Some standard content:
National Standard of the People's Republic of China
Determination of titratable acidity of fruit and vegetable products
Fruit and vegetable products Determination of titratable acidity
This standard adopts the international standard 1SO750-1981 "Fruit and vegetable products 1 Subject content and scope of application
GB12293-90
Determination of titratable acidity".
This standard specifies two methods for determining the titratable acidity of fruit and vegetable products, namely the potentiometric titration method and the indicator titration method. This standard is applicable to the determination of the titratable acidity of fruit and vegetable products and fresh fruits and vegetables. The potentiometric titration method is an arbitration method. The indicator titration method is a conventional method.
The indicator titration method is not applicable to samples with darker color of the overflow liquid. 2 Sample preparation
2.1 Instruments
2.1.1 Speed tissue crusher: 10000~12000r/min.
2.1.2 Pan balance: sensitivity 0.01g.
2.1.3 Electric constant temperature water bath.
2.1.4 Pipette: 50mL.
Beaker: 100, 600mL.
Volume flask: 250mL.
Funnel: 7cm in diameter.
2.1.8 Conical flask: 250mL.
2.1.9 Rapid filter paper: 12.5cm in diameter.
2.2 Preparation method
The water used in this test should be carbon dioxide-free or neutral distilled water. Before use, the distilled water can be boiled and cooled, or phenol indicator can be added and neutralized with 0.1 mol/L sodium hydroxide solution until a reddish color appears. 2.2.1 Liquid products (such as juice, canned fruit syrup, pickling liquid, fermentation liquid, etc.): Shake the sample thoroughly, pipette 50 mL, put it into a 250 mL volumetric flask, add water to dilute to the scale, shake well for testing. If the solution is turbid, filter it through filter paper. Note: (1) Liquid products containing carbonic acid need to be shaken under reduced pressure for 3 to 4 minutes to remove carbon dioxide. ② Liquid samples can also be weighed 50 g, accurate to 0.01 g. 2.2.2 Sauce products (such as jam, vegetable puree, jelly, etc.): Stir the sample evenly, take a portion and put it into a high-speed tissue crusher to crush, weigh 10-20g of the evenly crushed sample, accurate to 0.01g, wash it with 80-90℃ hot water into a 250mL volumetric flask, and add hot water to about 200mL, let it stand for 30min, cool to room temperature, add water to dilute to the scale, shake well, and filter through filter paper. 2.2.3 Fresh fruits and vegetables, whole fruits or cut pieces of canned and frozen products: Remove the inedible part of the sample (frozen products are pre-thawed in a covered container), use the quartering method to take the edible part, chop and mix, weigh 250g, accurate to 0.1g, put it into a high-speed tissue crusher, add an equal amount of water, and crush for 1-2min. Every 2g of pulp is converted into 1g of sample, weigh 50-100g of homogenate, accurate to 0.1g, wash it into a 250mL container bottle with 100mL of water, heat it in a 75-80℃ water bath for 30min, shake it several times, take it out and cool it, add water to the scale, shake it and filter it. Approved by the State Administration of Technical Supervision on March 29, 1990, implemented on December 1, 1990
GB 12293-90
2.2.4: Ten products: Take the edible part of the sample and chop it and mix it evenly, weigh 50g, accurate to 0.1g, put it into a centrifugal tissue pounder, add 450g of water, and pound it for 2-3min. Every 10g of homogenate is converted into 1g of sample, weigh 50-100g of the sample homogenate, accurate to 0.1g, extract it in a water bath according to 2.2.3, and filter it to a fixed volume.
3 Determination method
3.1 Potentiometric titration
3.1.1 Principle
The sample leachate is titrated potentiometrically with 0.1mol/L sodium hydroxide standard solution, with pH 8.1 as the titration end point. 3.1.2 Reagents
3.1.2.1 pH 4.01 standard buffer solution (25℃). 3.1.2.2
pH 19.18 standard buffer solution (25℃).
Sodium hydroxide (GB629) standard solution: c (NaOH) = 0.1mal/L, accurately calibrated with reference to GB601 "Preparation method of standard solution".
3.1.3 Instruments
Acidity meter: After calibration with pH 4.01 standard buffer solution, measure pH 9.18 standard buffer solution, the measurement error is not greater than 0.05pH. Glass electrode and calomel electrode.
Magnetic stirrer.
Stirring rod.
Pipette: 50, 100mL
Beaker: 100, 250mL.
Burette: basic type, 10, 25mL.
3.1.4 Determination steps
Use pH 4.01 and 9.18 standard buffers to calibrate the acidometer according to the instrument manual. 3.1.4.2 According to the predicted acidity, use a pipette to draw 50 or 100mL of the sample extract (see 2.2) and put it into a beaker of appropriate size so that the titration volume of the sodium hydroxide standard solution is not less than 5mL: 3.1.4.3 Place the beaker containing the sample solution on a magnetic stirrer, put in a stirring rod, insert a glass electrode and a calomel electrode, and insert the tip of the burette into the sample solution by 0.5~1cm. Rapidly titrate to pH 6 with sodium hydroxide solution under continuous stirring, and then slow down the titration speed. When the pH is close to 7.5, add 0.1-0.2 mL each time, and record the pH reading and the total volume of sodium hydroxide solution after each addition. Continue to titrate until at least pH 8.3. In the range of pH 8.1±0.2, use the interpolation method to calculate the volume of sodium hydroxide solution consumed to titrate to pH 8.1. 3.2 Indicator titration method
3.2.1 Principle
The sample extract is titrated with 0.1 mol/L sodium hydroxide standard solution using phenolic acid as the indicator. 3.2.2 Reagents
Sodium hydroxide standard solution: 0.1 mol/L (see 3.1.2.3). 3.2.2.1
3.2.2.2 Phenolphthalein indicator: 10 g/L 95% (u/u) ethanol (GB697) solution. 3.2.3 Apparatus
Pipette: 50, 100 mL.
Erlenmeyer flask: 150, 250mL.
Burette: basic type, 10, 25mL.
3.2.4 Determination stepsWww.bzxZ.net
According to the predicted acidity, use a pipette to draw 50 or 100mL of sample solution (see 2.2), add 5 to 10 drops of phenol indicator, and titrate with sodium hydroxide standard solution until a slightly reddish color appears and does not fade within 30 seconds as the end point, and record the consumed volume. Note: Some fruit and vegetable sample solutions turn yellow-brown when titrated to the end point. At this time, add 1 to 2 times the volume of the sample solution to dilute it, add 0.5 to 1mL of phenol indicator, and continue titrating to make the phenol change color and easy to observe. 172
Calculation of determination results
4.1 Calculation formula
GB 12293-90
The titratable acidity of the sample is expressed as millimoles of hydrogen ions per 100g or 100mL, and is calculated according to formula (1): Titratable acidity [mmol/100g (mL)] Where: c
Molar concentration of sodium hydroxide standard solution;
Volume of sodium hydroxide standard solution consumed during titration, mL, -Volume of sample solution used for titration, mL,
Mass of sample, g or volume, mL
Volume of sample after extraction, mL.
The titratable acidity of the sample is expressed as the percentage of a certain acid, and is calculated according to formula (2): c×v×k
Titratable acidity (%)=
————Coefficient for conversion to grams of a certain acid, see the table below. In the formula: k
Other symbols are the same as in formula (1).
Name of acid
Malic acid
Crystallized citric acid
(monocrystalline water)
Tartaric acid
4.2 Result expression
Conversion factor
-×100
Fruit and vegetable products commonly used for expression
Pome fruits, stone fruits
Citrus fruits, berry fruits
Salted and fermented products
Vinegar pickled products
. (1)
Take two parallel samples of the same sample for measurement, and take their arithmetic mean as the measurement result. When expressed in millimoles of hydrogen ions per 100g or 100mL, retain one decimal place; when expressed in percentage of acid, retain two decimal places. 4.3 Allowable difference
The difference between the measured values of two parallel samples shall not exceed 2% of the average value. Note: The test results shall be reported with the measurement method used. Additional remarks:
This standard was proposed by the Ministry of Agriculture of the People's Republic of China. This standard was drafted by the Vegetable and Flower Research Institute of the Chinese Academy of Agricultural Sciences. The main drafters of this standard are Yang Hongfu, Huang Wanchun, and Huang Qiaohua. This standard was first issued in 1989.
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