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1. Theme content and scope of application This standard specifies the method of solvent extraction to determine the total content of raw starch and modified starch.
This standard applies to starch samples with a total fat content of less than 1.5% (m/m).
2. The term total starch fat content: The total content of fat in the starch sample. It is expressed as the weight percentage of the sample weight to the original weight of the sample.
3. Principle After the sample is hydrolyzed by boiling hydrochloric acid, it cools and agglomerates insoluble substances. That is, all fats are included, separated by filtration, dried, and all the fat is extracted by the solvent. After drying, the total fat residue weight of the sample was obtained.
4. Reagents Analytical reagents and distilled water should only be used during the assay. 4.1 Solvents: n-hexane or petroleum ether (boiling range 0-60°C) or carbon tetrachloride (These solvents are toxic, use with caution).
4.2 Hydrochloric acid: Ï20 is 1.18 g/mL.
4.3 Iodine: 0.001 mol/L solution.
4.4 Methyl Orange: 2 g/L aqueous solution.
5. Instrument
5.1 Extractors: such as Soxhlet extractors.
5.2 Extraction flask: The lower end of the extractor (5.1) can be sealed.
5.3 disc filter paper: aperture lOμm. Soluble substances in solvent (4.1) can pass freely.
5.4 High-efficiency water-cooled snake condenser: The upper end of the extractor (5.1) can be sealed.
5.5 Electric heating device: a temperature controller.
5.6 water bath: temperature at 15 ~ 25 °C.
5.7 boiling water bath.
5.8 Oven: The temperature can be controlled at 50±1°C.
5.9 Vacuum Oven: The temperature can be controlled at 100±1°C.
5.10 Beaker: The capacity is 60OmL.
5.11 Dryer: There is a sufficient amount of desiccant and a porous metal plate inside.
5.12 Analyze the balance.
6. Analysis steps
6.1 Sample preparation Samples should be thoroughly mixed.
6.2 Sample Amount According to the estimated total fat content, weigh 25-50 g of the sample to the nearest 0.1 g, pour into a beaker (5.10) and add 100 mL of water.
6.3 Hydrolysis 100 mL of hydrochloric acid (4.2) was mixed with 2000 mL of water and the solution was boiled and then added to the sample solution (6.2).
The mixture was heated to boiling and maintained for 5 min.
Drop a few drops of this mixture into a test tube, allow it to cool to room temperature, and add a drop of iodine solution (4.3). If no color is present, no starch is present, and proceed as described in 6.4.
If blue appears, continue to boil the mixture and check continuously until the mixture is free of starch. Then proceed as described in 6.4.
6.4 Separation of agglomerates Place the beaker and the liquid mixture in a water bath (5.6) for 30 min. Stir from time to time to ensure that the temperature is even and the fat is precipitated.
Filter the cooled mixture with filter paper (5.3), remove the fat adhering to the inner wall of the beaker with a few pieces of dry filter paper, and add it together with the filter paper. Pour the water from the rinse beaker into the filter paper to filter. .
The separated agglomerates and the pieces of filter paper were washed with water at room temperature. Until the filtrate is neutral to the methyl orange indicator (4.4).
The filter paper containing the agglomerates and the pieces of filter paper were folded and placed on a watch glass and baked in an oven at 50±1° C. for 3 h.
6.5 Extraction of fat The dried filter paper containing agglomerates is sealed with a new filter paper and placed in an extractor (5.1).
About 50 mL of solvent (4.1) was poured into an extraction flask (5.2) that was pre-baked and weighed to the nearest 0.001 g. The flask was sealed with the extractor. Connect the condenser (5.4) to the upper end of the extractor and open the switch so that the condensed water enters the condenser.
Ensure that the extractor is tightly connected to other parts to prevent solvent loss during extraction.
The temperature is controlled so that 150 to 200 drops of condensed solvent can be produced per minute, or siphon cycles 7 to 10 times per hour, for continuous extraction for 3 hours.
Remove the flask containing the extracted fat, immerse it in a boiling water bath (5.7), evaporate almost all of the solvent from the flask, place the flask in a vacuum oven (5.9) for 1 h, and control the temperature to 100±1. °C. The flask was placed in a desiccator (5.11), allowed to cool to room temperature, and weighed to the nearest 0.001 g.
Prolonging the time for drying the extract leads to a higher result due to oxidation of the fat.
6.6 Number of measurements Two measurements were made on the same sample (t) (6.1).
7. Expression of results
6.1 Calculation method The total fat content is expressed as a percentage of the weight of the sample residue to the original weight of the sample.
X=[(m1-m2)/m0]×100
In the formula
X-sample total fat content, %;
M0 - the original weight of the sample, g;
M1-weight of the empty extraction flask, g;
m2-Extract and dry the total weight of the flask and fat, g;
If the allowable difference meets the requirement, the arithmetic average of the secondary determinations is taken as the result.
The result retains two decimal places. 7.2 The absolute value of the difference between the results allowed by the difference analyst to perform simultaneous or rapid consecutive measurements. This value should not exceed 5% of the average result.
Additional information:
This standard was proposed by the Ministry of Commerce
This standard is drafted by Shanghai Starch Technical Institute.
The main drafters of this standard: Xu Zumiao, Xu Zhimin, and Zhao Jie.
Starch total fat measurement method
This standard refers to the use of the international standard ISO 3947-1977 "Determination of total fat in starch."