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NY/T 939-2016: Identification of reconstituted milk in pasteurized and UHT milk
NY/T 939-2016
AGRICULTURE INDUSTRY STANDARD
OF THE PEOPLE’S REPUBLIC OF CHINA
ICS 67.050
X 04
Replacing NY/T 939-2005
Identification of Reconstituted
Milk in Pasteurized and UHT Milk
ISSUED ON: MARCH 23, 2016
IMPLEMENTED ON: APRIL 01, 2016
Issued by: Ministry of Agriculture of PRC
Table of Contents
Foreword ... 3
1 Scope ... 4
2 Normative References ... 4
3 Terms and Definitions ... 4
4 Test Methods ... 5
5 Identification of Reconstituted Milk ... 16
Appendix A (Informative) Furosine Liquid Chromatogram ... 18
Identification of Reconstituted
Milk in Pasteurized and UHT Milk
1 Scope
This Standard specifies the identification method of reconstituted milk in pasteurized
and UHT milk.
This Standard is applicable to the pasteurized and UHT milk.
2 Normative References
The following documents are essential to the application of this document. For the
dated documents, only the versions with the dates indicated are applicable to this
document; for the undated documents, only the latest version (including all the
amendments) are applicable to this document.
GB 5009.5 Determination of Protein in Foods
GB/T 6682 Water for Laboratory Use – Specifications
GB/T 10111 Generation of Random Numbers and Procedures Applied to Sampling
Inspection for Product Quality
3 Terms and Definitions
For the purposes of this document, the following terms and definitions apply.
3.1 Raw milk
The normal milk extruded from the breasts of the healthy dairy animals, it meets the
relevant national requirements and has no ingredient changes.
3.2 Reconstituted milk
The milk obtained by mixing a dried or concentrated dairy product with water in
proportion.
3.3 Heat treatment
4.1.1 Principle
Hydrolyze the specimen by hydrochloric acid, then determine its protein content; after
diluting, the hydrolysate shall be analyzed by high performance liquid chromatography
(HPLC) or ultra-high-performance liquid chromatography (UPLC) under ultraviolet
(wavelength 280nm) detector and quantify by external standard method.
4.1.2 Reagents and materials
Unless otherwise specified, all reagents used in this method shall be analytical
reagents; and the water shall be Class-I water in the laboratory specified in GB/T 6682.
4.1.2.1 Methanol (CH3OH): chromatographically pure.
4.1.2.2 Concentrated hydrochloric acid (HCl, density 1.19g/mL).
4.1.2.3 Trifluoroacetic acid: chromatographically pure.
4.1.2.4 Ammonium acetate.
4.1.2.5 Furosine: C12H17N2O4 • xHCl.
4.1.2.6 Hydrochloric acid solution (3mol/L): add 2.5 mL of concentrated hydrochloric
acid to 7.5mL of water; mix evenly.
4.1.2.7 Hydrochloric acid solution (10.6mol/L): add 88mL of concentrated hydrochloric
acid to 12mL of water, mix evenly.
4.1.2.8 Ammonium acetate solution (6g/L): accurately take 6g of ammonium acetate
to dissolve into water; make constant volume to 1L; pass through the 0.22µm aqueous
phase membrane; ultrasonically degas for 10min.
4.1.2.9 Ammonium acetate (6g/L) containing 0.1% trifluoroacetic acid solution:
accurately take 6g of ammonium acetate; dissolve into partial water; add 1mL of
trifluoroacetic acid; make constant volume to 1; pass through 0.22µm aqueous phase
membrane; ultrasonically degas for 10min.
4.1.2.10 Furosine standard stock solution (500.0mg/L): convert the furosine standard
substance as per the Net Peptide Content provided by the standard substance
certificate; then use 3mol/L hydrochloric acid solution to formulate into a standard stock
solution. It can be stored for 24 months at -20°C.
Example:
If the Net Peptide Content marked on the furosine standard substance certificate is 69.1%, then
take 7.24mg of furosine standard substance; use 3mol/L hydrochloric acid solution to dissolve
and make constant volume to 10mL; the concentration of standard stock solution is 500.0mg/L.
equivalent.
Column temperature: 35°C.
Mobile phase: 6g/L ammonium acetate containing 0.1% trifluoroacetic acid
aqueous solution is mobile phase A; methanol is mobile phase B; while pure
water is mobile phase C.
Elution conditions: mobile phase A. Isocratic elution, 0.4mL/min.
2) Determination
The mobile phase pure water and methanol should be used to wash the
chromatographic system; before the instrument is used, use mobile phase
pure water to transit; use mobile phase A to equilibrate the chromatographic
column at the flow rate of 0.4mL/min. Inject 0.5µL of 3mol/L hydrochloric acid
solution to check the purity of the solvent. Inject 0.5µL to-be-tested solution to
determine the furosien content. See Appendix A for chromatograms.
4.1.6 Result calculation
4.1.6.1 Furosine content in the specimen
The furosine is calculated by mass fraction F; the value of which is expressed in
mg/100g protein; and calculated as per Formula (1):
Where:
At – value of furosine peak area in the tested sample;
Astd – value of furosine peak area in the furosine standard solution;
Cstd – concentration of furosine standard solution, in mg/L;
D – when determining, the dilution factor (D=6);
m – protein concentration in the sample hydrolysate, in g/L,
The calculation result shall be retained to one digit after the decimal point.
4.1.6.2 Furosine content at the end of sterilization of pasteurized milk
At the end of sterilization of pasteurized milk, the furosine content is calculated by FT;
the value of which is expressed by mg/100g protein; and calculated as per Formula
(2):
Lactulose + H2O galactose + fructose
Then add glucose oxidase (GOD); oxidize most of the glucose into gluconic acid:
Glucose + H2O + O2 gluconic acid + H2O2
The above reaction generates the hydrogen peroxide, which can be removed by the
catalase:
2H2O2 2H2O + O2
A small amount of unoxidized glucose and lactulose are hydrolyzed to generate the
fructose; under the catalysis of hexokinase (HK), react with Adenosine Trihosphate
(ATP); separately generate glucose – 6 – phosphate and fructose – 6 – phosphate:
Glucose + ATP glucose – 6 – phosphate + ADP
Fructose + ATP fructose – 6 – phosphate + ADP
The generated glucose – 6 – phosphate, under the catalysis of glucose – 6 –
phosphate dehydrogenase (G – 6 – PD), reacts with oxidized coenzyme II, namely,
nicotinamide adenine dinucleotide phosphate (NADP-), and generates reduced
coenzyme II, namely, reduced nicotinamide adenine dinucleotide phosphate (NADPH):
Glucose – 6 – phosphate + NADP- 6 – phosphogluconate + NADPH + H+
The generated NADPH can be determined at the wavelength 340nm. However,
fructose – 6 – phosphate shall use phosphoglucose isomerase (PGI) to transfer into
glucose – 6 – phosphate:
Fructose – 6 – phosphate glucose – 6 – phosphate
The generated glucose – 6 – phosphate reacts with NADP-; and measure the
absorbance at the wavelength of 340nm. Calculate the lactulose content by the
difference of the above two measurement results. The original fructose in the sample
can be measured and deducted by the blank sample. The determination of the blank
sample is the same as the determination of the sample; only add no β – D –
galactosidase.
4.2.2 Reagents and materials
Unless otherwise specified, all reagents used in this method are analytical reagents;
while the water shall be Class-I water in the laboratory specified in GB/T 6682.
4.2.2.1 Sterilized water.
4.2.2.2 Hydrogen peroxide (H2O2, mass fraction of 30%).
β – D – galactosidase
glucose oxidase
catalase
hexokinase
hexokinase
G-6-PD
PGI
4.2.2.24 Sodium hydroxide solution (1mol/L): dissolve 4g of sodium hydroxide into
100mL of water.
4.2.2.25 Ammonium sulfate solution (3.2 mol/L): dissolve 42.24g of ammonium sulfate
into 100mL of water.
4.2.2.26 Buffer Solution A (pH 7.5): take 4.8g of disodium hydrogen phosphate, 0.86g
of sodium dihydrogen phosphate and 0.1g of magnesium sulfate; then dissolve into
80mL of water; use 1mol/L sodium hydroxide solution to adjust the pH to be 7.5±0.1
(20°C); make constant volume of 100mL.
4.2.2.27 Buffer Solution B (pH 7.6): take 14.00g of triethanolamine hydrochloride and
0.25g of magnesium sulfate; dissolve into 80mL of water; use 1mol/L sodium hydroxide
solution to adjust pH to be 7.6±0.1 (20°C); make constant volume of 100mL.
4.2.2.28 Buffer Solution C: pipette 40.0mL of Buffer Solution B; use water to make
constant volume of 100mL; mix evenly.
4.2.2.29 β – D – galactosidase suspension (150mg/mL): use 3.2mol/L ammonium
sulfate solution to prepare the β – D – galactosidase with activity of 12.6 IU/mg into
suspension with concentration of 150mg/mL. It shall be prepared for current use; and
not oscillate when preparing.
4.2.2.30 Glucose oxidase (GOD) suspension (20mg/mL): use sterilized water to
prepare the glucose oxidase with activity of 200 IU/mg into suspension with
concentration of 20mg/mL. It shall be prepared for current use.
4.2.2.31 Catalase suspension (20mg/mL): use sterilized water to prepare the catalase
with activity of 65000 IU/mg into suspension with concentration of 20mg/mL. It shall be
stored at 4°C; shake it before use to make it uniform.
4.2.2.32 Hexokinase (HK) / glucose – 6 – phosphate dehydrogenase (G - 6 -PD)
suspension: in 1mL of 3.2mol/L ammonium sulfate solution, add 2mg of hexokinase
with activity of 140 IU/mg, and 1mg of glucose – 6 – phosphate dehydrogenase with
activity of 140 IU/mg; gently shake to form suspension. It shall be stored at -20°C.
4.2.2.33 Phosphoglucose isomerase (PGI) suspension (2mg/mL): use 3.2 mol/L
ammonium sulfate solution to prepare the phosphoglucose isomerase with activity of
350 IU/mg into suspension with concentration of 2mg/mL; it shall be stored at 4°C.
4.2.2.34 5’- adenosine triphosphate (ATP) solution: dissolve 50mg of adenosine 5'-
triphosphate disodium salt (5’ – ATP – Na2) and 50mg of sodium bicarbonate into 1mL
of water; it shall be stored at -20°C.
4.2.2.35 Nicotinamide adenine dinucleotide phosphate (NADP) [Translator Note: here
it should be (NADP-)] solution: dissolve 10mg of triphosphopyridine nucleotide
Where:
ΔAL – net absorbance difference of the sample;
ML – molar mass of lactulose (342.3 g/mol);
ε – molar absorbance of NADPH at 340nm (6.3L•mmol-1•cm-1);
V1 – total volume of liquid in cuvette (3.240 mL);
V2 – volume of filtrate in the cuvette, in mL;
d – cuvette light path length (1.00cm);
8 – dilution factor.
The calculation result shall be retained one digit after the decimal point.
4.2.7 Precision
The absolute difference between two independent test results obtained under the
repeatability conditions is no more than 10% of the arithmetic mean.
The absolute difference between two independent test results obtained under the
reproductivity conditions is no more than 20% of the arithmetic mean.
4.2.8 Detection limit
The detection limit is 4.2mg/L.
4.3 Calculation of ratio between lactulose and furosine
The calculation result shall be retained two digits after the decimal point.
5 Identification of Reconstituted Milk
5.1 Pasteurized milk
When L< 100.0mg/L, it shall be judged as follows:
a) When 12.0mg/100g protein < FT ≤ 25.0mg/100g protein, if R< 0.50, then it shall
be judged as containing reconstituted milk.
b) When FT > 25.0mg/100g protein, if R< 1.00, then it shall be judged as containing