A method for producing low-acid kimchi by step-by-step fermentation

Abstract

The invention discloses a method for producing low-acid kimchi by step-by-step fermentation, which belongs to the technical field of kimchi production. The method comprises the following steps: performing a sterilization treatment on vegetables; inoculating lactic acid bacteria for the first step of fermentation; separating the vegetable liquid from the kimchi after the first step of fermentation; and inoculating yeast for the second step of fermentation. The invention starts the fermentation by first inoculating heterotypic lactic acid bacteria, so that the heterotypic fermentation strains can quickly form an advantage. When the heterotypic fermentation is about to end, the kimchi liquid and part of the lactic acid bacteria and lactic acid are removed to shorten the homotypic fermentation time. Then, anaerobic flavoring fermentation is performed by adding salt water containing yeast, thereby effectively preventing over-acidification and improving the kimchi flavor. The invention effectively shortens the overall fermentation time, and the entire fermentation process is controllable, simple to operate, and suitable for large-scale, standardized production.

Description

Technical Field

[0001] The invention belongs to the technical field of pickle production, and in particular relates to a method for producing low-acid pickles by step fermentation. Background Art

[0002] Kimchi is very popular among consumers. Due to the influence of factors such as raw materials, environmental climate, and processing technology, the changes in microbial communities during the fermentation of different vegetables have their own characteristics, but generally present two main stages: heterolactic fermentation and homolactic fermentation. In the early stage of kimchi fermentation, heterotypic fermentation is the main method. The heterotypic fermentation bacteria are rich in species and can decompose a large amount of organic matter to produce flavor substances. It is an important period for improving the flavor of kimchi. Heterotypic fermentation bacteria include Lactobacillus brevis, Lactobacillus fermentum, and Leuconostoc mesenteroides. As the fermentation process deepens, the acid in the fermentation liquid accumulates and the pH gradually decreases. The dominant heterotypic fermentation bacteria with weak acid resistance die and enter the homotypic fermentation stage. The dominant bacteria of homotypic fermentation have strong acid resistance, grow vigorously in a relatively acidic environment, and produce a large amount of lactic acid. The lactic acid bacteria of homotypic fermentation include Lactobacillus plantarum and Pediococcus pentosaceus.

[0003] Proper addition of yeast to naturally fermented kimchi can not only produce alcohol through alcohol fermentation to play an antibacterial role, but also further react with organic acids to produce some ester aromatic components, thereby increasing the flavor of the kimchi. Specific yeasts can fully utilize fermentable sugars in a relatively acidic environment, and form a competitive advantage with lactic acid bacteria, putrefactive bacteria and harmful bacteria in the later stage of fermentation, thus preventing the kimchi from becoming too sour and playing a beneficial role in its storage.

[0004] Low-salt, low-acid kimchi has become a new consumption trend, while traditional kimchi with high salt and acid content needs to be rinsed, desalted and other methods to reduce salt and acid, which is neither convenient and efficient nor energy-saving and environmentally friendly. In addition, due to the long fermentation cycle of traditional kimchi, the low acid level is difficult to control, which can easily lead to problems such as post-acidification and softening, affecting product quality. Although existing lactic acid bacteria agents can quickly and efficiently utilize raw materials to produce lactic acid, the flavor produced is relatively single and easily over-acidified. Adding lactic acid bacteria and yeast at the same time and adding yeast in the early stage of fermentation and lactic acid bacteria in the later stage are also used in kimchi, but most yeasts have poor acid and salt resistance and are difficult to grow and metabolize in a relatively acidic environment to produce a large amount of flavor substances. Summary of the invention

[0005] The object of the present invention is to provide a method for producing low-acid kimchi by step-by-step fermentation, so as to solve the technical problems of long natural fermentation period, over-acidity and relatively single flavor of kimchi.

[0006] The technical purpose of the present invention is achieved through the following technical solutions:

[0007] A method for producing low-acid kimchi by step-by-step fermentation comprises the following steps:

[0008] (1) Wash fresh vegetables and then treat them to reduce bacteria;

[0009] (2) Add the sterilized vegetables, spices and iodine-free salt water into a sterile container, then inoculate the lactic acid bacteria agent, mix them evenly and ferment them at room temperature for 3 to 5 days in a sealed container; the concentration of the iodine-free salt water is 2 to 6%; the lactic acid bacteria agent contains Leuconostoc mesenteroides AP7, which is preserved in Guangdong Microbiological Culture Collection Center, with the address of the preservation unit being 5th Floor, Building 59, No. 100 Xianlie Middle Road, Guangzhou, with the preservation number of GDMCC No: 62462, the preservation time being May 17, 2022, and the taxonomic name being Leuconostoc mesenteroide;

[0010] (3) filtering the kimchi fermented in step (2) to remove the fermentation liquid, and rinsing with sterile water to remove the lactic acid bacteria and lactic acid attached to the surface of the kimchi to obtain a fermentation semi-finished product;

[0011] (4) inoculating yeast in 2-6% iodine-free saline to prepare a yeast-containing saline; the yeast inoculant contains oligosporic Kazakhstan yeast (Kazachstania exigua AP8); the oligosporic Kazakhstan yeast (Kazachstania exigua AP8) is deposited in Guangdong Microbiological Culture Collection Center, the address of the depository is 5th Floor, Building 59, No. 100 Xianlie Middle Road, Guangzhou, the deposit number is GDMCC No: 62817, the deposit date is September 19, 2022, and the taxonomic name is Kazachstania exigua;

[0012] (5) Mix the fermented semi-finished product with salt water containing yeast, seal and ferment for 3 to 10 days to obtain edible kimchi.

[0013] Furthermore, the spice in step (2) is a mixture of dried prickly ash, star anise, tsaoko, cinnamon and crystal sugar, and the mass ratio of each component in the mixture is (20-25):(2-25):100:(100-150):(30-100).

[0014] Furthermore, the mass ratio of the vegetables, spices and iodine-free salt water in step (2) is (40-45):(1-2):(53.3-59).

[0015] Furthermore, after the lactic acid bacteria are inoculated in step (2), the number of live bacteria in the kimchi water reaches 1×10 6 CFU / mL~1×107 CFU / mL.

[0016] Furthermore, after the yeast is inoculated in step (4), the number of viable bacteria in the salt water containing the yeast is 1×10 6 CFU / mL~1×10 7 CFU / mL.

[0017] Furthermore, in step (5), the ratio of the fermentation semi-finished product to the yeast-containing brine is 100 g: (20-30) ml.

[0018] Furthermore, the sterilization treatment in step (1) is to soak the vegetables in liquor with an alcohol content of 42% or more, or 75% edible alcohol, or an electrolyzed hypochlorous acid solution to remove the bacteria on the surface of the vegetables;

[0019] Furthermore, the effective chlorine concentration of the hypochlorous acid electrolytic aqueous solution is 20-40 ppm, the pH value is 5.2-6.1, and the ORP is 720-810 mV.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] The method of the present invention starts fermentation by first inoculating a heterotypic lactic acid bacteria agent, so that the heterotypic fermentation bacteria can quickly form a dominant position. When the heterotypic fermentation is about to end, the kimchi water and part of the lactic acid bacteria are removed to shorten the homotypic fermentation time; a yeast agent is added to carry out anaerobic flavoring fermentation, thereby effectively preventing over-acidification and improving the kimchi flavor; the method is simple to operate and is suitable for large-scale and standardized production. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a comparison chart of total acid analysis between the experimental group and the control group during the fermentation process in the experimental example of the present invention;

[0023] Figure 2 This is a comparison chart of pH analysis of the experimental group and the control group during the fermentation process in the experimental example of the present invention;

[0024] Figure 3 It is the color diagram of kimchi when the experimental group and the control group in the experimental example of the present invention are fermented to maturity and stored for 30 days;

[0025] Figure 4 It is a sensory evaluation diagram of the experimental group and the control group during fermentation maturity in the experimental example of the present invention. DETAILED DESCRIPTION

[0026] To make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be described in detail below. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other implementation methods obtained by ordinary technicians in this field without creative work belong to the scope of protection of the present invention.

[0027] In this application document, % means wt% unless otherwise specified, proportions are by mass, and parts are by weight; raw materials used are commercially available products unless otherwise specified.

[0028] In this application document, the deposit information of Leuconostoc mesenteroides AP7 and Kazachstania exigua AP8 is as follows:

[0029] Name of the depository: Guangdong Provincial Microbiological Culture Collection Center; address of the depository: 5th Floor, Building 59, No. 100 Xianlie Middle Road, Guangzhou; the deposit dates are May 17, 2022 and September 19, 2022; the deposit numbers are GDMCC No: 62462 and GDMCC No: 62817; the taxonomic names are Leuconostoc mesenteroides and Kazachstania exigua.

[0030] Example 1

[0031] A method for producing low-acid kimchi by step-by-step fermentation comprises the following steps:

[0032] (1) Container sterilization: After cleaning the container, sterilize it with boiling water for 8 minutes;

[0033] (2) Raw material sterilization treatment: Soak fresh mustard greens in strong liquor for 7 minutes, drain and set aside; strong liquor refers to liquor with an alcohol content of 42 degrees or more;

[0034] (3) Preparation of spices: Mix dried pepper, star anise, tsaoko, cinnamon and crystal sugar in a mass ratio of 5:5:20:30:20, chop and set aside;

[0035] (4) adding spices and mustard greens into 3% iodine-free saline solution, with the ratio of mustard greens, spices, and saline solution being 40.0%:2.0%:58.0%;

[0036] (5) Lactic acid bacteria fermentation: Inoculation of Leuconostoc mesenteroides AP7 resulted in a live bacterial count of 3.99 × 10 6CFU / mL, sealed and fermented for 3 days at room temperature;

[0037] (6) Vegetable liquid separation: removing the fermentation liquid, removing the lactic acid bacteria and lactic acid attached to the surface of the kimchi by rinsing with sterile water, and obtaining a fermentation semi-finished product;

[0038] (7) Preparation of brine containing yeast: Kazachstania exigua AP8 was inoculated into 3% iodine-free saline to produce a solution with a viable count of 2.95 × 10 6 CFU / mL of saline containing yeast;

[0039] (8) Yeast fermentation: the fermentation semi-finished product was mixed with the brine containing yeast at a ratio of 100 g:20 mL, and the mixture was sealed and fermented for 6 days to obtain fermented mature kimchi;

[0040] (9) Seasoning and packaging the fermented kimchi.

[0041] Example 2

[0042] A method for producing low-acid kimchi by step-by-step fermentation comprises the following steps:

[0043] (1) Container sterilization: After cleaning, sterilize the container with boiling water for 5 minutes;

[0044] (2) Raw material sterilization treatment: Soak fresh mustard greens in 75% edible alcohol for 5 min and then drain for later use;

[0045] (3) Preparation of spices: Mix and chop dried pepper, star anise, tsaoko, cinnamon and crystal sugar in a mass ratio of 10:1:50:50:25 to obtain spices;

[0046] (4) adding spices and mustard greens into 2% iodine-free saline solution, with the ratio of mustard greens, spices, and saline solution being 45%:1.7%:53.3%;

[0047] (5) Lactic acid bacteria fermentation: Inoculation of Leuconostoc mesenteroides AP7 resulted in a live bacterial count in kimchi water of 4.50 × 10 6 CFU / mL, sealed and fermented for 3 days at room temperature;

[0048] (6) Vegetable liquid separation: removing the fermentation liquid, removing the lactic acid bacteria and lactic acid attached to the surface of the kimchi by rinsing with sterile water, and obtaining a fermentation semi-finished product;

[0049] (7) Preparation of brine containing yeast: Kazachstania exigua AP8 was inoculated into 2% iodine-free saline until the viable count reached 2.00 × 10 6CFU / mL of saline containing yeast;

[0050] (8) Yeast fermentation: The fermented semi-finished product was mixed with the brine containing yeast at a ratio of 100 g: 25 mL, and the mixture was sealed and fermented for 6 days to obtain fermented mature kimchi;

[0051] (9) Seasoning and packaging the fermented kimchi.

[0052] Example 3

[0053] A method for producing low-acid kimchi by step-by-step fermentation comprises the following steps:

[0054] (1) Container sterilization: After cleaning, sterilize the container with 121°C steam for 3 minutes;

[0055] (2) Raw material sterilization treatment: soak mustard in an electrolytic hypochlorous acid aqueous solution for 5 minutes, drain and set aside; wherein the electrolytic hypochlorous acid aqueous solution has an effective chlorine concentration of 20 to 40 ppm, a pH value of 5.2 to 6.1, and an ORP of 720 to 810 mV;

[0056] (3) Preparation of spices: Mix and chop dried pepper, star anise, tsaoko, cinnamon and crystal sugar in a mass ratio of 10:5:40:40:12 to obtain spices;

[0057] (4) Add spices and mustard greens into 6% iodine-free salt water, with the ratio of mustard greens, spices, and salt water being 40.0%:1.0%:59.0%

[0058] (5) Lactic acid bacteria fermentation: Inoculation of Leuconostoc mesenteroides AP7 resulted in a viable bacterial count of 5.00 × 10 6 CFU / mL, sealed and fermented for 3 days at room temperature;

[0059] (6) Vegetable liquid separation: removing the fermentation liquid, removing the lactic acid bacteria and lactic acid attached to the surface of the kimchi by rinsing with sterile water, and obtaining a fermentation semi-finished product;

[0060] (7) Preparation of brine containing yeast: Kazachstania exigua AP8 was inoculated into 6% iodine-free saline to produce a solution with a viable count of 2.90 × 10 6 CFU / mL of saline containing yeast;

[0061] (8) Yeast fermentation: the fermentation semi-finished product was mixed with the brine containing yeast at a ratio of 100 g:30 mL, and the mixture was sealed and fermented for 6 days to obtain fermented mature kimchi;

[0062] (9) Seasoning and packaging the fermented kimchi.

[0063] Experimental example

[0064] The beneficial effects of the present invention are illustrated by experiments below.

[0065] 1. Experimental Methods

[0066] The experimental group was the vacuum-packed sample without seasoning prepared by the method of Examples 1 to 3, and then 4 control groups were set up, namely:

[0067] Comparative Example 01

[0068] Natural fermentation (i.e., fermentation without inoculation at room temperature, other culture conditions are consistent with Example 1); Comparative Example 02

[0069] Yeast was added first and then lactic acid bacteria (yeast was added at the beginning of fermentation, lactic acid bacteria was added 4 days after fermentation, and fermentation was carried out. The types and quantities of added microorganisms and other culture conditions were consistent with those in Example 1); Control Example 03

[0070] Add lactic acid bacteria and yeast at the same time (at the beginning of fermentation, yeast and lactic acid bacteria are added at the same time for fermentation, and the type, amount and other culture conditions of added microorganisms are consistent with those in Example 1);

[0071] Comparative Example 04

[0072] Only lactic acid bacteria were added (lactic acid bacteria were added at the beginning of fermentation for fermentation, and the type and amount of added microorganisms and other culture conditions were the same as those in Example 1).

[0073] 2. Results and Analysis

[0074] 1. Use a potentiometric titrator and a pH meter to measure the total acid and pH of the sample. The results are shown in Figure 1 and Figure 2 .

[0075] Depend on Figure 1 and Figure 2 It can be seen that in the same period of time, the acidity of the kimchi juice and the acidity of the pickled cabbage stems in the experimental group were lower than those in the control group, and could be maintained at an acceptable low level after a total fermentation time of 9 days, while the acidity of the control group continued to rise with the fermentation time, resulting in over-acidity of the product.

[0076] 2. MRS and Bengal rose culture medium were used to count the colonies of lactic acid bacteria and yeast in the samples. The results are shown in Table 1:

[0077] Table 1 Number of viable microorganisms during fermentation

[0078]

[0079] Note: “ / ” indicates no inoculation, “-” indicates no detection, different letters in the same row indicate significant differences.

[0080] As can be seen from Table 1, the number of live lactic acid bacteria in the experimental group during the entire fermentation process was lower than that of the control examples (control examples 02, 03 and 04) in the fermentation with bacteria in the middle and late stages (6-9 days). No yeast was detected in the control examples 01 and 04 without yeast during the entire fermentation process, while the yeast in the experimental group, control examples 02 and 03 with yeast were reduced to varying degrees during the entire fermentation process, among which control examples 02 and 03 were not detected after the 6th day, while the example still had yeast alive on the 12th day.

[0081] 3. When the samples are fermented to maturity (i.e. the total fermentation time is 9 days) and the shelf life reaches 30 days, the samples are subjected to physical and chemical tests. The results are shown in Tables 2 and 3:

[0082] Table 2 Physical and chemical indicators at fermentation maturity

[0083]

[0084] Note: Different letters indicate significant differences.

[0085] Table 3 Physical and chemical indicators after 30 days of shelf life

[0086]

[0087] Note: Shelf life test: The kimchi samples (not sterilized) were vacuum-sealed and then subjected to accelerated shelf life test at 37°C for 30 days. Different letters indicate significant differences.

[0088] (1) Analysis of pH and total acid

[0089] The pH of the experimental group had no significant difference from that of control examples 03 and 04 and was able to remain stable. The total acid in the experimental group was significantly less than that in the control group and was able to remain stable. In addition, the maximum change in the total acid in the experimental group during the shelf life was 0.251-0.269%, indicating that the acidity change was very small, which could effectively prevent the product from being over-acidic.

[0090] (2) Analysis of total esters

[0091] The total ester content of the experimental group was significantly higher than that of the control group both during fermentation and after 30 days of shelf life. This is because the yeast added later survived longer and produced a large amount of flavor substances such as esters, which can effectively enrich the flavor of kimchi.

[0092] (3) Total Texture Analysis (TPA)

[0093] Hardness: On the 9th day of the total fermentation time, due to the short brewing time, the control example 01 was not mature yet, so it had a higher hardness. The experimental group and the control example 03 still had a high hardness after fermentation. After 30 days of storage, the experimental group still maintained a good crispness, and was significantly higher than the control example.

[0094] Elasticity: On the 9th day of the total fermentation time, there was no significant difference among the treatments, and all showed good elasticity; after 30 days of shelf life, the experimental group still maintained good elasticity, and was significantly higher than the control group.

[0095] Chewability: The chewiness of the experimental group was significantly higher than that of the control group, both during fermentation and after 30 days of shelf life.

[0096] TPA data shows that the experimental group can maintain a crisp taste for a long time after fermentation and maturity, and the kimchi will not become soft and chewy due to excessive fermentation of lactic acid bacteria.

[0097] 4. When the sample is fermented to maturity (i.e. the total fermentation time is 9 days) and the sample shelf life reaches 30 days, take samples to observe the color change of the sample. The results are shown in Figure 3 .

[0098] By sampling and observing the kimchi samples, it can be found that the color of the experimental group is brighter than that of the control group both when it is mature and after 30 days of storage.

[0099] 5. Sensory evaluation of fermented kimchi was performed. The results were as follows: Figure 4 and Table 4.

[0100] Table 4 Sensory rating table

[0101]

[0102] from Figure 4 As can be seen from Table 4, the experimental group was superior to the control group in terms of smell, crispness and overall taste. There was little difference between the groups in terms of color. The experimental group was slightly lower than the control group in terms of sourness.

[0103] In summary, the experimental group has the characteristics of not being overly acidic for a long time, strong ester and aroma production capabilities, and greater hardness and brittleness.

[0104] The above is only a preferred embodiment of the present invention, and is not intended to limit the present invention. For example, in the fermentation process, other lactic acid bacteria such as Lactobacillus brevis, Lactobacillus fermentum, Weissella can be used to replace Leuconostoc mesenteroides AP7, or / and other yeasts such as Kluyveromyces marx, Kazakhstan yeast, Yarrowia lipolytica, Kluyveromyces lactis, Saccharomyces cerevisiae can be used to replace Kazakhstan yeast oligospores (Kazachstania exigua AP8) for fermentation, and the same technical effect can be achieved. Of course, multiple lactic acid bacteria or / and multiple yeasts can also be used to form composite bacteria. Those skilled in the art should understand that, except mustard, the present invention is equally applicable to other vegetables such as Chinese cabbage, cabbage, radish or cowpea, and any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention should all be included in the protection scope of the present invention.

Claims

1. A method for producing low-acid kimchi by step-by-step fermentation, characterized in that: The following steps are involved: (1) Wash fresh vegetables and then treat them to reduce bacteria; (2) Adding the sterilized vegetables, spices and iodine-free salt water into a sterile container, then inoculating a lactic acid bacteria agent, mixing them evenly and sealing and fermenting them at room temperature for 3 to 5 days; the concentration of the iodine-free salt water is 2 to 6%; the lactic acid bacteria agent contains Leuconostoc mesenteroides AP7, which is preserved in Guangdong Province Microbiological Culture Collection Center with a preservation number of GDMCC No: 62462; (3) filtering the kimchi fermented in step (2) to remove the fermentation liquid, and rinsing with sterile water to remove the lactic acid bacteria and lactic acid attached to the surface of the kimchi to obtain a fermentation semi-finished product; (4) inoculating yeast in 2-6% iodine-free saline to prepare a yeast-containing saline; the yeast inoculant contains oligosporic Kazakhstan yeast Kazachstania exigua AP8; the oligosporic Kazakhstan yeast Kazachstania exigua AP8 is deposited in Guangdong Microbiological Culture Collection Center with a deposit number of GDMCC No: 62817; (5) mixing the fermented semi-finished product with salt water containing yeast, and sealing and fermenting for 3 to 10 days to obtain fermented mature kimchi; (6) Seasoning and packaging the fermented kimchi.

2. The method for producing low-acid kimchi by step-by-step fermentation according to claim 1, characterized in that: The spice in step (2) is a mixture of dried prickly ash, star anise, tsaoko, cinnamon and crystal sugar, and the mass ratio of each component in the mixture is (20-25):(2-25):100:(100-150):(30-100).

3. The method for producing low-acid kimchi by step-by-step fermentation according to claim 2, characterized in that: The mass ratio of the vegetables, spices and iodine-free salt water in step (2) is (40-45):(1-2):(53.3-59).

4. The method for producing low-acid kimchi by step-by-step fermentation according to claim 2, characterized in that: Step (2), after the lactic acid bacteria are inoculated in step (2), the number of live bacteria in the kimchi water reaches 1×10 6 CFU / mL~1×10 7 CFU / mL.

5. The method for producing low-acid kimchi by step-by-step fermentation according to claim 1, characterized in that: After yeast inoculation in step (4), the number of viable bacteria in the brine containing yeast is 1×10 6 CFU / mL~1×10 7 CFU / mL.

6. The method for producing low-acid kimchi by step-by-step fermentation according to claim 1, characterized in that: In step (5), the ratio of the fermentation semi-finished product to the brine containing yeast is 100 g: (20-30) ml.

7. The method for producing low-acid kimchi by step-by-step fermentation according to claim 1, characterized in that: The sterilization treatment in step (1) is to soak the vegetables in liquor with an alcohol content of 42 degrees or above, or 75% edible alcohol, or hypochlorous acid electrolyzed aqueous solution to remove the miscellaneous bacteria on the surface of the vegetables.

8. The method for producing low-acid kimchi by step-by-step fermentation according to claim 7, characterized in that: The hypochlorous acid electrolytic aqueous solution has an effective chlorine concentration of 20 to 40 ppm, a pH value of 5.2 to 6.1, and an ORP of 720 to 810 mV.

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