Method for improving hardness of canned peaches

Abstract

The invention belongs to the technical field of food processing, and particularly relates to a method for improving hardness of canned peaches. The invention provides a method for improving hardness of canned peaches. The method comprises the following preparation steps: S1, removing peach hair from yellow-meat wild peaches; s2, soaking peaches in alkali liquor, peeling the peaches, and cleaning the peaches until the peaches are neutral; s3, denucleating the peaches, cutting the peaches into petals to obtain peach petals, soaking the peach petals in a low-esterification-degree wild peach pectin-cane sugar solution, and carrying out electromagnetic treatment; and S4, soaking the peach petals in a calcium ion solution, carrying out vacuum treatment, and then cleaning the peach petals with deionized water to obtain the peach petals. The natural low-esterification-degree pectin is added into the sucrose solution, the characteristic that the low-esterification-degree pectin is combined with calcium ions to form gel under the acidic condition is utilized, and electromagnetic treatment is assisted to promote combination of the low-esterification-degree pectin and the calcium ions, so that the problem that the hardness of the yellow peaches for canning is reduced in the processing process is effectively solved; meanwhile, the integrity of the pulp tissue structure is protected, and the natural flavor and nutritional ingredients are effectively reserved.

Description

Technical Field

[0001] The invention belongs to the technical field of canned food processing, and in particular relates to a method for improving the hardness of canned peaches. Background Art

[0002] Yellow peaches for canning are mostly ripe from July to September, which is the rainy season. Rainfall has a significant impact on the quality of yellow peaches, especially rainfall in the early stage of harvest, which causes the yellow peaches to absorb water quickly and swell their cells, thus significantly reducing the hardness of the yellow peaches after picking. This reduction in hardness not only brings difficulties to canning processing, but also directly affects the final quality of canned yellow peach products, including taste, appearance and storage stability.

[0003] At present, there are two main solutions to the problem of reduced hardness of canned yellow peaches in production practice:

[0004] 1. Strengthen the selection of raw materials: By strictly selecting yellow peaches that meet the hardness standards as canned raw materials, although this method can ensure the quality of processed raw materials to a certain extent, its disadvantages are also obvious. Since a large number of yellow peaches that do not meet the hardness requirements are eliminated, raw materials are seriously wasted. This not only increases the production costs of enterprises, but also has an adverse impact on the income of local farmers, further exacerbating the conflict of interests between upstream and downstream of the industrial chain.

[0005] 2. Treatment with pectinesterase: Pectinesterase is an enzyme preparation commonly used in food processing. It can adjust the texture and hardness of yellow peaches by decomposing pectin substances. However, this method has many problems in practical applications. For example, the operation is highly complex: the use of pectinesterase in production requires strict control of the activity of pectinase and its action environment parameters. A slight deviation may lead to problems such as poor treatment effect or excessive softening; time cost and economic cost increase: due to the long action time of pectinase, the entire processing process will be extended during the reproduction process, reducing production efficiency, and pectinase itself is relatively expensive and needs to be replaced regularly, which greatly increases the processing cost of the enterprise. Furthermore, in actual production, it was found that the characteristic flavor of canned yellow peach products treated with pectinesterase would be significantly lost, resulting in a decline in product quality, making it difficult to meet consumers' demand for high-quality canned foods.

[0006] Therefore, it is necessary to develop a more efficient, economical and environmentally friendly technical means to solve the processing difficulties caused by the reduction of hardness of canned yellow peaches, while ensuring the quality of canned yellow peach products. Summary of the invention

[0007] In order to solve the problems existing in the prior art, the purpose of the present invention is to provide a method for improving the hardness of canned peaches. The present invention effectively solves the problem of reduced hardness of canned yellow peaches during processing by adding naturally extracted low-esterification light walnut pectin to a sucrose solution and utilizing its characteristic of combining with calcium ions to form a gel under acidic conditions. At the same time, through strict process control (such as acidification of the immersion solution, vacuum treatment of the calcium solution, electromagnetic field treatment, etc.), the interference of external gelation is avoided to ensure the pectin-sucrose-Ca 2+ The system only works inside the pulp, while protecting the integrity of the pulp's tissue structure. It not only improves the hardness of canned peaches, but also retains their natural flavor, providing important support for the technological upgrading and sustainable development of the canned fruit processing industry.

[0008] The technical solution of the present invention is:

[0009] A method for improving the hardness of canned peaches, comprising the following preparation steps:

[0010] S1. Select fresh, insect-free, mechanically-free yellow-fleshed peaches that are 70% mature, and use running water and a roller brush to remove the peach hairs;

[0011] S2, soaking the peaches obtained in step S1 in alkali solution, peeling the peaches, and then washing them with running water until they are neutral;

[0012] S3, removing the core and cutting the peeled peach obtained in step S2 to obtain peach petals; then soaking the obtained peach petals in a low-esterification degree pectin-sucrose solution, and placing them in an electromagnetic field for electromagnetic treatment;

[0013] S4, soaking the peach petals after the electromagnetic treatment in step S3 in a calcium ion solution, performing vacuum treatment, and then washing the peach petals with deionized water to rinse off the liquid on the surface of the peach petals.

[0014] Furthermore, the parameters of the electromagnetic field in step S3 are set as follows: the magnetic induction electric field is set to a non-thermal effect mode of 100-200 V / cm, the excitation voltage is 500-700 V, the frequency is 50-70 kHz, the magnetic field intensity is 3-12 mT, and the intermittent treatment time is 20-40 min. After the electromagnetic penetration treatment, the low esterification degree pectin-sucrose solution can be effectively promoted to penetrate into the yellow peach pulp tissue, accelerate its distribution in the yellow peach tissue, and improve the uniformity of the treatment.

[0015] Furthermore, in step S3, the weight ratio of peach petals to the low-esterification degree pectin-sucrose solution is 5:1.

[0016] Furthermore, the preparation method of the low esterification degree pectin-sucrose solution in step S3 is as follows:

[0017] The light walnut pectin with an esterification degree of 28-45% is dissolved in a sucrose solution with a mass concentration of 15-26%, stirred evenly, and then adjusted to a pH of 3.0-4.0 with citric acid to obtain the product.

[0018] Furthermore, the mass concentration of light walnut pectin in the low-esterification degree pectin-sucrose solution is 1-5%.

[0019] Furthermore, the preparation method of the light walnut pectin comprises the following steps:

[0020] (1) washing and removing the cores of walnuts, beating the walnuts in a pulper, and then subjecting the walnuts to ultrasonic treatment to obtain walnut pulp;

[0021] (2) adding a sodium citrate solution having a mass concentration of 0.74% to the walnut pulp obtained in step (1), and then shaking and mixing in a constant temperature shaker;

[0022] (3) adjusting the pH of the mixed walnut pulp obtained in step (2) to 3 to 3.5, preferably 3.25, and then cooling it in an ice water bath;

[0023] (4) centrifuging the cooled walnut pulp in step (3), and then taking the supernatant for standby use;

[0024] (5) The supernatant obtained in step (4) is washed with acidified ethanol to obtain a precipitate, and the precipitate is centrifuged again. The precipitate is then washed with 95% ethanol until the washing liquid is neutral, and the precipitate is then centrifuged again. The precipitate is placed in an oven to dry, thereby obtaining light walnut pectin.

[0025] Furthermore, the ultrasonic frequency in step (1) is 20 kHz, and the ultrasonic treatment time is 25 to 35 min.

[0026] Furthermore, in the step (2), the addition ratio of the light walnut pulp to the sodium citrate solution is 1 g:10 mL, the shaking time is 3 to 4 hours, and the temperature during shaking is 45 to 55°C.

[0027] Furthermore, the cooling time in step (3) is 25 to 35 minutes.

[0028] Furthermore, the preparation method of the acidified ethanol in step (5) is: slowly add 0.04% hydrochloric acid by mass to an ethanol solution with a mass concentration of 95%, and stir evenly to obtain the acidified ethanol.

[0029] Furthermore, the drying temperature in step (5) is 40° C., and the drying time is 10 to 12 hours.

[0030] Furthermore, the rotation speed during centrifugation in step (4) and step (5) is 10000 rpm, and the centrifugation time for each time is 10 minutes.

[0031] Furthermore, the esterification degree of the light walnut pectin obtained in step (5) is 28-45%.

[0032] Furthermore, the alkali solution in step S2 is a sodium hydroxide solution with a mass concentration of 8-12%.

[0033] Furthermore, the calcium ion solution in step S4 is a calcium chloride solution with a mass concentration of 1 to 3%.

[0034] Furthermore, in the step S4, the temperature during the vacuum treatment is 50° C., the vacuum degree is 0.08 MPa, and the treatment time is 10 to 20 minutes.

[0035] The core of the method for hardening canned peaches provided by the present invention is to add the low-esterification degree pectin (light walnut pectin) specially prepared by the present invention into a sucrose solution, and make full use of its unique property of combining with calcium ions to form a gel under acidic conditions. This property enables the pectin-sucrose composite system to construct a stable three-dimensional network structure inside the peach petals, thereby effectively enhancing the hardness of canned peaches, while retaining their natural flavor, and avoiding the flavor loss problem that may be caused by traditional hardeners (such as pectin esterase).

[0036] In order to ensure that sucrose and low-esterification pectin enter the peach petals in large quantities, the present invention creatively designs the production process flow: first, the concentration of light walnut pectin and sucrose solution with a specific esterification degree is selected, and the peach petals are immersed in the low-esterification pectin-sucrose solution that has been acidified, and then the electromagnetic field treatment technology is introduced. Under specific electromagnetic field treatment conditions, the low-esterification pectin-sucrose solution is effectively promoted to infiltrate the peach petal tissue in large quantities. Compared with traditional soaking or injection methods, the effect of the electromagnetic field can significantly improve the penetration efficiency of the solution and ensure that pectin and sucrose are evenly distributed inside the peach petals. This technology not only speeds up the processing speed, but also avoids mechanical damage to the pulp tissue. It provides more ideal conditions for subsequent gel formation and further alleviates the phenomenon of reduced hardness of canned peaches during processing.

[0037] Calcium ions are then added using vacuum technology to avoid the problem of gel formation on the outside due to premature addition of calcium ions, which would result in ineffective hardening of the pulp tissue. This critical step ensures that the pectin-sucrose-Ca 2+ The system undergoes cross-linking reaction only inside the peach petals, forming a gel network that supports the pulp.

[0038] Compared with the prior art, the method for improving the hardness of canned peaches provided by the present invention has the following advantages:

[0039] (1) The method for improving the hardness of canned peaches provided by the present invention can play a supporting role inside the yellow peach by adding natural low-esterification degree pectin to a sucrose solution and utilizing the characteristic that low-esterification degree pectin forms a gel with sugar and calcium ions under acidic conditions, thereby effectively alleviating the problem of reduced hardness caused by softening of the cell wall. At the same time, the present invention uses low-esterification degree pectin extracted from walnuts as a functional additive for the first time. Since low-esterification degree pectin comes from natural plants, it will not have a negative impact on the flavor of canned peaches, thereby ensuring that the product retains its original characteristic flavor and quality while improving its hardness, avoiding the use of artificial synthetic chemicals, and improving the safety of the product.

[0040] (2) The present invention strictly follows the steps of acidification of the impregnation solution and vacuum treatment of the calcium solution to prevent the pectin-sucrose from forming gel on the outside due to the early addition of calcium ions, thereby failing to harden the pulp tissue.

[0041] (3) The present invention also creatively introduces electromagnetic field treatment technology. Under specific electromagnetic field treatment conditions, it can effectively promote the large-scale entry of pectin and sucrose into yellow peaches without excessively destroying the tissue structure, ensuring the pectin-sucrose-Ca 2+ The system forms a gel inside the pulp to support the pulp tissue, thereby achieving the purpose of improving the hardness of canned peaches. DETAILED DESCRIPTION

[0042] The present invention is further illustrated below through the description of specific implementation methods, but this is not a limitation of the present invention. Those skilled in the art can make various modifications or improvements based on the basic idea of ​​the present invention, but as long as they do not deviate from the basic idea of ​​the present invention, they are all within the protection scope of the present invention.

[0043] In the following examples and comparative examples, reagents not otherwise specified are conventional reagents and can be purchased from conventional reagent production and sales companies. The methods used, unless otherwise specified, are all existing technologies. Information such as some raw material manufacturers is as follows:

[0044] Sucrose (Shandong Rizhao Lingxue Co., Ltd.); sodium hydroxide (Sinopharm Chemical Reagent Beijing Co., Ltd., analytical grade); calcium chloride (Sinopharm Chemical Reagent Beijing Co., Ltd., analytical grade); pectinesterase (product model P5400-1KU, Sigma-Aldrich, purchased from Jiuqu (Hainan) Technology Co., Ltd.).

[0045] Example 1

[0046] A method for improving the hardness of canned peaches, comprising the following preparation steps:

[0047] S1. Select fresh, insect-free, mechanically-free yellow-fleshed peaches that are 70% mature, and use running water and a roller brush to remove the peach hairs;

[0048] S2, soaking the peaches obtained in step S1 in an 8% sodium hydroxide alkaline solution, peeling the peaches, and then washing them with running water until they are neutral;

[0049] S3, remove the core of the peeled peach obtained in step S2, cut it into 2 petals, and obtain peach petals, soak them in a low-esterification pectin-sucrose solution, the mass ratio of the peach petals to the low-esterification pectin-sucrose solution is 5:1; then place them in an electromagnetic field for electromagnetic treatment, set the magnetic induction electric field to a non-thermal effect mode of 200V / cm, the excitation voltage is 700V, the frequency is 55kHz, the magnetic field intensity is 10mT, and the intermittent treatment time is 20min. After electromagnetic treatment, it can effectively promote the low-esterification pectin-sucrose solution to penetrate into the yellow peach pulp tissue, accelerate its distribution in the yellow peach tissue, and improve the uniformity of the treatment;

[0050] The preparation method of the low esterification degree pectin-sucrose solution in step S3 is as follows:

[0051] Dissolve walnut pectin with an esterification degree of 28% in a sucrose solution with a mass concentration of 25%, stir evenly, and then adjust the pH to 3.0 with citric acid to obtain the product; the mass concentration of walnut pectin in the low esterification degree pectin-sucrose solution is 5%;

[0052] S4. Soak the peach petals after the electromagnetic treatment in step S3 in a calcium chloride ion solution with a mass concentration of 2.5%, and vacuum treat them for 15 minutes at a temperature of 50° C. and a vacuum degree of 0.08 MPa, and then rinse off the liquid on the surface of the peach petals with deionized water.

[0053] The method for preparing the light walnut pectin used in step S3 comprises the following steps:

[0054] (1) Wash and remove the core of the walnuts, put them in a pulper for pulping, and then perform ultrasonic treatment at an ultrasonic frequency of 20 kHz for 25 minutes to obtain walnut pulp;

[0055] (2) adding a sodium citrate solution with a mass concentration of 0.74% to the walnut pulp obtained in step (1), wherein the ratio of the walnut pulp to the sodium citrate solution is 1 g:10 mL, and then shaking in a constant temperature shaker at a temperature of 45° C. for 3 h to mix;

[0056] (3) adjusting the pH of the mixed walnut paste obtained in step (2) to 3 with citric acid, and then cooling the mixture in an ice water bath for 25 minutes;

[0057] (4) centrifuging the cooled walnut pulp in step (3) at 10,000 rpm for 10 min, and then taking the supernatant for standby use;

[0058] (5) The supernatant obtained in step (4) is washed with acidified ethanol (ethanol with a mass concentration of 95%, and the amount of hydrochloric acid added is 0.04% of the total weight of ethanol), centrifuged again, and then the precipitate is washed with ethanol with a mass concentration of 95% until the washing liquid is neutral, and then centrifuged again, and the precipitate is placed in an oven at a temperature of 40° C. and dried for 10 hours to obtain light walnut pectin.

[0059] The rotation speed of the two centrifugations in step (5) is 10000 rpm and the time is 10 min.

[0060] Example 2

[0061] A method for improving the hardness of canned peaches, comprising the following preparation steps:

[0062] S1. Select fresh, insect-free, mechanically-free yellow-fleshed peaches that are 70% mature, and use running water and a roller brush to remove the peach hairs;

[0063] S2, soaking the peaches obtained in step S1 in a sodium hydroxide solution with a mass concentration of 10%, peeling the peaches, and then washing them with running water until they are neutral;

[0064] S3, remove the core of the peeled peach obtained in step S2, cut it into 2 petals, and obtain peach petals, soak them in a low-esterification pectin-sucrose solution, the mass ratio of the peach petals to the low-esterification pectin-sucrose solution is 5:1; then place them in an electromagnetic field for electromagnetic treatment, set the magnetic induction electric field to a non-thermal effect mode of 100V / cm, the excitation voltage is 600V, the frequency is 65kHz, the magnetic field intensity is 8mT, and the intermittent treatment time is 30min. After electromagnetic penetration treatment, it can effectively promote the low-esterification pectin-sucrose solution to penetrate into the yellow peach pulp tissue, accelerate its distribution in the yellow peach tissue, and improve the uniformity of the treatment;

[0065] The preparation method of the low esterification degree pectin-sucrose solution in step S3 is as follows:

[0066] Dissolve walnut pectin with an esterification degree of 33% in a sucrose solution with a mass concentration of 18%, stir evenly, and then adjust the pH to 3.5 with citric acid to obtain the product; the mass concentration of walnut pectin in the low esterification degree pectin-sucrose solution is 3%;

[0067] S4. Soak the peach petals after the electromagnetic treatment in step S3 in a calcium chloride ion solution with a mass concentration of 2.5%, and vacuum treat them for 15 minutes at a temperature of 50° C. and a vacuum degree of 0.08 MPa, and then rinse off the liquid on the surface of the peach petals with deionized water.

[0068] The method for preparing the light walnut pectin used in step S3 comprises the following steps:

[0069] (1) Wash and remove the core of the walnuts, put them in a pulper for pulping, and then perform ultrasonic treatment at an ultrasonic frequency of 20 kHz for 35 minutes to obtain walnut pulp;

[0070] (2) adding a sodium citrate solution with a mass concentration of 0.74% to the walnut pulp obtained in step (1), wherein the ratio of the walnut pulp to the sodium citrate solution is 1 g:10 mL, and then shaking in a constant temperature oscillator at a temperature of 55° C. for 4 h to mix;

[0071] (3) adjusting the pH of the mixed walnut paste obtained in step (2) to 3.5 with citric acid, and then cooling the mixture in an ice water bath for 35 minutes;

[0072] (4) centrifuging the cooled walnut pulp in step (3) at 10,000 rpm for 10 min, and then taking the supernatant for standby use;

[0073] (5) The supernatant obtained in step (4) is washed with acidified ethanol (ethanol with a mass concentration of 95%, and the amount of hydrochloric acid added is 0.04% of the total weight of ethanol), centrifuged again, and then the precipitate is washed with ethanol with a mass concentration of 95% until the washing liquid is neutral, and then centrifuged again, and the precipitate is placed in an oven at a temperature of 40° C. and dried for 12 hours to obtain light walnut pectin.

[0074] The rotation speed of the two centrifugations in step (5) is 10000 rpm and the time is 10 min.

[0075] Example 3

[0076] A method for improving the hardness of canned peaches, comprising the following preparation steps:

[0077] S1. Select fresh, insect-free, mechanically-free yellow-fleshed peaches that are 70% mature, and use running water and a roller brush to remove the peach hairs;

[0078] S2, soaking the peaches obtained in step S1 in a sodium hydroxide solution with a mass concentration of 12%, peeling the peaches, and then washing them with running water until they are neutral;

[0079] S3, remove the core of the peeled peach obtained in step S2, cut it into 4 petals, obtain peach petals, soak them in a low esterification degree pectin-sucrose solution, the mass ratio of the peach petals to the low esterification degree pectin-sucrose solution is 5:1; then place them in an electromagnetic field for electromagnetic treatment, set the magnetic induction electric field to a non-thermal effect mode of 200V / cm, the excitation voltage is 700V, the frequency is 60kHz, the magnetic field intensity is 6mT, and the intermittent treatment time is 20min. After electromagnetic penetration treatment, it can effectively promote the low esterification degree pectin-sucrose solution to penetrate into the yellow peach pulp tissue, accelerate its distribution in the yellow peach tissue, and improve the uniformity of the treatment;

[0080] The preparation method of the low esterification degree pectin-sucrose solution in step S3 is as follows:

[0081] Dissolve walnut pectin with an esterification degree of 37% in a sucrose solution with a mass concentration of 15%, stir evenly, and then adjust the pH to 3.5 with citric acid to obtain the product; the mass concentration of walnut pectin in the low esterification degree pectin-sucrose solution is 2.5%;

[0082] S4. Soak the peach petals after the electromagnetic treatment in step S3 in a calcium chloride ion solution with a mass concentration of 2%, and vacuum treat them for 15 minutes at a temperature of 50° C. and a vacuum degree of 0.08 MPa, and then rinse off the liquid on the surface of the peach petals with deionized water.

[0083] The method for preparing the light walnut pectin used in step S3 comprises the following steps:

[0084] (1) Wash and remove the core of the walnuts, put them in a pulper for pulping, and then perform ultrasonic treatment at an ultrasonic frequency of 20 kHz for 32 minutes to obtain walnut pulp;

[0085] (2) adding a sodium citrate solution with a mass concentration of 0.74% to the walnut pulp obtained in step (1), wherein the addition ratio of the walnut pulp to the sodium citrate solution is 1 g:10 mL, and then shaking in a constant temperature oscillator at a temperature of 53° C. for 3.5 h to mix;

[0086] (3) adjusting the pH of the mixed walnut paste obtained in step (2) to 3.25 with citric acid, and then cooling the mixture in an ice water bath for 30 minutes;

[0087] (4) centrifuging the cooled walnut pulp in step (3) at 10,000 rpm for 10 min, and then taking the supernatant for standby use;

[0088] (5) The supernatant obtained in step (4) is washed with acidified ethanol (ethanol with a mass concentration of 95%, and the amount of hydrochloric acid added is 0.04% of the total weight of ethanol), centrifuged again, and then the precipitate is washed with ethanol with a mass concentration of 95% until the washing liquid is neutral, and then centrifuged again, and the precipitate is placed in an oven at a temperature of 40° C. and dried for 11 hours to obtain light walnut pectin.

[0089] The rotation speed of the two centrifugations in step (5) is 10000 rpm and the time is 10 min.

[0090] Example 4

[0091] A method for improving the hardness of canned peaches, comprising the following preparation steps:

[0092] S1. Select fresh, insect-free, mechanically-free yellow-fleshed peaches that are 70% mature, and use running water and a roller brush to remove the peach hairs;

[0093] S2, soaking the peaches obtained in step S1 in a sodium hydroxide solution with a mass concentration of 10%, peeling the peaches, and then washing them with running water until they are neutral;

[0094] S3, remove the core of the peeled peach obtained in step S2, cut it into 4 petals, and obtain peach petals, soak them in a low-esterification pectin-sucrose solution, the mass ratio of the peach petals to the low-esterification pectin-sucrose solution is 5:1; then place them in an electromagnetic field for electromagnetic treatment, set the magnetic induction electric field to a non-thermal effect mode of 200V / cm, the excitation voltage is 500V, the frequency is 60kHz, the magnetic field intensity is 3mT, and the intermittent treatment time is 28min. After electromagnetic penetration treatment, it can effectively promote the low-esterification pectin-sucrose solution to penetrate into the yellow peach pulp tissue, accelerate its distribution in the yellow peach tissue, and improve the uniformity of the treatment;

[0095] The preparation method of the low esterification degree pectin-sucrose solution in step S3 is as follows:

[0096] The method comprises dissolving 45% esterification degree light walnut pectin in a 20% mass concentration sucrose solution, stirring evenly, and then adjusting the pH to 4.0 with citric acid to obtain the product; the mass concentration of the light walnut pectin in the low esterification degree pectin-sucrose solution is 1%.

[0097] S4. Soak the peach petals after the electromagnetic treatment in step S3 in a calcium chloride ion solution with a mass concentration of 3%, and vacuum treat them for 10 minutes at a temperature of 50° C. and a vacuum degree of 0.08 MPa. Then, rinse off the liquid on the surface of the peach petals with deionized water.

[0098] The method for preparing the light walnut pectin used in step S4 comprises the following steps:

[0099] (1) Wash and remove the core of the walnuts, put them in a pulper for pulping, and then perform ultrasonic treatment at an ultrasonic frequency of 20 kHz for 30 minutes to obtain walnut pulp;

[0100] (2) adding a sodium citrate solution with a mass concentration of 0.74% to the walnut pulp obtained in step (1), wherein the ratio of the walnut pulp to the sodium citrate solution is 1 g:10 mL, and then shaking in a constant temperature oscillator at a temperature of 50° C. for 3.5 h to mix;

[0101] (3) adjusting the pH of the mixed walnut paste obtained in step (2) to 3.25 with citric acid, and then cooling the mixture in an ice water bath for 30 minutes;

[0102] (4) centrifuging the cooled walnut pulp in step (3) at 10,000 rpm for 10 min, and then taking the supernatant for standby use;

[0103] (5) The supernatant obtained in step (4) is washed with acidified ethanol (ethanol with a mass concentration of 95%, and the amount of hydrochloric acid added is 0.04% of the total weight of ethanol), centrifuged again, and then the precipitate is washed with ethanol with a mass concentration of 95% until the washing liquid is neutral, and then centrifuged again, and the precipitate is placed in an oven at a temperature of 40° C. and dried for 12 hours to obtain light walnut pectin.

[0104] The rotation speed of the two centrifugations in step (5) is 10000 rpm and the time is 10 min.

[0105] Comparative Example 1

[0106] Compared with Example 4, the difference is that the process of electromagnetic field treatment of peach petals in low esterification degree pectin-sucrose solution in step S2 of the present invention is not adopted in Comparative Example 1, and other parameters and operations are the same as those in Example 4.

[0107] Specifically, the method for improving the hardness of canned peaches in Comparative Example 1 comprises the following preparation steps:

[0108] S1. Select fresh, insect-free, mechanically-free yellow-fleshed peaches that are 70% mature, and use running water and a roller brush to remove the peach hairs;

[0109] S2, soaking the peaches obtained in step S1 in a sodium hydroxide solution with a mass concentration of 10%, peeling the peaches, and then washing them with running water until they are neutral;

[0110] S3. Soak the peach petals obtained in step S3 in a calcium chloride ion solution with a mass concentration of 3%, vacuum treat for 10 minutes at a temperature of 50° C. and a vacuum degree of 0.08 MPa, and then rinse off the liquid on the surface of the peach petals with deionized water.

[0111] Comparative Example 2

[0112] Compared with Example 4, the difference is that in step S3, after the peach petals are immersed in the low-esterification degree pectin-sucrose solution, no electromagnetic field treatment is performed, and other parameters and operations are the same as those in Example 4.

[0113] Specifically, the method for improving the hardness of canned peaches in Comparative Example 2 comprises the following preparation steps:

[0114] S1. Select fresh, insect-free, mechanically-free yellow-fleshed peaches that are 70% mature, and use running water and a roller brush to remove the peach hairs;

[0115] S2, soaking the peaches obtained in step S1 in a sodium hydroxide solution with a mass concentration of 10%, peeling the peaches, and then washing them with running water until they are neutral;

[0116] S3, removing the core of the peeled peach obtained in step S2, cutting it into 4 petals to obtain peach petals, and then soaking the peach petals in a low-esterification degree pectin-sucrose solution for 35 minutes, wherein the mass ratio of the peach petals to the low-esterification degree pectin-sucrose solution is 5:1;

[0117] The preparation method of the low esterification degree pectin-sucrose solution in step S4 is as follows:

[0118] Dissolve walnut pectin with an esterification degree of 45% in a sucrose solution with a mass concentration of 20%, stir evenly, and then adjust the pH to 4.0 with citric acid to obtain the product; the mass concentration of walnut pectin in the low esterification degree pectin-sucrose solution is 1%;

[0119] S4, soaking the peach petals obtained in step S3 in a calcium chloride ion solution with a mass concentration of 3%, vacuum treating for 10 minutes at a temperature of 50°C and a vacuum degree of 0.08MPa, and then rinsing the liquid on the surface of the peach petals with deionized water to obtain the product.

[0120] The preparation method of light walnut pectin used in step S4 is the same as that in Example 4.

[0121] Comparative Example 3

[0122] Compared with Example 4, the difference is that in Comparative Example 3, the steps of soaking in a low-esterification pectin-sucrose solution and subjecting to electromagnetic field treatment in the present invention are not adopted, but pectinesterase combined with electromagnetic field treatment is used to treat the peach petals, and other parameters and operations are the same as those in Example 4.

[0123] Specifically, the method for improving the hardness of canned peaches in Comparative Example 3 comprises the following preparation steps:

[0124] S1. Select fresh, insect-free, mechanically-free yellow-fleshed peaches that are 70% mature, and use running water and a roller brush to remove the peach hairs;

[0125] S2, soaking the peaches obtained in step S1 in a sodium hydroxide solution with a mass concentration of 10%, peeling the peaches, and then washing them with running water until they are neutral;

[0126] S3, removing the core of the peeled peach obtained in step S2, cutting it into 4 petals to obtain peach petals, soaking it in a pectin esterase solution with a mass concentration of 0.4 mL / Kg, and then placing it in an electromagnetic field for electromagnetic treatment, setting the magnetic induction electric field to a non-thermal effect mode of 200 V / cm, an excitation voltage of 500 V, a frequency of 60 kHz, a magnetic field intensity of 3 mT, and an intermittent treatment time of 28 min;

[0127] S5. Soak the peach petals obtained in step S4 in a calcium chloride ion solution with a mass concentration of 3%, vacuum treat for 10 minutes at a temperature of 50° C. and a vacuum degree of 0.08 MPa, and then rinse off the liquid on the surface of the peach petals with deionized water.

[0128] Comparative Example 4

[0129] Compared with Example 4, the difference is that in step S2, the light walnut pectin with an esterification degree of 45% prepared in the present invention is not used, but is replaced by commercially available pectin with an esterification degree of 65% (product CAS number is 9000-69-5, item number is S11082, purchased from Shanghai Yuanye Biotechnology Co., Ltd.), and other parameters and operations are the same as those in Example 4.

[0130] Comparative Example 5

[0131] Compared with Example 4, the difference is that the parameter settings of the electromagnetic field treatment in step S3 are: the magnetic induction electric field is set to a non-thermal effect mode of 250 V / cm, the excitation voltage is 500 V, the frequency is 80 kHz, the magnetic field intensity is 3 mT, the intermittent treatment time is 35 min, and the other parameters and operations are the same as those in Example 4.

[0132] Test Example 1: Performance Testing

[0133] 1. Test materials: peach petals prepared by the methods of Examples 1 to 4 and Comparative Examples 1 to 5 of the present invention.

[0134] 2. Test methods:

[0135] (1) Hardness (g): The hardness of the can was measured using a texture analyzer. The test results are shown in Table 2.

[0136] (2) Carotenoids (mg / 100g): tested according to the method in GB 5009.83-2016 “National Food Safety Standard Determination of Carotene in Food”. The test results are shown in Table 2.

[0137] (3) Vitamin C (mg / 100g): The test was conducted according to the method in GB5009.86-2016 “National Food Safety Standard Determination of Ascorbic Acid in Food”. The test results are shown in Table 2.

[0138] (4) Sensory evaluation: A 10-member evaluation panel was formed to evaluate the hardness (50 portions) and taste and flavor (50 portions) of the peach segments prepared in Examples 1 to 4 of the present invention and Comparative Examples 1 to 5, respectively. The evaluation criteria and scores are shown in Table 1. The average scores of each group were calculated, and the results are shown in Table 3.

[0139] Table 1

[0140]

[0141] Table 2

[0142]

[0143]

[0144] Table 3

[0145]

[0146] It can be seen from Tables 2 and 3 that the peach segments prepared by the method for improving the hardness of canned peaches provided by Examples 1 to 4 of the present invention have a hardness of 28.73 to 33.37 g, a carotenoid content of 1.33 to 1.49 mg / 100 g, and a vitamin C content of 258.33 to 273.21 mg / 100 g, which are significantly higher than those of the comparative example group, indicating that the preparation method provided by the present invention effectively solves the problem of reduced hardness of canned yellow peaches during processing, and can also effectively retain the nutrients of the yellow peaches themselves without loss, and the sensory evaluation is above 94 points.

[0147] In Comparative Examples 1 to 4, when the preparation method provided by the present invention is changed or the process parameters in the preparation process are changed, the hardness of the obtained peach petals is significantly reduced, and the content of carotenoids and vitamin C is insufficient; and the peach petals in Comparative Example 3 have obvious odor, and when conventional commercially available pectin is used in Comparative Example 4, the texture of the obtained peach petals is very soft, indicating that the conventional commercially available pectin cannot penetrate into the pulp and the hardening effect is not obvious; when the parameters of the electromagnetic treatment are changed in Comparative Example 5, the hardness of the peach petals is abnormally increased, the texture is hard, and the excessively high electromagnetic field parameters cause serious damage to the pulp tissue, and the carotenoids and VC are significantly reduced.

[0148] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A method for improving the firmness of peaches for canning, characterized in that: The method comprises the following preparation steps: S1. Select fresh, insect-free, mechanically-free yellow-fleshed peaches that are 70% mature, and remove the peach hairs; S2, soaking the peaches obtained in step S1 in alkali solution, peeling the peaches, and then washing them with running water until they are neutral; S3, removing the core and cutting the peeled peach obtained in step S2 to obtain peach petals; then soaking the obtained peach petals in a low-esterification degree pectin-sucrose solution, and placing them in an electromagnetic field for electromagnetic treatment; S4, soaking the peach petals after the electromagnetic treatment in step S3 in a calcium ion solution, performing vacuum treatment, and then washing the peach petals with deionized water.

2. The method for improving the firmness of canned peaches according to claim 1, characterized in that: In step S3, the parameters of the electromagnetic field are set as follows: the magnetic induction electric field is set to a non-thermal effect mode of 100-200 V / cm, the excitation voltage is 500-700 V, the frequency is 50-70 kHz, the magnetic field strength is 3-12 mT, and the intermittent treatment time is 20-40 min.

3. The method for improving the firmness of canned peaches according to claim 1, characterized in that: In step S3, the weight ratio of peach segments to the low-esterification degree pectin-sucrose solution is 5:

1.

4. The method for improving the firmness of canned peaches according to claim 1, characterized in that: The preparation method of the low esterification degree pectin-sucrose solution in step S3 is as follows: dissolving walnut pectin with an esterification degree of 28-45% in a sucrose solution with a mass concentration of 15-26%, stirring evenly, and then adjusting the pH to 3.0-4.0 with citric acid to obtain the solution.

5. The method for improving the firmness of canned peaches according to claim 4, characterized in that: The preparation method of the light walnut pectin comprises the following steps: (1) washing and removing the cores of walnuts, beating the walnuts in a pulper, and then subjecting the walnuts to ultrasonic treatment to obtain walnut pulp; (2) adding a sodium citrate solution having a mass concentration of 0.74% to the walnut pulp obtained in step (1), and then shaking and mixing in a constant temperature shaker; (3) adjusting the pH of the mixed walnut pulp obtained in step (2) to 3 to 3.5, and then cooling it in an ice water bath; (4) centrifuging the cooled walnut pulp in step (3), and then taking the supernatant for standby use; (5) The supernatant obtained in step (4) is washed with acidified ethanol to obtain a precipitate, and the precipitate is centrifuged again. The precipitate is then washed with 95% ethanol until the washing liquid is neutral, and the precipitate is then centrifuged again. The precipitate is placed in an oven to dry, thereby obtaining light walnut pectin.

6. The method for improving the firmness of canned peaches according to claim 5, characterized in that: The ultrasonic frequency in step (1) is 20 kHz, and the ultrasonic treatment time is 25 to 35 minutes.

7. The method for improving the firmness of canned peaches according to claim 5, characterized in that: The addition ratio of the walnut pulp to the sodium citrate solution in the step (2) is 1 g:10 mL, the shaking time is 3 to 4 hours, and the temperature during shaking is 45 to 55° C.

8. The method for improving the firmness of canned peaches according to claim 5, characterized in that: The rotation speed during centrifugation in step (4) and step (5) is 10000 rpm, and the centrifugation time for each time is 10 minutes.

9. The method for improving the firmness of canned peaches according to claim 1, characterized in that: The alkali solution in step S2 is a sodium hydroxide solution with a mass concentration of 8-12%; the calcium ion solution in step S4 is a calcium chloride solution with a mass concentration of 1-3%.

10. The method for improving the firmness of canned peaches according to claim 1, characterized in that: The temperature during the vacuum treatment in step S4 is 50° C., the vacuum degree is 0.08 MPa, and the treatment time is 10 to 20 minutes.

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