A synergistic method for improving the thawing quality of frozen lemon juice

Abstract

The application discloses a kind of thawing quality improvement synergic method of frozen lemon juice, belongs to fruit juice processing technical field.The method is first to lemon juice Pickering emulsion prepared by adding nanocellulose, then low-temperature pasteurization to lemon juice, after cooling aseptic filling, then be placed in electromagnetic field equipment, under the condition of-20 ℃ Freezing, and exert magnetic field and electric field synergic auxiliary freezing.And after using ultrasonic wave processing after lemon juice thawing.The flocculation material of lemon juice after being treated by the application is reduced after thawing, and the stratification phenomenon is reduced.The addition of Pickering emulsion can improve its stability.The method provided by the application is simple in operation, short in freezing time, high in efficiency, low in cost, safe and effective, and maintains the flavor and nutritional value of lemon juice.

Description

TECHNICAL FIELD

[0001] The application discloses a thawing quality improvement synergistic method for frozen lemon juice and belongs to the technical field of fruit juice processing. BACKGROUND

[0002] Lemon, a woody plant of Rutaceae Citrus, is the third most important crop in citrus crops after oranges and mandarins, and is originally from Southeast and South Asia. The cultivation range of lemon is relatively wide in China. In the areas south of the Yangtze River, tropical and subtropical areas, there are many cultivations. There are also many types of lemons. Lemon is rich in nutrients, containing many vitamins such as vitamin C, vitamin B1, vitamin B2, and niacin, as well as many minerals such as calcium, phosphorus, and iron. In addition, it also contains effective components such as organic acids, amino acids, hesperidin, and flavonoids, which are very beneficial to the human body. Since it is a high-acid fruit with extremely sour taste, most of the fresh fruit is used as raw material or processed into other different types of products. At present, lemon is applied to the production of many products, such as dried lemon slices, lemon beverages, lemon essential oil, etc. The largest processed product is lemon juice.

[0003] Freezing is a conventional preservation method for maintaining the quality of fresh fruit juice. In the past production practice of factories, fruit juice is often frozen after rough filtration. In this process, some quality changes often occur. After heat sterilization treatment, the frozen lemon juice is rapidly frozen, and after thawing, stratification occurs, accompanied by a small amount of white flocculent material. This leads to a loss of commercial value.

[0004] Studies have shown that the cloud material in citrus juice is colored corpuscles, pulp or cell wall fragments, spherical oil droplets and needle-shaped crystals, containing a large amount of protein and carbohydrate. The presence of pectin, pectin methylesterase, turbidity agents such as protein, and the particle size and potential of the suspension will affect the cloud stability of the fruit juice.

[0005] The most commonly used method to increase the stability of fruit juice at present is heat treatment to inactivate pectin methyl esterase or addition of hydrophilic colloids, but the high temperature of these methods will affect the sensory indicators of fruit juice and reduce its nutritional value. The addition of colloids will increase the viscosity of fruit juice, affecting its taste and flavor.

[0006] Ma Yinfei (2022) discloses a composite stabilizer for mango juice beverage and a preparation method (publication number: 109527300A). The invention uses xanthan gum, carboxymethyl cellulose, propylene glycol alginate, gellan gum, and ethylenediaminetetraacetic acid disodium as a stabilizer. The method has many types of added substances and a complex preparation process, which not only significantly increases the production cost, but also more or less affects the taste of the fruit juice.

[0007] Zhang Fang (2019) disclosed a kind of stable cherry plum juice and its preparation method (publication number: 103564558A) described to cherry plum juice adds two or more than two hydrophilic colloids in carrageenan, gellan gum, guar gum, xanthan gum. And adopt high temperature 135 DEG C above instantaneous sterilization 3-8 seconds. Too high temperature can affect the original flavor of fruit juice taste and nutrients, and the addition of colloid can increase its viscosity.

[0008] Fang Hailing (2019) disclosed a method for maintaining the stability of south jujube juice (publication number: 109430620A), which adds 0.13% to 0.15% xanthan gum, 0.04% to 0.05% CMC-Na and 0.13% to 0.15% pectin to the jujube juice as a composite stabilizer. The addition of too much additive may affect the flavor and texture of the juice and may have a certain impact on human health. SUMMARY

[0009] The present application provides a method for improving the quality of frozen lemon juice thawing, which combines physical and chemical methods. Pickering emulsion is added, and electric or magnetic field is used to assist freezing to shorten the freezing time, inactivate enzyme activity, reduce particle size, increase solution potential, and ultrasonic treatment can also reduce particle size and improve uniformity. Multiple methods can effectively improve the stability of lemon juice.

[0010] The technical solution of the present application is as follows:

[0011] A method for improving the quality of frozen lemon juice thawing, mainly comprising the following steps:

[0012] (1) Lemon juice pretreatment: filter the lemon juice;

[0013] (2) Preparation of Pickering emulsion: mix nanocellulose water dispersion and fully dissolved pectin in a certain proportion, stir thoroughly, and then disperse with a high-speed disperser at 20000 r / min for 5 min to obtain a nanocellulose and pectin compound; add 50% volume fraction of blending oil as oil phase, and homogenize at 14000 r / min for 3 min to obtain Pickering emulsion;

[0014] (3) Add the emulsion prepared in step (2) to the lemon juice;

[0015] (4) Lemon juice sterilization: low-temperature pasteurization of lemon juice;

[0016] (5) Lemon juice bottling: cool the lemon juice after sterilization in step (4) and fill it into sterile bottles;

[0017] (6) Electromagnetic field synergistic auxiliary freezing: the lemon juice after filling in step (5) is placed on the rack in the center of the upper and lower electrode plates in the sample chamber of the electromagnetic field coupling device, is evenly placed without overlapping, and is subjected to synergistic auxiliary freezing by using a magnetic field and an electric field, and a thermocouple is used to measure the temperature of the center of the frozen lemon juice in real time until the temperature is reduced to-18 DEG C;

[0018] (7) Thawing of the frozen lemon juice: the frozen lemon juice obtained in step (6) is thawed.

[0019] (8) Ultrasonic treatment: the lemon juice after thawing in step (7) is subjected to ultrasonic treatment for 10-15 min.

[0020] In step (1), 200-mesh screen filtration is used to remove insoluble substances such as fruit pulp from the juice.

[0021] In step (2), the ratio of the nanocellulose to pectin is 3:7.

[0022] In step (4), the low-temperature pasteurization temperature is 65-70 DEG C, and the treatment time is 3-6 s.

[0023] In step (6), the electric field intensity applied ranges from 10 to 30 kV / cm, and the magnetic field intensity is 2-10 mT.

[0024] In step (6), the upper and lower electrode plates placed in the center of the sample chamber can discharge upwards and downwards to generate an electric field; the rack is placed in the center of the two electrode plates, and the distance therebetween can be adjusted; and the lemon juice is placed 10 cm below the upper electrode plate.

[0025] In step (6), the preset temperature of the electromagnetic field device is-20 DEG C, the lemon juice is placed in the electromagnetic field device after the temperature of the electromagnetic field device is reduced to-20 DEG C, and an electric field and a magnetic field are applied simultaneously.

[0026] In step (7), the frozen lemon juice is placed in a 4 DEG C refrigerator for static thawing.

[0027] In step (8), the ultrasonic treatment conditions are as follows: the ultrasonic power is 200-1500 W, and the temperature is 25 DEG C.

[0028] Compared with the prior art, the application has the following beneficial effects:

[0029] (1) The Pickering emulsion added in the application can stabilize the oil and other ingredients in the lemon juice, and can improve the cloud stability of the solution.

[0030] (2) The use of the electromagnetic field to assist in freezing the lemon juice can shorten the freezing time, and the shorter freezing time can improve the industrial production efficiency, reduce the energy consumption, and save the cost.

[0031] (3) The application can effectively inactivate the activity of enzymes by using electromagnetic field treatment. Pectin methyl esterase catalyzes the de-esterification reaction of methoxyl pectin, and low-esterification pectin is easy to combine with calcium ions to form insoluble pectin calcium salt, which is adsorbed on other turbidity components in the juice, thereby affecting the sensory and nutritional properties of the juice. The electromagnetic field treatment used in the application can effectively reduce the activity of pectin methyl esterase, thereby improving the stability of lemon juice; the use of electromagnetic field treatment can also reduce the particle size of the solution, reduce the polymer dispersion index, increase the absolute value of the Zeta potential of the solution, improve the uniformity of the juice, and make the juice more stable.

[0032] (4) The use of ultrasonic treatment in the application can reduce the particle size and polymer dispersion index of the solution through ultrasonic cavitation effect, improve the uniformity of the thawed lemon juice, and improve the stability.

[0033] (5) The use of electromagnetic field assisted freezing and ultrasonic treatment in the application will not affect the active ingredients such as total phenol and ascorbic acid content and antioxidant properties of lemon juice, and will not change the unique flavor of lemon juice. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 is the effect of different implementation methods on the pectin methyl esterase activity of lemon juice;

[0035] Figure 2 is the effect of different implementation methods on the cloud stability of lemon juice;

[0036] Figure 3 is the lemon juice radar chart of electronic nose of different implementation methods. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical scheme and advantages of the application more clear, the application will be further described in detail below in combination with examples. It should be understood that the specific examples described here are only used to explain the application, and are not used to limit the application.

[0038] The prepared lemon juice was subjected to particle size potential, pectin methyl esterase activity, cloud stability and electronic nose determination, and the specific contents are as follows:

[0039] Particle size and potential: Zetasizer (Nano ZS, Malvern, UK) nanoparticle size and ZETA potential instrument was used to analyze the particle size (average diameter), polymer dispersion index (PDI) and zeta potential. The sample was dispersed in distilled water and equilibrated at 25℃ for 60 seconds before measurement. The refractive index of water is 1.33, the viscosity is 0.8872 cP, the dielectric constant is 78.5, and the particle refractive index is 1.5.

[0040] Pectin methyl esterase activity: 10 mL of lemon juice was added to 20 mL of 2 mol / L NaCl solution containing 1% pectin. The pH of the pectin-juice mixture was adjusted to 7 with 1 mol / L NaOH. After the pH was stable, 1 mL of 0.05 mol / L NaOH was added, and the time required to restore the pH to 7 was measured. PME activity (U / mL) = V1C / VT, where V1 is the amount of NaOH consumed after the addition of lemon juice (mL), C is the concentration of NaOH (mol / L), V is the amount of lemon juice added (mL), and T is the reaction time (min).

[0041] Cloud stability: The lemon juice sample was centrifuged at 4200 g for 20 min at room temperature, and the supernatant was taken to measure the absorbance at 660 nm. The cloud stability was calculated as the percentage of the absorbance of the supernatant after centrifugation relative to the absorbance of the juice sample before centrifugation.

[0042] T% = Ta / Tb * 100, where Ta and Tb are the turbidity of the juice after and before centrifugation, respectively.

[0043] The experimental results of the following different examples were compared with lemon juice that had not undergone any addition or treatment as the control group.

[0044] Example 1

[0045] A method for preparing frozen lemon juice with added Pickering emulsion, the steps are as follows:

[0046] (1) Preparation of Pickering emulsion: Mix the nanocellulose water dispersion with the fully dissolved pectin in a certain proportion, stir thoroughly, and then disperse with a high-speed disperser at 20000 r / min for 5 min. Obtain the nanocellulose and pectin compound. Add 50% by volume of blended oil as the oil phase, and homogenize at 14000 r / min for 3 min to obtain the Pickering emulsion;

[0047] (2) Add the emulsion prepared in step (1) to the lemon juice;

[0048] (3) Treatment of lemon juice: Sterilize the lemon juice at 65-70°C for 3-6 s;

[0049] (4) Lemon juice bottling: After sterilization in step (3), the lemon juice is cooled and bottled in sterile bottles;

[0050] (5) Freezing: The lemon juice filled in step (4) is placed in a -20°C refrigerator for freezing.

[0051] (6) Thawing of frozen lemon juice: The frozen lemon juice obtained in step (5) is thawed at 4°C

[0052] The lemon juice prepared above was frozen at -20°C for one week, and after thawing, its particle size, potential, cloud stability were determined. The results showed that the addition of hydrophilic colloids increased its particle size, and significantly reduced PDI. As shown in Figure 2 It can be seen that the stability of lemon juice was significantly improved, and its cloud stability was increased by 41.82%. The electronic nose results of the lemon juice added with konjac gum are shown in Figure 3 As shown, the radar chart of the treated and untreated samples was similar, and it was difficult to see the difference between them, and this method did not significantly change the unique flavor of the lemon juice.

[0053] Example 2

[0054] A synergistic method for improving the thawing quality of frozen lemon juice treated by electromagnetic field, comprising the following steps:

[0055] (1) Treatment of lemon juice: the lemon juice was sterilized at 65-70°C for 3-6s;

[0056] (2) Bottling of lemon juice: after sterilization in step (1), the lemon juice was cooled and bottled in sterile bottles;

[0057] (3) Synergistic assisted freezing by electromagnetic field: the lemon juice bottled in step (2) was placed on the shelf under the electrode plate in the electromagnetic field coupling constant temperature device, and was uniformly placed without overlapping, and was synergistically assisted frozen by electromagnetic field. The applied electric field strength was 20kV / cm, and the applied magnetic field strength was 6mT.

[0058] (4) Thawing of frozen lemon juice: the frozen lemon juice obtained in step (3) was thawed at 4°C.

[0059] The lemon juice prepared above was frozen at -20°C for one week, and after thawing, its particle size, potential, pectin methyl esterase activity, cloud stability and electronic nose were determined. As shown in Table 1, the electromagnetic field synergistic treatment can reduce the particle size and PDI of the lemon juice, and increase the absolute value of Zeta potential. As shown in Figure 1 , the electromagnetic field synergistic treatment can effectively reduce the pectin methyl esterase activity. As shown in Figure 2 , the treated lemon juice had significantly improved stability, and its cloud stability was increased by 17.51%. The electronic nose results of the lemon juice treated by electromagnetic field synergistic assisted freezing are shown in Figure 3 , the radar chart of the treated and untreated samples was similar, and it was difficult to see the difference between them, and this method did not significantly change the unique flavor of the lemon juice.

[0060] Example 3

[0061] A synergistic method for improving the thawing quality of frozen lemon juice treated by electromagnetic field and ultrasonic wave, comprising the following steps:

[0062] (1) Lemon juice treatment: The lemon juice was sterilized at 65-70 °C for 3-6 s;

[0063] (2) Lemon juice bottling: After sterilization in step (1), the lemon juice was cooled and bottled in sterile bottles;

[0064] (3) Electromagnetic field-assisted freezing: The lemon juice after bottling in step (2) was placed on the shelf under the electrode plate in the electromagnetic field coupling constant temperature device, evenly placed without overlapping, and subjected to electromagnetic field-assisted freezing. The applied electric field strength was 20 kV / cm, and the applied magnetic field strength was 6 mT.

[0065] (4) Thawing of frozen lemon juice: The frozen lemon juice obtained in step (3) was thawed at 4 °C.

[0066] (5) Ultrasonic treatment: The thawed lemon juice in step (3) was subjected to ultrasonic treatment at 600 W for 15 min.

[0067] The lemon juice prepared above was frozen at -20 °C for one week, and after thawing, the particle size, zeta potential, pectin methylesterase activity, cloud stability, and electronic nose of the lemon juice were determined. As shown in Table 1, electromagnetic field-assisted freezing and ultrasonic treatment after thawing can reduce the particle size, PDI, and increase the absolute value of zeta potential of the lemon juice. As shown in Table 2, the pectin methylesterase activity can be effectively reduced. As shown in Table 3, the stability of the treated lemon juice was significantly improved, and the cloud stability was increased by 25.89%. As shown in Table 4, the radar chart of the treated and untreated samples was similar, and it was difficult to distinguish the difference between them, indicating that the method did not significantly change the unique flavor of the lemon juice. Figure 1 Figure 2 Figure 3

[0068] Example 4

[0069] A method for improving the thawing quality of frozen lemon juice treated by electromagnetic field and ultrasonic wave, comprising the following steps:

[0070] (1) Preparation of Pickering emulsion: A nanocellulose water dispersion and fully dissolved pectin were mixed in a certain proportion, and after thorough stirring, a high-speed disperser was used at 20000 r / min for 5 min. A nanocellulose and pectin compound was obtained. A volume fraction of 50% of blended oil was added as the oil phase, and homogenized at 14000 r / min for 3 min to obtain a Pickering emulsion;

[0071] (2) The emulsion prepared in step (1) was added to lemon juice;

[0072] (3) Lemon juice sterilization: The lemon juice was sterilized at 65-70 °C for 3-6 s; ​​​

[0073] (4) Bottling of lemon juice: After sterilization in step (3), the lemon juice was cooled and bottled in sterile bottles;

[0074] (5) Electromagnetic field assisted freezing: The bottled lemon juice from step (4) was placed on a shelf under the electrode plate in an electromagnetic field coupling constant temperature device, and was evenly placed without overlapping. Electromagnetic field was used for assisted freezing. The applied electric field strength was 20 kV / cm, and the applied magnetic field strength was 6 mT.

[0075] (6) Thawing of frozen lemon juice: The frozen lemon juice obtained in step (5) was thawed at 4°C.

[0076] (7) Ultrasonic treatment: The thawed lemon juice from step (6) was placed in an ultrasonic device and treated with ultrasonic waves at 600 W for 15 min.

[0077] The lemon juice prepared above was frozen at -20°C for one week, and after thawing, its particle size, zeta potential, pectin methylesterase activity, cloud stability and electronic nose were determined. As shown in Figure 2 , the stability of the treated lemon juice was significantly improved, and the cloud stability was increased by 65.75%. The electronic nose results of the synergistic treatment are shown in Figure 3 , the radar plots of the treated and untreated samples are similar, and it is difficult to distinguish the difference between them, indicating that this method does not significantly change the unique flavor of lemon juice.

[0078] The experimental data of the above three examples are shown in Table 1 and the accompanying Figures 1-3 .

[0079] Table 1 Effect of different example methods on particle size, PDI and zeta potential of lemon juice

[0080]

Claims

1. A synergistic method for improving the thawing quality of frozen lemon juice, characterized in that, The method mainly comprises the following steps: (1) Lemon juice pretreatment: filter the lemon juice to remove insoluble substances using a 200-mesh screen; (2) Preparation of Pickering emulsion: mix the nanocellulose water dispersion and the fully dissolved pectin in a certain proportion, stir thoroughly, and then disperse at a high speed of 20,000 r / min for 5 min to obtain a nanocellulose-pectin compound; add 50% (by volume) of blended oil as the oil phase, and homogenize at 14,000 r / min for 3 min to obtain a Pickering emulsion; the ratio of nanocellulose to pectin is 3:7; (3) Add the emulsion prepared in step (2) to the lemon juice; (4) Sterilization of lemon juice: perform low-temperature pasteurization on the lemon juice; the low-temperature pasteurization temperature is 65-70℃, and the treatment time is 3-6 s; (5) Lemon juice bottling: cool the lemon juice after sterilization in step (4) and fill it into sterile bottles; (6) Electromagnetic field synergistic assisted freezing: place the lemon juice filled in step (5) on a rack in the center of the upper and lower electrode plates in the sample chamber of the electromagnetic field coupling device, evenly place the lemon juice without overlapping, and use the magnetic field and electric field for synergistic assisted freezing; use a thermocouple to measure the temperature of the center of the frozen lemon juice in real time until the temperature drops to -18℃; the applied electric field strength ranges from 10 kV / cm to 30 kV / cm, and the magnetic field strength ranges from 2 mT to 10 mT; (7) Thawing of frozen lemon juice: place the frozen lemon juice obtained in step (6) in a 4℃ refrigerator for thawing; (8) Ultrasonic treatment: place the thawed lemon juice in step (7) in an ultrasonic device for ultrasonic treatment for 10-15 min; the ultrasonic power is 200-1500 W, and the temperature is 25℃.

2. A synergistic method of improving the quality of thawed frozen lemon juice according to claim 1, characterized in that, In step (6), the upper and lower electrode plates placed in the center of the sample chamber can discharge upward and downward to generate an electric field; the rack is placed in the center of the two electrode plates, and the distance between them can be adjusted; The lemon juice is placed 10 cm below the upper electrode plate.

3. A synergistic method of improving the quality of thawed frozen lemon juice according to claim 1, characterized in that, In step (6), the electromagnetic field device is preset to -20℃, and the lemon juice is placed in the device when the temperature drops to -20℃, and the electric field and magnetic field are applied simultaneously.

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