Preparation method of high-voltage pulsed electric field assisted preparation of green plum jam

Abstract

This invention discloses a method for preparing plum jam using a high-voltage pulsed electric field assisted preparation. Using 90% ripe fresh plums as raw material, the method involves sequential treatment with a high-voltage pulsed electric field, 10-15% vol low-alcohol immersion, a second pulsed electric field treatment, and sugar immersion. The plum pulp, white sugar, syrup, vitamin C, edible salt, and sodium citrate are then used to prepare the plum jam. This method effectively reduces the pickling time of the plums, improves production efficiency, reduces hardness, efficiently removes bitterness and acidity, effectively preserves the original aroma components and color of the plums, and enhances the taste. It solves the problems of long preparation time, poor water retention, low taste, and poor color in existing plum jam preparation techniques.

Description

Technical fields:

[0001] This invention relates to the field of jam preparation technology, specifically to a method for preparing plum jam using a high-voltage pulsed electric field. Background technology:

[0002] Green plums are an important fruit originating in China, with my country accounting for 70% of the world's total green plum production. Also known as sour fruit, green plums are rich in nutrients, but due to their high acidity and low sugar content, they are not suitable for fresh consumption and are generally processed into dried fruit, fruit wine, and jam. Fresh green plums have a high pectin content, a dense and smooth skin structure, high hardness, and poor permeability. The pulp contains abundant bitter substances (ketones / aldehydes) and acidic substances (malic acid, citric acid, etc.). The presence of bitter and acidic substances affects the sensory and quality characteristics of the final green plum product, requiring processing to remove them. Traditional processing methods generally use high temperatures or long-term soaking to pre-treat the fresh fruit by breaking down the tissue structure through boiling and prolonged osmotic pressure mass transfer. This process is time-consuming and severely damages the aroma and color of the green plum. Chinese patent CN2014106876509.6 discloses a production process for plum jam, in which plums are washed, soaked in dilute hydrochloric acid, steamed at 100℃ for 40 minutes, filtered, blended, and heat-sterilized to obtain the finished product; Chinese patent CN202211209055.4 discloses a plum jam that maintains the crispness of the fruit and its processing technology, which uses salted plums as raw materials, and obtains the finished product after desalting, blending, sterilization, and bottling.

[0003] In summary, the following problems still exist in the preparation of plum jam: 1) Traditional production methods. High-temperature steaming of fresh plums is often used, resulting in significant nutrient loss and insufficient aroma; alternatively, pickled plums are used as raw materials, typically with a pickling period of 2-6 months, leading to a reduction in total pectin content and severe textural damage. 2) Jams prepared using these methods have a thinner texture, making them prone to water seepage after storage, reducing their extensibility and elasticity. Both methods also damage the color of the plums and retain their high acidity, causing inconvenience for subsequent processing. 3) Due to the high acidity, large amounts of glycogen and thickeners are added to the finished jam to mask the original flavor, increasing costs and deteriorating the taste. Summary of the Invention:

[0004] The purpose of this invention is to provide a method for preparing plum jam with the assistance of a high-voltage pulsed electric field, which solves the problems of long preparation time, poor water retention, unpleasant taste, and dull color in the existing technology for preparing plum jam.

[0005] This invention is achieved through the following technical solutions:

[0006] A method for preparing plum jam using a high-voltage pulsed electric field assisted preparation method, comprising the following steps:

[0007] 1) One-time high field strength pulsed electric field treatment: Clean the undamaged fresh green plums with a maturity of 90%, remove the stems and stalks, and treat them with a high voltage pulsed electric field with an electric field strength of 3-5kV / cm, a pulse width of 8-15μs, a frequency of 80-100Hz, and a treatment time of 1-3min.

[0008] 2) Soaking in low-proof alcohol: Soak the plums after the pulse treatment in step 1) in a 10-15% vol low-proof alcohol solution at room temperature for 15-20 days;

[0009] 3) Secondary low field strength pulsed electric field treatment: After step 2), the plum fruit is treated with an electric field strength of 0.5-1.5kV / cm, a pulse width of 8-15μs, a frequency of 80-100Hz, and a treatment time of 1-2min.

[0010] 4) Sugar soaking: After the treatment in step 3), the green plums are soaked in sugar solution at room temperature for 5-10 days;

[0011] 5) Preparation of plum jam: Remove the pits from the plums treated in step 4) to obtain plum flesh. Take 30-40 wt% plum flesh, 15-20 wt% white sugar, 5-10 wt% sugar juice, 0.16-0.18 wt% vitamin C, 0.03-0.05 wt% edible salt, and 0.01-0.03 wt% sodium citrate. Boil until the soluble solids content is 40-42%, then sterilize and can the product to obtain the finished product.

[0012] Preferably, the waveform of the pulsed electric field is a unipolar square wave.

[0013] Preferably, in step 2), the alcohol is 95% vol edible corn alcohol, diluted with pure water to 10-15% vol.

[0014] Preferably, step 4) involves obtaining the sugar solution by boiling, dissolving, and sterilizing 30wt%-40wt% white granulated sugar.

[0015] Preferably, step 5) plum flesh refers to the plum flesh being crushed by a crusher until there are no obvious large fruit flesh particles.

[0016] Preferably, step 5) involves removing the pits from the plums treated in step 4), taking 30-40 wt% plum flesh, 15-20 wt% white sugar, 0.16-0.18 wt% vitamin C, 0.03-0.05 wt% edible salt, 0.01-0.03 wt% sodium citrate, and an appropriate amount of pure water. The mixture is heated to 70°C and kept warm for 3 minutes. Then, 5-10 wt% sugar-soaked juice is added, and the mixture is heated to 80°C and stirred continuously for 2 minutes. The volume is then adjusted to 100% using pure water. The soluble solids content is measured to be 40-42%. After bottling, the mixture is sterilized to obtain the finished product.

[0017] In this invention, fresh plums are first pretreated with a high-intensity pulsed electric field. Due to the difference in conductivity between the pulp and the pit (the pulp has more electrolyte components and higher conductivity, approximately 1800-3000 μS / cm), the pulp experiences internal and external tensile tension under the strong action of the directional electric field. In contrast, the pit has lower conductivity (low water content and fewer mobile electrolyte components, conductivity <800 μS / cm). Under the same electric field force, the pit exhibits stronger internal and external tensile strength. Due to the different resistance of different components to electric field force under the electric field, different deformations are formed. Macroscopically, the whole fruit becomes fuller and more swollen, structural stability decreases, and hardness decreases by about 50%. When the field strength is increased to above 3.0 kV / cm, the cellulose chains disperse, intercellular pores are generated, and tissue channels are formed in the pulp tissue structure. Then, the fruit is soaked in a 10-15% vol low-alcohol solution at room temperature. Bitter and sour substances dissolve in large quantities, and the hardness is further reduced under the osmotic pressure of the low-alcohol soaking. If the electric field strength increases further to more than 5.0 kV / cm, it will cause irreversible damage to the fresh plum fruit, causing excessive perforation of the skin, resulting in wrinkling and reducing the mass transfer rate.

[0018] The inventors unexpectedly discovered that by first subjecting undamaged, 90% ripe fresh plums to a 3-5kV / cm high-voltage pulse electric field treatment, followed by soaking in low-proof alcohol (10-15% vol), and then combining this with a second 0.5-1.5kV / cm low-field-strength pulse electric field treatment and sugar soaking, the synergistic effect resulted in an unexpectedly smooth texture and high adhesiveness.

[0019] This application first pre-treats fresh green plums with a high-intensity pulsed electric field, followed by a second treatment with a low-intensity pulsed electric field. During this process, the elasticity and adhesiveness of the green plums initially decrease and then increase (by 62% compared to fresh green plums). This is because the pectin content in the plums pre-treated with the high-intensity pulsed electric field decreases, the pectin molecular chains in the plum cells shorten, and the hydrogen bonding forces are strengthened, resulting in increased hydrophilicity and water-soluble pectin content. Therefore, the elasticity and adhesiveness of the green plums initially decrease. Then, after the second low-intensity pulsed electric field treatment, the activity of methyl esterase is activated, increasing methyl esterase activity and promoting the conversion of water-soluble pectin into pectic acid. This pectin acid then forms a pectate structure with an appropriate amount of sodium ions, increasing the insoluble pectin content and thus increasing adhesion. This effectively improves the adhesiveness of the plum jam and reduces water separation, resulting in the subsequent increase in the elasticity and adhesiveness of the green plums. During sugaring, under the influence of osmotic pressure, the cytosolic content undergoes a process of increasing from high to low and then back to high, further enhancing the compactness of the cell tissue structure. The prepared plum jam has a smaller particle size, a smoother texture, and higher adhesion.

[0020] Compared with the prior art, the beneficial effects of the present invention are:

[0021] 1. After being treated with a high field strength pulsed electric field, the structural stability of the fresh plum fruit is reduced, which is conducive to the dissolution of organic acids, especially citric acid, with a dissolution rate of over 50%. No chemical methods are needed to reduce acidity in subsequent processing. After soaking in 10-15% vol low-alcohol alcohol, bitter substances are dissolved, and the dissolution rate of amygdalin is 51%, which effectively reduces the astringency and bitterness of the plum and significantly reduces its hardness.

[0022] 2. The double low-field pulse treatment stabilizes the plum fruit structure, increases methyl esterase activity, promotes the conversion of pectin into pectic acid, forms pectate structures, and increases the content of insoluble pectin, thereby enhancing adhesion. Under osmotic pressure, the cytosap content undergoes a process of increasing then decreasing and then increasing again, further improving the compactness of the cell tissue structure.

[0023] 3. The aroma and color of the green plums are preserved, resulting in a smooth and creamy plum jam with high viscosity. The green plum pulp has higher soluble solids and smaller particle size, leading to improved texture and enhanced spreadability. The entire pretreatment stage of the fresh green plums involves low-temperature processing and alcohol soaking for color preservation, resulting in a yellow-green plum jam with significantly improved L* and a* values.

[0024] 4. Short processing time and material savings for large-scale processing of jam. Compared with the traditional method of making plum jam by soaking green plums, the preparation time of this invention is shortened by 50%, and the content of materials, especially white sugar, is reduced by more than 10%.

[0025] In summary, this invention uses 90% ripe fresh green plums as raw materials, and successively performs high-voltage pulsed electric field treatment, low-alcohol (10-15% vol) immersion, followed by a second low-field-strength pulsed electric field treatment and sugar immersion. Finally, green plum jam is prepared using plum flesh, white sugar, syrup, vitamin C, edible salt, and sodium citrate as raw materials. The synergistic effect between these steps effectively reduces the pickling time of the green plums, improves production efficiency, reduces hardness, efficiently removes bitterness and acidity, effectively preserves the original aroma components and color of the green plums, and enhances the taste. The resulting green plum jam has a dense texture and high adhesion, solving the problems of long preparation time, poor water retention, unpleasant taste, and dull color in existing green plum jam preparation techniques. Attached image description:

[0026] Figure 1 These are scanning electron microscope (SEM) images of plums before and after pulsed electric field treatment in Example 1.

[0027] The left image is a scanning electron microscope (SEM) image of the plum before pulse treatment, the middle image is a scanning electron microscope (SEM) image of the plum after one pulse treatment, and the right image is a scanning electron microscope (SEM) image of the plum after two pulse treatments.

[0028] As shown in the figure, after the first pulse treatment, the plum skin underwent significant deformation, forming undulating protrusions, making the whole fruit fuller and more swollen, reducing structural stability and hardness by about 50%; after the second pulse treatment, edge collapse occurred, but the shape and integrity of the cells were basically maintained.

[0029] Figure 2 The image shows the infrared spectra before and after the first pulsed electric field treatment in Example 1. From top to bottom, the images show the plum pulp treated with PEF, the plum peel treated with PEF, the plum pulp, and the plum peel. It can be seen that after PEF treatment, the strength of the plum peel and pulp groups is significantly reduced, the connection is loose, the hardness is reduced, and the mass transfer efficiency is significantly improved. Detailed implementation method:

[0030] The following is a further description of the invention, but not a limitation thereof.

[0031] The pulsed electric field device is manufactured by Guangzhou Paihu Technology Co., Ltd., model EX-500, and the waveform is a square wave.

[0032] Example 1:

[0033] A method for preparing plum jam using a high-voltage pulsed electric field assisted preparation method, comprising the following steps:

[0034] (1) One high field strength pulsed electric field treatment: clean the undamaged fresh green plums with 90% maturity, remove the stems and stalks, and treat them with a pulsed electric field with a field strength of 3kV / cm, a pulse width of 10us, a frequency of 100Hz, and a treatment time of 2min.

[0035] (2) Low alcohol soaking: The plums after the pulse treatment in step (1) were soaked in a 10% vol alcohol solution at room temperature for 20 days;

[0036] (3) Secondary low field strength pulse electric field treatment: The plums soaked in alcohol in step (2) are treated with a field strength of 1kV / cm, a pulse width of 8μs, a frequency of 80Hz, and a treatment time of 1.5min.

[0037] (4) Sugar soaking: Boil 30wt% white sugar to dissolve and sterilize, then add the green plums treated in step (3) and soak for 8 days;

[0038] (5) Preparation of plum jam: After removing the pits from the plums treated in step (4), the pulp is crushed by a crusher until there are no obvious large pulp particles. Take 32wt% plum pulp, 15wt% white sugar, 0.18wt% vitamin C, 0.04wt% edible salt, 0.02wt% sodium citrate, and an appropriate amount of pure water, heat to 70℃ and keep warm for 3 minutes, add 10wt% sugar juice, heat to 80℃ and stir continuously for 2 minutes, and use pure water to make up to 100%. The soluble solids are detected to be 41±1%. Sterilize and bottle to obtain the finished product.

[0039] Example 2

[0040] Clean undamaged, 90% ripe green plums, remove stems and strings, and treat with a pulsed electric field (5 kV / cm, 15 μs pulse width, 80 Hz frequency, 3 min). After pulse treatment, soak the plums in a 15% vol alcohol solution at room temperature for 15 days. Then, treat the alcohol-soaked plums with a pulsed electric field (0.5 kV / cm, 10 μs pulse width, 90 Hz frequency, 1 min). Sterilize by boiling and dissolving 40 wt% white sugar, then add the treatment... After soaking the green plums for 10 days, the pits were removed, and the pulp was crushed by a crusher until there were no obvious large pulp particles. 40 wt% of plum pulp, 17 wt% of white sugar, 0.16 wt% of vitamin C, 0.05 wt% of edible salt, 0.01 wt% of sodium citrate, and an appropriate amount of pure water were taken, heated to 70℃ and kept warm for 3 minutes, 5% of the sugar soaking juice was added, and the mixture was heated to 80℃ and stirred continuously for 2 minutes. The volume was adjusted to 100% with pure water, and the soluble solids content was 41±1%. The product was sterilized and bottled to obtain the finished product.

[0041] Comparative Example 1

[0042] Clean undamaged, 90% ripe fresh plums, remove stems and pits, crush and pit them, and take 40% plum flesh, 60% white sugar, 0.18% vitamin C, 0.05% edible salt, and 0.02% sodium citrate. Boil at high temperature until the soluble solids content is 41±1%, then sterilize and can the product.

[0043] Comparative Example 2

[0044] Clean undamaged, 90% ripe fresh green plums, remove stems and strings, and soak in 50% salt by dry method for 2 months; desalinate with running water, remove pits from the treated green plums, take 40% plum flesh, 60% white sugar, 0.18% vitamin C, and 0.02% sodium citrate, boil to obtain 40-42% soluble solids, sterilize and can to obtain the finished product.

[0045] Comparative Example 3:

[0046] Referring to Example 1, the difference is that in step (1), the electric field strength of 3 kV / cm in the first high field strength pulse electric field treatment is replaced with 10 kV / cm.

[0047] Comparative Example 4:

[0048] Referring to Example 1, the difference is that the secondary low field strength pulse electric field treatment in step (3) was not performed.

[0049] Comparative Example 5:

[0050] Referring to Example 1, the difference is that the electric field strength of 1kV / cm in the secondary pulse electric field processing of step (3) is replaced with 3kV / cm.

[0051] Comparative Example 6:

[0052] Referring to Example 1, the difference is that it did not undergo the high field strength pulsed electric field treatment in step (1) and the low alcohol immersion in step (2).

[0053] Clean undamaged, 90% ripe fresh plums, remove stems and calyxes, and treat them with an electric field strength of 1 kV / cm, pulse width of 8 μs, frequency of 80 Hz, and treatment time of 1.5 min. Sterilize by boiling and dissolving 30 wt% white sugar, then add the treated plums and soak for 8 days. After pitting, crush the pulp with a crusher until there are no obvious large pulp particles. Take 32 wt% plum pulp, 15 wt% white sugar, 0.18 wt% vitamin C, 0.04 wt% edible salt, 0.02 wt% sodium citrate, and an appropriate amount of pure water, heat to 70℃ and keep warm for 3 min, add 10 wt% sugar soaking juice, heat to 80℃ and stir continuously for 2 min, and make up to 100% volume with pure water. The soluble solids content is 41±1%, sterilize and bottle to obtain the finished product.

[0054] Comparative Example 7:

[0055] Referring to Example 1, the difference is that the secondary low-intensity pulsed electric field treatment in step (3) and the sugar impregnation in step (4) were not performed.

[0056] Clean undamaged, 90% ripe fresh plums, remove stems and berries, and treat with a pulsed electric field (3kV / cm, 10µs pulse width, 100Hz frequency, 2min). Soak the treated plums in a 10% vol alcohol solution at room temperature for 20 days. After pitting, crush the pulp until no large particles are visible. Take 32wt% plum pulp, 15wt% white sugar, 0.18wt% vitamin C, 0.04wt% edible salt, 0.02wt% sodium citrate, and an appropriate amount of pure water. Heat to 70℃ and hold for 3min. Add 10wt% sugar juice, heat to 80℃ and stir continuously for 2min. Adjust the volume to 100% with pure water. The soluble solids content is 41±1%. Sterilize and bottle to obtain the finished product.

[0057] After treatment with a pulsed electric field, the firmness of the fresh plums in Example 1 was significantly reduced (see [link]). Figure 1 and Figure 2The treatment time is 25-28 days, which achieves the immersion effect of the traditional treatment method of 60 days (Comparative Example 2), reducing the treatment time by more than half. In terms of color, Comparative Examples 1 and 2 turned brown due to high temperature and salting, especially Comparative Example 2, which turned reddish-brown, showing a huge difference in sensory perception. Comparative Example 3, treated with a high-intensity pulse (10kV / cm), caused irreversible damage to the fresh plums, resulting in excessive perforation of the skin, wrinkling, and a reduced mass transfer rate. Comparative Example 4, without secondary pulse electric field treatment, showed reduced skin permeability, decreased plum stability, loose structure, and a significantly reduced sugaring rate. Comparative Example 5, with the secondary pulse increased to 3kV / cm, caused a large amount of pectin and polysaccharides to dissolve from the plums, resulting in severe deformation and a lower chewiness. Comparative Example 6, treated only with a low-pulse electric field and a sugaring step, and Comparative Example 7, treated only with a high-pulse electric field and an alcohol soaking step, both resulted in a certain degree of reduction in the hardness of the plums, but also a decrease in elasticity and adhesion. The finished plum jam turned red in color and had a higher acidity. In Examples 1-2, the removal rates of harmful substances and the bitter substance amygdalin were more than 20% higher than those in the direct treatment control example 1; the content of the main acidic substance citric acid was within the range for direct use after treatment; it can be seen that the electric field strength is better controlled at 3-5 kV / cm during the first high field strength pulse electric field treatment, and the electric field strength is better at 0.5-1.5 kV / cm during the second low field strength pulse electric field treatment.

[0058] Table 1. Effects of different treatments on plums and plum jam.

[0059]

[0060] Note: Plum firmness refers to the firmness of the fruit before cooking after processing; L* value represents brightness, the larger the value, the brighter the fruit; a* value represents red and green, with red being a positive number and green being a negative number.

Claims

1. A method for the preparation of high pressure pulsed electric field assisted preparation of green plum jam, characterized by, The method comprises the following steps: 1) one high field intensity pulse electric field treatment: clean the fresh green plum fruit without damage and maturity of 9, remove the stem and peduncle, and treat by high pressure pulse electric field, electric field intensity of 3-5 kV / cm, pulse width of 8-15 μs, frequency of 80-100 Hz, and treatment time of 1-3 min; 2) low alcohol immersion: immerse the green plum fruit treated by pulse in step 1) in 10-15%vol low alcohol solution at room temperature for 15-20 days; 3) second low field intensity pulse electric field treatment: treat the green plum fruit treated by step 2) at field intensity of 0.5-1.5 kV / cm, pulse width of 8-15 μs, frequency of 80-100 Hz, and treatment time of 1-2 min; 4) sugar impregnation: immerse the green plum treated by step 3) in sugar impregnation solution at room temperature for 5-10 days; 5) preparation of green plum jam: remove the core of the green plum treated by step 4) to obtain plum meat, take 30-40 wt% plum meat, 15-20 wt% white sugar, 5-10 wt% sugar impregnation juice, 0.16-0.18 wt% vitamin C, 0.03-0.05 wt% edible salt, 0.01-0.03 wt% sodium citrate, cook until the soluble solid content is 40-42%, sterilize and can to obtain the finished product.

2. The production method according to claim 1, characterized by, The waveform of the pulse electric field is a unipolar square wave.

3. The preparation method according to claim 1, characterized in that, The alcohol in step 2) is 95%vol edible corn alcohol, which is diluted to 10-15%vol by pure water.

4. The method of claim 1, wherein, The sugar impregnation solution in step 4) is obtained by dissolving, sterilizing and cooking 30 wt%-40 wt% white sugar.

5. The preparation method according to claim 1, characterized in that, Step 5) is: remove the core of the green plum treated by step 4), take 30-40 wt% plum meat, 15-20 wt% white sugar, 0.16-0.18 wt% vitamin C, 0.03-0.05 wt% edible salt, 0.01-0.03 wt% sodium citrate, and appropriate amount of pure water, heat to 70℃ for 3 min, add 5-10 wt% sugar impregnation juice, heat to 80℃ for 2 min, add pure water to 100%, and the soluble solid content is 40-42%, can to obtain the finished product after sterilization.

6. The method of claim 1, wherein, The waveform of the pulse electric field is a unipolar square wave. The alcohol in step 2) is 95%vol edible corn alcohol, which is diluted to 10-15%vol by pure water. The sugar impregnation solution in step 4) is obtained by dissolving, sterilizing and cooking 30 wt%-40 wt% white sugar. Step 5) is: remove the core of the green plum treated by step 4), take 30-40 wt% plum meat, 15-20 wt% white sugar, 0.16-0.18 wt% vitamin C, 0.03-0.05 wt% edible salt, 0.01-0.03 wt% sodium citrate, and appropriate amount of pure water, heat to 70℃ for 3 min, add 5-10 wt% sugar impregnation juice, heat to 80℃ for 2 min, add pure water to 100%, and the soluble solid content is 40-42%, can to obtain the finished product after sterilization.

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