Low-pH (Potential of Hydrogen) color-protecting and crispness-increasing agent for fermented vegetables as well as preparation method and application thereof

Abstract

The invention discloses a low-pH (Potential of Hydrogen) color-protecting and crispness-increasing agent for fermented vegetables as well as a preparation method and application of the low-pH color-protecting and crispness-increasing agent. The low-pH color-protecting and crispness-increasing agent comprises the following components in percentage by mass: 30 to 45 percent of catechin, 20 to 40 percent of sodium tripolyphosphate, 15 to 25 percent of phytic acid, 2 to 15 percent of pullulan and 5 to 10 The sum of the mass percentages of the components is 100%. Through the synergistic effect of the catechin, the sodium tripolyphosphate, the phytic acid, the pullulan and the calcium lactate in the proportion range of the invention, the preservative has a good protection effect on the color, luster and texture of the low-pH fermented vegetables.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of food additives, in particular, the present application relates to a low-pH fermented vegetable color protection and crispness increasing agent, a preparation method and application thereof. BACKGROUND

[0002] Low-pH fermented vegetables are a large class of vegetable products in which a large amount of lactic acid is produced by lactic acid bacteria fermentation, thereby making the environment acidic (pH value decreases, usually less than or equal to 4.6). This acidic environment can effectively inhibit the growth of harmful microorganisms, so that the vegetables can be preserved for a long time. Common low-pH fermented vegetables mainly include fermented cowpeas, fermented radishes, fermented peppers, fermented cabbage, etc. Taking fermented cowpeas (in many places, it is directly called "acid bean") as an example, it is a very popular fermented vegetable, which has a very penetrating sour taste and can stimulate appetite well and remove greasiness. However, with the occurrence of the fermentation process, the sensory quality of cowpeas gradually deteriorates. For example, under acidic conditions, chlorophyll in vegetables will degrade to form de-magnesium chlorophyll. Under low-pH conditions, the de-magnesium reaction of chlorophyll is accelerated, resulting in the discoloration of green vegetables (such as cucumbers, green peppers, cowpeas) from green to gray-brown. In addition, low-pH conditions will lead to the hydrolysis of pectin, resulting in a decrease in the crispness of vegetables, which will cause problems such as soft and rotten texture. Overall, the color gradually becomes dark, the texture gradually becomes soft and crisp, which seriously damages the sensory quality and restricts the development of the vegetable deep processing industry. It is very important to solve the problem of sensory quality deterioration.

[0003] The color protection agent commonly used in the prior art (such as zinc salt and copper salt replacing magnesium in chlorophyll) may be ineffective due to too low pH; the prior art also discloses some color protection agents for fermented vegetables, for example, patent CN111449191A discloses a fermented vegetable color protection agent, a preparation method and application thereof. The fermented vegetable color protection agent is prepared from the following components by weight fraction: 1-20 parts of basil, 1-10 parts of anise, 20-60 parts of rosemary, 5-20 parts of turmeric, 0.5-3 parts of Chinese cinnamon, 5-20 parts of cassia bark and 0.5-15 parts of clove. It mainly provides flavor and antioxidant function of composite spices from the perspective of antioxidant and composite spices to protect the color of fermented vegetables, but has no effect on the change in texture during the fermentation of fermented vegetables. SUMMARY

[0004] The present application aims to at least partially solve one of the technical problems of the prior art, and for this purpose, the present application provides a low-pH fermented vegetable color protection and crispness increasing agent, a preparation method and application thereof.

[0005] The present application adopts the following technical solutions:

[0006] In a first aspect,

[0007] The application provides a low-pH fermented vegetable color protection and crispness increasing agent, which comprises the following components and their mass percentages: catechin 30-45%, sodium tripolyphosphate 20-40%, phytic acid 15-25%, pullulan 2-15%, and calcium lactate 5-10%, and the sum of the mass percentages of the components is 100%.

[0008] In some preferred embodiments, the low-pH fermented vegetable color protection and crispness increasing agent comprises the following components and their mass percentages: catechin 30-40%, sodium tripolyphosphate 25-35%, phytic acid 17-24%, pullulan 5-12%, and calcium lactate 5-8%, and the sum of the mass percentages of the components is 100%.

[0009] In some embodiments, the fermented vegetable is fermented cowpea, fermented radish, fermented pepper or fermented cabbage.

[0010] The application provides a color protection and crispness increasing agent which has good color protection and crispness increasing effects on fermented vegetables under low-pH conditions, and the components fully play a synergistic role. Specifically, phytic acid chelates metal ions (such as Fe 3+ , Cu 2+ ), eliminates the catalytic effect of these ions on the auto-oxidation of catechin, stabilizes the antioxidant activity of catechin, and makes the effect more persistent. In addition, the weak alkaline microenvironment created by sodium tripolyphosphate helps to improve the solubility and stability of catechin, and indirectly supports its antioxidant function. In addition to antioxidant activity, catechin can also directly bind to polyphenol oxidase (PPO) and inhibit the activity of the enzyme to some extent, thereby assisting in inhibiting enzymatic browning from the source. In addition, sodium tripolyphosphate creates conditions for the penetration and cross-linking of Ca 2+ , and may enhance the gel network together with Ca 2+ through bridging, thereby significantly improving the hardness and brittleness of the tissue. The color protection and crispness increasing agent of the application has reasonable compatibility, obvious color protection and crispness increasing effects, can effectively protect the color of low-pH fermented vegetables in a reasonable dose range, has a good protective effect on the texture, and improves the quality of low-pH fermented vegetables.

[0011] In a second aspect,

[0012] The application also provides a preparation method of the low-pH fermented vegetable color protection and crispness increasing agent, which comprises the following steps: uniformly mixing the catechin, the sodium tripolyphosphate, the phytic acid, the pullulan and the calcium lactate to obtain the low-pH fermented vegetable color protection and crispness increasing agent.

[0013] In a third aspect,

[0014] The application also provides application of the low-pH fermented vegetable color protection and crispness increasing agent in low-pH fermented vegetable processing.

[0015] In some application embodiments, the application comprises: adding the low-pH fermented vegetable color protection and crispness enhancer to water in an amount of 0.2% to prepare a color protection and crispness enhancer solution.

[0016] In some application embodiments, the application comprises: soaking the cut and washed vegetables in the color protection and crispness enhancer solution, and then performing conventional fermentation.

[0017] In some application embodiments, the soaking time is 1 h.

[0018] In some application embodiments, the fermented vegetables are fermented cowpeas, and the fermentation process comprises: taking 40-60 parts of the cowpeas soaked in the color protection and crispness enhancer solution, 40-60 parts of water, 2-6 parts of salt, 0.25-0.8 parts of glucose, and 0.2 parts of calcium chloride, the parts being parts by mass; adding lactic acid bacteria powder in an amount of 0.001-0.01%, and then allowing the mixture to stand for fermentation at 35-37°C for 14 days.

[0019] In some application embodiments, the amount of the lactic acid bacteria powder added is 0.003-0.005%.

[0020] The present application has the following advantages and beneficial effects:

[0021] (1) The present application has good protective effects on the color and texture of low-pH fermented vegetables through the synergistic effects of catechin, sodium tripolyphosphate, phytic acid, pullulan, and calcium lactate in the proportions specified in the present application.

[0022] (2) The catechin, sodium tripolyphosphate, phytic acid, pullulan, and calcium lactate used in the present application are safe and non-toxic, and can ensure the safety of low-pH fermented vegetable products.

[0023] (3) The catechin, sodium tripolyphosphate, phytic acid, pullulan, and calcium lactate used in the present application do not have chemical or irritating odors, do not mask the original aroma of low-pH fermented vegetables, and do not have an odor. In addition, the original flavor of low-pH fermented vegetables is not significantly affected during the entire fermentation process. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 The actual pictures of the fermented cowpeas prepared in Example 1 and Comparative Examples 1-6 and Comparative Example 12.

[0025] Figure 2 The actual pictures of the fermented cowpeas prepared in Example 1 and Comparative Examples 7-12. DETAILED DESCRIPTION

[0026] The embodiments of the present application are described in detail below, and the embodiments described below are exemplary and are intended to explain the present application, and cannot be understood as limiting the present application.

[0027] The raw materials and reagents used in the following examples are commercially available or can be prepared by known methods unless otherwise stated.

[0028] Unless otherwise defined, scientific and technical terms used herein have the meanings commonly understood by one of ordinary skill in the art.

[0029] In the present document, where a range of values is described, it is understood that such a disclosure includes disclosure of all possible subranges therein and specific numerical values within the range, whether explicitly stated or not.

[0030] In the present document, the terms "first", "second", "third", etc. are used only for descriptive purposes, and cannot be understood as indicating or implying relative importance or quantity, nor can they be understood as implicitly indicating the importance or quantity of the technical features indicated. Moreover, "first", "second", "third", "fourth", etc. only serve the purpose of non-exhaustive enumeration description, and it should be understood that they do not constitute a closed limitation on the quantity.

[0031] The following are specific examples and comparative examples of the present application. It should be further noted that the schemes of the following comparative examples are not prior art, but are set up only for comparison with the schemes of the examples, and do not limit the present application.

[0032] Example 1

[0033] A preparation method of a low-pH fermented vegetable color-protecting and crispness-increasing agent, comprising the following steps:

[0034] Catechin 350 g, sodium tripolyphosphate 300 g, phytic acid 200 g, pullulan 75 g, and calcium lactate 75 g are mixed uniformly to prepare a low-pH fermented vegetable color-protecting and crispness-increasing agent.

[0035] The color-protecting and crispness-increasing liquid is prepared by dissolving 0.2% of the agent in clean water. The cowpea is cleaned and cut (the stems, threads, and rotten leaves of the cowpea are removed, and the cleaned cowpea is cut into small pieces; the same applies hereinafter). The cowpea is soaked for 1 h, taken out, and dried in the shade (to ensure that there is no living water or oil).

[0036] Example 2

[0037] A preparation method of a low-pH fermented vegetable color-protecting and crispness-increasing agent, comprising the following steps:

[0038] Catechin 400 g, sodium tripolyphosphate 300 g, phytic acid 200 g, pullulan 50 g, and calcium lactate 50 g are mixed uniformly to prepare a low-pH fermented vegetable color-protecting and crispness-increasing agent.

[0039] The color protection and crispness increasing agent was prepared by dissolving catechin 300 g, sodium tripolyphosphate 350 g, phytic acid 180 g, pullulan 120 g, and calcium lactate 50 g in water, and then mixing them evenly.

[0040] Example 3

[0041] A method for preparing a low-pH fermented vegetable color protection and crispness increasing agent, comprising the following steps:

[0042] The color protection and crispness increasing agent was prepared by dissolving catechin 300 g, sodium tripolyphosphate 350 g, phytic acid 180 g, pullulan 120 g, and calcium lactate 50 g in water, and then mixing them evenly.

[0043] The color protection and crispness increasing agent was prepared by dissolving catechin 300 g, sodium tripolyphosphate 350 g, phytic acid 180 g, pullulan 120 g, and calcium lactate 50 g in water, and then mixing them evenly.

[0044] Comparative Example 1

[0045] The color protection and crispness increasing agent was prepared by dissolving catechin 300 g, sodium tripolyphosphate 350 g, phytic acid 180 g, pullulan 120 g, and calcium lactate 50 g in water, and then mixing them evenly.

[0046] The color protection and crispness increasing agent was prepared by dissolving catechin 300 g, sodium tripolyphosphate 350 g, phytic acid 180 g, pullulan 120 g, and calcium lactate 50 g in water, and then mixing them evenly.

[0047] Comparative Example 2

[0048] The color protection and crispness increasing agent was prepared by dissolving catechin 300 g, sodium tripolyphosphate 350 g, phytic acid 180 g, pullulan 120 g, and calcium lactate 50 g in water, and then mixing them evenly.

[0049] The color protection and crispness increasing agent was prepared by dissolving catechin 300 g, sodium tripolyphosphate 350 g, phytic acid 180 g, pullulan 120 g, and calcium lactate 50 g in water, and then mixing them evenly.

[0050] Comparative Example 3

[0051] The color protection and crispness increasing agent was prepared by dissolving catechin 300 g, sodium tripolyphosphate 350 g, phytic acid 180 g, pullulan 120 g, and calcium lactate 50 g in water, and then mixing them evenly.

[0052] The color protection and crispness increasing agent was prepared by dissolving catechin 300 g, sodium tripolyphosphate 350 g, phytic acid 180 g, pullulan 120 g, and calcium lactate 50 g in water, and then mixing them evenly.

[0053] Comparative Example 4

[0054] Catechin 280g, sodium tripolyphosphate 270g, pullulan 300g, calcium lactate 150g, mixed uniformly to prepare a low pH fermented vegetable color protection and crispness enhancer.

[0055] The color protection and crispness enhancer was prepared by dissolving catechin 280g, sodium tripolyphosphate 270g, pullulan 300g, and calcium lactate 150g in clean water according to an addition amount of 0.2%. The cowpea after washing and cutting was soaked for 1 h, taken out, and then air-dried (to ensure no living water and no oil).

[0056] Comparative Example 5

[0057] Catechin 400g, sodium tripolyphosphate 320g, phytic acid 205g, and pullulan 75g were mixed uniformly to prepare a low pH fermented vegetable color protection and crispness enhancer.

[0058] The color protection and crispness enhancer was prepared by dissolving catechin 400g, sodium tripolyphosphate 320g, phytic acid 205g, and pullulan 75g in clean water according to an addition amount of 0.2%. The cowpea after washing and cutting was soaked for 1 h, taken out, and then air-dried (to ensure no living water and no oil).

[0059] Comparative Example 6

[0060] Catechin 380g, sodium tripolyphosphate 370g, phytic acid 200g, and calcium lactate 50g were mixed uniformly to prepare a low pH fermented vegetable color protection and crispness enhancer.

[0061] The color protection and crispness enhancer was prepared by dissolving catechin 380g, sodium tripolyphosphate 370g, phytic acid 200g, and calcium lactate 50g in clean water according to an addition amount of 0.2%. The cowpea after washing and cutting was soaked for 1 h, taken out, and then air-dried (to ensure no living water and no oil).

[0062] Comparative Example 7

[0063] Catechin 350g, sodium tripolyphosphate 300g, phytic acid 200g, chitosan 75g, and calcium lactate 75g were mixed uniformly to prepare a low pH fermented vegetable color protection and crispness enhancer.

[0064] The color protection and crispness enhancer was prepared by dissolving catechin 350g, sodium tripolyphosphate 300g, phytic acid 200g, chitosan 75g, and calcium lactate 75g in clean water according to an addition amount of 0.2%. The cowpea after washing and cutting was soaked for 1 h, taken out, and then air-dried (to ensure no living water and no oil).

[0065] Comparative Example 8

[0066] Catechin 350g, sodium tripolyphosphate 300g, phytic acid 200g, pullulan 75g, and calcium ascorbate 75g were mixed uniformly to prepare a low pH fermented vegetable color protection and crispness enhancer.

[0067] The color protection and crispness enhancer was prepared by dissolving catechin 350g, sodium tripolyphosphate 300g, phytic acid 200g, pullulan 75g, and calcium ascorbate 75g in clean water according to an addition amount of 0.2%. The cowpea after washing and cutting was soaked for 1 h, taken out, and then air-dried (to ensure no living water and no oil).

[0068] Comparative Example 9

[0069] Catechin 350g, sodium tripolyphosphate 300g, phytic acid 200g, pullulan 75g, calcium chloride 75g, mix evenly, and prepare a low-pH fermented vegetable color-protecting and crispness-increasing agent.

[0070] Dissolve in clean water according to the addition amount of 0.2%, prepare a color-protecting and crispness-increasing liquid, soak the cut cowpeas after cleaning for 1 h, take them out, drain the water, and dry in the shade (ensure no living water and no oil).

[0071] Comparative Example 10:

[0072] Catechin 350g, sodium tripolyphosphate 300g, phytic acid 200g, pullulan 75g, calcium lactate 75g, mix evenly, and prepare a low-pH fermented vegetable color-protecting and crispness-increasing agent.

[0073] Dissolve in clean water according to the addition amount of 0.2%, prepare a color-protecting and crispness-increasing liquid, soak the cut cowpeas after cleaning for 1 h, take them out, drain the water, and dry in the shade (ensure no living water and no oil).

[0074] Comparative Example 11:

[0075] Tea polyphenol 350g, sodium tripolyphosphate 300g, phytic acid 200g, pullulan 75g, calcium lactate 75g, mix evenly, and prepare a low-pH fermented vegetable color-protecting and crispness-increasing agent.

[0076] Dissolve in clean water according to the addition amount of 0.2%, prepare a color-protecting and crispness-increasing liquid, soak the cut cowpeas after cleaning for 1 h, take them out, drain the water, and dry in the shade (ensure no living water and no oil).

[0077] Comparative Example 12: blank group

[0078] Comparative Example 13:

[0079] Catechin 350g, sodium tripolyphosphate 300g, phytic acid 200g, pullulan 75g, calcium lactate 75g, mix evenly, and prepare a low-pH fermented vegetable color-protecting and crispness-increasing agent.

[0080] Dissolve in clean water according to the addition amount of 0.1%, prepare a color-protecting and crispness-increasing liquid, soak the cut cowpeas after cleaning for 1 h, take them out, drain the water, and dry in the shade (ensure no living water and no oil).

[0081] Comparative Example 14:

[0082] Catechin 350g, sodium tripolyphosphate 300g, phytic acid 200g, pullulan 75g, calcium lactate 75g, mix evenly, and prepare a low-pH fermented vegetable color-protecting and crispness-increasing agent.

[0083] The color protection and crispness increasing liquid is prepared by dissolving 0.5% of the color protection and crispness increasing agent in clean water, and the cowpea after washing and cutting is soaked for 1h, then taken out, drained and dried (ensure no water and no oil).

[0084] Comparative Example 15:

[0085] The low-pH fermented vegetable color protection and crispness increasing agent is prepared by uniformly mixing 350g of catechin, 300g of sodium tripolyphosphate, 200g of phytic acid, 75g of pullulan and 75g of calcium lactate.

[0086] The color protection and crispness increasing liquid is prepared by dissolving 0.2% of the color protection and crispness increasing agent in clean water, and the cowpea after washing and cutting is soaked for 30min, then taken out, drained and dried (ensure no water and no oil).

[0087] Comparative Example 16:

[0088] The low-pH fermented vegetable color protection and crispness increasing agent is prepared by uniformly mixing 350g of catechin, 300g of sodium tripolyphosphate, 200g of phytic acid, 75g of pullulan and 75g of calcium lactate.

[0089] The color protection and crispness increasing liquid is prepared by dissolving 0.2% of the color protection and crispness increasing agent in clean water, and the cowpea after washing and cutting is soaked for 4h, then taken out, drained and dried (ensure no water and no oil).

[0090] Comparative Example 17:

[0091] The low-pH fermented vegetable color protection and crispness increasing agent is prepared by uniformly mixing 350g of catechin, 300g of sodium tripolyphosphate, 200g of phytic acid, 75g of pullulan and 75g of calcium lactate.

[0092] The color protection and crispness increasing liquid is prepared by dissolving 0.2% of the color protection and crispness increasing agent in clean water, and the cowpea after washing and cutting is soaked for 4h, then taken out, drained and dried (ensure no water and no oil).

[0093] The specific application steps of the examples 1-3 and the comparative examples 1-11 and 13-16 of the application are as follows:

[0094] The cowpea soaked by the color protection and crispness increasing liquid is taken 44 parts by mass, water is taken 50 parts by mass, salt is taken 5 parts by mass, glucose is taken 0.795 parts by mass, calcium chloride is taken 0.2 parts by mass, and then lactic acid bacteria powder is added 0.005 parts by mass (Sichuan Gaofukujimemo Biological Technology Co., Ltd., live bacteria number: ≥500 billion CFU / g), and then the mixture is placed at 35-37℃ for fermentation for 14 days. The fermented sample is placed in a water bath sterilizer, and sterilized at 88-92℃ for 15min. After sterilization, the product is rapidly cooled by spraying or soaking with cold water, so that the center temperature of the product is rapidly reduced to below 40℃.

[0095] The specific steps of the blank sample of the comparative example 12 are as follows:

[0096] S1: Selection of raw and auxiliary materials: all raw and auxiliary materials need to meet the food safety standards. Select the bean pods, thread, rotten leaves and other impurities;

[0097] S2: Slitting: wash the cowpea and cut it into small pieces, then dry it (ensure no living water, no oil);

[0098] S3: Raw material pretreatment: 44 parts by mass of cowpea, 50 parts by mass of water, 5 parts by mass of salt, 0.795 parts by mass of glucose, and 0.2 parts by mass of calcium chloride; then add 0.005 parts by mass of lactic acid bacteria powder (Sichuan Gaofuji Biological Technology Co., Ltd., viable bacterial count: ≥50 billion CFU / g).

[0099] S4: Fermentation: place at 35-37°C for 14 days.

[0100] S5: Sterilization: place the fermented sample in a water bath sterilizer and sterilize at 88-92°C for 15 minutes.

[0101] S6: Cooling: immediately cool after sterilization, use cold water spray or soak to quickly reduce the product center temperature to below 40°C.

[0102] The specific steps for Comparative Example 17 are as follows:

[0103] Take 44 parts by mass of cowpea after washing and cutting, 49.8 parts by mass of water, 5 parts by mass of salt, 0.795 parts by mass of glucose, 0.2 parts by mass of calcium chloride, and 0.2 parts by mass of low-pH fermented vegetable color protection and crispness enhancer, then add 0.005 parts by mass of lactic acid bacteria powder (Sichuan Gaofuji Biological Technology Co., Ltd., viable bacterial count: ≥50 billion CFU / g), then place at 35-37°C for 14 days. Place the fermented sample in a water bath sterilizer and sterilize at 88-92°C for 15 minutes; immediately cool after sterilization, use cold water spray or soak to quickly reduce the product center temperature to below 40°C. Table 1 and Table 2 are the formula components and mass percentages of the color protection and crispness enhancer in each example and comparative example.

[0104] Table 1 Formula components and mass percentages (unit wt%) of color protection and crispness enhancer in Example 1 and Comparative Examples 1-12

[0105]

[0106]

[0107] Table 2 Formula components and mass percentages (unit wt%) of the compounded color protection and crispness enhancer in Example 1 and Comparative Examples 13-16

[0108]

[0109] After the fermentation, the sensory evaluation of the fermented cowpea samples of each example and the comparative example was carried out. The sensory evaluation personnel consisted of 8 experienced, healthy, sensitive and high discriminative sensory evaluation engineers, aged between 30 and 35 years. The specific sensory evaluation standard and the sensory evaluation results are shown in Table 3 and Table 4, respectively.

[0110] Table 3 Sensory evaluation standard of color protection and crispness enhancement effect of each example and the comparative example

[0111]

[0112]

[0113] Table 4 Sensory evaluation score of color protection and crispness enhancement effect of each example and the comparative example

[0114]

[0115]

[0116] As shown in Table 4, the fermented cowpea treated with the color protection and crispness enhancement agent of Examples 1-3 all showed good color protection and crispness enhancement effect, and the color and texture scores of the fermented cowpea in the sensory evaluation were all above 80. During the experiment, the inventors found that the components of the color protection and crispness enhancement agent were indispensable, and when one of the components was missing (see Comparative Examples 3-6), the sensory evaluation results of the color protection and crispness enhancement effect were obviously poorer than those of Examples 1-3. Meanwhile, the applicant found that the mass ratio of the components was also very important. Although Comparative Examples 1-2 both contained 5 components, the amount of phytic acid accounted for a large proportion in Comparative Example 1, and the amount of catechin accounted for a large proportion in Comparative Example 2, and the sensory evaluation results of the color protection and crispness enhancement effect of Comparative Examples 1-2 were obviously poorer than those of Examples 1-3.

[0117] Comparative Examples 7-11 were examples of other component designs tried by the inventors during the test stage. Compared with Example 1, only some components were replaced, and it was found that only under the condition of the color protection and crispness enhancement agent components, the sensory evaluation scores of the color and texture of the fermented cowpea were obviously better than those of other comparative examples. This further illustrated the synergistic effect of catechin, sodium tripolyphosphate, phytic acid, pullulan and calcium lactate.

[0118] Comparative Examples 13-16 were studies of the same color protection and crispness enhancement agent with different adding amounts and different soaking times, and it was found that the adding proportion and soaking time of the color protection and crispness enhancement agent also had a significant effect on the color protection and crispness enhancement effect. The above results showed that the color protection and crispness enhancement agent had good color protection and crispness enhancement effect, and the effective components had good synergistic effect, and the fermented cowpea had the best effect when the adding amount was 0.2% and the soaking time was 1 h.

[0119] Example 17 is a control example in which the color-protecting and crispiness- enhancing agent is added during fermentation. It is found that the addition of the color-protecting and crispiness-enhancing agent during fermentation has no obvious effect on the color and texture of the fermented cowpea. The possible reason is that the effect of the acidic environment on the color and texture of the cowpea in the initial stage of fermentation is irreversible. Even if the color-protecting and crispiness-enhancing agent is added during fermentation, the chlorophyll of the vegetable has been degraded to form a de-magnesium chlorophyll under the acidic conditions, and the pectin and other substances have also been hydrolyzed, and the color and texture of the cowpea have already been changed irreversibly. This result also confirms that the color-protecting and crispiness-enhancing pretreatment of the cowpea before fermentation can effectively maintain the color and texture of the cowpea after the fermentation process, and the effect is obviously better than that of adding during fermentation.

[0120] Further, the inventors tested the color of the fermented cowpea in each of the above examples and the control example using a U.S. HunterLab agera colorimeter. The degree of color change was evaluated by comparing the L* value, a* value, and b* value measured by the colorimeter, and the color-protecting effect of the color-protecting and crispiness-enhancing agent can be determined according to the numerical values. The L* value is a brightness parameter, and the larger the L* value, the higher the brightness. The a* value is a red-green parameter, and a positive a* value represents red, a negative a* value represents green, and the smaller the negative a* value, the higher the greenness. The b* value is a yellow-blue parameter, and a positive b* value represents yellow, a negative b* value represents blue, and the larger the positive b* value, the higher the yellowness. Table 5 is the color determination index of the fermented cowpea by the colorimeter.

[0121] Table 5 Color index of fermented cowpea

[0122]

[0123] Comparative Example 12 is a low pH fermented cowpea sample without additional color-protecting and crispness-improving agent, which is a blank control. Comparative Examples 7-11 are based on the color-protecting and crispness-improving agent of Example 1, in which only one single component is replaced. As can be seen from the data, the component other than the raw material of Example 1 has no significant effect on the color protection of fermented cowpea. Comparative Examples 3-6 are five color-protecting and crispness-improving agent raw materials in which one component is reduced. Comparative Examples 1 and 2 are color-protecting and crispness-improving agents with different ratios. It is found that the color protection effect of the low pH fermented cowpea samples of Comparative Examples 1-6 decreases, which is obviously not as good as that of Examples 1-3. In addition, Comparative Examples 13-16 are control groups of color-protecting and crispness-improving agents with different addition amounts and soaking times. It is found that the color protection effect of fermented cowpea is not obvious when the addition amount is less than 0.2% or more than 0.2%, and the soaking time is too short or too long. In comparison with the three examples, the effect of Example 1 is the best. Comparative Example 17 is the addition of color-protecting and crispness-improving agent during fermentation. It is found that the addition of color-protecting and crispness-improving agent during fermentation has no obvious effect on the color of fermented cowpea. The possible reason is that the effect of acidic environment on the color and texture of cowpea in the initial stage of fermentation is irreversible. Even if color-protecting and crispness-improving agent is added during fermentation, the chlorophyll of the vegetable has been degraded by the acidic condition to form demagnified chlorophyll, and the pectin and other substances have also been hydrolyzed, so the color and texture of cowpea have changed irreversibly. This result also confirms that the color protection pretreatment of cowpea before fermentation can effectively maintain the color of cowpea during fermentation, which is obviously better than the addition during fermentation.

[0124] Further, the inventors used the puncture mode of TA.XT Plus texture analyzer to determine the surface hardness of fermented cowpea. The P / 2N-2mm stainless steel needle-shaped probe, pre-test speed 1.0mm / s, test speed 3.0mm / s, post-test speed 10.0mm / s, test distance 6mm, trigger force 3g, data acquisition rate 400pps, and test temperature were used. The probe was measured on the outer surface of the sample of each example and comparative example at three positions, i.e. upper, middle and lower, and the average value was taken as the result. Table 6 is the texture index of fermented cowpea.

[0125] Table 6 Texture index of fermented cowpea

[0126]

[0127]

[0128] Comparative Example 12 is a blank control. The texture measurement results of the three examples compared with Comparative Examples 1-11 show that the color-protecting and crispness-improving agent has a good stabilizing effect on the texture of fermented cowpea. Comparative Examples 7-11 are experiments in which one of the components of the color-protecting and crispness-improving agent is replaced. As can be seen from the data, the crispness-improving effect of Comparative Examples 7-11 on fermented cowpea is not as good as that of Examples 1-3. In addition, Comparative Examples 3-6 are experiments in which one of the five components of the color-protecting and crispness-improving agent is reduced, and Comparative Examples 1 and 2 are experiments in which the ratio of the components of the color-protecting and crispness-improving agent is changed. It is found that the crispness-improving effect on fermented cowpea is not as good as that of Examples 1-3. Comparative Examples 13-16 are control groups in which the color-protecting and crispness-improving agent is added in different amounts and soaked for different times. It is found that the crispness-improving effect on fermented cowpea is not obvious when the amount of the color-protecting and crispness-improving agent is less than 0.2% or more than 0.2%, and the soaking time is too short or too long. Comparative Example 17 is an experiment in which the color-protecting and crispness-improving agent is added during fermentation. It is found that the color-protecting and crispness-improving agent has no obvious effect on the texture of fermented cowpea. The possible reason is that the effect of the acidic environment on the color and texture of cowpea in the initial stage of fermentation is irreversible. Even if the color-protecting and crispness-improving agent is added during fermentation, the chlorophyll of the vegetable has been degraded to form de-magnesium chlorophyll, and pectin and other substances have been hydrolyzed, resulting in irreversible changes in the color and texture of cowpea. This result also confirms that the crispness-improving pretreatment of cowpea before fermentation can effectively maintain the texture of fermented cowpea, and the effect is obviously better than that of adding the color-protecting and crispness-improving agent during fermentation. The above results show that the color-protecting and crispness-improving agent has a good effect on improving the texture of fermented cowpea when the amount of the color-protecting and crispness-improving agent is 0.2% and the soaking time is 1 h.

[0129] In the present application, the terms "one embodiment", "some embodiments", "example", "specific example" or "some examples" etc. mean that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any appropriate manner in any one or more embodiments or examples. In addition, different embodiments or examples described in the present specification and the features of different embodiments or examples can be combined and combined by those skilled in the art without contradiction.

[0130] Although the embodiments of the present application have been shown and described above, it should be understood that the above embodiments are exemplary and should not be construed as limiting the present application, and those skilled in the art can make changes, modifications, replacements and variations to the above embodiments within the scope of the present application.

Claims

1. A low pH fermented vegetable color-protecting and crispness-improving agent, characterized by, The components and their mass percentages include catechin 30%-45%, sodium tripolyphosphate 20%-40%, phytic acid 15%-25%, pullulan 2%-15%, and calcium lactate 5%-10%, and the sum of the mass percentages of the components is 100%.

2. The low pH fermented vegetable color-protecting and crispness-improving agent according to claim 1, characterized by, The low-pH fermented vegetable color protection and crispness increasing agent includes the following components and their mass percentages: catechin 30%-40%, sodium tripolyphosphate 25%-35%, phytic acid 17%-24%, pullulan 5%-12%, and calcium lactate 5%-8%, and the sum of the mass percentages of the components is 100%. 3.The low-pH fermented vegetable color protection and crispness enhancer according to claim 1 or 2, characterized in that, The fermented vegetable is fermented cowpea, fermented radish, fermented pepper or fermented cabbage.

4. The method of preparing a low pH fermented vegetable color-protecting and crispness-improving agent according to any one of claims 1 to 3, characterized in that, The method includes the following steps: mixing the catechin, the sodium tripolyphosphate, the phytic acid, the pullulan and the calcium lactate uniformly.

5. The low-pH fermented vegetable color protection and crispness increasing agent according to any one of claims 1-3 is applied in the processing of low-pH fermented vegetables.

6. Use according to claim 5, characterized in that, The method includes the following steps: The low-pH fermented vegetable color protection and crispness increasing agent is added to water in an amount of 0.2% to prepare the color protection and crispness increasing liquid.

7. Use according to claim 6, characterized in that, The application includes the following steps: soaking the cut and washed vegetables in the color protection and crispness increasing liquid, and then performing conventional fermentation.

8. Use according to claim 7, characterized in that, The soaking time is 1 h.

9. Use according to claim 8, characterized in that, The fermented vegetable is fermented cowpea, and the fermentation process includes the following steps: taking 40-60 parts of cowpea soaked in the color protection and crispness increasing liquid, 40-60 parts of water, 2-6 parts of salt, 0.25-0.80 parts of glucose, and 0.2 parts of calcium chloride, wherein the parts are mass parts; adding lactic acid bacteria powder, and the amount of the lactic acid bacteria powder added is 0.001-0.01%, and then performing fermentation at 35-37°C for 14 days.

10. Use according to claim 9, characterized in that, The amount of the lactic acid bacteria powder added is 0.003%-0.005%.

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