitation mechanical action and thermal effect can easily cause chlorophyll degradation and color fading in green fruit and vegetable juices such as kale juice, and the process operation methods and equipment are complicated. Summary of the Invention

[0007] The main objective of this invention is to provide a method for improving the quality of heat-sensitive fruit and vegetable juices containing chlorophyll, thereby overcoming the shortcomings of the prior art.

[0008] To achieve the aforementioned objectives, the technical solution adopted by this invention includes: The first aspect of the present invention provides a method for improving the quality of chlorophyll-containing heat-sensitive fruit and vegetable juice, comprising: providing an alternating magnetic field, the intensity of which is 0.5-1 T, the excitation voltage for generating the alternating magnetic field being 1000-1200 V, the frequency being 30-50 kHz, and the duty cycle being 45%; allowing the heat-sensitive fruit and vegetable juice to enter the alternating magnetic field and flow within it to generate an induced electric field, thereby achieving at least sterilization of the heat-sensitive fruit and vegetable juice, wherein the intensity of the induced electric field is 20-24 V / cm, and the corresponding induced current density is 0.50-0.62 A / cm. 2 The heat-sensitive fruit and vegetable juice includes kale compound fruit and vegetable juice.

[0009] Compared with the prior art, the present invention has at least the following beneficial effects: (1) The method provided by the present invention utilizes an induced electric field to non-contactly process heat-sensitive fruit and vegetable juice containing chlorophyll. A stable induced electric field and induced current are generated inside the sample through electromagnetic coupling, thereby achieving a synergistic effect of thermal and non-thermal effects.

[0010] (2) Compared with traditional UHT heat treatment, the method provided by this invention can effectively sterilize at lower temperatures, significantly reduce the loss of heat-sensitive nutrients such as chlorophyll, maintain the natural green color and fresh flavor of heat-sensitive fruit and vegetable juices containing chlorophyll, and improve the sensory quality of the product. Compared with contact electric field technologies such as OH, the method provided by this invention does not require direct contact between the electrode and the food, avoiding corrosion of the metal electrode by acidic juice and precipitation of metal ions, thereby improving food safety and equipment stability. Moreover, without the need for other physical fields such as ultrasonic assistance, the "volume-based" energy input achieves a sterilization effect comparable to or even better than coupling technology, reducing uncontrollable local high temperatures and shear forces, while simplifying the process flow.

[0011] (3) The method provided by the present invention has low energy consumption, high efficiency and simple operation. It is suitable for the industrial processing of green fruit and vegetable juices such as heat-sensitive fruit and vegetable juices containing chlorophyll and has significant promotion and application value. Attached Figure Description

[0012] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0013] Figure 1 This is a schematic diagram of an induced electric field generating device in a typical embodiment of the present invention; Among them, 1 is a toroidal magnetic core, 2 is a metal coil, 3 is a coupling pipe, and 4 is an excitation power supply. Detailed Implementation

[0014] In view of the problems existing in the prior art, the inventors of this invention have conducted extensive and in-depth research and have provided a method for improving the quality of heat-sensitive fruit and vegetable juices containing chlorophyll.

[0015] The following will provide a further explanation of the technical solution, its implementation process, and its principles.

[0016] The first aspect of the present invention provides a method for improving the quality of chlorophyll-containing heat-sensitive fruit and vegetable juices, comprising: providing an alternating magnetic field, the intensity of which is 0.5-1 T, the excitation voltage for generating the alternating magnetic field being 1000-1200 V, the frequency being 30-50 kHz, and the duty cycle being 45%; allowing the heat-sensitive fruit and vegetable juice to enter the alternating magnetic field and flow within it to generate an induced electric field, thereby achieving at least sterilization of the heat-sensitive fruit and vegetable juice, wherein the intensity of the induced electric field is 20-24 V / cm, and the corresponding induced current density is 0.50-0.62 A / cm. 2 The heat-sensitive fruit and vegetable juice includes kale compound fruit and vegetable juice.

[0017] In some implementations, the method for improving the quality of chlorophyll-containing heat-sensitive fruit and vegetable juice specifically includes: flowing the heat-sensitive fruit and vegetable juice at a constant flow rate in the alternating magnetic field to generate the induced electric field. Since the chlorophyll-containing heat-sensitive fruit and vegetable juice is in a uniformly mixed state, flowing at a constant flow rate ensures that the chlorophyll-containing heat-sensitive fruit and vegetable juice receives uniform and effective processing.

[0018] Furthermore, the flow rate of the heat-sensitive fruit and vegetable juice is 3-6 L / h.

[0019] In some implementations, the sterilization treatment takes 2 to 4 minutes.

[0020] In some implementations, the method for improving the quality of chlorophyll-containing heat-sensitive fruit and vegetable juices specifically includes: before the sterilization treatment, the pH value of the heat-sensitive fruit and vegetable juice is 3.7~4.0, and the conductivity is 3300~3600 μS / cm.

[0021] In some implementations, the method for improving the quality of heat-sensitive fruit and vegetable juice containing chlorophyll specifically includes: the temperature of the heat-sensitive fruit and vegetable juice is 20°C to 25°C before the sterilization treatment.

[0022] In some embodiments, the heat-sensitive fruit and vegetable juice includes a mixture of at least one of lemon juice, apple juice, kiwi juice, and celery juice with kale juice.

[0023] In some implementations, the method for improving the quality of heat-sensitive fruit and vegetable juice containing chlorophyll specifically includes: after the sterilization treatment, the temperature of the heat-sensitive fruit and vegetable juice is 55°C to 65°C.

[0024] In some specific implementation schemes, the method for improving the quality of heat-sensitive fruit and vegetable juices containing chlorophyll specifically includes the following steps: An induced electric field generating device is provided, the induced electric field generating device includes a ring magnetic core, a metal coil and an insulated coupling pipe, the coupling pipe is spirally symmetrically wound in parallel on the left and right sides of the ring magnetic core, and the metal coil is tightly wrapped around the upper side of the ring magnetic core; The metal coil is connected to a high-frequency excitation power supply to generate the alternating magnetic field on the toroidal magnetic core. The heat-sensitive fruit and vegetable juice is continuously flowed in the coupling pipeline to generate the induced electric field.

[0025] In some more specific implementations, the method for improving the quality of chlorophyll-containing heat-sensitive fruit and vegetable juices specifically includes the following steps: A uniformly mixed thermosensitive fruit and vegetable juice containing chlorophyll, with a pH of 3.7–4.0, a conductivity of 3300–3600 μS / cm, and an initial temperature of 20–25°C, is introduced into a coupling tube and continuously flows through it at a rate of 3–6 L / h. The excitation power supply is set to an excitation voltage of 1000–1200 V, a frequency of 30–50 kHz, and a duty cycle of 45%. An alternating magnetic field is used to induce an electric field and an induced current in the thermosensitive fruit and vegetable juice containing chlorophyll. The magnetic field strength is 0.5–1 T, the induced electric field strength is 20–24 V / cm, and the induced current density is 0.50–0.62 A / cm. 2 The heat-sensitive fruit and vegetable juice containing chlorophyll is treated in an induced electric field for 2 to 4 minutes, and the stable temperature at the outlet of the coupling pipeline is 55℃ to 65℃.

[0026] Furthermore, the temperature of the heat-sensitive fruit and vegetable juice output from the outlet of the coupling pipeline is 55℃~65℃. Under this temperature condition, the induced electric field treatment has little impact on the sensory quality of the chlorophyll-containing heat-sensitive fruit and vegetable juice, effectively maintaining its color and chlorophyll content, and achieving a balance between sterilization and quality preservation.

[0027] Furthermore, considering the overall sterilization effect, taste, and retention of nutrients, the temperature of the heat-sensitive fruit and vegetable juice output from the outlet of the coupling pipeline is 60℃~65℃.

[0028] An exemplary schematic diagram of an induced electric field generating device in a typical embodiment of the present invention is shown below. Figure 1 As shown, 1 is a toroidal magnetic core, 2 is a metal coil, 3 is a coupling pipe, and 4 is an excitation power supply. The heat-sensitive fruit and vegetable juice to be treated flows continuously in the coupling pipe 3 to generate the induced electric field, at least for sterilization.

[0029] The method provided by this invention utilizes the electromagnetic coupling effect to generate a stable induced electric field non-contactly within the heat-sensitive fruit and vegetable juice containing chlorophyll. Due to its inherent impedance characteristics, an induced current is generated. The high current density and high potential difference formed in the processing area by the aforementioned induced electric field generating device not only produce a moderate temperature rise through the Joule effect, but also induce electroporation of the microbial cell membrane during sterilization, altering the phospholipid molecular structure and membrane permeability, causing intracellular substances to leak out, ultimately leading to cell inactivation. The synergistic effect of thermal and non-thermal effects ensures sterilization while minimizing damage to color and the color of the heat-sensitive chlorophyll nutrient during low-temperature treatment.

[0030] Furthermore, the treatment temperature and time significantly impact the quality improvement and sterilization effect of heat-sensitive fruit and vegetable juices containing chlorophyll. Excessively high treatment temperatures and / or prolonged treatment times can lead to the degradation of nutrients such as chlorophyll in the juices; conversely, excessively low temperatures and / or short treatment times result in insignificant sterilization. A treatment temperature of 55℃~65℃ combined with a treatment time of 2~4 minutes yields the best overall results.

[0031] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Modifications or equivalent substitutions made by those skilled in the art based on their understanding of the technical solutions of this invention, without departing from the spirit and scope of the invention, should be covered within the protection scope of this invention.

[0032] For experiments not specifically described in the examples, the procedures or conditions can be performed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available. Other unmentioned raw materials and instruments are all conventionally chosen and do not involve the core technical means of this invention.

[0033] For example, the following embodiments and comparative examples use an induced electric field generating device comprising an excitation power supply, a ring magnetic core, a metal coil, and an insulated coupling conduit. The coupling conduit is spirally and symmetrically wound in parallel around both sides of the ring magnetic core. The metal coil is tightly wound around the ring magnetic core and located in the middle of the coupling conduit. The metal coil is connected to a high-frequency excitation power supply. The excitation power supply, the metal coil, and the ring magnetic core work together to generate an alternating magnetic field. The alternating magnetic field generates the induced electric field in the conductive kale compound fruit and vegetable juice that flows continuously in the coupling conduit.

[0034] To accurately evaluate the impact of the sterilization method of this invention on the quality of kale compound fruit and vegetable juice, a series of baseline trait measurements were performed on untreated kale compound fruit and vegetable juice in the early stages of this study to determine its original quality characteristics. The baseline trait values ​​were as follows: pH 3.85, conductivity 3500 μS / cm, Brix value (soluble solids content) 12%, and total chlorophyll content 6.6 mg / 100 mL. These trait values ​​provided important baseline data for the subsequent evaluation of the treatment effects of this invention.

[0035] Example 1 This embodiment provides a method for improving the quality of heat-sensitive fruit and vegetable juices containing chlorophyll, specifically including the following steps: (1) Raw material pretreatment: Kale, apples, and lemons were pulped and filtered separately. Kale was pre-chilled at 4°C for 12 h before pulping and pulped in a low-temperature environment to reduce the risk of degradation of heat-sensitive components (such as chlorophyll) caused by localized frictional heat generation during pulping. Lemons were pulped first, while lemon juice (2.5 mL / 100 g apple) was added to apples during pulping to utilize the antioxidant effect of lemon juice to slow down the enzymatic browning of apple polyphenols during pulping. The resulting kale juice and apple-lemon juice were then mixed at a volume ratio of 1:4 and degassed under vacuum to obtain a composite fruit and vegetable juice matrix that retains both nutritional value and sensory quality. 1 L of the kale composite fruit and vegetable juice was placed in a suitable sealed container, ensuring it was homogeneous when entering the coupling pipeline.

[0036] (2) Electric Field Treatment: The kale compound fruit and vegetable juice in the above container was introduced into the coupling pipeline and allowed to flow continuously in the pipeline at a flow rate of 5 L / h. The excitation voltage of the excitation power supply was set to 1000 V, the frequency to 50 kHz, and the duty cycle to 45%, generating a corresponding alternating magnetic field strength of 0.5 T. The alternating magnetic field formed an induced electric field and an induced current in the kale compound fruit and vegetable juice. The induced electric field strength was 20.25 V / cm, and the induced current density was 0.50 A / cm. 2 The kale compound fruit and vegetable juice was treated in an induced electric field for 2.5 minutes, and the stable temperature at the outlet of the coupling pipeline was 55℃.

[0037] (3) Indicator detection: After sterilization, the total bacterial count of the kale compound fruit and vegetable juice was tested. The test method was GB4789.2-2022 National Food Safety Standard for Food Microbiology Examination: Determination of Total Bacterial Count. Each sample was tested three times. The total bacterial count of the kale compound fruit and vegetable juice in Example 1 after sterilization by induction electric field was reduced by 1.4 log compared with that before sterilization.

[0038] The color difference of kale compound fruit and vegetable juice before and after processing was detected. An NR 110 precision colorimeter (Shenzhen 3NH Technology Co., Ltd.) was used to measure the L, a, and b values ​​of the kale juice, and the results were analyzed according to the formula... The color difference of the kale compound fruit and vegetable juice before and after treatment was calculated. Each sample was tested six times. The color difference ΔE of the kale compound fruit and vegetable juice in Example 1 after sterilization by induction electric field was 0.78.

[0039] The total chlorophyll content of the kale compound fruit and vegetable juice after treatment was detected using the spectrophotometric method of "NY / T3082-2017 Determination of chlorophyll content in fruits, vegetables and their products". Each sample was tested three times. The total chlorophyll content of the kale compound fruit and vegetable juice in Example 1 after sterilization by induction electric field was 6.1 mg / 100 mL.

[0040] Example 2 This embodiment provides a method for improving the quality of heat-sensitive fruit and vegetable juices containing chlorophyll, specifically including the following steps: (1) Raw material pretreatment: Kale, celery, kiwi, and lemon were pulped and filtered separately. Among them, kale and celery were pre-cooled at 4°C for 12 h before pulping and pulped in a low-temperature environment to reduce the risk of degradation of heat-sensitive components (such as chlorophyll) caused by local frictional heat generation during pulping. The obtained kale juice, celery juice, kiwi juice, and lemon juice were mixed in a volume ratio of 3:1:15:1 and degassed under vacuum to obtain a compound fruit and vegetable juice matrix that combines nutrient retention and sensory quality. 1 L of the kale compound fruit and vegetable juice was selected and placed in a suitable sealed container to ensure that it was in a uniform state when entering the coupling pipeline.

[0041] (2) Electric field treatment: The kale compound fruit and vegetable juice in the above container was introduced into the coupling pipeline and allowed to flow continuously in the pipeline at a flow rate of 3 L / h. The excitation voltage of the excitation power supply was set to 1100 V, the frequency to 40 kHz, and the duty cycle to 45%, generating a corresponding alternating magnetic field strength of 0.8 T. The alternating magnetic field formed an induced electric field and an induced current in the kale compound fruit and vegetable juice. The strength of the induced electric field was 22.08 V / cm, and the induced current density was 0.56 A / cm. 2 The kale compound fruit and vegetable juice was treated in an induced electric field for 4 minutes, and the stable temperature at the outlet of the coupling pipeline was 60℃.

[0042] (3) Index detection: After sterilization, the same method as in Example 1 was used for detection. The total number of colonies of the kale compound fruit and vegetable juice in Example 2 after sterilization by induction electric field was reduced by 1.8 log compared with that before sterilization; the color difference ΔE after sterilization by induction electric field was 1.08; and the total chlorophyll content after sterilization by induction electric field was 5.8 mg / 100 mL.

[0043] Example 3 This embodiment provides a method for improving the quality of heat-sensitive fruit and vegetable juices containing chlorophyll, specifically including the following steps: (1) Raw material pretreatment: Same as in Example 1.

[0044] (2) Electric Field Treatment: The kale compound fruit and vegetable juice in the above container was introduced into the coupling pipeline and allowed to flow continuously in the pipeline at a flow rate of 3 L / h. The excitation voltage of the excitation power supply was set to 1200 V, the frequency to 30 kHz, and the duty cycle to 45%, generating a corresponding alternating magnetic field strength of 1 T. The alternating magnetic field formed an induced electric field and an induced current in the kale compound fruit and vegetable juice. The induced electric field strength was 23.83 V / cm, and the induced current density was 0.62 A / cm. 2 The kale compound fruit and vegetable juice was treated in an induced electric field for 4 minutes, and the stable temperature at the outlet of the coupling pipeline was 65℃.

[0045] (3) Index detection: After sterilization, the same method as in Example 1 was used for detection. The total number of colonies of the kale compound fruit and vegetable juice in Example 3 after sterilization by induction electric field was reduced by 2.4 log compared with that before sterilization; the color difference ΔE after sterilization by induction electric field was 1.55; and the total chlorophyll content after sterilization by induction electric field was 5.3 mg / 100 mL.

[0046] Example 4 This embodiment provides a method for improving the quality of heat-sensitive fruit and vegetable juices containing chlorophyll, specifically including the following steps: (1) Raw material pretreatment: Same as in Example 1.

[0047] (2) Electric field treatment: The kale compound fruit and vegetable juice in the above container was introduced into the coupling pipeline and allowed to flow continuously in the pipeline at a flow rate of 6 L / h. The excitation voltage of the excitation power supply was set to 1200 V, the frequency to 50 kHz, and the duty cycle to 45%, generating a corresponding alternating magnetic field strength of 1 T. The alternating magnetic field formed an induced electric field and an induced current in the kale compound fruit and vegetable juice. The strength of the induced electric field was 23.83 V / cm, and the induced current density was 0.60 A / cm. 2The kale compound fruit and vegetable juice was treated in an induced electric field for 2 minutes, and the stable temperature at the outlet of the coupling pipeline was 60℃.

[0048] (3) Index detection: After sterilization, the same method as in Example 1 was used for detection. The total number of colonies of the kale compound fruit and vegetable juice in Example 4 after sterilization by induction electric field was reduced by 2.0 log compared with that before sterilization; the color difference ΔE after sterilization by induction electric field was 1.14; and the total chlorophyll content after sterilization by induction electric field was 5.9 mg / 100 mL.

[0049] Comparative Example 1 This comparative example provides a method for improving the quality of heat-sensitive fruit and vegetable juices containing chlorophyll, which differs from Example 1 in that: Instead of subjecting the kale compound fruit and vegetable juice to induced electric field treatment, the juice was treated with a water bath using the same "time-temperature" heating curve as in Example 1, and the rest of the process was the same as in Example 1.

[0050] Index testing: The total bacterial count of the kale compound fruit and vegetable juice in Comparative Example 1 after water bath treatment was reduced by 0.7 log compared with that before sterilization treatment; the color difference ΔE after water bath treatment was 0.75; and the total chlorophyll content after water bath treatment was 6.1 mg / 100 mL.

[0051] The results above show that the chlorophyll retention rate and color difference of the kale compound fruit and vegetable juice in Comparative Example 1 after water bath treatment are comparable to those in Example 1. However, the sterilization efficiency of the kale compound fruit and vegetable juice in Comparative Example 1 after water bath treatment is much lower than that in Example 1. This indicates that under the same temperature conditions, induced electric field treatment can generate additional non-thermal effects while ensuring chlorophyll and color quality, thereby enhancing the inactivation effect on microorganisms. The reason for this is that the water bath treatment in Comparative Example 1 relies solely on thermal effects for sterilization, which has limited effect on heat-resistant bacteria and some heat-resistant enzymes. In contrast, the induced electric field treatment in Example 1, while generating Joule heating effects, can also form an induced electric field and induced current inside the kale juice through electromagnetic coupling, inducing electroporation of the microbial cell membrane, changing membrane permeability, and causing leakage of intracellular substances, thereby inactivating the microorganisms. Therefore, the method provided by this invention significantly improves sterilization efficiency while maintaining the color and chlorophyll content of the kale compound fruit and vegetable juice through the synergistic effect of thermal and non-thermal effects.

[0052] Comparative Example 2 This comparative example provides a method for improving the quality of heat-sensitive fruit and vegetable juices containing chlorophyll, which differs from Example 1 in that: The excitation voltage of the power supply was set to 1400 V, the frequency to 50 kHz, and the duty cycle to 45%, generating a corresponding alternating magnetic field strength of 1.5 T. This alternating magnetic field induced an electric field and an induced current in the kale compound fruit and vegetable juice. The induced electric field strength was 26.92 V / cm, and the induced current density was 0.80 A / cm. 2 The kale compound fruit and vegetable juice was treated in the induced electric field for 2.5 minutes, and the stable temperature at the outlet of the coupling pipeline was 70°C. The rest of the procedure was the same as in Example 1.

[0053] Index detection: The total number of colonies of the kale compound fruit and vegetable juice in Comparative Example 2 after treatment with an induced electric field decreased by 2.7 log compared with that before sterilization; the color difference ΔE after sterilization with an induced electric field was 3.88; and the total chlorophyll content after sterilization with an induced electric field was 2.8 mg / 100 mL.

[0054] Comparing the test results of Example 1 and Comparative Example 2, it can be seen that although Comparative Example 2 can slightly improve the sterilization efficiency of kale compound fruit and vegetable juice by induction electric field, the chlorophyll retention rate is greatly reduced, and the color difference with untreated kale compound fruit and vegetable juice is large.

[0055] Comparative Example 3 This comparative example provides a method for improving the quality of heat-sensitive fruit and vegetable juices containing chlorophyll, which differs from Example 1 in that: The excitation power supply was set with an excitation voltage of 900 V, a frequency of 50 kHz, and a duty cycle of 45%, generating a corresponding alternating magnetic field strength of 0.3 T. This alternating magnetic field induced an electric field and an induced current in the kale compound fruit and vegetable juice. The induced electric field strength was 18.08 V / cm, and the induced current density was 0.40 A / cm. 2 The kale compound fruit and vegetable juice was treated in the induced electric field for 2.5 minutes, and the stable temperature at the outlet of the coupling pipe was 50°C. The rest of the procedure was the same as in Example 1.

[0056] Index detection: The total number of colonies in the kale compound fruit and vegetable juice of Comparative Example 3 after treatment with an induced electric field decreased by 0.6 log compared with that before sterilization; the color difference ΔE after sterilization with an induced electric field was 0.56; and the total chlorophyll content after sterilization with an induced electric field was 6.3 mg / 100 mL.

[0057] Comparing the test results of Example 1 and Comparative Example 3, it can be seen that the sterilization efficiency of the kale compound fruit and vegetable juice in Comparative Example 3 through the induced electric field is low and cannot meet the sterilization requirements.

[0058] The results above show that although Comparative Examples 2 and 3 had the same flow rate, frequency, and processing time as Example 1, different excitation voltages led to significant differences in the treatment effects. When the excitation voltage was too high, the intensity of the induced electric field and the density of the induced current increased significantly, resulting in a significant increase in Joule heating in the system. The outlet temperature of the coupling pipe rose to 70°C, exceeding the thermal stability threshold of chlorophyll. Under these conditions, the thermosensitive nutrient chlorophyll rapidly degraded in the high temperature and acidic environment, producing pheophytin and its derivatives, leading to color deterioration. This indicates that while an excessively strong electric field can exacerbate cell structure damage, it can also negatively impact the pigment system and other nutrients. When the excitation voltage was too low, the intensity of the induced electric field and the current density were insufficient, as evidenced by the outlet temperature of the coupling pipe dropping to 50°C. The sterilization effect decreased significantly, failing to meet the sterilization requirements and failing to balance safety and effectiveness. Based on the comparison of Comparative Examples 2 and 3 with Example 1, it can be seen that excessively high excitation voltage will lead to overheating of the system, severe degradation of chlorophyll, and a significant increase in color difference, while excessively low excitation voltage will result in insufficient electric field effect and difficulty in achieving the required sterilization efficiency. Only under a moderate excitation voltage can a high chlorophyll retention rate and color stability be achieved while ensuring the sterilization effect, thus achieving the best balance between sterilization and quality.

[0059] Comparative Example 4 This comparative example provides a method for improving the quality of heat-sensitive fruit and vegetable juices containing chlorophyll, which differs from Example 3 in that: The kale compound fruit and vegetable juice was continuously flowed in the pipeline at a flow rate of 8 L / h. The kale compound fruit and vegetable juice was treated in the induced electric field for 1.6 min, and the stable temperature at the outlet of the coupling pipeline was 50°C. The rest of the procedure was the same as in Example 3.

[0060] Index detection: The total number of colonies in the kale compound fruit and vegetable juice of Comparative Example 4 decreased by 0.5 log after treatment with an induced electric field compared with that before sterilization; the color difference ΔE after sterilization with an induced electric field was 0.53; and the total chlorophyll content after sterilization with an induced electric field was 6.3 mg / 100 mL.

[0061] Comparing the test results of Example 3 and Comparative Example 4, it can be seen that the sterilization efficiency of the kale compound fruit and vegetable juice in Comparative Example 4 through the induced electric field is low and cannot meet the sterilization requirements.

[0062] Comparative Example 5 This comparative example provides a method for improving the quality of heat-sensitive fruit and vegetable juices containing chlorophyll, which differs from Example 3 in that: The kale compound fruit and vegetable juice was continuously flowed in the pipeline at a flow rate of 1.5 L / h. The kale compound fruit and vegetable juice was treated in the induced electric field for 8.2 min, and the stable temperature at the outlet of the coupling pipeline was 85°C. The rest of the procedure was the same as in Example 3.

[0063] Index detection: The total number of colonies in the kale compound fruit and vegetable juice of Comparative Example 5 after treatment with an induced electric field decreased by 3.0 log compared with that before sterilization; the color difference ΔE after sterilization with an induced electric field was 5.56; and the total chlorophyll content after sterilization with an induced electric field was 0.9 mg / 100 mL.

[0064] Comparing Example 3 and Comparative Example 5, it can be seen that the chlorophyll retention rate of the kale compound fruit and vegetable juice in Comparative Example 5 decreased significantly after being treated with an induction electric field sterilization, and the color difference between it and the untreated kale compound fruit and vegetable juice was large, with the color turning olive green.

[0065] The results above show that although Comparative Examples 4, 5, and Example 3 were under the same electric field conditions, the difference in flow rate led to significant differences in processing time and temperature rise, thus disrupting the balance between sterilization effect and quality maintenance. When the flow rate was too fast, the sample's residence time in the electric field was short, and the kale juice failed to accumulate sufficient energy and achieve uniform heating in the induced electric field, resulting in a significant reduction in sterilization efficiency and failing to meet the requirements. When the flow rate was too slow, the sample's residence time in the electric field was prolonged, which not only increased the sample processing time but also caused a significant increase in outlet temperature due to excessive energy input during processing. Although longer processing times and higher processing temperatures could achieve higher sterilization efficiency, excessive heat accumulation accelerated chlorophyll degradation, resulting in a color that was significantly more olive green compared to the untreated sample, severely affecting sensory quality. In summary, both excessively fast and excessively slow flow rates have negative effects: the former results in insufficient sterilization, while the latter leads to excessive heating, making it difficult to achieve the desired effect. Therefore, properly controlling the flow rate to keep the treatment time and temperature rise within an appropriate range is key to ensuring that kale juice treated with an induction electric field has both effective bactericidal effect and maintains a high chlorophyll retention rate and good color.

[0066] Comparative Example 6 This comparative example provides a method for improving the quality of heat-sensitive fruit and vegetable juices containing chlorophyll, which differs from Example 4 in that: Pure kale juice (pH 5.85, conductivity 2000 μS / cm, Brix value 8%, total chlorophyll content 28 mg / 100 mL) was used for induced electric field treatment, with constant excitation power supply and flow rate. The alternating magnetic field induced an electric field and current in the kale juice, with an electric field strength of 23.83 V / cm and an induced current density of 0.30 A / cm. 2The kale juice was treated in an induced electric field for 2 minutes, and the stable temperature at the outlet of the coupling pipe was 45℃.

[0067] Index detection: The total number of colonies in the kale juice of Comparative Example 6 after treatment with an induced electric field decreased by 0.1 log compared with that before sterilization; the color difference ΔE after sterilization with an induced electric field was 0.15; and the total chlorophyll content after sterilization with an induced electric field was 27.7 mg / 100 mL.

[0068] Comparing Example 4 with Comparative Example 6, it can be seen that the sterilization efficiency of pure kale juice in Comparative Example 6 after treatment with an induced electric field is significantly lower and cannot meet the sterilization requirements, but its chlorophyll retention rate is higher and the color change is smaller.

[0069] The core reason for this difference lies in their different physicochemical properties. Pure kale juice has a low electrical conductivity, resulting in insufficient induced current density and Joule heating under the same excitation conditions. This leads to a processing temperature of only 45°C, significantly weakening the electrothermal synergistic sterilization effect. Simultaneously, while the higher pH of the pure juice helps mitigate the synergistic degradation effect of acid and heat, improves chlorophyll stability, and reduces color difference, the system also weakens the synergistic inhibitory advantage of the acidic environment on microorganisms, further diminishing the sterilization effect. This indicates that pure kale juice, due to its inherent limitations in electrical conductivity and pH, is not suitable for the combination of process conditions provided in this invention.

[0070] Table 1 shows the test results of the sterilization logarithm, total chlorophyll content, and color difference of kale juice treated with an induced electric field in the embodiments and comparative examples of the present invention.

[0071] Table 1. Detection results of kale juice treated with induced electric field in the embodiments and comparative examples of the present invention.

[0072] Note: The “blank control” in Table 1 refers to the control group that did not undergo any sterilization treatment.

[0073] As shown in Table 1, the chlorophyll content and color of kale juice treated by the method provided in this invention remained relatively stable. While Comparative Example 2 (high excitation voltage and high induced electric field strength) and Comparative Example 5 (low flow rate and long treatment time) showed good sterilization effects, they led to a decrease in chlorophyll content and color deterioration in the kale juice. Comparative Example 1 (no induced electric field treatment, only thermal effect), Comparative Example 3 (low excitation voltage and low induced electric field strength), and Comparative Example 4 (high flow rate and short treatment time) did not significantly affect chlorophyll content and color quality, but their sterilization effects were poor.

[0074] In summary, the induced electric field treatment of the present invention not only relies on the thermal effect during the sterilization process, but can also generate an induced electric field and induced current through electromagnetic coupling under the same temperature conditions, inducing electroporation of microbial cell membranes, forming a synergistic effect of thermal and non-thermal effects, thereby significantly improving sterilization efficiency while maintaining chlorophyll and color.

[0075] Furthermore, compared to ordinary fruit juices (such as orange juice and passion fruit juice), kale juice, rich in chlorophyll, is more sensitive to external conditions such as temperature under acidic conditions, resulting in significant differences in its quality stability. Existing inductive electric field treatment conditions for fruit juices often aim only at commercial sterility. While the set electric field strength, action time, or temperature rise window can ensure sterilization, it is difficult to avoid the browning caused by the significant degradation of chlorophyll into pheophytin, which cannot be directly applied to the treatment of kale juice. Therefore, this invention specifically optimizes the matching relationship between the defined inductive electric field strength, inductive current density, flow rate, and temperature range, enabling both electric field-induced destruction of the microbial membrane structure and control of the system temperature rise within a safe range to avoid significant chlorophyll degradation. The non-contact electric field generating device and its mechanism further reduce quality deterioration caused by electrode reactions or localized high temperatures, thereby achieving a stable sterilization effect at relatively low temperatures.

[0076] In addition, the combination of process conditions of the present invention exhibits unique applicability and superior balance in the kale juice system, solving the problem that traditional heat sterilization and other electric field treatment technologies cannot simultaneously achieve sterilization efficiency and color retention. It provides an efficient, safe and widely applicable solution for the industrial production and quality maintenance of kale juice and other heat-sensitive fruit and vegetable juice beverages containing chlorophyll.

[0077] All aspects, embodiments, features, and examples of this invention should be considered illustrative in all respects and are not intended to limit the invention; the scope of the invention is defined only by the claims. Other embodiments, modifications, and uses will become apparent to those skilled in the art without departing from the spirit and scope of the invention.

[0078] In addition, the inventors of this case also conducted experiments with other raw materials, process operations, and process conditions described in this specification, referring to the aforementioned embodiments, and obtained relatively ideal results in all cases.

[0079] Although the invention has been described with reference to illustrative embodiments, those skilled in the art will understand that various other changes, omissions, and / or additions can be made without departing from the spirit and scope of the invention, and that elements of the described embodiments can be substituted with substantially equivalents. Furthermore, many modifications can be made without departing from the scope of the invention to adapt particular situations or materials to the teachings of the invention. Therefore, this invention is not intended to be limited to the specific embodiments disclosed for carrying out the invention, but rather is intended to encompass all embodiments falling within the scope of the appended claims.

Claims

1. A method for improving the quality of heat-sensitive fruit and vegetable juices containing chlorophyll, characterized in that, include: An alternating magnetic field is provided, the intensity of which is 0.5~1 T, the excitation voltage for generating the alternating magnetic field is 1000~1200 V, the frequency is 30~50 kHz, and the duty cycle is 45%. The heat-sensitive fruit and vegetable juice is introduced into the alternating magnetic field and flows within it to generate an induced electric field, thereby achieving at least sterilization of the juice. The intensity of the induced electric field is 20-24 V / cm, and the corresponding induced current density is 0.50-0.62 A / cm². 2 ; The heat-sensitive fruit and vegetable juice includes kale compound fruit and vegetable juice.

2. The method according to claim 1, characterized in that, include: The heat-sensitive fruit and vegetable juice is made to flow at a constant flow rate in the alternating magnetic field to generate the induced electric field.

3. The method according to claim 1, characterized in that: The flow rate of the heat-sensitive fruit and vegetable juice is 3-6 L / h.

4. The method according to claim 1, characterized in that: The sterilization process takes 2 to 4 minutes.

5. The method according to claim 1, characterized in that: Before the sterilization treatment, the pH value of the heat-sensitive fruit and vegetable juice is 3.7~4.0 and the conductivity is 3300~3600 μS / cm.

6. The method according to claim 1, characterized in that: Before the sterilization treatment, the temperature of the heat-sensitive fruit and vegetable juice is 20°C to 25°C.

7. The method according to claim 1, characterized in that: The heat-sensitive fruit and vegetable juices include a mixture of at least one of lemon juice, apple juice, kiwi juice, and celery juice with kale juice.

8. The method according to claim 1, characterized in that: After the sterilization treatment, the temperature of the heat-sensitive fruit and vegetable juice is 55℃~65℃.

9. The method according to claim 1, characterized in that, Specifically, it includes: An induced electric field generating device is provided, the induced electric field generating device includes a ring magnetic core, a metal coil and an insulated coupling pipe, the coupling pipe is spirally symmetrically wound in parallel on the left and right sides of the ring magnetic core, and the metal coil is tightly wrapped around the upper side of the ring magnetic core; The metal coil is connected to a high-frequency excitation power supply to generate the alternating magnetic field on the toroidal magnetic core. The heat-sensitive fruit and vegetable juice is continuously flowed in the coupling pipeline to generate the induced electric field.

10. The method according to claim 9, characterized in that: The temperature of the heat-sensitive fruit and vegetable juice output from the outlet of the coupling pipeline is 55°C to 65°C, preferably 60°C to 65°C.

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