A method for digitally evaluating the sourness of beverages based on free organic acid content

Abstract

The present invention relates to a method for digitally evaluating the sourness of beverages based on the free organic acid content, the method comprising: detecting the organic acid radical content and the solution pH value in an aqueous solution of an organic acid standard, and calculating the free organic acid content in the solution; having national-level professional judges taste and obtain sourness scores; drawing a relationship curve between the sourness score and the free organic acid content, and obtaining the fitting coefficient k of the organic acid; respectively detecting the content B of the organic acid radical and the sample pH value in the beverage sample to be tested, and calculating each free organic acid content C; respectively multiplying C by the corresponding k, and obtaining the sourness score of each organic acid, and summing up the results to obtain the total sourness score Y of the beverage. The method of the present invention only requires the detection and calculation of conventional parameters of the beverage sample, and the obtained sourness score result is highly consistent with the judges' score, and can be processed in high throughput, which can completely replace the professional judges' scoring method, and more objectively reflects the sourness of the sample.

Description

Technical Field

[0001] The invention belongs to the field of beverage quality evaluation, and relates to a method for digitally evaluating the sourness of beverages based on free organic acid content, and specifically to a beverage sourness evaluation method that is highly consistent with the evaluation results of judges and is simple, efficient and universal. Background Art

[0002] Acids are the main flavoring substances in beverages and are also important buffer substances in beverages, controlling the pH of beverages. A moderate amount of acid makes the beverage taste lively and refreshing; excessive acid makes the beverage taste rough, unsoft and uncoordinated.

[0003] Sourness is a taste sensation that will leave a heavy residue when tasting, causing the tongue to adapt. It is difficult to judge the sourness of a beverage based on sensory perception alone. Currently, studies on the sourness of beverages include sour peptides, pH, and organic acids, but there is no comprehensive measurement method or standard to describe the sourness of a beverage.

[0004] The difference in sourness between beverages is caused by many reasons, such as the organic acid in the beverages and the buffer system of the beverages. At present, the method of evaluating the sourness of beverages in this field is for judges to score. This method is very labor-intensive. Moreover, when the judges taste too many samples in a short period of time, due to mutual interference, it will affect the judges' sourness judgment and cause some errors. Therefore, the judges' evaluation method is not reproducible.

[0005] Therefore, how to provide an efficient, universal, stable and accurate digital method for evaluating the sourness of beverages to replace the judges' scoring has become an urgent problem that needs to be solved in this field and is of great significance to the standardization of beverage products. Summary of the invention

[0006] In view of the deficiencies in the prior art, the purpose of the present invention is to provide a method for digitally evaluating the sourness of beverages based on the free organic acid content, specifically a beverage sourness evaluation method that is highly consistent with the evaluation results of judges and is simple, efficient and universal.

[0007] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a method for digitally evaluating the sourness of a beverage based on the free organic acid content, the method comprising the following steps:

[0009] A single organic acid standard was mixed with water to obtain a standard solution of a series of concentrations. The organic acid radical content and pH value of the standard solution were detected. The free organic acid content in the standard solution was calculated. National professional judges evaluated the standard solution and scored the acidity. A curve of the relationship between the acidity score and the free organic acid content was plotted to obtain the fitting coefficient k of the organic acid. The fitting coefficients of different types of organic acids obtained by the above method were recorded as k. n , n is an integer greater than or equal to 1;

[0010] The content of each organic acid radical in the tested beverage sample is detected respectively, the pH value of the tested beverage sample is detected, and the content of each free organic acid in the tested beverage sample is calculated, which is recorded as C according to the type of organic acid. n , n is an integer greater than or equal to 1;

[0011] Calculate the sourness score Y of the beverage sample to be tested according to the formula:

[0012] Preferably, the free organic acid content is calculated as follows: free organic acid content C = B × (1-α), B is the organic acid radical content, α = K a1 / (K a1 +[H + ]), K a1 is the first ionization constant of organic acids, [H + ]=10 -pH .

[0013] Preferably, the organic acid comprises any one of lactic acid, citric acid, succinic acid, tartaric acid, fumaric acid, acetic acid, oxalic acid, pyruvic acid, formic acid, propionic acid, butyric acid, caproic acid, caprylic acid, capric acid, crotonic acid, strawberry acid or malic acid, or a combination of at least two thereof.

[0014] Preferably, the beverage comprises any one of an alcoholic beverage, a tea beverage, a fruit and vegetable juice beverage, a protein beverage, a flavored beverage, a coffee beverage, a plant beverage or a carbonated beverage.

[0015] Preferably, the alcoholic beverages include beer, liquor, wine, whiskey and the like.

[0016] Preferably, the method for detecting the pH value comprises detecting using a pH meter.

[0017] Preferably, the method for detecting the organic acid radical content includes any one of ion chromatography, spectrophotometry, gas chromatography, gas-solid chromatography or thin layer chromatography.

[0018] Preferably, the method for detecting the organic acid radical content is ion chromatography.

[0019] Preferably, before detecting the organic acid radical content in the beverage sample to be tested, the method further includes pre-treating the beverage sample to be tested, wherein the pre-treatment includes diluting the beverage sample to be tested with water, passing through a C18 column, filtering a membrane, and collecting the filtrate for sampling and testing;

[0020] Preferably, the dilution factor is 5-20 times, for example, 5 times, 6 times, 7 times, 8 times, 9 times, 10 times, 11 times, 12 times, 15 times, 17 times, 20 times, etc.

[0021] Preferably, the size of the filter membrane is 0.2-0.6 μm, for example, 0.2 μm, 0.25 μm, 0.3 μm, 0.35 μm, 0.4 μm, 0.45 μm, 0.5 μm, 0.55 μm, 0.6 μm, etc.

[0022] Preferably, when the beverage is a gas-containing beverage, the dilution further includes degassing the beverage sample to be tested before dilution, and the gas-containing beverage includes beer or carbonated beverage.

[0023] Preferably, the degassing method includes ultrasound.

[0024] The numerical range described in the present invention not only includes the point values ​​listed above, but also includes any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] At present, the method for evaluating the sourness of beverages in this field is for judges to score. This method is very labor-intensive. Moreover, when the judges taste too many samples in a short period of time, due to mutual interference, it will affect the judges' sourness judgment and cause some errors. Judges need professional training, and it is difficult to gather multiple judges to evaluate at the same time. Therefore, the evaluation method of judges is very inefficient.

[0027] The method provided by the present invention only requires the detection and calculation of conventional parameters of the beverage sample, and the obtained sourness score result is highly consistent with the judges' score (for beer samples, the score result of the present invention is only within 0.1 of the judges' score, and the two have a good correlation R 2 =0.981, so the method of the present invention can directly calculate the sourness score of beer; for sweet drinks such as juice, due to the influence of the sweetness of the beverage, the calculated sourness score is not as consistent with the value scored by the judges as the beer sample, but the two have a good correlation R 2 =0.9868, so it can be used to evaluate the sourness of beverages), and the processing efficiency is high, high-throughput processing can be performed, and it can completely replace the judges' scoring method.

[0028] Studies have shown that the sourness of beverages is related to the organic acid radical content therein. However, in practice, it is found that this conclusion is sometimes accurate and sometimes inaccurate. The conclusion is applicable when the pH values ​​are consistent, and it is not applicable when the pH values ​​are inconsistent. For some beverages, the two are not related. In view of this defect in the prior art, the present invention conducts further research and creatively finds that the reason affecting the sourness of beverages is the free organic acid content, not the organic acid radical content. When the organic acid radical content of some beverages is the same, the sourness results obtained by calculating the organic acid radical content are the same, but there are large differences in their sourness during actual tasting. The method of the present invention is used to successfully and accurately characterize the sourness of these beverages, realize digital evaluation, overcome the defects of the prior art, and is more versatile. The method is simple and has good accuracy and stability. The proposal of the method of the present invention is of great significance for the standardization of beverage products. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a graph showing the relationship between the sourness scores given by judges and the free organic acid content of samples with the same organic acid radical content.

[0030] Figure 2 is the standard fitting curve of tartaric acid.

[0031] Figure 3 is the standard fitting curve of fumaric acid.

[0032] Figure 4 It is a correlation analysis result diagram between the calculated sourness score Y value of the beer sample obtained by the method of the present invention and the judges' scores.

[0033] Figure 5 It is a correlation analysis result diagram between the calculated sourness score Y value of the beverage sample obtained by the method of the present invention and the score given by the judges. DETAILED DESCRIPTION

[0034] In order to further explain the technical means and effects adopted by the present invention, the technical solution of the present invention is further described below in conjunction with the preferred embodiments of the present invention, but the present invention is not limited to the scope of the embodiments.

[0035] In the following examples, unless otherwise specified, all reagents and consumables were purchased from conventional reagent manufacturers in the field; unless otherwise specified, the experimental methods and technical means used were conventional methods and means in the field.

[0036] Example 1

[0037] This example verifies that the sourness of a beverage is not necessarily correlated with the organic acid radical content therein, but is positively correlated with the free organic acid content therein.

[0038] Taking lactic acid in beer as an example, beer samples with the same lactate content and different free lactic acid content were prepared and scored for sourness (the higher the score, the stronger the sourness). The results are shown in Tables 1 and Figure 1 .

[0039] Table 1. Sourness score results of the same lactic acid root beer tasting

[0040]

[0041] The results showed that the lactate content of each sample was the same, but the sourness scores were significantly different, indicating that the sourness of a beverage is not necessarily related to the organic acid content. In order to more intuitively reflect the relationship between free lactic acid content and sourness score, the free lactic acid content and sourness score values ​​were plotted as Figure 1 , it can be clearly seen that the two are positively correlated.

[0042] Example 2

[0043] This embodiment provides a method for digitally evaluating the sourness of a beverage based on the free organic acid content.

[0044] After the beverage is produced, the organic acid content and pH value in the beverage are basically fixed.

[0045] The specific steps for evaluating sourness are as follows:

[0046] 1. Detection of organic acid content in beverages (ion chromatography):

[0047] 1.1 Preparation of standard solution (for instrument calibration):

[0048] 1.1.1 Weigh 0.2240 g of citric acid standard, 0.1989 g of succinic acid standard, 0.1149 g of tartaric acid standard, 0.2480 g of fumaric acid standard, 0.5319 g of acetic acid standard, 0.2398 g of malic acid standard, and 0.0500 g of lactic acid standard into seven 50 mL volumetric flasks, add water to the mark, and mix well.

[0049] 1.1.2 According to Table 2, take lactic acid solution, citric acid solution, succinic acid solution, tartaric acid solution, fumaric acid solution, acetic acid solution and malic acid solution in turn, put them into a 50mL volumetric flask, add water to the scale, mix well, and obtain a mixed standard solution.

[0050] Table 2. Organic acid standard sample preparation table

[0051] Element Final volume (ml) Final concentration (mg / ml) Actual weighing mass Measured volume (ml) Citric acid(s) 50 10 0.2240g 0.112 Succinic acid(s) 50 8 0.1989g 0.101 Tartaric acid(s) 50 6 0.1149g 0.131 Fumaric acid(s) 50 10 0.2480g 0.101 Acetic acid(l) 50 10 0.5319g 0.047 Malic Acid(s) 50 10 0.2398g 0.104 lactic acid 50 10 0.0500g 0.5

[0052] Note: The standard solution should be stored at 3-5°C and has a shelf life of one month.

[0053] 1.2 Ion Chromatograph:

[0054] DIONEX ICS-3000 ion chromatograph, anion analysis column AS11-HC, 4×250 mm;

[0055] Parameter settings are shown in Table 3:

[0056] Table 3. Instrument parameter settings

[0057]

[0058]

[0059] 1.3. Sample determination:

[0060] 1.3.1 Turn on the ion chromatograph: Turn on the instrument according to the standard operating procedures of the ion chromatograph, set the flow rate to 1.5 mL / min, the current to 0 mA, and the alkali concentration to 0.00 mM (%), flush with 20-30 times the column volume for about half an hour to allow the instrument to reach equilibrium, set the current to 186 mA, the alkali concentration to 2 mM (%), inject a blank sample, and indicate a stable baseline, indicating that the column is in stable equilibrium and working well.

[0061] 1.3.2 Calibration: Inject the standard solution into the injection system and draw a working curve based on the peak area.

[0062] 1.3.3 Sample analysis and pretreatment: Beer and other samples should be degassed (ultrasonic degassing for 10-15 minutes and filtered with filter paper. No degassing is required for gas-free beverages). Then the samples should be diluted, usually 10 times. The samples should be filtered with a C18 column and a 0.45μm filter membrane in turn and placed in a 20mL sample bottle for later use.

[0063] 1.3.4 Injection: Inject the pretreated sample into the chromatograph injection system and record the peak area.

[0064] 1.3.5 Calculation of results: The mass concentration of various acid radical ions is calculated by manual (or automatic) integration based on the peak area. The results are expressed in mg / L and reported to one decimal place. The standard deviation of the instrument is <2.0%, and the instrument injection volume is 25μL.

[0065] 2. Use a pH meter to measure the pH of the beverage and calculate the hydrogen ion concentration [H + ],[H + ]=10 -pH .

[0066] 3. Calculate the total sourness score Y of the beverage

[0067] 3.1. Since the second ionization constant of polyacids is much smaller than the first ionization constant, the calculation of free organic acid content only considers the first ionization constant K a1, find the ionization constant K of each organic acid by looking up the table (Table 4) a1 .

[0068] Table 4. First ionization constants and acidity characteristics of organic acids

[0069]

[0070] 3.2. Based on the ionization constant K of each organic acid a1 The free organic acid content in the beverage can be calculated by the pH of the beverage. C = B × (1-α); ionization degree α = K a1 / (K a1 +[H + ]), B is the concentration of organic acid radical (mg / L).

[0071] 3.3. Prepare standard solutions of organic acids and evaluate

[0072] After evaluation, the fitting curves of free organic acid content and acidity score were drawn to obtain the fitting coefficient k of each organic acid.

[0073] 3.4. Definition: The calculation method of the total sourness Y of a beverage is: the concentration of each free organic acid in the beverage sample × the fitting coefficient k of each organic acid. The results of each organic acid are added together to obtain the total sourness score Y.

[0074] Draw the fitting curve of each free organic acid content and acidity score

[0075] 1. According to the application guide of GB / T 29604 "General Guidelines for Establishing Sensory Reference Samples for Sensory Analysis", 0%, 0.05%, 0.08% and 0.15% citric acid aqueous solutions were prepared, and the corresponding sourness scores were 0, 2, 5 and 10, respectively, so that the judges were familiar with the sourness scoring scale (no sourness 0, very slight sourness 1, slight sourness 2-3, slightly sourness 4-5, obvious sourness 6-7, very sourness 8-10).

[0076] 2. Use food-grade organic acid and saturated baking soda (NaHCO3) to prepare free organic acid aqueous solution samples of different concentrations (see Table 5 for preparation method).

[0077] Table 5. Organic acid standard evaluation sample preparation table

[0078]

[0079]

[0080] 3. Calculate the free organic acid content. The calculation formula for the free organic acid content (mg / L) is: C = B × (1-α), ionization degree α = K a1 / (K a1 +[H+ ]); and ask the judges to score the sourness. The correlation analysis between the sourness score results and the free organic acid content was conducted, and the fitting curve between the free organic acid content and the sourness score was established (see the example figure Figure 2 , Figure 3 ), and obtain the fitting coefficient of each organic acid: k 乳酸 =0.0067, k 乙酸 =0.0077, k 琥珀酸 =0.0087, k 柠檬酸 =0.0187, k 苹果酸 =0.0129, k 酒石酸 =0.0155, k 富马酸 =0.0181.

[0081] 4. Definition The calculation method of the total acidity Y of the beverage is: the concentration of each free organic acid in the beverage sample × the fitting coefficient k of each organic acid, and the sum of the results of each organic acid is as follows:

[0082] Total acidity of beverage Y = 0.0067 × C 游离乳酸 +0.0077×C 游离乙酸 +0.0087×C 游离琥珀酸 +0.0187×C 游离柠檬酸 +0.0129×C 游离苹果酸 +0.0155×C 游离酒石酸 +0.0181×C 游离富马酸 .

[0083] Verify the accuracy of the method of the present invention

[0084] (1) Beer test:

[0085] After adding a certain amount of lactic acid, acetic acid, and citric acid to beer, and adjusting the pH of the beer with baking soda, the total acidity Y value was calculated according to the method of the present invention, and the judges were asked to evaluate and score the beer, and the results were compared with the total acidity Y value. Figure 4 .

[0086] Table 6 Evaluation and calculation results of beer with different free lactic acid

[0087]

[0088] Table 7 Evaluation and calculation results of beer with different free acetic acid

[0089]

[0090]

[0091] Table 8 Evaluation and calculation results of beer with different free citric acid

[0092]

[0093] The results show that, for beer samples, the sourness score Y value calculated by the method of the present invention is highly consistent with the judges' scores, which fully demonstrates the feasibility and accuracy of the method of the present invention, and can completely replace the way judges score. The method of the present invention uses instruments for high-throughput processing, with high processing efficiency, and does not require the trouble of judges. Moreover, when the judges taste too many samples in a short period of time, due to mutual interference, it will affect the judges' sourness judgment and cause some errors. The method of the present invention completely avoids this problem.

[0094] (2) Juice beverage test:

[0095] After adjusting the citrate content and pH of the beverage using citric acid and saturated baking soda solution, the total acidity Y value was calculated according to the method of the present invention, and the judges were asked to evaluate and score the beverage, and the results were compared with the total acidity Y value. The detailed data results are shown in Table 9, and the correlation results between the acidity calculation score Y value and the judges' scores are shown in Figure 5 .

[0096] Table 9. Test of adding citric acid to sweetened beverages

[0097]

[0098] The results showed that due to the influence of the sweetness of the beverage, the calculated sourness score was inconsistent with the judges' score, but the two were well correlated (R 2 =0.9868), so the method of the present invention is generally applicable to sweetened beverages.

[0099] The applicant declares that the present invention uses the above-mentioned embodiments to illustrate a method of digitally evaluating the sourness of beverages based on the free organic acid content, but the present invention is not limited to the above-mentioned embodiments, that is, it does not mean that the present invention must rely on the above-mentioned embodiments to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of the raw materials of the product of the present invention, addition of auxiliary ingredients, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

[0100] The preferred embodiments of the present invention are described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, a variety of simple modifications can be made to the technical solution of the present invention, and these simple modifications all belong to the protection scope of the present invention.

[0101] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

Claims

1. A method for digitally evaluating the sourness of a beverage based on the free organic acid content, characterized in that: The method comprises the following steps: A single organic acid standard was mixed with water to prepare a series of standard solutions. The organic acid radical content and pH value of the standard solution were tested. The free organic acid content in the standard solution was calculated. The judges were asked to taste the standard solution and score the acidity. A curve of the relationship between the acidity score and the free organic acid content was drawn to obtain the linear fitting coefficient k of the organic acid. The linear fitting coefficients of different types of organic acids obtained by the above method were recorded as k. n , n is an integer greater than or equal to 1; The content of each organic acid radical in the tested beverage sample is detected respectively, the pH value of the tested beverage sample is detected, and the content of each free organic acid in the tested beverage sample is calculated, which is recorded as C according to the type of organic acid. n , n is an integer greater than or equal to 1; Calculate the sourness score Y of the beverage sample to be tested according to the formula: The calculation method of the free organic acid content is: free organic acid content C = B × (1-α), B is the organic acid radical content, α = K a1 / (K a1 +[H + ]), K a1 is the first ionization constant of organic acids, [H + ]=10 -pH .

2. The method for digitally evaluating the sourness of a beverage based on the free organic acid content according to claim 1, characterized in that: The organic acid includes any one of lactic acid, citric acid, succinic acid, tartaric acid, fumaric acid, acetic acid, oxalic acid, pyruvic acid, formic acid, propionic acid, butyric acid, caproic acid, caprylic acid, capric acid, crotonic acid, strawberry acid and malic acid, or a combination of at least two thereof.

3. The method for digitally evaluating the sourness of a beverage based on the free organic acid content according to claim 1, characterized in that: The beverage includes any one of alcoholic beverages, tea beverages, fruit and vegetable juice beverages, protein beverages, coffee beverages and carbonated beverages.

4. The method for digitally evaluating the sourness of a beverage based on the free organic acid content according to claim 3, characterized in that: The alcoholic beverage includes any one of beer, liquor, wine and whiskey.

5. The method for digitally evaluating the sourness of a beverage based on the free organic acid content according to claim 1, characterized in that: The method for detecting the pH value includes detecting using a pH meter.

6. The method for digitally evaluating the sourness of a beverage based on the free organic acid content according to claim 1, characterized in that: The method for detecting the organic acid radical content includes any one of ion chromatography, spectrophotometry, gas chromatography and thin layer chromatography.

7. The method for digitally evaluating the sourness of a beverage based on the free organic acid content according to claim 6, characterized in that: The method for detecting the organic acid radical content is ion chromatography.

8. The method for digitally evaluating the sourness of a beverage based on the free organic acid content according to claim 7, characterized in that: Before detecting the organic acid radical content in the beverage sample to be tested, the beverage sample to be tested is also pretreated, and the pretreatment includes diluting the beverage sample to be tested with water, passing through a C18 column, filtering a membrane, and collecting the filtrate for sampling and testing.

9. The method for digitally evaluating the sourness of a beverage based on the free organic acid content according to claim 8, characterized in that: When the beverage is a gas-containing beverage, the dilution further includes degassing the beverage sample to be tested before dilution, and the gas-containing beverage includes beer or carbonated beverage.

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