T.C.
TARIM ve KÖYİŞLERİ BAKANLIĞI
Koruma ve Kontrol Genel Müdürlüğü
Communiqué on the Methods of Analysis for Edible Casein and Caseinates 
Authorization Law: Turkish Food Codex
The Official Gazette: 21.03.2002-24702
Communication No : 2002/18
Objective
Article 1- The objective of this Communiqué is to determine the methods of analysis for edible casein and caseinates.
Scope
Article 2- This Communiqué covers the methods of analysis for edible casein and caseinates.
Legal basis
Article 3- This Communiqué has been prepared in accordance with the Turkish Food Codex Regulation published in the Official Gazette, dated 16/11/1997, reiterated No. 23172
Methods of Analysis
Article 4- Methods of analysis are applied in accordance with the general principles in ANNEX-I as follows:
Determination of moisture is carried out as per the 1st method in ANNEX-II for edible acid casein, edible rennet casein and caseinates.
Determination of protein content is carried out as per the 2nd method in ANNEX-II for edible acid casein, edible rennet casein and caseinates.
Titratable acidity is determined as per the 3rd method in ANNEX-II for Edible acid casein
Ash including P2O5 content is determined as per the 4th method in ANNEX-II for edible acid casein, ash including P2O5 content is determined as per the 5th method in ANNEX-II for edible rennet casein.
Determination of pH is carried out as per 6th method in ANNEX-II for caseinates.
Compliance with European Union
Article 5- This Communiqué has been prepared within the framework of compliance with European Union having regard to the Commission Directive 85/503/EEC. This Communiqué does not prevent the laboratories from using the methods experienced according to relevant legislation and having scientific validity. Implementation of this Communiqué for the relations with European Union is compulsory.
Provisional Article-1 Presently active institutions and establishments using sampling methods specified in this Communiqué are obliged to obey with the provisions of this Communiqué within 1 year.
Enforcement
Article 6- This Communiqué enters into force on the date of publication.
Execution
Article 7- The provisions of this Communiqué are executed by the Minister of Health and the Minister of Agriculture and Rural Affairs.
ANNEX-1
General Principles
1. Preparation of the Analysis Sample
1.1. General
The mass of the sample presented to the laboratory for analysis shall be at least 200 grams.
1.2. Preparation of the Sample for Analysis
1.2.1. If any lumps, etc. exist in the sample, the sample is mixed well after transferring into an air-tight container of sufficient capacity, and the lumps are broken down by shaking and inverting the container few times.
1.2.2. A representative portion of the sample, about 50 grams of the thoroughly mixed laboratory sample is transferred into the test sieve as explained in 3.3.
1.2.3. The sample prepared as in 1.2.1 is used for analysis if the 50 gram portion completely or at least 95 % by weight passes through the sieve
1.2.4. If the sample does not fit the sieving criteria at 1.2.3, 50 g portion of the sample is ground with a grinding device mentioned at 3.4 until the criteria in 1.2.3 are met. Whole ground sample is immediately transferred into an air-tight container with a capacity of twice volume of sample. It is mixed thoroughly by shaking and inverting again. During these operations, necessary precautions to avoid any change in the moisture content of the product are taken.
1.2.5. Once the test sample is ready, determination should be proceeded with as soon as possible.
1.3. Containers
The sample shall always be kept in an air-tight and moisture-tight container.
2. Reagents
2.1. Water
2.1.1. The term water mentioned in the text, used for solution, dilution or washing purposes; defines distilled water or demineralized water at least in equivalent purity.
2.1.2. Solution or dilution means, unless otherwise expressed differently, 'solution in water' or 'dilution with water'.
2.2. Chemicals
All chemicals should be in analytical purity. Otherwise, their specifications should be indicated precisely.
3. Equipment
3.1. List of equipment
Equipments shall contain only those items with a specialized use and items to a particular specification.
3.2. Analytical balance, capable of weighing to at least 0,1 mg
3.3. Test sieve
The test sieves are to be of diameter 200 mm, to be fitted with a lid, to be constructed of wire cloth with a nominal aperture size of 500 mm. The sieves are to be fitted with a receiver.
3.4. Grinding Device
It is used to grind the laboratory sample if necessary. Hammer mill should not be used to enable to manage grinding operation without undue heat generation and any loss of moisture or without any moisture absorption.
4. Expression of Results
4.1. Results
The result stated in the analysis report should be the mean value obtained from the two determinations in accordance with the repeatability criteria of the method.
4.2. Calculation of percentage
Unless otherwise stated, the result is calculated in percentage by mass of the sample.
5. Test Report
Analysis method used should also be indicated together with the results in the test report. Besides, the details of any circumstance and procedure that may affect the results should be indicated in the report. The test report shall give all the information necessary for the complete identification of the sample.
ANNEX-II
Methods of Analysis
Method 1: Determination of Moisture Content
1. Scope and Field of Application
This method is used in determination of moisture content in edible acid caseins, edible rennet caseins and caseinates.
2. Definition
Moisture content of casein and caseinates; determination of the loss of mass by the specified method.
3. Principle
After drying the experiment sample to a constant weight under atmospheric pressure in an oven at 102 ± 1 °C, residual mass is determined. Loss of mass is calculated as percentage by the mass of sample.
4. Equipment and Material
4.1. Analytical balance
4.2. Dishes; made of non-corrodible material under test conditions such as nickel, aluminum, stainless steel or glass, flat bottomed, with tightly fit and easily removed lids, 60-80 mm in diameter and about 25 mm in depth.
4.3. Oven; well ventilated, thermostatically adjustable at 102 ± 1 °C, uniform heat distribution.
4.4. Desiccator; containing a moisture absorbing material such as freshly activated silica gel or an equivalent dessicator, having moisture sensitive indicator.
4.5. Tongs; suitable for handling the petries.
5. Procedure
5.1. Preparation of test sample
It is prepared as indicated in Article 1.2. of general principles in Annex-I.
5.2. Preparation of dish
5.2.1. Dish and its cover uncovered is kept in the oven at 102 ±1 °C for at least 1 hour.
5.2.2. The cover is placed on petri, closed petri is placed in the desiccator. It is left to cool down to room temperature and weighed in sensitivity of 0.1 mg (m0).
5.3. Test sample
3-5 grams of test sample is taken into dish, the cover is closed and weighed in a sensitivity of 0.1 mg (m1).
5.4. Determination
5.4.1. The cover of petri is removed and cover and petri is left in the oven at 102 ±1 °C for 4 hours.
5.4.2. The cover of petri is closed and put into the desiccator. It is left to cool down to room temperature and weighed in sensitivity of 0.1 mg.
5.4.3. Petri is left in the oven for 1 hour without its cover. Later the process in 5.4.2. is repeated.
5.4.4. If the mass obtained in 5.4.3 exceeds more than 1 mg over the mass obtained in 5.4.2, then the process in 5.4.3 is repeated.
If any increase in mass is observed, the lowest recorded value of mass is used for calculation.
Last weight is recorded as m2. Total drying time should not normally exceed 6 hours.
6. Expression of results
6.1. Formula and method of calculation
Loss in mass of the sample while drying is calculated with the following formula as percentage of sample in 0.01 mg accuracy:
(m1 – m2)
----------------------- X 100
(m1 – m0) x 100
m0 = Mass of petri and its cover after the process in 5.2, g
m1 = Mass of petri, its cover and experiment sample prior to drying, g
m2 = Mass of petri, its cover and experiment sample after drying, g
6.2. Repeatability
The difference between the results of two analysis carried out simultaneously or in rapid succession on the same sample by the same analyst, under the same conditions shall not exceed 0.1g of moisture per 100 g of sample. In case the repeatability interval reaches to 95 %, the method is accepted as correct and carried out.
Method 2: Determination of protein content
1. Scope and Field of Application
This method is used in determining the amount of protein in edible acid casein, edible rennet casein and caseinates, except ammonium caseinate, other ammonium compounds or those containing nitrogen compounds that are not in protein structure.
2. Definition
Protein content; is the value of expression as percentage by mass of the result obtained by multiplying the amount of nitrogen that is determined as described by the method specified with 6.38.
3. Principle
Test sample is digested with a mixture of potassium sulfate and sulfuric acid together with copper (II) sulfate solution as catalyst and organic nitrogen is converted into inorganic nitrogen. Ammonia is distilled, absorbed into boric acid solution and titrated with standard hydrochloric acid solution. The nitrogen content is converted to protein content by multiplying by 6.38.
4. Reagents
4.1. Sulfuric acid, concentrated, (H2SO4) 1.84 g/mL
4.2. Potassium sulfate, anhydrous (K2SO4)
4.3. Copper (II) sulfate pentahydrate (CuSO4.5H2O)
4.4. Saccharose (C12H22O11)
4.5. Boric acid solution, 40 g/L
4.6. Sodium hydroxide solution, 30 % (mass/mass) carbonate free
4.7. Hydrochloric acid solution, 0.1 M
4.8. Mixed indicator; mixture in equal volumes of 2 g/L methyl red solution in at least 95% (volume/volume) ethanol and 1 g/L methylene blue solution in at least 95% (volume/volume) ethanol.
5. Equipment and materials
5.1. Analytical balance
5.2. Kjeldahl flask, 500 mL capacity
5.3. Digestion apparatus, in an inclined position and with a heating device which will not heat the part of the flask above the surface of the liquid contents.
5.4. Condenser, with straight inner tube.
5.5. Outlet tube with safety bulb connected to the lower end of the condenser (5.4) by a ground glass joint and a rubber tube. If the connection is made with rubber tube, the glass ends must be near one another.
5.6. Splash- head, connected to the Kjeldahl flask (5.2) and to the condenser (5.4) by soft, close-fitting rubber or other appropriate stoppers.
5.7. Conical flask, with 500 mL capacity.
5.8. Graduated cylinders, with 50 mL and 100 mL capacities.
5.9. Burette, graduated at 0.1 mL, with 50 mL capacity.
5.10. Boiling aids.
5.10.1. For digestion, small pieces of hard porcelain, or glass beads
5.10.2. For distillation, freshly activated pumice pieces.
6. Procedure
6.1. Test sample is prepared as explained in Article 1.2. of General Principles.
6.2. Test for presence of inorganic nitrogen
If the presence ammonium caseinate or any other ammonium compound is suspected, then the following experiment is carried out:
1 gram of sample is added into a small conical flask containing 10 ml water and 100 mg magnesium oxide and if there is any magnesium oxide adhering on the walls of conical flask, this is rinsed and taken into the conical flask. Conical flask is closed with a cork stopper together with a piece of moistened litmus paper between the neck and the cork. Content of conical flask is mixed carefully and heated in water bath adjusted at 60-65 °C. If the color of the litmus paper turns out to blue in 15 minutes, this means ammonia is present and the method can not be applied.
6.3. Blank test
Blank test is performed by using 0.5 saccharose (4.4) instead of testsample in order to determine the presence of nitrogen, by using the same apparatus, all the reagents in the same amounts and the procedure described in 6.5. If, during blank test, more than 0.5 mL of 0.1 M acid in titration is exceeded, the reagents are checked and those that are impure are purified or replaced.
6.4. Test Sample
0.3-0.4 g test sample (6.1) is weighed in 0.1 mg sensitivity and transferred into the Kjeldahl flask.
6.5. Determination
6.5.1. A few pieces porcelain or glass beads (5.10.1.) and 10 g anhydrous potassium sulfate (4.2) are added into the flask. 0.2 g copper (II) sulfate (4.3) is added on top and remainders on the neck of the flask is washed. Content of the flask is mixed by adding 20 mL concentrated sulfuric acid (4.1). It is heated in the digestion apparatus (5.3) until any frothing has ceased and boiled carefully until the solution is clear and a pale green-blue color is formed. Flask is rotated occasionally while heating. Boiling continues by adjusting the temperature to enable the condensation of vapor in the middle section of the neck of flask. Heating is carried on for 90 minutes as not to increase any local heating. It is cooled down to room temperature, about 20 ml of water and a few pieces of pumice stone (5.10.2) is added carefully. It is mixed and cooled again.
6.5.2. 50 ml of boric acid solution (4.5) together with 4 drops of indicator (4.8) is put in conical flask and mixed. Conical flask is placed under the condenser (5.4) in such a way that the tip of outlet tube (5.5) immerses in the boric acid solution. 80 ml of sodium hydroxide solution (4.6) is slowly added into the Kjeldahl flask downward from the edge of the flask by using the graduated cylinder and keeping the flask in inclined position and hence it is ensured to form bottom layer of sodium hydroxide solution. Kjeldahl flask is immediately connected to the condenser by means of splash-head (5.6). Content of the Kjeldahl flask is mixed by rotating carefully. It is boiled paying attention to avoid any frothing. Distillation continues until 150 ml of distillate is collected in about 30 minutes. Distillate should be at a temperature below 25 °C. In just 2 minutes before the end of distillation, conical flask is lowered so that the tip of the outlet tube is no longer immersed in the acid solution and tip is rinsed with water. Heating is stopped, outlet tube is removed, and outer surface and inner walls are rinsed with some water and collected in the conical flask.
6.5.3. Distillate in the conical flask is titrated by using standard volumetric hydrochloric acid solution (4.7).
7. Expression of results
7.1. Formula and method of calculation
Protein content is calculated in ratio to mass as given in the following formula:
(V1 – V2) x T x 14 x 100 x 6.38 8.932 (V1 – V2) x T
---------------------------------------- - --------------------------
m x 1000 m
where : V1 : Volume of standard volumetric hydrochloric acid solution (4.7) used in the
test (6.5), ml
V2 : Volume of standard volumetric hydrochloric acid solution (4.7) used in the blank test (6.3), ml
T : Effectiveness factor as mol/L of standard volumetric hydrochloric acid solution (4.7)
m : Amount of sample, g.
Amount of protein is calculated in accuracy of 0.1 %.
7.2. Repeatability
The difference between the results of two analysis carried out simultaneously or in rapid succession on the same sample, by the same analyst and under the same conditions shall not exceed 0.5 grams of protein per 100 grams of sample. In case the interval of repeatability reaches to 95 %, the method is accepted as correct and carried out.
Method 3 : Determination of Titratable Acidity
1. Scope and Field of Application
This method is used in determination of the titratable acidity of edible acid caseins.
2. Definition
Titratable acidity of acid caseins; is the volume in milliliter of 0.1 M standard sodium hydroxide solution required to neutralize 1 grams of aqueous extract of the product.
3. Principle
Aqueous extract of the product is obtained at 60 °C and filtered. It is based on the principle of titration of filtrate against standard sodium hydroxide by using phenolphthalein indicator.
4. Reagents
The water used during application of the method or preparation of the reagents is boiled for 10 minutes just before usage and so freed from carbon dioxide.
4.1. Sodium hydroxide solution, 0.1 M
4.2. Phenolphthalein indicator solution; 10 g/L is dissolved in 10 g phenolphthalein ethanol (95% v/v) and completed up to 1 liter with ethanol.
5. Equipment and material
5.1. Analytical balance
5.2. Conical flask, in 500 mL capacity with ground neck and fitted with a ground glass stopper.
5.3. Pipette, in 100 mL capacity
5.4. Pipette, suitable to measure 0.5 ml indicator solution (4.2).
5.5. Conical flask, with 250 mL capacity.
5.6. Measuring cylinder, with 250 ml capacity.
5.7. Burette, degreed in 0.1 ml.
5.8. Water bath, able to be kept at 60 ± 2 °C.
5.9. Appropriate filter.
6. Procedure
6.1. Preparation of the sample: As explained in Article 1.2. of General Principles.
6.2. Sample
About 10 g of sample (6.1) is weighed in accuracy of 10 mg and transferred in conical flask (5.2).
6.3. Determination
200 ml water that is freshly boiled and then cooled to 60 °C is added by using a measuring cylinder of 250 ml. Conical flask is closed with its stopper, mixed by rotating and is left in the water bath at 60 °C (5.8) for 30 minutes. Conical flask is shaked at intervals of about 10 minutes. It is filtered and the filtrate is cooled to about 20 °C. Filtrate should be clear. 100 ml from the cool filtrate is transferred into conical flask (5.5) by a pipette (5.3). 0.5 ml of phenolphthalein indicator solution (4.2) is added by pipette (5.4). It is titrated with standard volumetric sodium hydroxide solution (4.1) until light pink color is appeared persisting in this color for about 30 seconds. The volume of solution spent in titration is recorded in sensitivity of 0.01 ml.
7. Expression of Results
7.1. Formula and method of calculation
Titration acidity of edible acid casein is calculated as per the following formula:
20 x V x T
-----------------
m
where: V: Volume of standard volumetric sodium hydroxide solution (4.1) used in the test, ml
T: Effectiveness degree in mol/L of standard volumetric sodium hydroxide solution (4.1) used in the experiment, ml
m: Quantity of sample
Titratable acidity is calculated with two decimal digits.
7.2. Repeatability
The difference between the results of two analysis carried out simultaneously or in rapid succession on the same sample, by the same analyst and under the same conditions shall not exceed 0.02 ml of 0.1 M sodium hydroxide solution per 1 grams of the product. In case the interval of repeatability reaches to 95 %, the method is accepted as correct and carried out.
Method 4: Determination of Ash (including P2O5)
1. Scope and Field of Application
This method is used in determination of the ash content including P2O5 in edible acid caseins.
2. Definition
Ash content including P2O5 in edible acid caseins; is the amount of the residue at the end of the procedures explained in the method.
3. Principle
It is based on the principle of adding magnesium acetate solution in order to bind all of the organic phosphorus of the sample, formation of ash at 825 ± 25 °C and subtracting the amount of ash originating from magnesium acetate from the amount of ash obtained.
4. Reagents
4.1. Magnesium acetate tetrahydrate solution; 120 g/L, 120 grams magnesium acetate tetrahydrate [Mg(CH3CO2)2.4H2O] is dissolved in water and completed up to one liter with water.
5. Equipment and material
5.1. Analytical balance
5.2. Pipette, with 5 mL capacity
5.3. Silica or platinum containers, about 70 mm in diameter and 25 – 50 mm deep.
5.4. Oven, adjustable to 102 ± 1 °C.
5.5. Ash oven, adjustable to 825 ± 25 °C.
5.6. Water bath, having boiling property.
5.7. Desiccator; containing a moisture absorbing material such as freshly activated silica gel or an equivalent dessicator, having moisture sensitive indicator.
6. Procedure
6.1. Preparation of the sample:
As explained in Article 1.2. of General Principles.
6.2. Preparation of dishes
Two dishes (A and B) are heated for 30 minutes in the ash oven adjusted to 825 ± 25 °C. The dishes are left to cool, by transferring into desiccator (5.7) it is further cooled down to room temperature and weighed in sensitivity of 0.1 mg.
6.3. Test sample
About 3 grams of test sample (6.1) is weighed in sensitivity of 0.1 mg and placed in one (A) of the prepared dishes.
6.4. Determination
Precisely 5 ml of magnesium acetate solution (4.1) is put in dish (A) by means of the pipette (5.2) and allowed for 20 minutes so as to wet all of the test sample. Precisely 5 ml of magnesium acetate solution (4.1) is put in the other prepared dish (B) by means of the pipette (5.2). The contents of both of the dishes (A and B) are evaporated in the boiling water bath (5.6) to dryness. The dishes further are placed in the oven adjusted to 102 ± 1 °C and kept there for 30 minutes. Dish A together with its contents is heated on a hot plate over a low flame or under I/R lamp until the experiment sample becomes completely charred, by being careful for the pieces not to burst into the flames. Both of the dishs (A and B) are placed in ash oven (5.5) at 825 ± 25 °C and kept there for at least 1 hour until all the carbon disappears and left to cool. It is then placed in the desiccator (5.7) and let it cool down to room temperature and weighed in sensitivity of 0.1 mg. The process is repeated by heating in electrical furnace (5.5) for about 30 minutes, by cooling and weighing until the mass content remains constant in 1 mg or exceeds, finally the minimum mass is recorded.
7. Expression of Results
7.1. Method of calculation
Ash content including P2O5 in the sample is expressed as the ratio to mass as per the following formula:
(m1 – m2) – (m3 – m4)
--------------------------- x 100
m0
where: m0 = amount of sample, g
m1 = mass of dish A and residue, g
m2 = mass of prepared dish A, g
m3 = mass of dish B and residue, g
m4 = mass of prepared dish B, g
The result is calculated in a sensitivity of 0.01 %.
7.2. Repeatability
The difference between the results of two analysis carried out simultaneously or in rapid succession on the same sample, by the same analyst and under the same conditions shall not exceed 0.1 grams per 100 grams of sample. In case the interval of repeatability reaches to 95 %, the method is accepted as correct and carried out.
Method 5: Determination of Ash (including P2O5)
1. Scope and Field of Application
This method is used in determination of ash content including P2O5 in edible rennet caseins.
2. Definition
Content of ash including P2O5 in edible rennet caseins; is the amount of the residue at the end of the procedures explained in the method.
3. Principle
The principle is to incinerate the test sample to the form of ash until it reaches a constant weight at 825 ± 25 °C and to weigh the residue and to express a percentage by mass of the sample.
4. Equipment and material
4.1. Analytical balance
4.2. Silica or platinum dishes, about 70 mm in diameter and 25 – 50 mm deep.
4.3. Ash oven, with air circulation, adjustable to 825 ± 25 °C.
4.4. Desiccator; containing a moisture absorbing material such as freshly activated silica gel or equivalent, having moisture sensitive indicator.
5. Procedure
5.1. Preparation of the sample:
As explained in Article 1.2. of General Principle
5.2. Preparation of the dish
The dish (4.2) is heated for 30 minutes in the ash oven (4.3) adjusted to 825 ± 25 °C. The dish is left to cool, by transferring into desiccator (4.4) it is further cooled down to room temperature and weighed in sensitivity of 0.1 mg.
5.3. Test sample
About 3 grams of test sample (5.1) is weighed in sensitivity of 0.1 mg and placed in the previously prepared dish.
5.4. Determination
Dish together with its contents is heated on a hot plate over a low flame or under I/R lamp until the test sample becomes completely charred, by being careful for the pieces not to burst to the flames. The dish is placed in ash oven (4.3) adjusted to 825 ± 25 °C and kept there for at least 1 hour until all the carbon disappears and left to cool. It is then placed in the desiccator (4.4) and let it cool down to room temperature and weighed in sensitivity of 0.1 mg. The process is repeated by heating in electrical furnace (4.3) for about 30 minutes, by cooling and weighing until the mass content remains constant in 1 mg or exceeds. Finally the minimum mass is recorded.
6. Expression of Results
Method of calculation and formula
6.1. Ash content including P2O5 in the sample is expressed as the ratio to mass as per the following formula:
m1 – m2
-------------- x 100
m0
where: m0 = quantity of sample, g
m1 = mass of dish and residue, g
m2 = mass of previously prepared dish, g
The result is calculated in a sensitivity of 0.01 %.
6.2. Repeatability
The difference between the results of two analysis carried out simultaneously or in rapid succession on the same sample by the same analyst and under the same conditions shall not exceed 0.15 gram of ash per 100 grams of sample. In case the interval of repeatability reaches to 95 %, the method is accepted as correct and carried out.
Method 6 : Determination of pH
1. Scope and Filed of Application
This method is used in determining pH of caseinates.
2. Definition
pH of caseinates; pH of a aqueous caseinate solution at 20 °C is the pH determined as explained in the method.
3. Principle
It is based on the principle of electrometrical determination of pH for a aqueous caseinate solution by using pH meter.
4. Reagents
The water used during the procedure (6) or for preparation of the reagents should not contain any carbon dioxide; it should be freshly distilled water.
4.1. Buffer solutions for calibration of pH meter;
In order to measure the pH value of the sample correctly, two standard buffer solutions for which the pH values at 20 °C are known up to the second decimal points, for example; phthalate buffer solution with approximately 4 pH and borax buffer solution with approximately 9 pH.
5. Equipment and material
5.1. Analytical balance, accuracy 0.1 g.
5.2. pH meter, with sensitivity of at least 0.05 pH unit, properly calibrated electrodes, (glass electrode and one calomel or another reference electrode).
5.3. Thermometer, accuracy 0.5 °C
5.4. Conical flask, with 100 ml capacity, fitted with a ground glass stopper.
5.5. Beaker, with 50 ml capacity.
5.6. Mixer.
5.7. Beaker, with min. 250 ml capacity for the mixer.
6. Procedure
6.1. Preparation of the sample
As explained in Article 1.2. of General Principles.
6.2. Determination
6.2.1. Calibration of pH meter.
Temperature of the buffer solution (4.1) is set to 20 °C and pH meter is adjusted according to instructions of the producer.
Note:
1. Adjustments should be made after the conical flasks are left for 20 minutes (please see 6.2.2)
2. If a series of sample is being tested, calibration of pH meter is checked at least once in every 30 minutes with one or more standard buffer solution.
6.2.2. Preparation of test solution
95 ml of water is filled in the beaker, 5.0 grams of test sample (6.1) is added and mixed for 30 minutes with the mixer (5.6).It is left at about 20 °C for 20 minutes as covered with the glass of a watch.
6.2.3. Measurement of pH
Approximately 20 ml of solution is placed in beaker (5.5). After rinsing the glass electrode with water carefully, the pH of this liquid is measured immediately with the pH meter (5.2).
7. Expression of Results
7.1. The pH of aqueous solution of caseinate is read at the face of pH meter at least up to second digit and recorded.
7.2. Repeatability
The difference between the results of two analysis carried out simultaneously or in rapid succession on the same sample by the same analyst and under the same conditions should not exceed 0.05 pH unit. In case the interval of repeatability reaches to 95 %, the method is accepted as correct and carried out.