Some standard content:
National Standard of the People's Republic of China
Method for determination of wet gluten in flour
Method for determination of wet gluten in flour1 Subject content and scope of application
GB/T 14608--93
This standard specifies the principle of the method for determining the wet gluten content of wheat flour by mechanical washing method and manual washing method, as well as the instruments, utensils, reagents, operating procedures and experimental result expression method used. This standard is applicable to the determination of wet gluten content of various wheat flours and also to the determination of wet gluten content of whole wheat flour. 2 Referenced standards
GB 5497 Method for determination of moisture content in grains and oilseeds 3 Principle of the method
Wet gluten is a kind of elastic and plastic colloidal hydrate mainly composed of gliadin and glutenin obtained from wheat flour by the method specified in this standard.
Wheat flour sample is made into dough with sodium chloride buffer solution, then washed with sodium chloride buffer solution to separate starch, sugar, cellulose and soluble protein in the dough, and then the excess washing liquid is removed. The remaining gelatinous substance is wet gluten. 4 Reagents
4.1 Sodium chloride buffer solution
20g/L: 200g sodium chloride is dissolved in water, 7.54g potassium dihydrogen phosphate (KH,PO,) and 2.46g disodium hydrogen phosphate (Na2HPO.2H,0) are added, and diluted with water to 10L, pH5.9～6.2. 4.2 Iodine solution
0.1g iodine and 1.0g potassium iodide are dissolved in water and then water is added to 250mL. 5 Instruments
5.1 Gluten washing instrument (for mechanical washing method): It is mainly composed of a washer, a screen, a stirrer, a stirring shaft, a motor and a control system, a flushing device, a timing control device and other parts (see the figure below). The main technical parameters are as follows: Approved by the State Bureau of Technical Supervision on September 5, 1993, and implemented on July 1, 1994
Agitator speed
GB/T14608-93
Main structure of gluten washing instrument
Washing wheat flour amount
Washing liquid flow
Washing bloodwww.bzxz.net
Agitator
120r/min
50～54 mL/min
CB33 (33 holes/crn)
Plastic cup or glass cup (for mechanical washing method to receive washing liquid): 500～600mL5.2
5.3 Centrifugal drainage machine: with symmetrical sieve plate, speed 3000r/min, 2min automatic stop or speed 6000r/min, 1min automatic stop. 5.4 Balance, sensitivity 0.01g.
5.5 Glass bottle with bottom opening (for sodium chloride buffer solution): 5L. 5.6 Burette: 1025mL, graduated in 0.05mL 5.7 Porcelain bowl: 910~15cm
5.8 Glass rod or ox-horn spoon
5.9 Squeezing plate (for gluten drainage): 9cm×16cm, 3~~5mm thick, with 0.3~~0.4mm adhesive tape (paper) around, two pieces in total. 5.10. Sieve with sieve silk (for hand washing method) 30cm×40cm, with CQ20 sieve stretched tight at the bottom, and the sieve frame can be made of wood or metal. 424
5.11 Frosted glass plate: about 40cm×40cm2
5.12 Stopwatch
5.13 Metal tweezers
6 Sample preparation and moisture determination
GB/T 14608--93
6.1 Commercial wheat flour: Take about 100g from the average sample and set aside. 6.2 Whole wheat flour: Take 100g of wheat sample and grind it with a grinder so that the sample passing through the CQ16 sieve accounts for more than 95%. 6.3 Moisture determination: Determine according to GB5497.
7 Operation steps
7.1 Gluten washing method
7.1.1 Instrument preparation and adjustment: Adjust the mixing time of dough preparation to 20s and the washing time to 5min. Clean the washer. Put the screen on the pad and wet the screen with a little sodium cyanide buffer. 7.1.2 Weighing and preparing dough: Weigh 10.00±0.01g wheat flour sample into a washing dish, add 4.6~5.2mL sodium chloride buffer solution, place the washing dish on the fixed position of the instrument, start the instrument, stir for 20s to make dough, and then wash automatically. Determination of whole wheat flour wet gluten or wheat flour with poor gluten quality (referring to wheat flour that is difficult to form a ball and forms fragments after kneading according to the above operation): Weigh 10.00±0.01g sample into a small porcelain bowl, add about 4.5mL sodium chloride solution, use a horn spoon or glass rod to make a dough ball, place the dough ball on the frosted glass plate (6.11), roll the dough into 7~8cm long strips by hand, fold them, and roll them into long strips again, repeat five times, then knead the dough into a ball and put it into the washing bowl, start the instrument for washing. 7.1.3 The instrument automatically washes with sodium chloride buffer solution at a flow rate of 50~54mL/min for 5min, automatically stops, removes the washing blood, and takes out the gluten. About 250~280mL of solution is needed. 7.1.4 Wash the gluten washed above by hand under running water for more than 2min. The washing of whole wheat flour gluten must be appropriately extended. After washing, check the squeezed water of wet gluten with iodine solution and it will be slightly blue, then the washing is finished. 7.1.5 Cleaning the instrument: After each day's experiment, the instrument must be washed with distilled water. 7.2 Manual gluten washing method
7.2.1 Weigh 10.00±0.01g of wheat flour sample, put it in a small porcelain bowl, add 4.6~5.2mL of sodium chloride buffer solution, and prepare dough in the same way as (7.1.2).
7.2.2 Washing: Put the dough in the palm of your hand, and drip the sodium oxide solution from the container (5.5) containing sodium nitride buffer into the dough. Wash at a flow rate of about 50 mL per minute for 8 minutes. During the washing process, use the fingers of the other hand to squeeze the dough, and repeatedly flatten, roll and roll the dough. To prevent the loss of dough and broken gluten during washing, the operation should be carried out on a sieve with a sieve. After washing with sodium fluoride buffer, knead and wash with tap water for more than 2 minutes (the time should be appropriately extended for the determination of whole wheat flour gluten). When the gluten extrusion liquid is slightly blue when checked with iodine solution, the washing is finished.
7.3 Drainage
7.3.1 Centrifuge and drain. Divide the washed gluten ball into two halves, place them on two sieves of the centrifuge respectively, and centrifuge to remove the surface attached water. 7.3.2 Drainage of extrusion plate: If there is no centrifuge, drain the water with an extrusion plate. Place the washed gluten balls on the extrusion plate, and press another extrusion plate to squeeze the gluten (about 5 seconds). After each squeeze, remove the next extrusion plate and wipe it with dry gauze, squeeze it again, wipe it dry again, and repeat the squeeze 15 times. 7.4 Weighing of wet gluten
Use tweezers to take out the wet gluten after centrifugal drainage or extrusion drainage, and weigh the mass of the wet gluten to an accuracy of 0.01g7.5 Calculation of results
Express as the percentage of wet gluten in wheat flour with a moisture content of 14%, % (m/m). The calculation formula is as follows:
×100=×100=
Wet gluten (%)=
GB/T14608--93
Wherein: W is the mass of wet gluten, g,
M is the number of grams of moisture per 100 grams of wheat flour, g; 86 is the coefficient for converting to a sample with a 14% reference moisture content; 10 is the mass of the sample, g.
8 Repeatability
The same sample is used for two determinations. The difference between the two determination results should not exceed 1.0%. The average value is the determination result, with one decimal place.
Additional remarks:
This standard is proposed by the Ministry of Commerce of the People's Republic of China. This standard is under the jurisdiction of the Grain Storage and Transportation Bureau of the Ministry of Commerce of the People's Republic of China. This standard was drafted by the Chengdu Grain Storage Science Research Institute of the Ministry of Commerce. The main drafters of this standard are Qi Xianmei, Wang Xingjuan, Fan Chuntao, and Yang Haoran. This standard adopts the international standards ISO7495-1990 "Determination of wet gluten content in wheat flour - Mechanical washing method" and ISO5531-1987 "Determination of wet gluten in wheat flour".
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