A food gas production detection method and a detection kit thereof

Abstract

The present application relates to a method for detecting the gas expansion of vinegar and a kit thereof. The method comprises providing a vinegar to be tested and an acid-base indicator in a sealable container, sealing the container and observing the color change of the acid-base indicator; wherein the vinegar to be tested is not in direct contact with the acid-base indicator, and the color change of the acid-base indicator indicates that the vinegar to be tested produces gas. The method of the present application can determine whether the vinegar expands in a very short time.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of food, especially vinegar quality detection, and specifically relates to a food gas production detection method and a detection kit thereof. BACKGROUND

[0002] As a traditional condiment in China, vinegar is deeply loved by the public, and thus has a huge production and consumption volume. In China, solid-state fermentation process is usually used for brewing vinegar, and various microbial communities constitute a complex fermentation system, thus making vinegar produce unique flavor. Due to the multi-strain fermentation process, the production process is prone to microbial contamination, which leads to the phenomenon of bottle and bag swelling of vinegar products during the shelf life (ENTANI E, MASAI H, SUZUKI K. Lactobacillus acetotolerans, a new species from fermented vinegar broth [J]. International Journal of Systematic Bacteriology, 1986, 36(4): 544-549.; Ma Jingli, Qian Feng. Discussion on solving the problem of vinegar swelling [J]. China Brewing, 2010, 29(9): 123-127). This swelling and deterioration not only affects the quality of vinegar, but also affects the safety of the product, becomes a thorny problem that plagues production enterprises, and brings huge economic losses.

[0003] In view of this phenomenon, the total number of colonies and the number of mold and yeast of the vinegar before leaving the factory are detected according to the national standard method, and there is no abnormality, so the detection of the gas expansion of the vinegar becomes an important indicator for measuring whether the vinegar product is qualified. At present, the method for detecting the gas expansion of the vinegar mainly uses a balloon or a Durham tube to collect the gas produced from the vinegar to test whether the vinegar is gas-expanded, and generally can detect whether the sample contains gas expansion within about 20 days. In order to improve the detection efficiency, the gas-producing bacteria in the vinegar are enriched by centrifugation or membrane filtration, and then used to detect whether the gas expansion exists, but even so, the detection time is shortened to 10-15 days (Liu Fang. Research on the characteristics of gas-expanded deteriorated vinegar and the detection and control of the contaminated microorganisms. Sichuan Agricultural University. 2018.06.; Zheng Yu, Jiwei Niu, Xianglong Zhang, et al. Isolation and identification of potential contaminating microorganisms in traditional vinegar [J]. Modern Food Science and Technology, 2016, 32(11): 334-339.; Sun Wenli, Sun Ling, Xing Zheng, Hou Xiaoshan, He Ronghai, Ma Haile. Isolation and identification of contaminating microorganisms in gas-expanded vinegar and their physiological and biochemical characteristics [J]. Food Industry Science and Technology, 2018, 17(39): 99-105). In addition, some vinegar production enterprises learn from the method of detecting the gas expansion of canned food, that is, the sample is poured into a plastic soft bottle for incubation, and if the sample does not appear gas expansion within a certain time, it indicates that the product is qualified. Since this method cannot timely feedback the contamination of microorganisms, the detection time is relatively long (usually 30 days or even 60 days or longer), and the product backlog will cause great economic pressure on the enterprise (Liu Fang, Research on the characteristics of gas-expanded deteriorated vinegar and the detection and control of the contaminated microorganisms, Sichuan Agricultural University, 2018.06).

[0004] Other foods such as soy sauce, beverages, and vacuum-packed foods such as bread also have the phenomenon of gas expansion. Therefore, there is a need in the art for a method for rapidly detecting the gas production of foods, and a method for predicting the gas expansion of foods. SUMMARY

[0005] The first aspect of the present application provides a method for detecting the gas production of foods or predicting the gas expansion of foods using an acid-base indicator, the method comprising: providing an acid-base indicator and an optional nutrient-containing food to be tested in a sealable container, sealing the container and observing the color change of the acid-base indicator; wherein the food to be tested is not in direct contact with the acid-base indicator, and the color change of the acid-base indicator indicates that the food to be tested produces gas, or there is a possibility of gas expansion.

[0006] In one or more embodiments, the food to be tested is separated from the acid-base indicator by a layer of mineral oil.

[0007] In one or more embodiments, the food is a liquid condiment, including vinegar, soy sauce, and cooking wine.

[0008] In one or more embodiments, the food is a beverage.

[0009] In one or more embodiments, the mineral oil is white oil or liquid paraffin.

[0010] In one or more embodiments, the acid-base indicator is a single or mixed acid-base indicator that undergoes color change in the range of pH≥5.6.

[0011] In one or more embodiments, the acid-base indicator is selected from the group consisting of methyl red, bromophenol red, p-nitrophenol, bromothymol blue, curcumin, cresol red, neutral red, resorcinol, 1-naphthol, orange I, phenolphthalein, o-cresolphthalein, thymolphthalein, alizarin red S, alizarin yellow R, alizarin yellow GG, nitramine, phenol red, fast yellow, a mixture of bromocresol green and chlorophenol red, a mixture of bromothymol blue and bromocresol purple, a mixture of neutral red and methyl blue, a mixture of bromothymol blue and phenol red, and a mixture of cresol red and thymol blue.

[0012] In one or more embodiments, the acid-base indicator is bromothymol blue or cresol red.

[0013] In one or more embodiments, the acid-base indicator is provided in the form of a solution dissolved in a solvent.

[0014] In one or more embodiments, the solvent is ethanol or an aqueous ethanol solution.

[0015] In one or more embodiments, the aqueous ethanol solution has a weight percentage concentration≥70%, preferably≥90%, more preferably≥95%.

[0016] In one or more embodiments, the pH of the solution of the acid-base indicator is not lower than the lowest pH value of the color change range of the acid-base indicator used, preferably differs from the lowest pH value by at least 0.2, more preferably by at least 0.5.

[0017] In one or more embodiments, the pH of the solution of the acid-base indicator is >5.6, preferably≥6.0, more preferably≥7.0.

[0018] In one or more embodiments, the density of the solution of the acid-base indicator is lower than the density of the mineral oil layer.

[0019] The present application also provides a method for detecting gas production or predicting gas swelling of food using an acid-base indicator, the method comprising:

[0020] (1) forming an oil seal layer on the test vinegar optionally containing nutrients in a container, so as to isolate the test vinegar from air; preferably, the oil seal layer is formed using mineral oil;

[0021] (2) adding an acid-base indicator on the oil seal layer to form an indicator layer;

[0022] (3) sealing the container and observing the color change of the indicator;

[0023] wherein the color change of the indicator indicates that the food under test produces gas, or indicates that the food under test has the possibility of bloating.

[0024] In one or more embodiments, the food is a liquid condiment, including vinegar, soy sauce and cooking wine.

[0025] In one or more embodiments, the food is a beverage.

[0026] In one or more embodiments, the density of the indicator layer is lower than the density of the oil seal layer.

[0027] In one or more embodiments, the acid-base indicator is a single or mixed acid-base indicator that changes color in the range of pH≥5.6.

[0028] In one or more embodiments, the acid-base indicator is selected from the group consisting of methyl red, bromophenol red, p-nitrophenol, bromothymol blue, turmeric, cresol red, neutral red, resorcinol, 1-naphthol phthalein, orange I, phenolphthalein, o-cresolphthalein, thymolphthalein, alizarin red S, alizarin yellow R, alizarin yellow GG, nitramine, phenol red, fast yellow, a mixture of bromocresol green and chlorophenol red, a mixture of bromothymol blue and bromocresol purple, a mixture of neutral red and methyl blue, a mixture of bromothymol blue and phenol red, and a mixture of cresol red and thymol blue.

[0029] In one or more embodiments, the acid-base indicator is bromothymol blue or cresol red.

[0030] In one or more embodiments, the indicator layer contains a solvent.

[0031] In one or more embodiments, the solvent is ethanol or an aqueous ethanol solution.

[0032] In one or more embodiments, the aqueous ethanol solution has a weight percentage concentration of≥70%, preferably≥90%, more preferably≥95%.

[0033] In one or more embodiments, the pH of the indicator layer is not lower than the minimum pH value of the color change range of the acid-base indicator used, preferably at least 0.2 different from the minimum pH value, more preferably at least 0.5 different.

[0034] In one or more embodiments, the pH of the indicator layer is >5.6, preferably≥6.0, more preferably≥7.0.

[0035] In one or more embodiments, the mineral oil is white oil or liquid paraffin.

[0036] The present application also provides a food gas production detection or prediction of food bloating kit, said kit comprising a mineral oil, an acid-base indicator and optionally a container.

[0037] In one or more embodiments, the mineral oil is a white oil or a liquid paraffin.

[0038] In one or more embodiments, the acid-base indicator is a single or mixed acid-base indicator that changes colour in the range of pH > 5.6.

[0039] In one or more embodiments, the acid-base indicator is selected from the group consisting of methyl red, bromophenol red, p-nitrophenol, bromothymol blue, curcumin, cresol red, neutral red, resorcinol, 1-naphthol phthalein, orange I, phenolphthalein, o-cresolphthalein, thymolphthalein, alizarin red S, alizarin yellow R, alizarin yellow GG, nitramine, phenol red, fast yellow, a mixture of bromocresol green and chlorophenol red, a mixture of bromocresol purple and bromothymol blue, a mixture of neutral red and methyl blue, a mixture of bromothymol blue and phenol red, and a mixture of cresol red and thymol blue.

[0040] In one or more embodiments, the acid-base indicator is bromothymol blue or cresol red.

[0041] The present application also provides the use of a single or mixed acid-base indicator that changes colour in the range of pH > 5.6 and / or a mineral oil for the detection of food gas production and / or the prediction of food bloating, or for the preparation of a kit for the detection of food gas production and / or the prediction of food bloating.

[0042] In one or more embodiments, the acid-base indicator is selected from the group consisting of methyl red, bromophenol red, p-nitrophenol, bromothymol blue, curcumin, cresol red, neutral red, resorcinol, 1-naphthol phthalein, orange I, phenolphthalein, o-cresolphthalein, thymolphthalein, alizarin red S, alizarin yellow R, alizarin yellow GG, nitramine, phenol red, fast yellow, a mixture of bromocresol green and chlorophenol red, a mixture of bromocresol purple and bromothymol blue, a mixture of neutral red and methyl blue, a mixture of bromothymol blue and phenol red, and a mixture of cresol red and thymol blue.

[0043] In one or more embodiments, the acid-base indicator is bromothymol blue or cresol red.

[0044] In one or more embodiments, the acid-base indicator is provided in the form of a solution dissolved in a solvent.

[0045] In one or more embodiments, the solvent is ethanol or an aqueous ethanol solution.

[0046] In one or more embodiments, the weight percentage concentration of the aqueous ethanol solution is ≥70%, preferably ≥90%, more preferably ≥95%.

[0047] In one or more embodiments, the pH of the solution of the acid-base indicator is not lower than the lowest pH value of the color change range of the acid-base indicator used, preferably differing from the lowest pH value by at least 0.2, more preferably by at least 0.5.

[0048] In one or more embodiments, the pH of the solution of the acid-base indicator is >5.6, preferably ≥6.0, more preferably ≥7.0.

[0049] In one or more embodiments, the mineral oil is white oil or liquid paraffin. Attached Figure Description

[0050] Figure 1 Gas production test results of Example 1. Left column: Normal vinegar; Right column: Gas-producing vinegar.

[0051] Figure 2 Gas production test results of Example 2. Left column: Normal vinegar; Right column: Gas-producing vinegar.

[0052] Figure 3 The balloon markers indicate the results of vinegar gas production testing. Tube 1: Gas-producing vinegar + oil seal; Tube 2: Gas-producing vinegar + nutrients + oil seal; Tube 3: Gas-producing vinegar; Tube 4: Gas-producing vinegar + nutrients.

[0053] Figure 4 The results of Duchenne tubule labeling for detecting gas production in vinegar are shown below. From left to right: gas-producing bacteria + linoleic acid, gas-producing bacteria, gas-producing bacteria + nutrients + oil seal, and gas-producing bacteria + oil seal.

[0054] Figure 5 Results of gas production tests on oil seals using different types of oil. 1: Mineral oil; 2: Olive oil; 3: Peanut oil; 4: Corn oil; 5: Soybean oil. In each numbered chart, the left column represents normal vinegar, and the right column represents gas-producing vinegar.

[0055] Figure 6 Gas production test results of 10 batches of vinegar products.

[0056] Figure 7 Gas production test results of 12 different brands of vinegar products.

[0057] Figure 8 : Results of gas production detection using cresol red as an acid-base indicator.

[0058] In the centrifuge tubes shown in the figure, the colorless layer in the middle is the mineral oil layer. Detailed Implementation

[0059] To enable persons skilled in the art to understand the features and effects of the present application, the following is a general description and definition of the terms and phrases mentioned in the specification and claims. Unless otherwise specified, all technical and scientific words used herein have their usual meanings to those skilled in the art of the present application, and in the event of conflict, the definitions in the specification shall prevail.

[0060] Theories or mechanisms described and disclosed herein, whether correct or not, should not be considered limiting the scope of the present application, i.e., the present application can be practiced without regard to any particular theory or mechanism.

[0061] Herein, all features defined in the form of numerical ranges or percentage ranges, such as numerical values, amounts, contents and concentrations, are for the sake of brevity and convenience. Accordingly, the description of numerical ranges or percentage ranges should be considered to have encompassed and specifically disclosed all possible sub-ranges and individual numerical values within the range (including integers and fractions).

[0062] Herein, unless otherwise specified, the ratio refers to the mass ratio, and the percentage content refers to the mass percentage content.

[0063] Herein, for the sake of brevity, all possible combinations of the technical features in each embodiment or example are not described. Therefore, as long as the combinations of the technical features do not conflict, the technical features in each embodiment or example can be combined arbitrarily, and all possible combinations should be considered as the scope disclosed in the specification.

[0064] The inventors found that by using an oil seal to isolate air, a sealed state of the finished vinegar is simulated, and then an indicator is added on the oil layer, the gas generated by the oil-sealed vinegar will pass through the oil seal layer, reach the upper layer, and contact with the indicator, causing the color of the indicator to change, so that the vinegar gas generation can be quickly judged, effectively solving the problem of vinegar swelling gas discrimination during shelf life.

[0065] Therefore, the present application provides a vinegar gas generation detection method, or a method for predicting vinegar swelling gas, which comprises the following steps:

[0066] (1) forming an oil seal layer on the vinegar to be tested in the container to isolate the vinegar from air; and

[0067] (2) adding an acid-base indicator on the oil seal layer to form an indicator layer.

[0068] The vinegar can be of any brand and specification, and can be vinegar to be marketed or already marketed. In some embodiments, nutrients suitable for uptake by microorganisms present in the vinegar can be added to the vinegar to be tested prior to forming the oil seal. Such nutrients include, but are not limited to, carbohydrates such as various sugars, e.g., glucose, and nitrogen sources such as peptone. Typically, the nutrients are sterile and are added in a total amount in the range of 0.05 to 1% based on the total weight of the vinegar to be tested.

[0069] The container can be any sealable container, including but not limited to a centrifuge tube. Preferably, the container is transparent so that the change in color of the indicator can be visually observed. The volume of the container is not particularly limited, but is typically in the range of 30 to 100 mL for convenience and economy of testing.

[0070] The present application preferably uses mineral oil to form the oil seal to isolate the vinegar to be tested from air. Mineral oil is a mixture of refined liquid hydrocarbons obtained from petroleum, and mainly includes two major categories of straight-chain, branched-chain alkanes and alkyl-substituted cycloalkanes (MOSH) and alkyl-substituted aromatic hydrocarbons (MOAH). Food-grade mineral oil is white oil (liquid paraffin) which is essentially all MOSH, while industrial-grade mineral oil contains a higher content of MOSH and about 15 to 35% MOAH. Various commercially available mineral oils can be used to practice the present application. When adding mineral oil to the vinegar to be tested to form the oil seal, care should be taken to avoid the formation of air bubbles between the vinegar and the oil layer.

[0071] The amount of mineral oil used is not particularly limited and can be readily determined based on the size of the container, the amount of acid-base indicator used, etc., as long as the mineral oil seal formed is thick enough so that the indicator layer cannot penetrate through the seal to directly contact the vinegar within the testing time.

[0072] The carbon dioxide produced during the gas / flatulence production of the vinegar dissolves in water to form a weak acid, and the pH of the saturated carbon dioxide aqueous solution is about 5.6. The color change of the acid-base indicator caused by the weak acid can be used to determine whether the vinegar produces gas and to predict whether it will be flatulence during the shelf life. Therefore, the acid-base indicator suitable for the present application should change color in the pH range of > 5.6, more preferably in the pH range of > 6. The acid-base indicator suitable for the present application can be a single acid-base indicator or a mixed acid-base indicator. Preferably, the acid-base indicator suitable for the present application is selected from the group consisting of methyl red, bromophenol red, p-nitrophenol, bromothymol blue, turmeric, cresol red, neutral red, resorcinol, 1-naphthol phthalein, orange I, phenolphthalein, o-cresolphthalein, thymolphthalein, alizarin red S, alizarin yellow R, alizarin yellow GG, nitramine, phenol red, fast yellow, a mixture of bromocresol green and chlorophenol red, a mixture of bromocresol purple and bromothymol blue, a mixture of neutral red and methyl blue, a mixture of bromothymol blue and phenol red, and a mixture of cresol red and thymol blue. In some embodiments, a single or mixed acid-base indicator with a color change range of pH 6.8-7.5, preferably pH 6.5-7.5, is used. The most preferred acid-base indicator is bromothymol blue or cresol red.

[0073] There is no particular limitation on the amount of acid-base indicator used. It should be understood that the sensitivity of the detection will change when the amount of acid-base indicator used is different. The concentration of the indicator solution is increased, and in the case of the same amount of vinegar to be tested, more gas needs to be produced to change color, which will make the detection of vinegar flatulence longer and reduce the sensitivity. The optimal detection sensitivity can be obtained by testing as described herein. In preferred embodiments, the content of acid-base indicator in the indicator layer can be in the range of 0.005-1 g / 100 mL of the indicator layer, for example, 0.01-0.1 g / 100 mL of the indicator layer, or 0.01-0.05 g / 100 mL of the indicator layer.

[0074] In addition to the acid-base indicator, the indicator layer usually contains a solvent for dissolving the acid-base indicator. The requirement for the solvent is that the density of the indicator layer formed by the solvent and the acid-base indicator should be lower than that of the oil seal layer (i.e. the mineral oil layer) to avoid the solution in the indicator layer from penetrating the oil seal layer and directly contacting the vinegar due to density reasons. A particularly preferred solvent is ethanol or an aqueous solution thereof. When an aqueous ethanol solution is used, the density of the solution after the aqueous ethanol solution dissolves the acid-base indicator should also be less than that of mineral oil. For example, the weight percentage of ethanol in the aqueous ethanol solution is usually not less than 70%, preferably not less than 90%, and more preferably not less than 95%.

[0075] The initial pH of the indicator layer should generally be above the lowest pH value of the color change range of the indicator used, preferably at least 0.2, more preferably at least 0.5, above the lowest pH value. In some embodiments, the initial pH of the indicator layer is > 5.6, such as > 6.0 or > 7.0. For example, the color change range (pH value) of bromothymol blue is 6.2-7.6, blue in alkaline condition and yellow in acidic condition, thus the initial pH of the indicator layer can be set to 6.4 or higher, such as > 7, preferably > 7.6, most preferably between 7 and 7.6. The color change range of neutral red is 6.8-8.0, yellow-orange in alkaline condition and red in acidic condition, thus the initial pH of the indicator layer is preferably set between 7 and 8. The color change range of phenol red is 6.7-8.4, red in alkaline condition and yellow in acidic condition, thus the initial pH of the indicator layer is preferably set between 7 and 8.4, more preferably between 7 and 8. It should be understood that the initial pH of the indicator layer should not be set too high, such as beyond the color change range of the indicator. A higher initial pH requires more gas to be generated to lower the pH and thus to change the color of the indicator solution, resulting in a longer time to detect the gas generation of the vinegar and a lower sensitivity.

[0076] Generally, after the addition of the indicator, the container is sealed and allowed to stand.

[0077] The gas generation of the vinegar can be determined by observing the color change of the indicator. For example, for the indicator layer containing bromothymol blue, the initial color is blue, and if the color of the indicator layer is observed to change from blue to another color, such as dark green, light green, or even yellow, it indicates that the vinegar has generated gas or has undergone gas expansion. Generally, if the vinegar has generated gas, a noticeable color change can be observed within about 1 hour after the start of the test, such as from dark blue to dark green. If it is desired to further shorten the time to detect the gas generation of the vinegar, the container can be placed in an incubator with a temperature controlled at 25-40 °C; and / or, nutrients known in the art to promote the growth of bacteria that are usually present in vinegar, including but not limited to the carbon and nitrogen sources described above, can be added to the vinegar to be tested.

[0078] In some embodiments, the method for detecting the gas expansion of vinegar of the present application comprises the following steps:

[0079] (1) Sampling: taking the vinegar to be tested into a detection container;

[0080] (2) Oil sealing: adding mineral oil on top of the vinegar sample to form an oil sealing layer, which is sufficient to prevent air from contacting the vinegar;

[0081] (3) Adding indicator: adding an indicator on top of the oil sealing layer to form an indicator layer;

[0082] (4) Observation: After the indicator is added, seal the lid of the container and let it stand to observe the color change of the indicator;

[0083] The indicator color changed, indicating that gas was produced in the vinegar.

[0084] In this invention, if any sample adheres to the wall when the sample to be tested is added to the testing container, it can be removed by centrifugation or wiping.

[0085] In other embodiments of the present invention, a method for detecting gas production in vinegar using an acid-base indicator is provided. This method includes adding the vinegar to be tested and the acid-base indicator to a sealable container, wherein the vinegar and the indicator do not directly contact each other, then sealing the container and observing the color change of the indicator. In these embodiments, an oil seal may not be necessary; simply placing the vinegar and the indicator in the same sealable container without direct contact is sufficient. If the vinegar produces gas, the generated gas comes into contact with the indicator, causing a color change in the indicator. These embodiments differ from the previously described method with an oil seal in that they do not use an oil seal. In these embodiments, if necessary, air can be removed from the container, such as by vacuuming; or, a sufficient amount of the vinegar to be tested can be provided to fill as much space as possible, excluding the space containing the indicator, to minimize the influence of air inside the container on the detection results.

[0086] In some embodiments of the present invention, a test kit for detecting bloating from vinegar is provided, comprising mineral oil and an acid-base indicator. The mineral oil and acid-base indicator are as described above. The test kit may also contain a suitable container, such as a sealable and preferably transparent container, such as centrifuge tubes. The test kit may also contain a suitable solvent, such as an alcohol solution with a density lower than that of mineral oil, such as an aqueous solution of ethanol of 90% or higher. The test kit may also include instructions for guiding technicians to use the kit to detect whether vinegar produces bloating according to the method described in the present invention. This kit provides a rapid and effective detection of bloating from vinegar, using untreated vinegar. The mineral oil and indicator in the detection system are easy to use, and the test kit can be stored at room temperature.

[0087] In this invention, the time it takes for the indicator color to change varies depending on the actual testing conditions, such as the amount of vinegar produced, the amount of vinegar used, and the amount of indicator used. Typically, after sealing the container and letting it stand for a period of time, the color of the indicator layer is observed. If the color changes, it indicates that the vinegar is producing gas. This period is usually more than 10 minutes, such as more than 30 minutes or more than 1 hour.

[0088] The general detection method is to observe the gas generated by the vinegar through the gas ball or the duthie small tube collection, the gas amount is used to judge the gas production cycle, which has poor accuracy and is easy to misjudge, and it is difficult to realize the quality control detection of the vinegar expansion. The gas producing bacteria in the vinegar are enriched by centrifugation or membrane filtration, which can accelerate the gas production to a certain extent, but the operation is relatively complicated and the accuracy is poor, and it also depends on the knowledge level and experience skill of the operator. Therefore, the amount of collected gas is used to judge the vinegar expansion, which has certain limitations.

[0089] The present application has the following advantages:

[0090] 1. The present application detects the vinegar expansion by using the color change caused by the reaction of the indicator and the gas generated by the vinegar. The result is intuitive and objective, can avoid human judgment, is easy and fast to operate, can greatly reduce the probability of false judgment, and is not affected by varieties, regions, environment and other factors, and the detection is more sensitive and efficient.

[0091] 2. In the preferred embodiment of the present application, mineral oil is used to prevent the vinegar from contacting with air, which can be regarded as simulating the sealed environment of finished vinegar (bottled, bagged, barrelled and other airtight packaging), providing a relatively suitable survival environment for anaerobic or facultative anaerobic gas-producing miscellaneous bacteria, so that the gas-producing miscellaneous bacteria can relatively quickly reproduce and produce gas. On the other hand, the gas produced by the gas-producing miscellaneous bacteria will not escape or stagnate, and even a small amount of gas will directly pass through the intermediate oil seal layer and contact with the upper indicator to cause color change. In addition, the indicator reacts quickly with the gas, and the color change is intuitive and obvious. The above points promote the fastness, high sensitivity and intuitiveness of the present application.

[0092] 3. In the preferred embodiment, the present application only needs to place the sample vinegar, oil and indicator in layers, which is simple to operate and does not rely too much on the knowledge reserve and experience skill of the operator. Moreover, it does not need the assistance of related equipment, and is very suitable for on-site practical application, and will become a convenient tool for vinegar production enterprises to test whether the vinegar is expanded.

[0093] It should be understood that in addition to the vinegar gas detection, the method of the present application is also applicable to other foods that need to ensure that the food does not expand during the shelf life, including but not limited to liquid foods, such as liquid or semi-solid condiments, including soy sauce, cooking wine, various sauces, and various vacuum-packed foods, such as vacuum-packed bread, snacks and the like, and various drinks, such as packaged beverages that need to meet a certain shelf life. Similarly, the sample to be tested can be placed in a sealable container, an acid-base indicator can be added (not in direct contact with the sample), then sealed, and the color change of the indicator can be observed. For cases where an oil seal layer is desired, a suitable solution can be used to dissolve or dilute the semi-solid or solid food, for example, sterile water can be used to dilute or dissolve, and then the detection can be carried out according to the foregoing method.

[0094] The present application is comprehensively illustrated by the following examples, but these examples are only used to illustrate the present application and are not intended to limit the scope of the present application. The protection scope of the present application is only defined by the claims, and any omission, replacement or modification made by a person skilled in the art on the basis of the disclosed embodiments of the present application will fall within the protection scope of the present application.

[0095] The following examples and comparative examples use the instruments and equipment commonly used in the art. The experimental methods in the following examples and comparative examples not specified in the specific conditions are generally carried out according to the conventional conditions, or according to the conditions recommended by the manufacturer. Various raw materials are used in the following examples and comparative examples, unless otherwise specified, the conventional commercially available products are used, and the specifications are commonly used in the art. In the specification of the present application and the following examples and comparative examples, unless otherwise specified, “%” means weight percent, “parts” means weight parts, and the ratio means weight ratio.

[0096] The different varieties of vinegar samples in the following examples and comparative examples are provided by Fengyi (Shanghai) Biotechnology Research and Development Center Co., Ltd., and the reagents are purchased from National Pharmaceutical Group Chemical Reagent Co., Ltd.

[0097] The indicator in the following examples and comparative examples is prepared by the following method:

[0098] A certain amount of bromothymol blue powder is dissolved in ethanol to prepare a 0.02 g / 100 mL indicator solution in ethanol. The indicator solution is adjusted from orange to deep blue using NaOH solution.

[0099] Example 1

[0100] 1. Materials

[0101] The different varieties of vinegar samples are provided by Fengyi (Shanghai) Biotechnology Research and Development Center Co., Ltd.

[0102] 2. Reagents

[0103] The reagents are purchased from National Pharmaceutical Group Chemical Reagent Co., Ltd.

[0104] 3. Experimental methods

[0105] 3.1. Sampling

[0106] After shaking the normal vinegar and the gas-expanded vinegar (the vinegar bottle is expanded and deformed before opening, and the gas is sprayed out after opening), the bottle opening is opened, and 40 ml of vinegar is taken into a 50 ml centrifuge tube.

[0107] 3.2. Oil seal

[0108] Add 5 ml of mineral oil on top of the vinegar in the centrifuge tube, forming an oil layer to prevent air from contacting the vinegar. Be careful not to create air bubbles between the vinegar and the oil layer when adding the oil.

[0109] 3.3. Add indicator

[0110] After adding the oil layer on top of the vinegar, try not to shake it and gently add 5 ml of indicator on top of the oil layer. Be careful not to let the indicator contact the vinegar below, otherwise the color of the indicator will change immediately.

[0111] 3.4. Observe

[0112] After adding the indicator, tighten the cap of the centrifuge tube or other container and observe the color change of the indicator.

[0113] 4. Experimental results

[0114] The experimental results are shown in Table 1. Figure 1 At the beginning of the experiment, the color of the indicator in each tube was dark blue. After 1 h, the color of the indicator layer on the overgrown vinegar changed to dark green, while the color of the indicator layer on the normal vinegar did not change. After 6 h, the color of the indicator layer on the overgrown vinegar changed from dark green to light green, while the color of the indicator layer on the normal vinegar did not change. After 24 h, the color of the indicator layer on the overgrown vinegar changed from light green to yellow, while the color of the indicator layer on the normal vinegar did not change. From the observed color change of the indicator, it can be inferred that the overgrown vinegar produces gas, thereby distinguishing the normal vinegar from the overgrown vinegar.

[0115] Example 2

[0116] 1. Materials

[0117] Different varieties of vinegar samples were provided by Fengyi (Shanghai) Biotechnology Research and Development Center Co., Ltd.

[0118] 2. Reagents

[0119] Reagents were purchased from National Pharmaceutical Group Chemical Reagent Co., Ltd.

[0120] 3. Experimental methods

[0121] 3.1. Sampling

[0122] After shaking the normal vinegar and overgrown vinegar (the vinegar bottle is deformed before opening, and the gas is sprayed after opening), open the bottle mouth, take 40 ml of vinegar respectively, and add 0.5 wt% of sterilized glucose and peptone to the total weight of the final mixture.

[0123] 3.2. Oil sealing

[0124] Gently add 5 ml of mineral oil to the top of the vinegar in each centrifuge tube to form an oil seal and prevent air from contacting the vinegar. Be careful to avoid air bubbles forming between the vinegar and the oil layer when adding the oil.

[0125] 3.3. Add indicator

[0126] After adding the oil layer on top of the vinegar, try not to shake it. Gently add 5ml of indicator on top of the oil layer. Be careful not to let the indicator come into contact with the vinegar underneath, otherwise the indicator's color will change immediately.

[0127] 3.4. Observation

[0128] After adding the indicator, tighten the cap of the centrifuge tube or other container and let it stand to observe the color change of the indicator.

[0129] 4. Experimental Results

[0130] Experimental results are as follows Figure 2 As shown in the diagram. At the start of the experiment, the indicator was dark blue. After 1 hour, the indicator layer on the gas-producing vinegar had changed to or was changing to light green, while the indicator layer on normal vinegar remained unchanged. After 6 hours, the indicator layer on the gas-producing vinegar changed from light green to yellow, while the indicator layer on normal vinegar remained unchanged. After 24 hours, the indicator layer on the gas-producing vinegar changed from yellow to dark yellow, while the indicator layer on normal vinegar still remained unchanged. This demonstrates that adding nutrients such as glucose and peptone can promote gas production in gas-producing vinegar, thus enabling a faster distinction between normal and gas-producing vinegar.

[0131] Comparative Example 1 (Balloon Marking Method)

[0132] 1. Materials

[0133] The samples of different types of vinegar were all provided by Wilmar (Shanghai) Biotechnology R&D Center Co., Ltd.

[0134] 2. Reagents

[0135] The reagents were purchased from Sinopharm Chemical Reagent Co., Ltd.

[0136] 3. Experimental Methods

[0137] 3.1. Sampling

[0138] After the swollen vinegar was shaken evenly, the bottle was opened and 40 ml of the vinegar was transferred into a 50 ml centrifuge tube. The centrifuge tube was centrifuged at 8000 rpm for 10 min, and then the supernatant was discarded and an appropriate amount of the swollen vinegar was added and mixed. Then the precipitates in the two centrifuge tubes were collected into one centrifuge tube, and the volume was the same as the initial volume. One group was not added with glucose and proteose peptone, and the other group was added with 0.5% sterilized glucose and proteose peptone, i.e. divided into the swollen vinegar group and the swollen vinegar + nutrients group.

[0139] 3.2. Oil seal

[0140] The sampled vinegar was divided into the oil seal group and the non-oil seal group. In the oil seal group, 5 ml of mineral oil was added on the vinegar to form an oil layer to prevent air from contacting the vinegar. When the oil was added, attention should be paid to avoid bubbles between the vinegar and the oil layer. Finally, four groups were formed, i.e. the swollen vinegar + oil seal group, the swollen vinegar + nutrients + oil seal group, the swollen vinegar group and the swollen vinegar + nutrients group.

[0141] 3.3. Sealing and balloon marking

[0142] Each centrifuge tube containing the vinegar sample was sealed with a sterilized breathable sealing film, and then a balloon was covered on the centrifuge tube opening and was reinforced with a rubber ring. Attention should be paid to exhaust all the gas in the balloon.

[0143] 3.4. Observation

[0144] The centrifuge tube containing the vinegar sample was placed in a 37°C constant temperature incubator, and the change of the balloon was observed.

[0145] 4. Experimental results

[0146] The results are shown in Table 1. Figure 3 After about 5-6 days, the balloon on the centrifuge tube of the swollen vinegar + oil seal group began to swell, and the other three groups had no change. After continuous observation, there was still no change after one month. Although the gas production of the swollen vinegar + oil seal group made the balloon swell obviously, there was no change in the other groups, especially no gas production was observed in the swollen vinegar + nutrients + oil seal group, so that the normal vinegar and the swollen vinegar could not be accurately distinguished.

[0147] Comparative Example 2 (Du's small tube marking method)

[0148] 1. Materials

[0149] The different varieties of vinegar samples were provided by Fengyi (Shanghai) Biotechnology Research and Development Center Co., Ltd.

[0150] 2. Reagents

[0151] The reagents were purchased from National Pharmaceutical Group Chemical Reagent Co., Ltd.

[0152] 3. Experimental method

[0153] 3.1. Inoculation

[0154] Vinegar detection medium: The first group of vinegar was divided into test tubes with inverted Durham tubes, 18 mL per tube, and rubber stoppers were covered. The second group of vinegar was divided into test tubes with inverted Durham tubes after adding 0.5wt% glucose and proteose to the vinegar, 18 mL per tube, and rubber stoppers were covered. 115°C sterilization for 20 min. Used for gas-producing bacteria back-inoculation verification experiment.

[0155] The gas-producing vinegar was centrifuged (4000 rpm, 5 min), and the bacterial precipitate was collected, and then a bacterial suspension was prepared with sterilized vinegar equivalent to 1 / 20 of the original volume. 2 mL of bacterial suspension was added to each of the two sterilized vinegar detection media (inverted Durham tubes) respectively.

[0156] 3.2. Oil seal

[0157] The vinegar with bacterial suspension was divided into oil-sealed and non-oil-sealed groups. 5 ml of mineral oil was added on top of the vinegar in the oil-sealed group to form an oil layer, preventing air from contacting the vinegar. Care should be taken to avoid air bubbles between the vinegar and the oil layer during addition. Finally, four groups were formed, namely gas-producing bacteria + oil seal, gas-producing bacteria + nutrients + oil seal, gas-producing bacteria, and gas-producing bacteria + nutrients.

[0158] 3.4. Observation

[0159] The mixed test tubes after inoculation were placed in a 37°C constant temperature incubator for incubation, and the experimental phenomena were observed and recorded every 24 h.

[0160] 4. Experimental results

[0161] The results are shown in Table 1. Figure 4 After about 11 days, small bubbles appeared in the Durham tubes of the gas-producing bacteria + nutrients group; the Durham tubes of the gas-producing bacteria + nutrients + oil seal group were almost filled with bubbles; and no bubbles were observed in the Durham tubes of the gas-producing bacteria + oil seal group and the gas-producing bacteria group.

[0162] In Comparative Examples 1 and 2, the presence of gas-producing bacteria in vinegar samples and gas production were determined by observing the inflation of the balloon and the bubbles in the Durham tubes. Since the balloon needs a certain amount of gas to inflate, the Durham tube cannot completely collect the gas, so the phenomena observed by these two methods have a lag. The indicator identification method of the present application can quickly and intuitively observe the results by changing the color of the indicator through a chemical reaction, which is a rapid detection method for gas-expanding deteriorated vinegar.

[0163] Comparative Example 3

[0164] 1. Materials

[0165] Different varieties of vinegar samples were provided by Fengyi (Shanghai) Biotechnology Research and Development Center Co., Ltd.

[0166] 2. Reagents

[0167] Reagents were purchased from National Pharmaceutical Group Chemical Reagent Co., Ltd.

[0168] 3. Experimental Methods

[0169] 3.1. Sampling

[0170] After shaking the known normal vinegar and the gassy vinegar evenly, open the bottle mouth, and respectively take 25 ml of vinegar into a 50 ml centrifuge tube.

[0171] 3.2. Oil Seal

[0172] Respectively use 5 different oil materials (1. mineral oil, 2. olive oil, 3. peanut oil, 4. corn oil, 5. soybean oil) to perform oil sealing. Lightly add 5 ml of oil on top of the vinegar in the centrifuge tube to form an oil sealing layer to prevent air from contacting the vinegar. When adding, pay attention to avoid air bubbles between the vinegar and the oil layer.

[0173] 3.3. Add Indicator

[0174] After adding the oil layer on top of the vinegar, try not to shake it, and lightly add 5 ml of indicator on top of the oil layer. Pay attention not to let the indicator contact the bottom layer of vinegar, otherwise the color of the indicator will change immediately.

[0175] 3.4. Observation

[0176] After the indicator is added, tighten the lid of the centrifuge tube or other container, and observe the color change of the indicator.

[0177] 4. Experimental Results

[0178] The results are as follows Figure 5The color of the indicator was dark blue at the beginning of the experiment. After 24 h, the indicator layer on the normal vinegar and the blown gas vinegar sealed with olive oil, peanut oil, corn oil, and soybean oil changed to dark green, while the indicator layer on the normal vinegar sealed with mineral oil did not change in color, and the indicator layer on the blown gas vinegar sealed with mineral oil changed to dark green. After 48 h, the indicator layer on the normal vinegar and the blown gas vinegar sealed with olive oil, peanut oil, corn oil, and soybean oil changed to light green to yellow, while the indicator layer on the normal vinegar sealed with mineral oil did not change in color, and the indicator layer on the blown gas vinegar sealed with mineral oil changed from dark green to light green. After 72 h, the indicator layer on the normal vinegar and the blown gas vinegar sealed with olive oil, peanut oil, corn oil, and soybean oil changed to yellow, while the indicator layer on the normal vinegar sealed with mineral oil did not change in color, and the indicator layer on the blown gas vinegar sealed with mineral oil changed to light green. From the observed color change of the indicator, it can be inferred that plant oils such as olive oil, peanut oil, corn oil, and soybean oil are better than mineral oil in detecting the blown gas oil seal of vinegar.

[0179] Application Example 1

[0180] 1. Materials

[0181] Different varieties of vinegar samples were provided by Fengyi (Shanghai) Biotechnology Research and Development Center Co., Ltd.

[0182] 2. Reagents

[0183] The reagents were purchased from National Pharmaceutical Group Chemical Reagent Co., Ltd.

[0184] 3. Experimental Methods

[0185] 3.1. Sampling

[0186] After shaking the 10 batches of the same brand of vinegar evenly, the bottle opening was opened, and 25 ml of vinegar was taken into a 50 ml centrifuge tube.

[0187] 3.2. Oil Seal

[0188] On the top of the vinegar in the centrifuge tube, 5 ml of mineral oil was added gently to form an oil layer of a certain thickness to prevent air from contacting the vinegar. When adding, attention should be paid to avoid air bubbles between the vinegar and the oil layer.

[0189] 3.3. Adding Indicator

[0190] After adding the oil layer on top of the vinegar, try not to shake it, and gently add 5 ml of indicator on top of the oil layer. Pay attention not to let the indicator come into contact with the underlying vinegar, otherwise the color of the indicator will change.

[0191] 3.4. Observation

[0192] After the indicator is added, tighten the cap of the centrifuge tube or other container and observe the color change of the indicator.

[0193] 4. Experimental results

[0194] The results are shown in Table 1. At the beginning of the experiment, the color of the indicator was dark blue. After 3 hours, the indicator layer of samples 7 and 8 changed to dark green, while the color of the indicator layer of other samples did not change. After 24 hours, the indicator layer of samples 7 and 8 changed from dark green to light green and then to yellow, while the color of the indicator layer of other samples did not change. After 48 hours, the indicator layer of samples 7 and 8 changed from light green to yellow, while the color of the indicator layer of other samples did not change. Figure 6

[0195] The samples were stored for half a year, during which samples 7 and 8 expanded, while the other samples did not expand after being stored for more than half a year.

[0196] Therefore, the possibility of expansion of the vinegar during the shelf life can be predicted from the observed color change of the indicator.

[0197] Application Example 2

[0198] 1. Materials

[0199] The different varieties of vinegar samples were provided by Fengyi (Shanghai) Biotechnology Research and Development Center Co., Ltd.

[0200] 2. Reagents

[0201] The reagents were purchased from National Pharmaceutical Group Chemical Reagent Co., Ltd.

[0202] 3. Experimental methods

[0203] 3.1. Sampling

[0204] Twelve different brands of vinegar and known normal vinegar and expanded vinegar were shaken evenly, and then the bottle opening was opened. 25 ml of vinegar was taken into a 50 ml centrifuge tube, and was numbered as samples 1-14, respectively.

[0205] 3.2. Oil seal

[0206] 5 ml of mineral oil was added on the top of the vinegar in the centrifuge tube to form an oil seal layer to prevent air from contacting the vinegar. When adding, attention should be paid to avoid air bubbles between the vinegar and the oil layer.

[0207] 3.3. Adding indicator

[0208] ​After adding the oil layer on the vinegar, try not to shake it, and gently add 5ml of the indicator on the oil layer. Be careful not to let the indicator contact the vinegar in the bottom layer, otherwise the color of the indicator will change.

[0209] 3.4. Observation

[0210] After the indicator is added, tighten the cap of the centrifuge tube or other container, and observe the color change of the indicator.

[0211] 4. Experimental results

[0212] The results are shown in Table 1. At the beginning of the experiment, the color of the indicator was dark blue. After 18-24h, the indicator layer of vinegar No. 11, No. 12 and the known gas-producing vinegar changed to dark green, while the color of the indicator layer of other vinegars did not change. After 48h, the indicator layer of vinegar No. 11, No. 12 and the known gas-producing vinegar changed from dark green to light green to yellow, while the color of the indicator layer of other vinegars did not change. From the observed color change of the indicator, it is predicted that vinegar No. 11 and No. 12 have the possibility of gas production. Figure 7

[0213] The samples were stored for half a year, during which vinegar No. 11 and No. 12 produced gas, while the other numbered vinegars did not produce gas after being stored for more than half a year. Thus, the method of the present application can distinguish between normal vinegar and gas-producing vinegar, and also predict the possibility of gas production of vinegar that has not yet produced gas during the shelf life.

[0214] Example 3

[0215] 1. Materials

[0216] Different varieties of vinegar samples were provided by Fengyi (Shanghai) Biotechnology Research and Development Center Co., Ltd.

[0217] 2. Reagents

[0218] The reagents were purchased from National Pharmaceutical Group Chemical Reagent Co., Ltd.

[0219] 3. Experimental method

[0220] Preparation of indicator solution: weigh a certain amount of cresol red powder, dissolve it in ethanol to prepare a 0.02g / 100ml ethanol solution. Adjust the indicator solution from yellow to purple using NaOH solution.

[0221] 3.1. Sampling

[0222] After shaking the normal vinegar and gas-producing vinegar (the vinegar bottle is deformed before opening, and the gas is sprayed out after opening), open the bottle mouth, and take 25ml of vinegar into a 50ml centrifuge tube.

[0223] 3.2. Oil sealing ​

[0224] Gently add 5 ml of mineral oil above the vinegar in the centrifuge tube to form an oil seal and prevent air from contacting the vinegar. Be careful to avoid creating air bubbles between the vinegar and the oil layer when adding the oil.

[0225] 3.3. Add indicator

[0226] After adding the oil layer on top of the vinegar, try not to shake it. Gently add 5ml of indicator on top of the oil layer. Be careful not to let the indicator come into contact with the vinegar underneath, otherwise the indicator's color will change immediately.

[0227] 3.4. Observation

[0228] After adding the indicator, tighten the cap of the centrifuge tube or other container and let it stand to observe the color change of the indicator.

[0229] 4. Experimental Results

[0230] Experimental results are as follows Figure 8 As shown, "-" indicates normal vinegar, and "+" indicates vinegar containing gas. At the start of the experiment, the indicator in each tube was purple. After 1 hour, the indicator on the vinegar containing gas lightened slightly, while the indicator layer on the normal vinegar remained unchanged. After 3 hours, the indicator on the vinegar containing gas turned dark red, while the indicator layer on the normal vinegar remained unchanged. After 24 hours, the indicator on the vinegar containing gas turned yellow, while the indicator layer on the normal vinegar remained unchanged. From the observed changes in indicator color, we can infer the gas production in the vinegar containing gas, thus distinguishing it from normal vinegar.

Claims

1. A method for detecting gas production in food or predicting bloating in food using an acid-base indicator, characterized in that, The method comprises: providing an acid-base indicator and an optional nutrient-containing food sample to be tested in a sealable container, sealing the container and observing the color change of the acid-base indicator; wherein the food sample to be tested is not in direct contact with the acid-base indicator, a mineral oil layer is formed on the food sample to be tested, the acid-base indicator is added on the mineral oil layer, the food sample to be tested is isolated from the acid-base indicator through the mineral oil layer, and the color change of the acid-base indicator indicates that the food sample to be tested produces gas; and the food is a liquid seasoning or beverage, including vinegar, soy sauce and cooking wine.

2. The method of claim 1, wherein, The acid-base indicator is a single or mixed acid-base indicator that changes color in the range of pH≥5.

6.

3. The method of claim 1, wherein, The acid-base indicator is selected from the group consisting of methyl red, bromophenol red, p-nitrophenol, bromothymol blue, turmeric, cresol red, neutral red, resorcinol, 1-naphthol phthalein, orange I, phenolphthalein, o-cresol red, thymolphthalein, alizarin red S, alizarin yellow R, alizarin yellow GG, nitramine, phenol red, dianthus yellow, a mixture of bromocresol green and chlorophenol red, a mixture of bromocresol purple and bromothymol blue, a mixture of neutral red and methyl blue, a mixture of bromothymol blue and phenol red, and a mixture of cresol red and thymol blue.

4. The method of claim 1, wherein, The acid-base indicator is bromothymol blue or cresol red.

5. The method of any one of claims 1-4, wherein, The acid-base indicator is provided in the form of a solution dissolved in a solvent.

6. The method of claim 5, wherein, The solvent is ethanol or an aqueous ethanol solution.

7. The method of claim 6, wherein, The aqueous ethanol solution has a weight percentage concentration of ≥70%.

8. The method of claim 6, wherein, The aqueous ethanol solution has a weight percentage concentration of ≥90%.

9. The method of claim 6, wherein, The aqueous ethanol solution has a weight percentage concentration of ≥95%.

10. The method of claim 5, wherein, The pH of the solution of the acid-base indicator is not lower than the minimum pH value of the color change range of the acid-base indicator used.

11. The method of claim 10, wherein, The pH of the solution of the acid-base indicator differs from the minimum pH value by at least 0.

2.

12. The method of claim 10, wherein, The pH of the solution of the acid-base indicator differs from the minimum pH value by at least 0.

5.

13. The method of claim 10, wherein, The pH of the solution of the acid-base indicator is >5.

6.

14. The method of claim 10, wherein, The pH of the solution of the acid-base indicator is ≥6.

0.

15. The method of claim 10, wherein, The pH of the solution of the acid-base indicator is ≥7.

0.

16. The method of claim 5, wherein, The content of the acid-base indicator in the solution of the acid-base indicator is 0.001-1 g / 100 mL of the solution.

17. The method of claim 16, wherein, The content of the acid-base indicator in the solution of the acid-base indicator is 0.01-0.1 g / 100 mL of the solution.

18. The method of claim 16, wherein, The content of the acid-base indicator in the solution of the acid-base indicator is 0.01-0.05 g / 100 mL of the solution.

19. A method for detecting gas production in food or predicting bloating in food using an acid-base indicator, characterized in that, The method comprises: (1) forming an oil seal layer on the optional nutrient-containing food sample to be tested in the container to isolate the food sample to be tested from air; (2) adding an acid-base indicator on the oil seal layer to form an indicator layer; (3) sealing the container and observing the color change of the indicator; wherein the color change of the indicator indicates that the food sample to be tested produces gas, the oil seal layer is formed using mineral oil, and the food is a liquid seasoning or beverage, including vinegar, soy sauce and cooking wine.

20. The method of claim 19, wherein, The pH of the indicator layer is not lower than the minimum pH value of the color change range of the acid-base indicator used, and the density of the indicator layer is lower than that of the oil seal layer.

21. The method of claim 20, wherein, The pH of the indicator layer differs from the minimum pH value by at least 0.

2.

22. The method of claim 20, wherein, The pH of the indicator layer is at least 0.5 different from the lowest pH value.

23. The method of claim 20, wherein, The pH of the solution of the acid-base indicator is > 5.

6.

24. The method of claim 20, wherein, The pH of the solution of the acid-base indicator is ≥ 6.

0.

25. The method of claim 20, wherein, The pH of the solution of the acid-base indicator is ≥ 7.

0.

26. The method of claim 20, wherein, The content of the acid-base indicator in the indicator layer is 0.001-1 g / 100 mL of the indicator layer.

27. The method of claim 20, wherein, The content of the acid-base indicator in the indicator layer is 0.01-0.1 g / 100 mL of the indicator layer.

28. The method of claim 20, wherein, The content of the acid-base indicator in the indicator layer is 0.01-0.05 g / 100 mL of the indicator layer.

29. The method of any one of claims 19-28, wherein, The acid-base indicator is a single or mixed acid-base indicator that changes color in the range of pH ≥ 5.

6.

30. The method of claim 29, wherein, The acid-base indicator is selected from the group consisting of methyl red, bromophenol red, p-nitrophenol, bromothymol blue, turmeric, cresol red, neutral red, resorcinol, 1-naphthol phthalein, orange I, phenolphthalein, o-cresolphthalein, thymolphthalein, alizarin red S, alizarin yellow R, alizarin yellow GG, nitramine, phenol red, fast yellow, a mixture of bromocresol green and chlorophenol red, a mixture of bromocresol purple and bromothymol blue, a mixture of neutral red and methyl blue, a mixture of bromothymol blue and phenol red, and a mixture of cresol red and thymol blue.

31. The method of claim 29, wherein, The acid-base indicator is bromothymol blue or cresol red.

32. The method of any one of claims 19-28, wherein, The indicator layer contains a solvent.

33. The method of claim 32, wherein, The solvent is ethanol or an aqueous ethanol solution.

34. The method of claim 33, wherein, The aqueous ethanol solution has a weight percentage concentration ≥ 70%.

35. The method of claim 33, wherein, The aqueous ethanol solution has a weight percentage concentration ≥ 90%.

36. The method of claim 33, wherein, The aqueous ethanol solution has a weight percentage concentration ≥ 95%.

37. A food vinegar gas detection or bloating pretest kit, characterized by, The kit comprises a mineral oil, an acid-base indicator, and optionally a container, and further comprises an instruction for guiding the use of the kit to detect whether a food vinegar is gassy according to the method of any one of claims 1-36.

38. The kit of claim 37, wherein The acid-base indicator is a single or mixed acid-base indicator that changes color in the range of pH ≥ 5.

6.

39. The kit according to claim 37, characterized in that, The acid-base indicator is selected from the group consisting of methyl red, bromophenol red, p-nitrophenol, bromothymol blue, turmeric, cresol red, neutral red, resorcinol, 1-naphthol phthalein, orange I, phenolphthalein, o-cresolphthalein, thymolphthalein, alizarin red S, alizarin yellow R, alizarin yellow GG, nitramine, phenol red, fast yellow, a mixture of bromocresol green and chlorophenol red, a mixture of bromocresol purple and bromothymol blue, a mixture of neutral red and methyl blue, a mixture of bromothymol blue and phenol red, and a mixture of cresol red and thymol blue.

40. The kit according to claim 37, characterized in that, The acid-base indicator is bromothymol blue or cresol red.

41. Use of a single or mixed acid-base indicator that changes color in the range of pH ≥ 5.6 and a mineral oil in detecting gas production of a food and / or predicting gassiness of a food, or in preparing a kit for detecting gas production of a food and / or predicting gassiness of a food, wherein a mineral oil layer is formed on the food to be tested, and an acid-base indicator is added on the mineral oil layer, the food and the acid-base indicator are isolated by the mineral oil layer, and the food is a liquid condiment or beverage, including food vinegar, soy sauce, and cooking wine.

42. The use of claim 41, wherein the compound is ###00021### 41 The acid-base indicator is selected from the group consisting of methyl red, bromophenol red, p-nitrophenol, bromothymol blue, curcumin, cresol red, neutral red, resorcinol, 1-naphthol phthalein, orange I, phenolphthalein, o-cresolphthalein, thymolphthalein, alizarin red S, alizarin yellow R, alizarin yellow GG, nitramine, phenol red, fast yellow, a mixture of bromocresol green and chlorophenol red, a mixture of bromocresol purple and bromothymol blue, a mixture of neutral red and methyl blue, a mixture of bromothymol blue and phenol red, and a mixture of cresol red and thymol blue.

43. The use of claim 42, wherein the compound is ###00023### 43A or ###00024### 43B. The acid-base indicator is bromothymol blue or cresol red.

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