A method for processing preserved mustard greens

Abstract

The present invention belongs to the technical field of food processing, and particularly relates to a method for processing preserved mustard greens. The method for processing preserved mustard greens is as follows: Wash fresh mustard greens, drain them, blanch them, dry them, steam them, then put them into a pickling pool, add salt and a treatment liquid, and ferment for 10 days at a temperature of 10 - 25°C. After pickling, take them out, add water for pulse treatment, then soak for 20 - 30 minutes, take them out, drain, and perform vacuum freeze-drying to obtain the product. The method for processing preserved mustard greens provided by the present invention can significantly reduce the nitrite content generated during the pickling process and reduce the salt content of the preserved mustard greens, thereby ensuring the quality and safety of the preserved mustard greens and effectively reducing the harm of nitrite and high salt to people. Moreover, the preserved mustard greens prepared by the present invention have unchanged color, are light green, have a rich taste, and have good rehydration property, and it is an ideal method for processing preserved mustard greens.

Description

Technical Field

[0001] The present invention belongs to the technical field of food processing, and particularly relates to a method for processing preserved mustard greens. Background Art

[0002] Preserved mustard greens are mainly made from fresh mustard greens through processes such as sun drying, pickling, and desalting. Preserved mustard greens are rich in potassium, calcium, magnesium, phosphorus, glutamic acid, etc. Potassium helps the human body maintain blood pressure and respiratory metabolism. Calcium plays an important role in the development of human bones and preventing osteoporosis. Magnesium can play a certain role in reducing the occurrence of cardiovascular diseases in the human body. Phosphorus is an important component element of human cells. Preserved mustard greens are rich in amino acids, and the content of essential amino acids is also relatively high, making it a food with relatively high nutritional value.

[0003] Nitrite is a precursor of the strong carcinogen nitrosamine. The nitrite content in preserved mustard greens will increase rapidly after pickling. Research shows that the detection rate of nitrite in pickled vegetables is as high as 94.7%. With the increasing attention of people to health, low-nitrite and low-salt foods are favored by more and more people, and the demand for low-nitrite and low-salt preserved mustard greens is also increasing continuously. Therefore, how to achieve low-salinity of preserved mustard greens and effectively reduce the nitrite content in preserved mustard greens during the production and processing process is an urgent problem to be solved. Achieving low-salinity and low-nitrite content of preserved mustard greens will be an important trend in the development of preserved mustard greens.

[0004] Patent document CN103610003A discloses a method for pickling preserved mustard greens. This method uses mustard greens as raw materials and pickles them twice with salt, and adds green tea extract to ferment together during the second pickling process. A process of desalinated water is also included between the two picklings. This method can reduce the nitrite content during pickling; the preserved mustard greens obtained by this method can reduce the addition of artificial antioxidants for the subsequent processing of instant preserved mustard greens products, reducing production costs; in addition, due to the addition of green tea extract, the pickled preserved mustard greens can also have the fragrance of tea and a special taste.

[0005] Patent document CN104286741A discloses a method for preparing preserved mustard greens, including the following steps: harvesting fresh preserved mustard greens, removing the roots and rotten leaves, blanching, sun drying, fermenting and pickling, and dehydrating to obtain preserved mustard greens. Before fermentation, a bitter taste remover composed of salt, old brine, white wine, brown sugar, and glycyrrhizin is also added. At the same time, 5% - 14% of Lactobacillus plantarum or Lactobacillus casei is inoculated for fermentation, and a nitrite inhibitor composed of vitamin C, tea polyphenols, citric acid, glucose, and green tea powder is also added. The preserved mustard greens prepared by this method for preparing preserved mustard greens have good color, flavor, crispness, and are rich in nutrition and health care functions. In addition, the nitrite content of the above-mentioned preserved mustard greens is relatively low, ensuring the health of consumers.

[0006] However, although the current processing method of preserved mustard can make the nitrite content of the prepared preserved mustard lower than the national limit (<20 mg / kg) by adding nitrite inhibitors, most of the preserved mustard products are close to the national nitrate limit. The main reason is that most of the externally added nitrite inhibitors can only reduce the nitrite in the pickling solution leached from the preserved mustard, and cannot fundamentally eliminate the nitrite in the preserved mustard itself. Moreover, the added inhibitors are generally antioxidants, with poor stability during the pickling process and unable to fully play the role of effectively reducing the nitrite content of the preserved mustard. Summary of the Invention

[0007] To solve the defects of the prior art, the present invention provides a processing method for preserved mustard, which is mainly improved in view of the technical defects of the poor stability of the existing nitrite inhibitors and the limited effect of externally added inhibitors on reducing the nitrite content. The present invention adopts a special preparation method to improve the stability of the nitrite inhibitor, which can well maintain the function of the nitrite inhibitor during the pickling process, significantly reduce the nitrite content during the pickling process. At the same time, the present invention also adopts a specific pulse treatment process to further reduce the nitrite content of the preserved mustard, making the nitrite content of the prepared preserved mustard far lower than the national standard, and greatly improving the safety of the preserved mustard food.

[0008] The processing method for preserved mustard provided by the present invention includes the following steps:

[0009] Step S1. Remove the roots, insect-eaten parts, damaged parts and crushed parts of the fresh mustard, wash, drain, then blanch at 85 - 95 °C for 1 - 3 min, drain, bake at 40 - 50 °C for 6 - 8 h, and then steam for 25 - 35 min to obtain pretreated mustard.

[0010] Step S2. Add xanthan gum to water and stir evenly, then add vitamin C and stir evenly. After standing for 5 - 8 min, add citric acid and stir evenly to obtain a treatment solution.

[0011] Step S3. Put the pretreated mustard obtained in Step S1 into a pickling pool, add salt and stir evenly. The addition amount of the salt is 6 - 8% of the mass of the pretreated mustard. Add water to the pickling pool to submerge the mustard, then add the treatment solution obtained in Step S2, stir evenly, seal, and ferment at 10 - 25 °C for 10 days to obtain pickled mustard.

[0012] Step S4. Add water to the pickled mustard obtained in Step S3, perform pulse treatment, then soak for 20 - 30 min. The material-liquid ratio of the pickled mustard to water is 1 g:2 mL. Lift it out, drain, and perform vacuum freeze-drying to obtain the product.

[0013] Further, the concentrations of the components in the treatment liquid in step S2 are as follows: xanthan gum 0.04 - 0.08 g / L, vitamin C 0.4 - 0.8 g / L, and citric acid 0.4 - 0.8 g / L.

[0014] Further, the concentrations of the components in the treatment liquid in step S2 are as follows: xanthan gum 0.05 g / L, vitamin C 0.6 g / L, and citric acid 0.6 g / L.

[0015] Further, the addition amount of the treatment liquid in step S3 is 4 - 6% of the mass of the pretreated mustard greens.

[0016] Further, the pulse treatment conditions in step S4 are as follows: high - voltage pulsed electric field treatment is adopted, the treatment temperature is 25 - 30 °C, the electric field strength is 20 - 30 kV / cm, the pulse width is 2 - 4 μs, the pulse frequency is 100 - 200 Hz, and the treatment time is 200 - 300 pulse numbers.

[0017] Further, the pulse treatment conditions in step S4 are as follows: high - voltage pulsed electric field treatment is adopted, the treatment temperature is 25 °C, the electric field strength is 30 kV / cm, the pulse width is 3 μs, the pulse frequency is 150 Hz, and the treatment time is 200 pulse numbers.

[0018] Further, the vacuum freeze - drying conditions in step S4 are as follows: the air pressure in the vacuum chamber is 8 - 15 kPa, the cold trap temperature is reduced to - 35 - 45 °C within 1 - 2 h, and the holding time is 40 - 60 min; the air pressure in the vacuum drying chamber is 3 - 5 kPa, and it is heated to 5 - 10 °C within 8 - 12 h, and the holding time is 2 - 3 h.

[0019] Further, the vacuum freeze - drying conditions in step S4 are as follows: the air pressure in the vacuum chamber is 12 kPa, the cold trap temperature is reduced to - 35 - 45 °C within 1 - 2 h, and the holding time is 40 - 60 min; the air pressure in the vacuum drying chamber is 4 kPa, and it is heated to 5 - 10 °C within 8 - 12 h, and the holding time is 2 - 3 h.

[0020] Currently, the most important problems in the deep processing of preserved mustard greens are the excessive content of nitrite and high salt content in pickled preserved mustard greens. The existing technologies generally solve the above problems by adding nitrite inhibitors and rinsing for desalting. However, nitrite inhibitors such as tea polyphenols, citric acid, and ascorbic acid, which are widely used, generally have poor stability and are easily degraded during the pickling process, and cannot guarantee the nitrite removal effect. Moreover, most of the externally added nitrite inhibitors have a significant effect on removing nitrite in the pickling liquid, but have a limited effect on removing nitrite in the preserved mustard greens themselves.

[0021] To solve the above technical problems, through a large number of exploratory experiments, the inventor came up with the idea of adding an emulsifier to improve the stability of nitrite inhibitors. However, considering that the pickling process is a high-salt, acidic, and oxygen-containing aqueous solution system, and nitrite inhibitors are generally strong antioxidants, the screening of stabilizers is very difficult. Not only the stability of the stabilizer itself needs to be considered, but also issues such as the stabilizing effect of the stabilizer on nitrite inhibitors need to be considered. The inventor screened a variety of salt-tolerant and acid-tolerant stabilizers. After a large number of exploratory experiments, it was determined that xanthan gum has the best stability in the pickling environment. However, when xanthan gum is mixed with vitamin C and citric acid to prepare a nitrite inhibitory solution, the nitrite scavenging effect on preserved vegetables increases, and the nitrite content is basically <10 mg / kg, which is lower than half of the national standard, but it does not reach the expected effect of the inventor.

[0022] After repeated experiments, the inventor unexpectedly found that the addition order of xanthan gum, vitamin C, and citric acid in the nitrite inhibitory solution has a great influence on the nitrite scavenging effect. The inventor first dissolved xanthan gum to prepare a xanthan gum aqueous solution, then added vitamin C first, and after standing for 5-8 minutes, added citric acid. The prepared nitrite inhibitory solution can effectively reduce the nitrite content in the pickled vegetable solution of preserved vegetables. The measured nitrite content dropped to 2 mg / kg, far lower than the national standard, greatly improving the safety of preserved vegetable food.

[0023] The inventor guessed the principle as follows: After dissolving xanthan gum into a uniform emulsion solution, adding vitamin C solution, the xanthan gum emulsion can fully wrap vitamin C. Then, adding citric acid, citric acid can be evenly distributed on the outer layer of the emulsion. When in use, the xanthan gum emulsion can quickly penetrate vitamin C and citric acid into the pickling solution, giving full play to the role of vitamin C and citric acid in scavenging nitrite. The specific scavenging effect may be that citric acid on the outer layer first reacts with nitrite to form nitrous acid, thus decomposing nitrite, and the H + can reduce NO2 - to NH 4+ , and then the encapsulated vitamin C can also stably and continuously reduce NO2 - to NH 4+ , accelerating the decomposition and elimination of nitrite.

[0024] In addition, to enhance the desalination effect, the inventor subjects the preserved mustard greens to pulsed and rinsed desalination. The pulsed treatment with specific parameters can not only reduce the salt content of the preserved mustard greens, but also further decrease the nitrite content. Additionally, it can achieve a sterilization effect, preventing the re-generation of nitrite by miscellaneous bacteria and extending the shelf life of the preserved mustard greens. The pulse frequency provided by the present invention is obtained by the inventor through extensive experiments. This pulsed treatment can fully disperse the preserved mustard greens, promote the dissolution of the surface salt, and at the same time, it can also dissolve the salt solution that has penetrated into the interior of the preserved mustard greens, dissociating the sodium chloride in the water into Na + and Cl - to flow directionally, thereby promoting the directional flow of salt, reducing the chance of salt coming into contact with the preserved mustard greens again, and achieving the effect of quickly and effectively eluting the salt. At the same time, it can also solve the problem that the prior art uses an acidic solution for rinsing, reducing the impact of the acidic aqueous solution on the taste and flavor of the preserved mustard greens.

[0025] Furthermore, the inventor found that the nitrite content in the preserved mustard greens themselves is also very high, and the externally added inhibitors have a poor effect on removing nitrite inside the preserved mustard greens. After pulsed treatment, the inventor unexpectedly found that the antioxidant components in the preserved mustard greens themselves also have a certain effect on removing nitrite. After the pulsed treatment provided by the present invention opens the hydrogen bonds of cellulose in the primary and secondary layers of the cell wall of the preserved mustard greens, the cell wall of the preserved mustard greens becomes loose, allowing the exudation of antioxidant components such as flavonoids, chlorophyll, and carotenoids. These antioxidant active ingredients can reduce the NO2 - of nitrite inside the preserved mustard greens to NH 4+ , achieving the effect of reducing the nitrite content inside the preserved mustard greens and further reducing the nitrite content of the preserved mustard greens.

[0026] In addition, the vacuum freeze-drying method with specific conditions used in the present invention for drying the preserved mustard greens can not only retain the thermosensitive nutrients and flavor substances in the preserved mustard greens, but also keep the product color unchanged, showing a light green color, and the product has good rehydration properties.

[0027] In summary, compared with the prior art, the preserved mustard greens processing method provided by the present invention has the following advantages:

[0028] (1) The preserved mustard greens processing method provided by the present invention can significantly reduce the nitrite content generated during the pickling process and reduce the salt content of the preserved mustard greens, thereby ensuring the quality and safety of the preserved mustard greens and effectively reducing the harm of nitrite and high salt to people;

[0029] (2) The preserved mustard greens prepared by the preserved mustard greens processing method provided by the present invention have an unchanged color, showing a light green color, a rich taste, and good rehydration properties, and it is an ideal method for processing preserved mustard greens. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a diagram of the preserved mustard greens prepared in Example 2 of the present invention. Detailed implementation manners

[0031] The present invention will be further described below through specific embodiments. The present invention is not limited to the following embodiments. Changes, combinations or substitutions made within the scope of the present invention or without departing from the content, spirit and scope of the present invention are obvious to those skilled in the art and are included in the scope of the present invention.

[0032] Embodiment 1, Method for processing preserved mustard greens

[0033] Step S1. Remove the root whiskers, worm-eaten parts, damaged parts and crushed parts of fresh Brassica juncea var. gracilis (produced in Kunming, Yunnan), wash, drain, then blanch at 95°C for 1 min, drain, bake at 40°C for 8 h, and then steam for 25 min to obtain pretreated mustard greens;

[0034] Step S2. Add xanthan gum to water and stir evenly, then add vitamin C and stir evenly. After standing for 5 min, add citric acid and stir evenly to obtain a treatment liquid. The concentrations of each component in the treatment liquid are: xanthan gum 0.06 g / L, vitamin C 0.8 g / L, and citric acid 0.8 g / L;

[0035] Step S3. Put the pretreated mustard greens prepared in Step S1 into a pickling tank, add salt and stir evenly. The addition amount of the salt is 6% of the mass of the pretreated mustard greens. Add water to the pickling tank to submerge the mustard greens, then add the treatment liquid prepared in Step S2. The addition amount of the treatment liquid is 4% of the mass of the pretreated mustard greens. Stir evenly, seal, and ferment at 10 - 25°C for 10 days to obtain pickled mustard greens;

[0036] Step S4. Add water to the pickled mustard greens prepared in Step S3, and after pulsed treatment, the pulsed treatment conditions are: using high-voltage pulsed electric field treatment, the treatment temperature is 25°C, the electric field strength is 20 kV / cm, the pulse width is 2 μs, the pulse frequency is 100 Hz, the treatment time is 200 pulse numbers, then soak for 20 min, fish out, drain, and perform vacuum freeze-drying. The vacuum freeze-drying conditions are: the air pressure in the vacuum chamber is 8 kPa, the cold trap temperature is reduced to -35°C within 1 h, and the holding time is 40 min; the air pressure in the vacuum drying chamber is 3 kPa, and it is heated to 5°C within 8 h, and the holding time is 2 h, thus obtaining.

[0037] Embodiment 2, Method for processing preserved mustard greens

[0038] Step S1. Remove the root whiskers, worm-eaten parts, damaged parts and crushed parts of fresh Brassica juncea var. gracilis (produced in Kunming, Yunnan), wash, drain, then blanch at 90°C for 2 min, drain, bake at 45°C for 7 h, and then steam for 30 min to obtain pretreated mustard greens;

[0039] Step S2. Add xanthan gum to water and stir evenly, then add vitamin C and stir evenly. After standing for 6 min, add citric acid and stir evenly to obtain a treatment liquid. The concentrations of each component in the treatment liquid are: xanthan gum 0.05 g / L, vitamin C 0.6 g / L, and citric acid 0.6 g / L;

[0040] Step S3. Put the pretreated mustard prepared in Step S1 into a pickling tank, add salt and stir evenly. The addition amount of the salt is 7% of the mass of the pretreated mustard. Add water to the pickling tank to submerge the mustard, then add the treatment liquid prepared in Step S2. The addition amount of the treatment liquid is 5% of the mass of the pretreated mustard. Stir evenly, seal, and ferment at 10 - 25 °C for 10 days to obtain pickled mustard;

[0041] Step S4. Add water to the pickled mustard prepared in Step S3, and after pulsed treatment, the pulsed treatment conditions are: using high - voltage pulsed electric field treatment, the treatment temperature is 25 °C, the electric field strength is 30 kV / cm, the pulse width is 3 μs, the pulse frequency is 150 Hz, the treatment time is 200 pulse numbers, then soak for 25 min. The material - liquid ratio of the pickled mustard to water is 1 g:2 mL. Fish out, drain, and perform vacuum freeze - drying. The vacuum freeze - drying conditions are: the air pressure in the vacuum chamber is 12 kPa, the cold trap temperature is reduced to - 40 °C within 1.5 h, and the holding time is 50 min; the air pressure in the vacuum drying chamber is 4 kPa, and it is heated to 8 °C within 10 h, and the holding time is 2 h, thus obtaining the product.

[0042] Example 3. Method for processing preserved mustard greens

[0043] Step S1. Remove the root whiskers, parts eaten by insects, damaged, and crushed parts of fresh Brassica juncea var. gracilis (produced in Kunming, Yunnan), wash, drain, then blanch at 85 °C for 3 min, drain, bake at 50 °C for 6 h, and then steam for 35 min to obtain pretreated mustard;

[0044] Step S2. Add xanthan gum to water and stir evenly, then add vitamin C and stir evenly. After standing for 8 min, add citric acid and stir evenly to obtain a treatment liquid. The concentrations of each component in the treatment liquid are: xanthan gum 0.04 g / L, vitamin C 0.4 g / L, and citric acid 0.4 g / L;

[0045] Step S3. Put the pretreated mustard prepared in Step S1 into a pickling tank, add salt and stir evenly. The addition amount of the salt is 8% of the mass of the pretreated mustard. Add water to the pickling tank to submerge the mustard, then add the treatment liquid prepared in Step S2. The addition amount of the treatment liquid is 6% of the mass of the pretreated mustard. Stir evenly, seal, and ferment at 10 - 25 °C for 10 days to obtain pickled mustard;

[0046] Step S4. Add water to the pickled mustard prepared in Step S3, and after pulsed treatment, the pulsed treatment conditions are as follows: high-voltage pulsed electric field treatment is adopted, the treatment temperature is 30°C, the electric field strength is 30 kV / cm, the pulse width is 4 μs, the pulse frequency is 200 Hz, the treatment time is 300 pulse numbers, then soak for 20 min, the material-liquid ratio of the pickled mustard to water is 1 g: 2 mL, fish out, drain, and perform vacuum freeze-drying. The vacuum freeze-drying conditions are as follows: the air pressure in the vacuum chamber is 12 kPa, the cold trap temperature is reduced to -45°C within 2 h, and the holding time is 55 min; the air pressure in the vacuum drying chamber is 5 kPa, and it is heated to 10°C within 8 h, and the holding time is 3 h, thus obtaining.

[0047] Comparative Example 1, Preserved Vegetable Processing Method

[0048] Step S1. Remove the roots, parts eaten by insects, damaged, and crushed parts of fresh mustard greens (produced in Kunming, Yunnan), wash, drain, then blanch at 90°C for 2 min, drain, and bake at 45°C for 7 h, then steam for 30 min to obtain pretreated mustard greens;

[0049] Step S2. Put the pretreated mustard greens prepared in Step S1 into the pickling pool, add salt and stir evenly. The addition amount of salt is 7% of the mass of the pretreated mustard greens. Add water to the pickling pool to submerge the mustard greens, stir evenly, seal, and ferment at 10 - 25°C for 10 days to obtain pickled mustard greens;

[0050] Step S3. Soak the pickled mustard greens prepared in Step S2 in water for 25 min. The material-liquid ratio of the pickled mustard greens to water is 1 g: 2 mL, fish out, drain, and perform vacuum freeze-drying. The vacuum freeze-drying conditions are as follows: the air pressure in the vacuum chamber is 12 kPa, the cold trap temperature is reduced to -40°C within 1.5 h, and the holding time is 50 min; the air pressure in the vacuum drying chamber is 4 kPa, and it is heated to 8°C within 10 h, and the holding time is 2 h, thus obtaining.

[0051] The difference from Example 2 is that there is no treatment liquid and pulsed treatment, and the other steps are similar to those in Example 2.

[0052] Comparative Example 2, Preserved Vegetable Processing Method

[0053] Step S1. Remove the roots, parts eaten by insects, damaged, and crushed parts of fresh mustard greens (produced in Kunming, Yunnan), wash, drain, then blanch at 90°C for 2 min, drain, and bake at 45°C for 7 h, then steam for 30 min to obtain pretreated mustard greens;

[0054] Step S2. Add xanthan gum, vitamin C and citric acid into water and stir evenly to obtain a treatment solution. The concentrations of each component in the treatment solution are: xanthan gum 0.05 g / L, vitamin C 0.6 g / L, and citric acid 0.6 g / L;

[0055] Step S3. Put the pretreated mustard prepared in Step S1 into a pickling tank, add salt and stir evenly. The addition amount of the salt is 7% of the mass of the pretreated mustard. Add water to the pickling tank to submerge the mustard, and then add the treatment solution prepared in Step S2. The addition amount of the treatment solution is 5% of the mass of the pretreated mustard. Stir evenly, seal, and ferment at 10 - 25 °C for 10 days to obtain pickled mustard;

[0056] Step S4. Add water to the pickled mustard prepared in Step S3, and after pulsed treatment, the pulsed treatment conditions are: use high - voltage pulsed electric field treatment, the treatment temperature is 25 °C, the electric field strength is 30 kV / cm, the pulse width is 3 μs, the pulse frequency is 150 Hz, the treatment time is 200 pulse numbers, then soak for 25 min. The material - to - liquid ratio of the pickled mustard to water is 1 g:2 mL. Lift it out, drain, and perform vacuum freeze - drying. The vacuum freeze - drying conditions are: the air pressure in the vacuum chamber is 12 kPa, cool the cold trap temperature to - 40 °C within 1.5 h, and keep the time for 50 min; the air pressure in the vacuum drying chamber is 4 kPa, heat up to 8 °C within 10 h, and keep the time for 2 h, thus obtaining the product.

[0057] The difference from Example 2 lies in the different preparation steps of the treatment solution, and the remaining steps are similar to those in Example 2.

[0058] Comparative Example 3, Method for processing preserved mustard greens

[0059] Step S1. Remove the root whiskers, worm - eaten parts, damaged parts, and crushed parts of fresh oil mustard (produced in Kunming, Yunnan), wash, drain, then blanch at 90 °C for 2 min, drain, and bake at 45 °C for 7 h, and then steam for 30 min to obtain pretreated mustard;

[0060] Step S2. Add xanthan gum into water and stir evenly, then add vitamin C and stir evenly. After standing for 6 min, add citric acid and stir evenly to obtain a treatment solution. The concentrations of each component in the treatment solution are: xanthan gum 0.05 g / L, vitamin C 0.6 g / L, and citric acid 0.6 g / L;

[0061] Step S3. Put the pretreated mustard greens obtained in Step S1 into a pickling tank, add salt and stir evenly. The addition amount of the salt is 7% of the mass of the pretreated mustard greens. Add water to the pickling tank to submerge the mustard greens, and then add the treatment liquid obtained in Step S2. The addition amount of the treatment liquid is 5% of the mass of the pretreated mustard greens. Stir evenly, seal, and ferment for 10 days under the condition of 10 - 25 °C to obtain pickled mustard greens;

[0062] Step S4. Add water to the pickled mustard greens obtained in Step S3, soak for 25 min. The material - liquid ratio of the pickled mustard greens to water is 1 g: 2 mL. Scoop up, drain, and conduct vacuum freeze - drying. The vacuum freeze - drying conditions are as follows: the air pressure in the vacuum chamber is 12 kPa, the cold trap temperature is reduced to - 40 °C within 1.5 h, and the holding time is 50 min; the air pressure in the vacuum drying chamber is 4 kPa, and it is heated to 8 °C within 10 h, and the holding time is 2 h, thus obtaining.

[0063] The difference from Example 2 is that there is no pulse treatment step, and the other steps are similar to those in Example 2.

[0064] Test Example 1. Quality detection test of preserved mustard greens

[0065] 1. Test objects:

[0066] The preserved mustard greens obtained in Example 1, Example 2, and Example 3.

[0067] 2. Test methods:

[0068] Measure the rehydration and browning degree of the preserved mustard greens obtained in Example 1, Example 2, and Example 3. Among them:

[0069] 2.1. The measurement method of rehydration is as follows:

[0070] Weigh 5 g of each preserved mustard green sample, record the mass m0, add 500 g of water at 90 °C, place it in a water - bath pot at 90 °C for heat preservation, take it out and drain the water after 3 min, and then weigh and record the mass m1. The rehydration of the dried product can be measured by the rehydration rate.

[0071]

[0072] In the formula: m1 is the mass of the rehydrated preserved mustard greens, g; m0 is the mass of the preserved mustard greens before rehydration, g.

[0073] 2.2. The measurement method of browning degree is as follows:

[0074] Weigh 5 g of each preserved mustard green sample, add 20 mL of distilled water, soak for 30 min, centrifuge at 4000 r / m for 10 min, filter through a 0.45 - μm polytetrafluoroethylene needle - shaped filter, and take 3 mL of the filtrate to measure the absorbance value at 420 nm at room temperature.

[0075] 3. Test results:

[0076] The test results are shown in Table 1.

[0077] Table 1 Rehydration and Browning Degree of Preserved Vegetables with Plum

[0078] Rehydration property Degree of browning Example 1 3.6453±0.1461 0.1610±0.0263 Example 2 3.8603±0.1587 0.1173±0.0395 Example 2 3.6726±0.2597 0.1795±0.0370

[0079] As can be seen from Table 1, the preserved vegetables prepared by the processing method of preserved vegetables provided by the present invention have good rehydration, low browning degree, and good finishing quality. In addition, the preserved vegetables prepared in Example 2 of the present invention are as Figure 1 shown.

[0080] Test Example 2: Nitrite Detection Test of Preserved Vegetables with Plum

[0081] 1. Test method:

[0082] Detect the nitrite content of the preserved vegetables prepared in Example 1, Example 2, Example 3, Comparative Example 1, Comparative Example 2, and Comparative Example 3. Specifically, detect the nitrite content of the preserved vegetable leaves, preserved vegetable petioles, and pickling solution on the 10th day after pickling is completed. The detection method refers to the second method in the national food safety standard "Determination of Nitrite and Nitrate in Foods" GB 5009.33-2010, and the spectrophotometry is used for detection. Take 100 samples of preserved vegetable leaves and preserved vegetable petioles respectively, smash them with a tissue grinder, stir evenly, and use them as test samples. After mixing the pickling solution evenly, use it as a test sample.

[0083] 2. Test results:

[0084] The test results are shown in Table 2.

[0085] Table 2 Nitrite Detection Data of Preserved Vegetables with Plum

[0086]

[0087]

[0088] As can be seen from Table 2, the nitrite content of the preserved vegetables prepared by the processing method of preserved vegetables provided by the present invention is reduced to 2 mg / kg, far lower than the national standard, and greatly improves the safety of preserved vegetable food.

[0089] Test Example 3: Salinity Detection Test of Preserved Vegetables with Plum

[0090] 1. Test method:

[0091] Detect the salt content of the preserved vegetables prepared in Example 1, Example 2, and Example 3. The detection method refers to the indirect titration method in "Determination of Sodium Chloride in Vegetable Products" GB / T 12457-90. 2. Test results

[0092] The test results are shown in Table 3 as follows:

[0093] Table 3 Salinity detection data of preserved mustard greens

[0094] Salt content (%) Example 1 2.7％ Example 2 2.4％ Example 3 2.8％

[0095] The salt content of preserved mustard greens within the range of 2% - 5% is an acceptable range. As can be seen from Table 3, the preserved mustard greens prepared by the preserved mustard greens processing method provided by the present invention have a salt content lower than 3%, which are preserved mustard greens with a relatively low salt content and can effectively reduce the harm of high-salt preserved mustard greens to the human body.

Claims

1. A method for processing preserved mustard greens, characterized in that, It includes the following steps: Step S1. Remove the roots, parts eaten by insects, damaged and crushed parts of the fresh Brassica juncea var. gracilis produced in Kunming, Yunnan, wash, drain, then blanch at 90 °C for 2 min, drain, bake at 45 °C for 7 h, and then steam for 30 min to obtain pretreated mustard; Step S2. Add xanthan gum to water and stir evenly, then add vitamin C and stir evenly. After standing for 6 min, add citric acid and stir evenly to obtain a treatment liquid. The concentrations of each component in the treatment liquid are: xanthan gum 0.05 g / L, vitamin C 0.6 g / L, and citric acid 0.6 g / L; Step S3. Put the pretreated mustard obtained in Step S1 into a pickling pool, add salt and stir evenly. The addition amount of the salt is 7% of the mass of the pretreated mustard. Add water to the pickling pool to submerge the mustard, then add the treatment liquid obtained in Step S2. The addition amount of the treatment liquid is 5% of the mass of the pretreated mustard. Stir evenly, seal, and ferment at 10-25 °C for 10 days to obtain pickled mustard; Step S4. Add water to the pickled mustard obtained in Step S3, and after pulsed treatment, the pulsed treatment conditions are: using high-voltage pulsed electric field treatment, the treatment temperature is 25 °C, the electric field strength is 30 kV / cm, the pulse width is 3 μs, the pulse frequency is 150 Hz, the treatment time is 200 pulse numbers, then soak for 25 min. The material-liquid ratio of the pickled mustard to water is 1 g:2 mL. Lift it out, drain, and perform vacuum freeze-drying. The vacuum freeze-drying conditions are: the air pressure in the vacuum chamber is 12 kPa, the cold trap temperature is reduced to -40 °C within 1.5 h, and the holding time is 50 min; the air pressure in the vacuum drying chamber is 4 kPa, and it is heated to 8 °C within 10 h, and the holding time is 2 h, thus obtaining the product.

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