GB/T 21121-2007 English PDF (GBT21121-2007)

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GB/T 21121-2007: Animal and vegetable fats and oils -- Determination of oxidation stability (accelerated oxidation test)
GB/T 21121-2007
GB
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 67.200.10
X 14
GB/T 21121-2007 / ISO 6886:2006
Animal and vegetable fats and oils - Determination of
oxidation stability (Accelerated oxidation test)
(ISO 6886:2006, IDT)
ISSUED ON: OCTOBER 16, 2007
IMPLEMENTED ON: MAY 1, 2008
Issued by: General Administration of Quality Supervision, Inspection and
Quarantine of PRC;
Standardization Administration of PRC.
Table of Contents
Foreword ... 3
1 Scope ... 4
2 Normative references ... 4
3 Terms and definitions ... 4
4 Principle ... 5
5 Reagents and materials ... 5
6 Apparatus ... 6
7 Sampling ... 9
8 Preparation of samples and apparatus ... 9
9 Analysis steps ... 11
10 Calculation of results ... 12
11 Precision ... 13
12 Test report ... 13
Appendix A (Informative) Summary of the method and examples of conductivity curves
and the determination of induction time ... 15
Appendix B (Informative) Results of an interlaboratory test ... 18
References ... 22
Animal and vegetable fats and oils - Determination of
oxidation stability (Accelerated oxidation test)
1 Scope
This standard specifies the method for the determination of the oxidative stability of
oils and fats under extreme conditions that induce rapid oxidation: high temperature
and high air flow.
This standard applies to unrefined and refined animal and vegetable fats and oils.
This standard is not applicable to the determination of oil stability at room temperature,
but it can be used to compare the efficacy of antioxidants added to oils and fats.
NOTE: The presence of volatile fatty acids and unstable acidic oxidation products affects the accuracy
of the measurement results.
2 Normative references
The provisions in the following documents become the provisions of this standard
through reference in this standard. For the dated references, the subsequent amendments
(excluding corrections) or revisions do not apply to this standard, however, parties who
reach an agreement based on this standard are encouraged to study if the latest versions
of these documents are applicable. For undated references, the latest edition of the
referenced document applies to this standard.
GB/T 15687 Animal and vegetable fats and oils - Preparation of test sample (eqv
ISO 661)
3 Terms and definitions
The following terms and definitions apply to this standard.
3.1 induction period
The time from the start of the measurement to when the formation of oxidation products
begins to increase rapidly.
3.2 oxidative stability
The induction period determined according to the steps specified in this standard and
expressed in hours (h).
NOTE: The temperature usually used in the determination of oxidative stability is 100 ℃~120 ℃.
According to the oxidative stability of the tested sample, or by an extrapolation of regression method,
other temperature conditions can be used for the determination. The optimal induction period shall be
between 6 h to 24 h. A temperature increase or decrease of 10 °C decreases or increases the induction
period by a factor of approximately 2.
3.3 conductivity
The ability of a substance to conduct electric current.
4 Principle
A stream of purified air is passed through the sample, which has been brought to a
specified temperature. The gases released during the oxidation process, together with
the air, are passed into a long-necked flask containing water that has been demineralized
or distilled and contains an electrode for measuring the conductivity. The electrode is
connected to a measuring and recording device. During oxidation, a rapid increase in
conductivity is caused by the accumulation of volatile carboxylic acid species. The end
of the induction period is indicated when the conductivity begins to increase rapidly.
5 Reagents and materials
Unless otherwise stated, this standard only uses reagents of recognized analytical grade,
and distilled or deionized water.
5.1 Molecular sieve: spherical, with beads of approximately 1 mm diameter and a pore
size of 0.3 nm, and with moisture indicator.
Molecular sieves must be dried in an oven set at 150 °C and cooled down to room
temperature in a desiccator.
5.2 Acetone.
5.3 Alkaline cleaning solution: used for cleaning laboratory glassware.
5.4 Glycerol.
5.5 Thermostable oil.
6.1.2 Gas diaphragm pump: The flow rate is adjusted to 10 L/h manually or through an
automatic flow rate regulator, and the maximum deviation is ±1.0 L/h.
NOTE: When the OSI instrument is adjusted to a pressure of 0.038 MPa (5.5 psi), the flow rate is
approximately 10 L/h.
6.1.3 Borosilicate glass aeration vessels (usually 8), equipped with sealing plugs.
The sealing plug shall be fitted with an air inlet and outlet tube. The cylindrical part of
the vessel shall be narrower by a few centimeters below the top in order to break up any
emerging foam. Foam can also be eliminated with an artificial foam blocker such as a
glass ring.
6.1.4 Closed measuring cells (usually 8): about 150 mL in capacity, with a gas inlet tube
extending directly to the inner bottom of the cell, and a ventilation hole at the top of the
cell.
6.1.5 Electrodes (usually 8): They are used to measure conductivity, with a measuring
range of 0 μS/cm~300 μS/cm, matched with the size of the measuring cell.
6.1.6 Measuring and recording apparatus: An amplifier and a recorder that records the
measurement signals of each electrode are included.
NOTE: Oxidative stability testers of the Rancimat of Swiss Metrohm and the OSI of American Omnion
use a computer-controlled central processing unit.
6.1.7 Certified and calibrated contact thermometer: The accuracy is 0.1 °C or Pt-100
element (platinum resistance thermometer) is used to measure the temperature of the
heating block, connected with a control relay and a heating element; the temperature
range is 0 °C ~150 °C.
6.1.8 Heating block: It is made of cast aluminum. The temperature can be adjusted to
150 ℃±0.1 ℃. There are round holes (usually 8) on the heating block for placing the
aeration vessels (6.1.3) and an aperture for inserting the contact thermometer (6.1.7).
A heating bath can also be used, filled with thermostable oil, and the temperature is
adjusted to 150 °C±0.1 °C through an oil bath.
The temperature can be kept constant at 150 ℃±3 ℃.
6.5 Connecting hoses
They are flexible and made of inert material (polytetrafluoroethylene or silicone rubber).
7 Sampling
Samples received by the laboratory shall be truly representative and have not been
damaged or changed during transportation and storage.
Sampling is not the content stipulated in this standard, and ISO 5555 is recommended.
The samples shall be stored in the dark at 4 °C.
8 Preparation of samples and apparatus
8.1 Preparation of samples
Samples shall be prepared according to the provisions of GB/T 15687.
Use a pipette to remove the required sample volume from the center of the carefully
homogenized sample.
Heat semi-solid or solid samples to a temperature slightly above their melting point,
mix carefully, and avoid overheating. The pipette is also heated to the same temperature
as the sample.
8.2 Preparation of apparatus
8.2.1 Cleaning procedures
In order to remove organic residues as much as possible, wash the aeration vessels,
measuring cells, and air inlet and outlet tubes with acetone more than three times, and
then rinse with tap water.