1、 Determination of ash content in grains
In addition to containing a large amount of organic matter, grains also contain abundant inorganic components. The inorganic substances left behind by high-temperature burning are called ash. The ash content of various grains varies depending on the variety, soil, climate, fertilizer, and irrigation conditions. The ash mass fraction in cereal grains is generally between 1.5% and 3.0%.
The distribution of ash in grains is extremely uneven, with the lowest ash content in the endosperm, followed by the embryo, and the highest in the cortex. The mass fraction of ash in wheat grains (accounting for dry matter) is about 1.7%, and the mass fraction of ash in endosperm is about 0.6%; Rice and flour with high processing accuracy have low ash content, while those with high processing accuracy have high ash content. At present, most countries around the world use ash to distinguish the accuracy of flour.
There are two methods for measuring ash content: the 550 ℃ calcination method and the magnesium acetate method.
1. 550 ℃ calcination method (standard method)
1) Measurement principle
This method is based on the principle of ashing, which involves burning the sample at high temperature under free air flow. During the burning process, organic matter is oxidized into gas and escapes, while oxides generated by mineral elements remain. This residue is called ash.
2) Instruments and tools
① High temperature furnace.
② Analytical balance: The division value is 0.0001g/division.
③ Porcelain crucible: 18-20mL.
④ A dryer equipped with color changing silicone.
⑤ Crucible pliers: long and short handles.
3) Reagent: 0.05g/ml FeCl3 blue ink aqueous solution.
4) Operation method
① Crucible treatment: First, number the crucible with FeCl3 blue ink aqueous solution, and then burn it in a high-temperature furnace at 500-550 ℃ for 30-60 minutes. Take out the crucible and place it outside the furnace door. After the red heat disappears, cool it in a dryer to room temperature, weigh it, and then burn, cool, and weigh it until the difference in mass between the two times does not exceed 2mg.
② Measurement: Weigh 2-3 g (accurate to 0.0002g) of the crushed sample using a crucible that has been burned to a constant temperature, place it on an electric furnace with the crucible cover staggered, and heat it until the sample is completely carbonized. Then place the crucible at the high-temperature furnace mouth for a moment, then move it into the furnace, stagger the crucible cover, close the furnace door, and burn it at 500-550 ℃ for 2-3 hours. During the burning process, the position of the crucible can be changed 1-2 times until all black spots disappear and turn gray white. Take out the crucible and cool it to room temperature, then weigh it. Burn for another 30 minutes until the mass remains constant. If the mass of the last burn increases, take the previous mass for calculation.
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