CN111912841A - A rapid detection method for whether the amino acid nitrogen content of brewed soy sauce meets a certain level - Google Patents

Abstract

The invention provides a method for rapidly detecting whether the content of amino acid nitrogen in brewed soy meets a certain level, which comprises the steps of decoloring the soy, dripping an indicator, dripping monobasic strong base for neutralizing acid, dripping neutral formaldehyde for conversion, dripping the monobasic strong base with the quantity of substances of the lowest standard and the like, and directly judging whether a sample is qualified or not according to color change. The titration by instruments such as a power supply, an acidimeter and the like is not needed, the phenomena of 'sodium difference' and 'response' hysteresis of an electrode do not exist, the operation is simple and convenient, the calculation is not needed, and the result judgment is visual and accurate; the discrimination result can be obtained within a few minutes after sampling. The method has wide application range and strong practicability, and the result is completely consistent through comparison and determination with the national standard method.

Description

A rapid detection of whether the amino acid nitrogen content of brewed soy sauce meets a certain level method

technical field

The invention relates to the quality of brewed soy sauce, in particular to a rapid detection method for whether the amino acid nitrogen content of brewed soy sauce meets a certain level.

Background technique

Brewed soy sauce is a liquid condiment with special color, aroma and taste, which is made of soybean, wheat or bran as raw materials and fermented by certain technology and microorganisms. The taste is fresh, salty and palatable, and it is rich in nutrition.

The country has promulgated relevant standards for the quality of brewed soy sauce products. In the standard of GB18186-2000 "brewed soy sauce", it is stipulated that whether it is high-salt diluted soy sauce or low-salt solid-state fermented soy sauce, amino acid nitrogen (calculated as nitrogen) is used. The content level is used as an indicator, and it is divided into four grades: special grade, first grade, second grade, and third grade. In brewed soy sauce, the amino acid nitrogen content ≥ 0.80g/100mL is the special grade; ≥ 0.70g/100mL is the first grade; High-salt dilute fermented soy sauce); ≥0.40g/100mL is grade 3, and those below grade 3 are unqualified products.

The first method of the national food safety standard GB5009.235-2016 "Determination of Amino Acid Nitrogen Content in Food" is the acidity meter method. This method uses NaOH standard solution to treat the soy sauce sample to be alkaline (pH=8.2), remove the content of the sample The titratable acidic substance, then add formaldehyde to display the acidity of the amino acid carboxyl group and other substances, titrate with NaOH standard solution to the end point, and measure the blank at the same time. According to the amount of NaOH consumed by the blank and the sample, substitute the corresponding Calculate the result of the formula, and judge the quality and corresponding level of the brewed soy sauce according to the calculation result. The national standard law has the following shortcomings:

(1) It is not suitable to use NaOH standard solution for titration when measuring with acidity meter, because soy sauce contains a lot of salt (sodium chloride), and, with the progress of titration, due to the addition of sodium hydroxide standard solution, the amount of With a large amount of sodium ions, the pH glass electrode used will produce a significant "sodium difference", which will make the result significantly lower and introduce errors; the national standard method does not consider the influence of "sodium difference" on the measurement results.

(2) Formaldehyde reagents are often oxidized by air and contain formic acid during transportation and placement. They must be processed into neutral formaldehyde to eliminate the possible interference of formic acid and improve the measurement accuracy. The national standard method does not consider the influence of this factor.

(3) The first method of GB5009.235-2016, before adding formaldehyde to convert amino acid nitrogen, the pH of the test solution was titrated to 8.2, to remove the acidic substances in soy sauce, after adding formaldehyde, titrate with NaOH standard solution to pH 9.2 as the end point , which violates the "principle of quantitative transformation and reaction of equal substances" in quantitative analysis of analytical chemistry, and the experimental design lacks scientific basis to support, and it is unreasonable.

(4) The pH meter used needs to be calibrated with a suitable pH standard solution, and the glass electrode needs to be soaked in distilled water for more than 24 hours before it can be put into use; it will affect the measurement speed and work efficiency.

(5) The acidity meter must use power supply to work. For occasions without power supply, the application is limited and cannot work.

(6) The temperature change of the test solution will affect the measurement results. It is necessary to perform temperature correction on the acidity meter at any time or install a temperature compensation sensor through the relevant socket of the instrument to eliminate the interference of temperature, which will bring a lot of inconvenience to the work and affect the accuracy of the measurement. Spend.

(7) The amount of test solution and reagents used in the national standard method is relatively large, and the input cost is relatively high;

(8) The operation is relatively complicated, and the result judgment needs to be substituted into the formula for calculation, and the result judgment is not intuitive.

(9) From sampling, sample processing, titration to obtaining calculation results, it usually takes more than 2 hours, and the work efficiency is low.

(10) During the titration process, it takes a certain period of time for the membrane potential of the pH glass electrode to reach equilibrium, and there will be a "end point lag phenomenon", which is easy to drip, and introduces errors and affects the measurement results.

SUMMARY OF THE INVENTION

In order to solve the above problems, the present invention provides a rapid detection method for whether the amino acid nitrogen content of brewed soy sauce meets a certain level, without the need for titration with instruments such as a power supply and an acidity meter, and there is no "sodium difference" of electrodes and "hysteresis" in response. The operation is simple and convenient, no calculation is required, and the result judgment is intuitive and accurate; the screening result can be obtained within a few minutes after sampling. The method has a wide range of applications and strong practicability. The results are completely consistent with the national standard method.

The purpose of the present invention is to achieve in the following way: a kind of rapid detection method of whether the amino acid nitrogen content of brewed soy sauce meets a certain level, comprising the following steps, (1) take the brewed soy sauce sample a, and decolorize, after decolorization is decolorized (2) Take the decolorized soy sauce sample b containing V ₂ mL of soy sauce sample a, and add the indicator dropwise to it. At this time, the solution shows the acid color of the indicator, and then drip it with a plastic-tip dropper. Add 0.050mol/L NaOH until the color of the solution shows a mixture of acid color and basic color of the indicator, and does not fade for half a minute; then add neutral formaldehyde to completely convert the amino acid nitrogen in the soy sauce sample b into Acidic substance (-COOH), the solution is the acid color of the indicator at this time; then add V ₃ mL of strong monobasic solution, shake gently and observe the color of the solution, at this time, the solution shows the acid color of the indicator or the acid color of the solution When the alkali "equivalent point" shows the mixed color of the acid color and the basic color of the indicator, and the color does not fade for half a minute, the sample is qualified brewed soy sauce with a certain level, if the solution shows the basic color of the indicator and does not fade for half a minute. Discoloration means unqualified brewed soy sauce that does not meet a certain level; the concentration of the monobasic strong alkali solution is equal to the lowest concentration of the level of the soy sauce sample a, and V ₂ =V ₃ .

The monobasic strong alkali solution is sodium hydroxide solution, potassium hydroxide solution or lithium hydroxide solution.

Soy sauce sample a is the original soy sauce, and the original soy sauce is the soy sauce products sold in the market or produced by the factory; the original soy sauce is Lee Kum Kee Super Fresh, Chubang Seafood Soy Sauce/Light Soy Sauce, Haitian Soy Sauce King Soy Sauce, Lee Kum Kee Selected Light Soy Sauce, Lee Kum Kee Jinzhen Dark soy sauce, Jiajia straw mushroom dark soy sauce, Jiajia Golden Label light soy sauce, Luhua natural fresh soy sauce.

The indicator is purple potato pigment.

The preparation method of purple potato pigment is as follows: take purple potato, grind it into a paste, add distilled water according to the ratio of material to liquid 1:5, transfer it into a 100 mL colorimetric tube, and use ultrasonic assisted extraction, the ultrasonic power is 500W, and the extraction temperature is 55 ℃, the time is 15-20min, and then filter to obtain purple potato pigment; the pH of the distilled water used is 6.8.

The decolorization of soy sauce in the step (1) is as follows: use a pipette to pipette 1.00 mL of the original sample of soy sauce into a 25 mL colorimetric tube, add 9.00 mL of water to dilute, add 0.30 g of activated carbon, and gently stir with a glass rod to decolorize for 2 min After filtering, the obtained clear liquid after filtering is the soy sauce sample b after decolorization.

In the step (2), use a pipette to take 1.00 mL of soy sauce sample b into a 10 mL colorimetric tube, and add 2 to 3 drops of natural purple potato pigment dropwise. At this time, the solution is red or reddish-orange. Add 0.050mol/L NaOH standard solution dropwise until the color is orange-gray, add 2.00mL neutral formaldehyde, and the solution is red or red-orange at this time.

The acid color of purple potato pigment is shown as red or reddish-orange, and the basic color of purple potato pigment is shown as gray-blue, green earth or yellow-brown. A mixture of orange and gray-blue, it is orange-gray.

The amount of the remaining acidic substances in the solution of each grade of product, the red is greater than the red-orange, the red-orange is greater than the orange-gray; the amount of the remaining monobasic strong alkali in the solution, the yellow-brown is greater than the green earth color, and the green earth color is greater than the gray-blue color.

Beneficial effect: with respect to the prior art, the method for rapid detection of whether the amino acid nitrogen content of soy sauce provided by the present invention is qualified, according to GB18186-2000, the classification parameter index of amino acid nitrogen in the standard of "Brewing Soy Sauce", according to "equivalent quantity". "Reaction principle", scientifically set the concentration and amount of NaOH required to identify all levels of soy sauce products, and optimized decolorizing agents and natural color indicators. This method does not require titration with instruments such as power supply and acidity meter, and there is no "sodium difference" of the electrode and "hysteresis" of the response, and the required amount of test solution and standard solution is reduced by about 10 times. The invention provides a rapid detection method for whether the amino acid nitrogen content of brewed soy sauce meets a certain level, the operation is simple and convenient, no calculation is required, and the result judgment is intuitive and accurate; the screening result can be obtained within a few minutes after sampling. The method has a wide range of applications and strong practicability. The results are completely consistent with the national standard method.

Description of drawings

Figure 1 is the color change of purple potato pigment in different pH solutions, from left to right: pH is 2.00, 3.00, 4.00, 5.00, 6.00, 7.00, 8.00, 9.00, 10.00, 11.00, 12.00 and 13.00, respectively. Colors range from red (pH 2, 3), reddish-orange (pH 4, 5, 6, 7), orange-grey (pH 8), grey-blue (pH 9), green earth (pH 10, 11) to yellow-brown (pH 12, 13).

Figure 2 is the effect of the amount of activated carbon on the decolorization of soy sauce.

Figure 3 is the effect of time on the decolorization of soy sauce.

Detailed ways

A rapid detection method for whether the amino acid nitrogen content of brewed soy sauce conforms to a certain level, comprising the following steps: (1) taking a brewed soy sauce sample a, and decolorizing it, and decolorizing the soy sauce sample b after decolorization; ₂ mL of soy sauce sample b after decolorization of soy sauce sample a, add indicator to it, the solution shows the acid color of indicator, and then add 0.050mol/L NaOH with a plastic tip dropper until the color of the solution shows It is the mixed color of the acid color and the basic color of the indicator, and it does not fade for half a minute; then add neutral formaldehyde to completely convert the amino acid nitrogen in the soy sauce sample b into an acidic substance (-COOH), and the solution shows It is the acid color of the indicator; then add V3 mL of strong monobasic solution, shake gently and observe the color of the solution. At this time, the solution shows the acid color of the indicator or the acid-base "equivalent point" of the solution. If the mixed color of acid color and basic color does not fade in half a minute, the sample is qualified brewed soy sauce; if the solution shows the basic color of the indicator and does not fade in half a minute, the sample is not qualified for a certain level Brewing soy sauce; the concentration of the monobasic strong alkali solution is equal to the lowest concentration of the grade of the soy sauce sample a, and V ₂ =V ₃ .

The monobasic strong alkali solution is sodium hydroxide solution, potassium hydroxide solution or lithium hydroxide solution.

Soy sauce sample a is the original brewed soy sauce, and the original soy sauce is the soy sauce products sold in the market or produced by the factory; the original soy sauce is Lee Kum Kee Extremely Fresh, Chubang Seafood Soy Sauce/Light Soy Sauce, Haitian Soy Sauce Dark Soy Sauce King, Lee Kum Kee Selected Light Soy Sauce, Lee Kum Kee Noodle Soy Sauce Rare dark soy sauce, Jiajia straw mushroom dark soy sauce, Jiajia golden standard light soy sauce, Luhua natural fresh soy sauce.

The indicator is purple potato pigment.

The preparation method of purple potato pigment is as follows: take purple potato, grind it into a paste, add distilled water according to the ratio of material to liquid 1:5, transfer it into a 100 mL colorimetric tube, and use ultrasonic assisted extraction, the ultrasonic power is 500W, and the extraction temperature is 55 ℃, the time is 15-20min, and then filter to obtain purple potato pigment; the pH of the distilled water used is 6.8.

The decolorization of brewed soy sauce in the step (1) is as follows: pipette 1.00mL of the original soy sauce sample into a 25mL colorimetric tube, add 9.00mL of water to dilute, add 0.30g of activated carbon, and gently stir with a glass rod to decolorize, Filter after 2 minutes, and the obtained filtered clear liquid is decolorized soy sauce sample b.

In the step (2), use a pipette to take 1.00 mL of soy sauce sample b into a 10 mL colorimetric tube, and add 2 to 3 drops of natural purple potato pigment dropwise. At this time, the solution is red or reddish-orange. Add 0.050mol/L NaOH standard solution dropwise until the color is orange-gray, add 2.00mL neutral formaldehyde, and the solution is red or red-orange at this time.

The acid color of purple potato pigment is shown as red or reddish-orange, the basic color of purple potato pigment is shown as gray-blue, green earth or yellow-brown, and the mixed color of red-orange and gray-blue of purple potato pigment is orange-gray; press During the identification by the step method, the amount of the remaining acidic substances in the identified sample solution, the red is greater than the reddish-orange, the reddish-orange is greater than the orange-gray; the amount of the unary strong alkali remaining in the solution, the yellow-brown is greater than the smectite color, and the smectite color is greater than Grey blue.

The present invention will be specifically described below in conjunction with specific embodiments. It is necessary to point out that this embodiment is only used to further illustrate the present invention, and should not be construed as a limitation on the protection scope of the present invention. Those skilled in the art can Some non-essential improvements and adjustments are made to the content of the invention. In the present application, the color of the solution is observed after shaking gently, and shaking is the normal shaking degree in the titration process.

1. Preparation of purple potato pigment (with distilled or purified water)

Cut 10g-15g of fresh purple potato (purple potato sample was purchased from Lianhe 100 supermarket in Mazhai Town, Erqi District, Zhengzhou City on October 30, 2019, it was very fresh at the time of purchase, the color was purple to dark purple) into small pieces, After grinding into a paste in a mortar, add distilled water according to the ratio of material to liquid 1:5, transfer it into a 100mL colorimetric tube, and use ultrasonic waves (power 500W) to assist extraction. The extraction temperature is 55 ℃ and the time is 10-20min. Then filter into a dropping bottle, which is purple potato pigment. The pH of the distilled water used was 6.8.

Take 12 clean 100mL small beakers, add about 40mL distilled water to each, carefully add 0.10mol/L hydrochloric acid or 0.10mol/L sodium hydroxide solution dropwise on the acidity meter, adjust to pH 2.00, 3.00, 4.00, 5.00, 6.00 respectively , 7.00, 8.00, 9.00, 10.00, 11.00, 12.00, and 13.00, then add 4 drops of purple potato pigment filtrate dropwise to each, shake well, and transfer them into 25.00 ml colorimetric tubes respectively, observe the purple potato pigment in different pH solutions The color changes in Figure 1, from left to right: color from red (pH 2, 3), red-orange (pH 4, 5, 6, 7), orange-gray (pH 8), gray-blue (pH 9) ), smectite (pH 10, 11) to yellowish brown (pH 12, 13).

2. Preparation, calibration, and concentration adjustment of NaOH standard solution

1. Concentration setting

Amino acid is a neutral inner salt. When neutral formaldehyde is added, the basic amino group (-NH ₂ ) combines with formaldehyde, the basicity disappears, and the acid carboxyl group (-COOH) appears, which can be combined with strong alkali standard solution and other substances. The reaction is especially suitable for the determination of amino nitrogen in fermentation broth. Each amino group ( _-NH2 ) contains one nitrogen. Whether it is high-salt dilute fermented soy sauce or low-salt solid-state fermented soy sauce, the content of amino acid nitrogen (calculated as nitrogen) is the main physical and chemical index of the products at all levels. The minimum concentration of required nitrogen is the minimum concentration of amino acid and the minimum concentration of carboxyl group after conversion. Therefore, the minimum concentration of carboxyl group (-COOH) in qualified products at all levels should be:

Level 3:

（对高盐稀态发酵酱油）Secondary:

(for high-salt diluted fermented soy sauce)

（对低盐固态发酵酱油）

(for low-salt solid-state fermented soy sauce)

Level 1:

Premium:

Therefore, according to the principle of "reaction of equivalent amount", the present invention prepares a strong base standard solution of NaOH (or KOH) of the same level and concentration, and "reaction of equivalent amount" occurs with the carboxyl group (-COOH) in the sample, and the reaction is completed. If the carboxyl group of the sample remains, it is a qualified product of the corresponding level; if the carboxyl group is insufficient and the strong alkali remains, the brewed soy sauce is an unqualified product of the corresponding level. If the amount of the carboxyl group (-COOH) in the sample is exactly equal to the amount of the strong base added, there is no residue after the neutralization reaction, and the theoretical end point of the required minimum level index is just reached, and the solution shows the indicator A mixture of red-orange and gray-blue, or orange-gray, is extremely rare. After removing the interfering color of soy sauce with a decolorizing agent, it can be quickly identified and judged with a suitable indicator.

2. Preparation, calibration and adjustment of NaOH standard solutions of different concentrations

First, use an electronic balance to weigh the required amount of NaOH (A.R), dissolve it, and dilute to volume. Use the potassium hydrogen phthalate reference substance baked to constant quality for calibration, carry out 4 parallel calibrations, and take the average value after checking that there is no suspicious value. If the concentration is lower than the target concentration, calculate and add the required solid NaOH (A.R); If the concentration is higher than the target concentration, calculate and add the required distilled water.

(1) Preparation, calibration and adjustment of 0.2857 mol/L NaOH standard solution

Quickly weigh 5.714 g of NaOH (A.R, analytical grade) in a small beaker with an electronic balance, dissolve it in about 80 mL of distilled water, cool it to room temperature, and quantitatively transfer it into a 500 mL volumetric flask, use distilled water to make up to the mark, mix well, and set aside.

Accurately weigh 0.6g-1.2g (accurate to 0.0001g) of potassium hydrogen phthalate reference reagent baked at 105°C to a constant mass on an analytical balance into a clean conical flask, add about 40mL of distilled water to dissolve it completely, Add 4 drops of purple potato pigment prepared in this application, calibrate with the above-mentioned sodium hydroxide solution in the treated basic burette, and titrate until the red-orange color just disappears into orange-gray and does not fade for half a minute as the end point, and record the consumption of sodium hydroxide. The volume V ₁ (ml) of the solution, meanwhile, take 40 mL of distilled water for blank test and color comparison, and calculate the concentration as follows:

C(NaOH)=(m×1000÷204.22)/(V ₁ -V ₀ )

Wherein, C (NaOH): the amount concentration of the substance of sodium hydroxide standard solution, mol/L; m is the quality of the potassium hydrogen phthalate reference reagent accurately weighed, g; 204.22 is the potassium hydrogen phthalate Molar mass, g/mol; V ₀ is the volume of sodium hydroxide solution consumed by the blank solution (mL); V ₁ is the volume of sodium hydroxide solution consumed by the potassium hydrogen phthalate reference reagent with a calibrated mass of m (mL).

Do 4 parallel calibrations, and take the average value after checking that there are no suspicious values. If the concentration is lower than 0.2857 mol/L, calculate and add the required solid NaOH; if the concentration is higher than 0.2857 mol/L, calculate and add the required distilled water until The target concentration is reached after recalibration.

It can also prepare 0.2857mol/L potassium hydroxide standard solution for work, the present invention selects a relatively cheap sodium hydroxide standard solution, and the input cost is relatively reduced.

(2) Preparation, calibration and adjustment of 0.3929mol/L NaOH standard solution

Use an electronic balance to quickly weigh 7.858 g of NaOH (analytical grade) into a small beaker, dissolve it in about 80 mL of distilled water, and after cooling to room temperature, quantitatively transfer it into a 500-mL volumetric flask, dilute to the mark with distilled water, mix well and set aside.

On the analytical balance, accurately weigh 0.8 g-1.6 g (accurate to 0.0001 g) of the reference reagent potassium hydrogen phthalate, which is baked to constant mass at 105 °C, into a clean conical flask, and add about 40 mL of distilled water to dissolve it completely. Add 4 drops of purple potato pigment prepared in this application, calibrate with the above-mentioned sodium hydroxide solution in the treated basic burette, titrate until the red-orange color just disappears into orange-gray, and the color does not fade for half a minute as the end point, and record the consumption of hydrogen The volume V ₁ (mL) of the sodium oxide solution, and at the same time, take 40 mL of distilled water for blank test and color comparison, and calculate the concentration as follows:

C(NaOH)=(m×1000÷204.22)/(V ₁ -V ₀ )

Wherein, C (NaOH): the amount concentration of the substance of sodium hydroxide standard solution, mol/L; m is the quality of the potassium hydrogen phthalate reference reagent accurately weighed, g; 204.22 is the potassium hydrogen phthalate Molar mass, g/mol; V ₀ is the volume of sodium hydroxide solution consumed by the blank solution (mL); V ₁ is the volume of sodium hydroxide solution consumed by the potassium hydrogen phthalate reference reagent with a calibrated mass of m (mL).

Do 4 parallel calibrations. After checking that there is no suspicious value, take the average value. If the concentration is lower than 0.3929mol/L, calculate and add the required solid NaOH; if the concentration is higher than 0.3929mol/L, calculate and add the required distilled water. until the target concentration is reached after recalibration.

It can also prepare 0.3929mol/L potassium hydroxide standard solution for work, the present invention selects a relatively cheap sodium hydroxide standard solution, and the input cost is relatively reduced.

(3) Preparation, calibration and adjustment of 0.4286mol/L NaOH standard solution

Use an electronic balance to quickly weigh 8.5720 g of NaOH (analytical grade) into a small beaker, dissolve it in about 80 mL of distilled water, and after cooling to room temperature, quantitatively transfer it into a 500 mL volumetric flask, use distilled water to make up to the mark, mix well and set aside.

On the analytical balance, accurately weigh 0.8g-1.8g (accurate to 0.0001g) of the reference reagent potassium hydrogen phthalate, which has been baked to constant mass at 105°C, into a clean conical flask, add about 40mL of distilled water to dissolve it completely, Add 4 drops of purple potato pigment prepared in this application, calibrate with the above-mentioned sodium hydroxide solution in the treated basic burette, titrate until the red-orange color just disappears into orange-gray, and the color does not fade for half a minute as the end point, record the consumption of hydrogen The volume of sodium solution V ₁ (mL), at the same time, take 40 mL of distilled water for blank test and color comparison, and calculate the concentration as follows:

C(NaOH)=(m×1000÷204.22)/(V ₁ -V ₀ )

Wherein, C(NaOH) is the substance concentration of sodium hydroxide standard solution, mol/L; m is the mass of the accurately weighed potassium hydrogen phthalate reference reagent, g; 204.22 is the amount of potassium hydrogen phthalate Molar mass, g/mol; V ₀ is the volume of sodium hydroxide solution consumed by the blank solution (mL); V ₁ is the volume of sodium hydroxide solution consumed by the potassium hydrogen phthalate reference reagent with a calibrated mass of m (mL).

Do 4 parallel calibrations. After checking that there is no suspicious value, take the average value. If the concentration is lower than 0.4286mol/L, calculate and add the required solid NaOH; if the concentration is higher than 0.4286mol/L, calculate and add the required distilled water. until the target concentration is reached after recalibration.

The standard solution of potassium hydroxide of 0.4286mol/L can also be prepared for work. In this invention, a standard solution of sodium hydroxide with a lower price is selected, and the input cost is relatively reduced.

(4) Preparation, calibration and adjustment of 0.5000mol/L NaOH standard solution

Use an electronic balance to quickly weigh 10.00 g of NaOH (analytical grade) into a small beaker, dissolve it in about 80 mL of distilled water, and after cooling to room temperature, quantitatively transfer it into a 500 mL volumetric flask, and make up to the mark with distilled water, mix well and set aside.

On the analytical balance, accurately weigh 1.0g-2.0g (accurate to 0.0001g) of the reference reagent potassium hydrogen phthalate, which is baked to constant mass at 105°C, into a clean conical flask, add about 40mL of distilled water to dissolve it completely, Add 4 drops of purple potato pigment prepared in this application, calibrate with the above-mentioned sodium hydroxide solution in the treated basic burette, titrate until the red-orange color just disappears into orange-gray, and the color does not fade for half a minute as the end point, record the consumption of hydrogen The volume of sodium solution V ₁ (mL), at the same time, take 40 mL of distilled water for blank test and color comparison, and calculate the concentration as follows:

C(NaOH)=(m×1000÷204.22)/(V ₁ -V ₀ )

Wherein, C(NaOH) is the substance concentration of sodium hydroxide standard solution, mol/L; m is the mass of the accurately weighed potassium hydrogen phthalate reference reagent, g; 204.22 is the amount of potassium hydrogen phthalate Molar mass, g/mol; V ₀ is the volume of sodium hydroxide solution consumed by the blank solution (mL); V ₁ is the volume of sodium hydroxide solution consumed by the potassium hydrogen phthalate reference reagent with a calibrated mass of m (mL).

Do 4 parallel calibrations. After checking that there is no suspicious value, take the average value. If the concentration is lower than 0.5000mol/L, calculate and add the required solid NaOH; if the concentration is higher than 0.5000mol/L, calculate and add the required distilled water. until the target concentration is reached after recalibration.

The standard solution of potassium hydroxide of 0.5000mol/L can also be prepared for work. In this invention, a standard solution of sodium hydroxide with a lower price is selected, and the input cost is relatively reduced.

(5) Preparation, calibration and adjustment of 0.5714mol/L NaOH

Use an electronic balance to quickly weigh 11.428g of NaOH (analytical grade) into a small beaker, dissolve it in about 80mL of distilled water, and after cooling to room temperature, quantitatively transfer it into a 500mL volumetric flask, use distilled water to make up to the mark, mix well and set aside.

On the analytical balance, accurately weigh 1.2g-2.5g (accurate to 0.0001g) of the reference reagent potassium hydrogen phthalate, which has been baked to constant mass at 105°C, into a clean conical flask, and add about 40mL of distilled water to dissolve it completely. Add 4 drops of purple potato pigment prepared in this application, calibrate with the above-mentioned sodium hydroxide solution in the treated basic burette, and titrate until the red-orange color just disappears into orange-gray and does not fade for half a minute as the end point, and record the consumption of sodium hydroxide. The volume V ₁ (mL) of the solution, meanwhile, take 40 mL of distilled water for blank test and color comparison, and calculate the concentration as follows:

C(NaOH)=(m×1000÷204.22)/(V ₁ -V ₀ )

Wherein, C(NaOH) is the substance concentration of sodium hydroxide standard solution, mol/L; m is the mass of the accurately weighed potassium hydrogen phthalate standard reagent, g; 204.22 is the amount of potassium hydrogen phthalate Molar mass, g/mol; V ₀ is the volume of sodium hydroxide solution consumed by the blank solution (mL); V ₁ is the volume of sodium hydroxide solution consumed by the potassium hydrogen phthalate reference reagent with a calibrated mass of m (mL).

Do 4 parallel calibrations, and take the average value after checking that there are no suspicious values. If the concentration is lower than 0.5714 mol/L, calculate and add the required solid NaOH; if the concentration is higher than 0.5714 mol/L, calculate and add the required distilled water until The target concentration is reached after recalibration.

The standard solution of potassium hydroxide of 0.5714mol/L can also be prepared for work. In this invention, a standard solution of sodium hydroxide with a lower price is selected, and the input cost is relatively reduced.

3. Preparation of neutral formaldehyde

Add 4-6 drops of the purple potato pigment prepared in this application to the 36%-38% analytically pure formaldehyde solution dropwise, add NaOH solution dropwise to the formaldehyde solution, shake gently while dripping, until the formaldehyde solution changes from red to orange. Disappeared, just turned orange-gray, sealed and kept for later use.

4. Decolorization treatment and effect of soy sauce

Experimental instruments and reagents: UV-2800AH UV-Vis Spectrophotometer (Unico Instrument Co., Ltd.), 200-mesh food carbohydrate activated carbon (Ron's reagent).

Experimental steps:

(1) Take 1.00 mL of Lee Kum Kee Weiji Xian original soy sauce in a clean test tube, add 9.00 mL of deionized water, mix well and set aside, this is the test solution to be scanned.

(2) Preparation of blank solution: Take 1.00 mL of Lee Kum Kee Weiji Xian original soy sauce in a clean test tube, add 9.00 mL of deionized water, add 0.40 g of activated carbon for treatment, let stand for 2 minutes, filter with a funnel, and use the filtrate as a blank (to exclude Factors other than pigments have an effect on absorbance).

(3) Drawing of the absorption spectrum: Take the sample solution diluted 10 times as the test solution and the blank sample solution as the control, and scan the absorption spectrum of the test solution between 200-800 nm with a 1cm cuvette. The maximum wavelength λ _max =336.0nm.

(4) Research on decolorization rate: take 20 mL of 10-fold diluted soy sauce and place them in seven 50.00 mL colorimetric tubes, and add 0.12 g, 0.16 g, 0.20 g, 0.24 g, 0.28 g, 0.30 g, and 0.32 g respectively in turn. Activated carbon was shaken gently, let stand for 1min-2min, and filtered with filter paper. Taking the blank sample solution as the control, and taking 336.0 nm as the incident light, the absorbance of each test solution was measured with a 1 cm cuvette. Calculate the decolorization rate of the sample as follows:

Decolorization rate, %=(A ₀ -A)÷A ₀ ×100% (3)

In the formula, A ₀ is the absorbance measured when the 10-fold diluted soy sauce sample is not decolorized, and A is the absorbance of the filtrate after adding different amounts of activated carbon to decolorize the 10-fold diluted soy sauce sample. The results are shown in Figure 2. It can be seen from Figure 2 that when 0.30 g of activated carbon is added, the decolorization rate is 92.56%, which can achieve a better decolorization effect.

Weigh 0.30g of activated carbon and let it stand for 2min, 4min and 6min respectively, then filter, measure the absorbance according to the above method and calculate the decolorization rate. The results are shown in Figure 3. As can be seen from Figure 3, the effect of decolorization from 2min to 6min is satisfactory. In order to improve work efficiency, the decolorization time of the present invention is selected as 2min.

5. Determination by the national standard potentiometric titration method

(1) Determination by potentiometric titration with potassium hydroxide standard solution

Operation steps: suck 5.00mL of soy sauce into a 100mL volumetric flask, add water to the mark, and after mixing, suck 20mL, put it in a 100mL beaker, and add 60mL of water. Use potassium hydroxide standard solution c (KOH=0.050mol/L) to titrate to pH=8.2 of ion meter, and record the volume of KOH consumed. Add 20 mL of neutral formaldehyde, mix well, and record the pH at this time. Continue the titration with KOH to pH=8.2, and record the volume of KOH consumed.

At the same time, take 20 mL of water, first adjust pH=8.2 with 0.050mol/LKOH, then add 20mL neutral formaldehyde, titrate with 0.050mol/LKOH to pH=8.2, record the volume of KOH consumed, as a blank experiment for the reagent.

The formula for calculating the amino acid nitrogen content in the sample is:

(1)

(1)

where:

X—the amino acid nitrogen content in the sample, g/100mL;

V ₁ —the volume of KOH consumed after adding formaldehyde to the sample diluent for determination, mL;

V ₀ —the volume of KOH consumed after adding formaldehyde to the reagent blank experiment, mL;

V—the amount of sample diluent taken, mL;

The concentration of the substance of C—KOH, mol/L;

0.014—the mass of nitrogen equivalent to 1.00 mmol (millimol) KOH, g.

The calculation result retains three significant figures.

(2) Determination by potentiometric titration with sodium hydroxide standard solution

Operation steps: suck 5.00mL of soy sauce into a 100mL volumetric flask, add water to the mark, and after mixing, suck 20mL, put it in a 100mL beaker, and add 60mL of water. Titrate with sodium hydroxide standard solution c (NaOH=0.050mol/L) to pH=8.2 of ion meter, and record the volume of NaOH consumed. Add 20 mL of formaldehyde that has not been adjusted to neutrality, mix well, and record the pH at this time. Continue titration with NaOH to pH=9.2, and record the volume of NaOH consumed.

At the same time, take 20 mL of water, first adjust pH=8.2 with 0.050mol/L NaOH, then add 20 mL of formaldehyde that has not been adjusted to neutrality, titrate with 0.050mol/L NaOH to pH=9.2, record the volume of NaOH consumed, as the blank of the reagent experiment.

The formula for calculating the amino acid nitrogen content in the sample is:

(1)

(1)

where:

X—the amino acid nitrogen content in the sample, g/100mL;

V ₁ —the volume of the strong alkali standard solution consumed after adding the formaldehyde to the sample diluent for determination, mL;

V ₀ —the volume of the strong alkali standard solution consumed after adding formaldehyde in the reagent blank experiment, mL;

V—the amount of sample diluent taken, mL;

C—the amount concentration of the substance in the strong alkali standard solution, mol/L;

0.014—the mass of nitrogen equivalent to 1.00 mmol (millimol) of strong base, g.

The calculation result retains three significant figures.

(3) The test results and analysis of the sample control are shown in Table 1 below.

The detection value of the national standard method is always slightly larger than the detection value of this project. The main reason is that the pH of the test solution is 8.2 before adding formaldehyde to convert amino acid nitrogen into the national standard method. After adding formaldehyde, titration with NaOH standard solution to pH 9.2 is the end point. The "principle of quantitative transformation and reaction of equal substances" in quantitative analysis of analytical chemistry is adopted, which makes the determination result on the high side.

6. Determination results of the original brewed soy sauce according to the first method of national standard method acidity meter method

According to the national standard GB5009.235-2016 "Determination of Amino Acid Nitrogen Content in Food", the samples were measured by the first method of acidity meter, and compared with the color of the reagent tube solution and the marked value of the product. The results are shown in Table 2.

It can be seen from Table 2 that the measurement results of the samples by the national standard method are all higher than the marked value of the commodity.

7. Whether the amino acid nitrogen content of brewed soy sauce meets a certain level of rapid detection method and result verification

(1) Whether the amino acid nitrogen content of the original soy sauce conforms to a certain level of rapid detection methods and result verification

(1) Premium soy sauce (amino acid nitrogen content ≥ 0.80g/100mL)

Experimental reagents: 0.5714mol/L NaOH solution, neutral formaldehyde

Operation steps: Pipette 1.00mL of soy sauce into a 25mL colorimetric tube, add 9.00mL of water to dilute, add 0.30g of activated carbon, gently stir with a glass rod to decolorize, filter after 2min, and use a pipette to remove 1.00mL Filter the clear liquid into a 10mL colorimetric tube, add 2 to 3 drops of purple potato natural pigment dropwise, the solution is red at this time, add 0.050mol/L NaOH dropwise with a plastic tip dropper until the solution color is orange-gray, add 2.00mL neutral Formaldehyde, the solution is red at this time, add 100 μL of 0.5714mol/L NaOH solution with a pipette gun, and observe the color of the solution after shaking gently. At this time, the solution is red, red-orange or orange-gray and does not fade for half a minute, then the product is special brewing If the soy sauce is gray-blue, green earth or yellow-brown and does not fade in half a minute, the product quality does not meet the requirements of special-grade brewed soy sauce.

The amino acid nitrogen and other substances are converted into acid (-COOH) with neutral formaldehyde, so the acidity of the solution is greatly increased, and the pigment appears red. Then add the strong alkali required for the corresponding grade of products and observe the color of the solution for rapid identification. The following is the same. 2.00mL of neutral formaldehyde can completely convert the amino acid nitrogen in the 100μL original soy sauce sample into an equivalent amount of acidic substances (-COOH).

(2) Grade 1 soy sauce (amino acid nitrogen content ≥ 0.70g/100mL)

Experimental reagents: 0.5000mol/L NaOH solution, neutral formaldehyde

Operation steps: Pipette 1.00mL of soy sauce into a 25mL colorimetric tube, add 9.00mL of water to dilute, add 0.30g activated carbon, gently stir with a glass rod to decolorize, filter after 2min, and use a pipette to transfer 1.00mL Filter the clear liquid into a 10mL colorimetric tube, add 2 to 3 drops of natural purple potato pigment dropwise, the solution is red at this time, add 0.050mol/L NaOH dropwise with a plastic tip dropper until the solution color is orange-gray, add 2.00mL neutral Formaldehyde, the solution is red at this time, add 100 μL of 0.5000mol/L NaOH solution with a pipette, and observe the color of the solution after shaking gently. If the solution is still red, red-orange or orange-gray and does not fade for half a minute, the product is first-class If the fermented brewed soy sauce is gray-blue, green earth or yellow-brown and does not fade within half a minute, the product does not meet the requirements of the first-grade fermented brewed soy sauce.

(3) Secondary soy sauce (high-salt, dilute fermented soy sauce, amino acid nitrogen content ≥ 0.55g/100mL)

Experimental reagents: 0.3929mol/L NaOH standard solution, neutral formaldehyde

Operation steps: Pipette 1.00mL of soy sauce into a 25mL colorimetric tube, add 9.00mL of water to dilute, add 0.30g of activated carbon, gently stir with a glass rod to decolorize, filter after 2min, take 1.00mL of clear liquid in 10mL ratio. In the color tube, add 2 to 3 drops of natural purple potato pigment dropwise, the solution is red at this time, add 0.050mol/L NaOH solution dropwise with a plastic tip dropper until the color is orange-gray, add 2.00mL of neutral formaldehyde, the solution at this time is Red, add 100μL of 0.3929mol/L NaOH solution with a pipette, shake gently and observe the color of the solution. At this time, the solution is still red, red-orange or orange-gray and does not fade for half a minute, then the product is secondary high-salt diluted state fermentation Soy sauce, if it is gray-blue, green earth or yellow-brown and does not fade in half a minute, the product does not meet the requirements of secondary high-salt dilute fermented soy sauce.

(4) Secondary soy sauce (low-salt solid-state fermented soy sauce, amino acid nitrogen content ≥ 0.60g/100mL)

Experimental reagents: 0.4286mol/L NaOH solution, neutral formaldehyde

Operation steps: Pipette 1.00mL of soy sauce into a 25mL colorimetric tube, add 9.00mL of water to dilute, add 0.30g of activated carbon, gently stir with a glass rod to decolorize, filter after 2min, take 1.00mL of clear liquid in 10mL ratio. In the color tube, add 2 to 3 drops of natural purple potato pigment dropwise, the solution is red at this time, add 0.050mol/L NaOH solution dropwise with a plastic tip dropper until the color is orange-gray, add 2.00mL of neutral formaldehyde, the solution at this time is Red, add 100μL of 0.4286mol/L NaOH standard solution with a pipette, shake gently and observe the color of the solution. At this time, the solution is still red, red-orange or orange-gray and does not fade for half a minute, then the product is secondary low-salt solid state fermentation Soy sauce, if it is gray-blue, green earth or yellow-brown and does not fade in half a minute, the product does not meet the requirements of secondary low-salt solid-state fermented soy sauce.

(5) Grade 3 soy sauce (amino acid nitrogen content ≥ 0.40g/100mL)

Experimental reagents: 0.2857mol/L NaOH standard solution, neutral formaldehyde

Operation steps: Pipette 1.00mL of soy sauce into a 25mL colorimetric tube, add 9.00mL of water to dilute, add 0.30g of activated carbon, gently stir with a glass rod to decolorize, filter after 2 minutes, and use a pipette to take 1.00mL to clarify Put the solution in a 10mL colorimetric tube, add 2 to 3 drops of natural purple potato pigment dropwise, the solution is red at this time, add 0.050mol/L NaOH standard solution with a plastic tip dropper until the color is orange-gray, add 2.00mL neutral formaldehyde , the solution is red at this time, add 100 μL of 0.2857mol/L NaOH standard solution with a pipette gun, and observe the color of the solution after shaking gently. At this time, the solution is still red, red-orange or orange-gray and does not fade for half a minute, then the product is three If the fermented soy sauce is gray-blue, green earth or yellow-brown and does not fade in half a minute, the product does not meet the requirements of the tertiary fermented soy sauce, that is, it does not meet the relevant national standards.

Result verification: The results obtained by the rapid detection method provided in this application are completely consistent with the results obtained by the national standard method, as shown in Table 3.

(2) The rapid detection method and result verification of whether the amino acid nitrogen content of the diluted brewed soy sauce is qualified

Dilute the original soy sauce with distilled water in a certain proportion as a sample. According to the national food safety standard GB5009.235-2016 "Determination of Amino Acid Nitrogen Content in Food", the first method is the acidity meter method, and the results are calculated according to (1) , parallel determination 3 times, take the average value report after checking no suspicious value, after the sample is diluted in different proportions, the results of the determination according to the national standard method are shown in Table 4 and Table 5.

1. Preparation and determination of brewed soy sauce with a double dilution of the original sample

Transfer 12.50mL of soy sauce with a pipette to a 25.00mL volumetric flask, dilute to the mark with C’estbon pure water (pH=6.80), and mix well for later use. According to the national standard method GB5009.235-2016 "Determination of Amino Acid Nitrogen Content in Food", the first method of acidity meter method was used to measure the samples in parallel for 3 times. After no suspicious value was detected, the average value was reported.

At the same time, use a pipette to transfer 1.00mL of the soy sauce diluted sample into a 25mL colorimetric tube, add 9.00mL of water to dilute, add 0.30g of activated carbon, gently stir with a glass rod to decolorize, filter after 2 minutes, and use a pipette Take 1.00mL of the decolorized clear solution into a 10mL colorimetric tube, add 2 to 3 drops of purple potato pigment prepared in this application, the solution is red at this time, and dropwise add 0.050mol/L NaOH standard with a plastic tip dropper The solution is orange-gray, add 2.00mL of neutral formaldehyde, the solution is red at this time, use a pipette to add 100μL of the above NaOH standard solution of the corresponding concentration required for each level, shake gently to observe the color of the solution, at this time the solution is still If it is red, red-orange or orange-gray and does not fade in half a minute, the product is a qualified brewed soy sauce. If it is gray-blue, green earth or yellow-brown and does not fade in half a minute, the product does not meet the requirements of the corresponding grade of brewed soy sauce , that is, it does not meet the relevant national standards. The color of the reagent tube solution and the measurement results of the national standard method are shown in Table 4.

2. Preparation and determination of soy sauce samples after five-fold dilution

Transfer 5.00mL of soy sauce with a pipette to a 25.00mL volumetric flask, dilute to the mark with C’estbon pure water (pH=6.80), and mix well for later use. According to the national standard method GB5009.235-2016 "Determination of Amino Acid Nitrogen Content in Food", the first method of acidity meter method was used to measure the samples in parallel for 3 times. After no suspicious value was detected, the average value was reported.

At the same time, use a pipette to transfer 1.00 mL of the soy sauce diluted five times as it was in a 25 mL colorimetric tube, add 9.00 mL of water to dilute, add 0.30 g of activated carbon, gently stir with a glass rod to decolorize, filter after 2 minutes, and use a pipette to remove the color. Take 1.00mL of the decolorized clear liquid from the liquid gun into a 10mL colorimetric tube, add 2 to 3 drops of the purple potato pigment prepared in this application, the solution is red at this time, and dropwise add 0.050mol/L NaOH standard solution with a plastic tip dropper When the color is orange-gray, add 2.00mL of neutral formaldehyde. At this time, the solution is red. Use a pipette to add 100μL of the above NaOH standard solution of the corresponding concentration required for each level. After shaking gently, observe the color of the solution. At this time, the solution is still red. , reddish-orange or orange-gray and does not fade in half a minute, the product is a qualified brewed soy sauce, if it is gray-blue, green earth or yellow-brown and does not fade in half a minute, the product does not meet the requirements of the corresponding grade of brewed soy sauce. That is, it does not meet the relevant national standards. The color of the reagent tube solution and the measurement results of the national standard method are shown in Table 5.

According to the qualified index of amino acid nitrogen of brewed soy sauce at various levels, the present invention sets the volume of the standard sodium hydroxide solution to be added to 100 microliters, that is, 0.10 mL of original brewed soy sauce, according to the principle of "reaction of equivalent amount" for rapid identification. . When identified according to the above-mentioned steps, the amount of the remaining acidic substances (-COOH) in the sample solution, the red is greater than the red-orange, the red-orange is greater than the orange-gray; the amount of the remaining monobasic strong base (-OH) in the solution, the yellow-brown is greater than the green Earth color, green earth color is greater than gray-blue.

The invention scientifically designs the concentration of a strong base of a single element according to the minimum requirements for the qualified amino acid nitrogen of the physical and chemical indexes of different grades of brewed soy sauce. According to the principle of quantity reaction of equal substances, when the volume of the original sample of soy sauce is determined, add the same volume of strong base solution. The concentration of the acidic substance (-COOH) generated by the conversion of amino acid nitrogen is also greater than the concentration of the monobasic strong base solution. After the reaction is completed, the acidic substance remains, and the product is a qualified product. The more the remaining acid, the better the product quality; if The concentration of the acid substances converted from the brewed soy sauce and other substances is exactly equal to the concentration of the monobasic strong alkali solution. After the reaction is completed, it just reaches the theoretical end point that meets the minimum requirements of the corresponding level of soy sauce, and there are no acid and alkali substances remaining. The brewed soy sauce is a Qualified products that meet the minimum index requirements; if the concentration of the acidic substance (-COOH) converted from the soy sauce is less than the concentration of the monobasic strong alkali solution, after the reaction is completed, the strong alkali remains and the -COOH is insufficient, the amino acid state in the brewed soy sauce Nitrogen is lower than the minimum requirements for the corresponding level, and it is a product that does not meet the corresponding level. This conclusion can be quickly identified with a suitable indicator.

A strong monobasic base titrates a weak acid, and the titration jump always falls in the alkaline region. The size of the jump range is related to the concentration of acid and alkali and the size of Ka of weak acid. For example: 0.01000mol/L acetic acid is titrated with 0.01000mol/L sodium hydroxide, and the titration jump is from pH 7.7 to pH 8.7. The theoretical end point is pH 8.23 (refer to books on Analytical Chemistry); purple potato pigments are red (pH 2, 3), red-orange (pH 4, 5, 6, 7), orange-grey (pH 8), grey-blue (pH 9), smectite (pH 10, 11) to yellowish brown (pH 12, 13).

Therefore, brewing soy sauce solution, according to the technical operation of the present invention, purple potato pigment color results are red, red-orange, after the reaction, all levels of products are located before the theoretical end point that meets the minimum amino acid nitrogen requirements for brewing soy sauce at the corresponding level, and acidic substances (- COOH) remaining, it can be immediately judged as a qualified sample; if the purple potato pigment color is orange-gray, the reaction just reaches the "theoretical end point" that meets the minimum amino acid nitrogen requirements of the corresponding level of soy sauce, and the amount of acid and alkali in the solution is exactly equal. If it is not excessive, it can be judged that the brewed soy sauce is just a qualified sample of the corresponding level; if it is gray-blue, green earth or yellow-brown, the reaction has exceeded the theoretical end point of the minimum amino acid nitrogen requirement, and the strong alkali is excessive, which is not acceptable. Qualified samples.

As mentioned above, if the color of purple potato pigment is orange-gray, the reaction just reaches the theoretical end point that meets the requirements of the minimum amino acid nitrogen of soy sauce at all levels. Qualified; the end of the reaction is near the theoretical end point, which is rarely seen, and the relative error caused by this will not be greater than 0.1%, that is, the accuracy of the determination is greater than 99.9% (the range of the titration jump is that the relative error before and after the theoretical end point is -0.1% to +0.1% range), which is the allowable range for titration reactions and assays. In a large number of specific samples identified by actual operations, the orange-gray or gray-blue hue of purple potato pigment in actual samples has not been seen. Because in the products of the manufacturer, the amino acid nitrogen is almost zero according to the minimum design process required by the national standard, so far it has not been seen.

In addition, supplementary note: Since the acidity of the solution, that is, the pH value, determines the existence form of the acid-base indicator and the ratio of the acid color and the alkali color form, it also determines the specific color of the indicator, that is, the acidity of the solution determines the acid-base indicator. color. The depth of the same color is related to the concentration of color substances, that is, related to the amount of related color substances in a unit volume, that is, the concentration of the indicator determines the depth of the color. At the same acidity, the color of the solution is proportional to the amount of indicator added. If the samples of the same volume, only one drop of purple potato pigment is added to the identification, the color will be lighter, but it will not affect the judgment of the conclusion. Because the amount of the indicator added will usually not affect the acidity of the solution, nor will it affect the presence and ratio of the indicator. The added purple potato pigment is less, and the purple potato pigment has less colored particles per unit volume, and the same color will become lighter. If the purple potato pigment is added, the same color will be darker, but they are still their respective reds (with darker colors). red, red, light red, orange-red, pink, reddish, etc.), respective greens (including green, dark green, grass green, green earth, light green, light green, etc.) and respective yellows (including tan , dark yellow, yellow, light yellow, green-yellow, etc.), only the shades of their respective colors are different, as long as the acidity of the indicator and the solution is fixed, and it is not disturbed by other substances and factors in the solution and the air, the color is usually There is no fundamental change, green does not become yellow, nor red, and vice versa. As long as you can judge correctly, you can get the actual results.

The above are only the preferred embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Under the premise of the concept, equivalent replacements or changes according to the technical solution of the present invention and its inventive concept, as well as some changes and improvements made, should also be regarded as the protection scope of the present invention.

Claims (8)

1. Whether a brewed soy sauce amino acid nitrogen content meets a certain level of rapid detection method, it is characterized in that: comprise the following steps, (1) get brewed soy sauce sample a, and carry out decolorization, after decolorization is decolorized brewed soy sauce sample b ; (2) Take the decolorized soy sauce sample b containing V ₂ mL of soy sauce sample a, and add the indicator dropwise to it, at this time the solution shows the acid color of the indicator, and then add 0.050mol/ The color of L NaOH to the solution is the mixed color of the acid color and the basic color of the indicator, and neutral formaldehyde is added after half a minute without fading, and the amino acid nitrogen in the soy sauce sample b is completely converted into an acidic substance. The solution shows the acid color of the indicator again; then add V ₃ mL of monobasic strong base solution, shake gently and observe the color of the solution. At this time, the solution shows the acid color of the indicator or the acid-base "equivalent point". The mixed color of the acid color and the basic color of the indicator, and the color does not fade in half a minute, the sample is a qualified product that meets a certain level, and the solution shows the basic color of the indicator and does not fade in half a minute, it is not qualified for a certain level. Product; the concentration of the monobasic strong alkali solution is equal to the lowest concentration of the grade of the soy sauce sample a, and V ₂ =V ₃ . 2. Whether the amino acid nitrogen content of brewed soy sauce according to claim 1 meets the rapid detection method of a certain level, it is characterized in that: the monobasic strong alkali solution is sodium hydroxide solution, potassium hydroxide solution or lithium hydroxide solution. 3. whether brewing soy sauce amino acid nitrogen content according to claim 1 meets the rapid detection method of a certain level, it is characterized in that: brewing soy sauce sample a is soy sauce as-is, and soy sauce as-is is the soy sauce product sold in the market or factory; soy sauce as-is For Lee Kum Kee Extremely Fresh, Chu Bang Seafood Soy Sauce/Light Soy Sauce, Haitian Soy Sauce King, Lee Kum Kee Select Light Soy Sauce, Lee Kum Kee Jinzhen Dark Soy Sauce, Jia Jia Mushroom Dark Sauce, Jia Jia Golden Label Light Soy Sauce, Luhua Natural Fresh Sauce soy sauce. 4. Whether the amino acid nitrogen content of brewed soy sauce according to claim 1 meets the rapid detection method of a certain level, it is characterized in that: the indicator is purple potato pigment. 5. Whether the amino acid nitrogen content of brewed soy sauce according to claim 1 meets a certain level of rapid detection method, it is characterized in that: the preparation method of purple sweet potato pigment is: get purple sweet potato, and be ground into paste, according to the ratio of material to liquid Add distilled water at 1:5, transfer it into a 100 mL colorimetric tube, extract with ultrasonic assistance, the extraction temperature is 55 °C, the extraction time is 15-20 min, and then filter to obtain purple potato pigment; the pH of the distilled water used is 6.8. 6. The rapid detection method for whether the amino acid nitrogen content of brewed soy sauce according to claim 4 complies with a certain level, characterized in that: in the step (1), the soy sauce is decolorized as follows: using a pipette gun to pipette 1.00 mL of the original soy sauce The sample was placed in a 25mL colorimetric tube, diluted with 9.00mL of water, added with 0.30g of activated carbon, gently stirred with a glass rod to decolorize, and filtered after 2 minutes. The filtered clear solution was decolorized soy sauce sample b. 7. The rapid detection method for whether the amino acid nitrogen content of brewed soy sauce conforms to a certain level according to claim 6, wherein in the step (2), 1.00 mL of soy sauce sample b is taken with a pipette and placed in 10 mL of colorimetric In the tube, add 2 to 3 drops of natural purple potato pigment dropwise, the solution is red or reddish-orange at this time, dropwise add 0.050mol/L NaOH standard solution with a plastic tip dropper until the color is orange-gray, add 2.00mL neutral formaldehyde , the solution is red or red-orange at this time. 8. whether the amino acid nitrogen content of brewed soy sauce according to claim 4 meets the rapid detection method of a certain level, it is characterized in that: the acid color of purple potato pigment is shown as red or reddish-orange, and the basic color of purple potato pigment is shown as gray Blue, green earth or yellow-brown, when the acid-base "equivalent point" is used, the indicator shows that the mixture of red-orange and gray-blue is orange-gray.

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