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National Standard of the People's Republic of China
Quality Examination Methods of the Chinese Pastry
The quality examination methods of the Chinese pastryGB3865-83
This standard applies to Chinese pastries made of flour as the main ingredient and oil, sugar, eggs, nuts and other raw materials as auxiliary ingredients, and baked, steamed or fried.
1 Sampling method
Take 250 grams of samples from the finished product warehouse. For samples with a unit weight of more than 250 grams, take 1 piece or 1 bag. Take 1/3 to 1/4 of each piece and grind it in a mortar. Hard fillings can be chopped with a knife first and then ground. Mix well and put in a wide-mouth bottle for later use. 2 Determination of crude fat content (Soxhlet extraction method) 2.1 Principle
Immerse the sample in anhydrous ether and perform cyclic extraction with the help of a Soxhlet extractor. The obtained crude fat is dried and weighed. 2.2 Reagents
Anhydrous ether: analytical grade.
2.3 Instruments
Soxhlet extractor.
Analytical balance: sensitivity 0.0001 g, maximum weighing 200 g. Electric constant temperature water bath: six holes or four holes. Electric constant temperature drying oven: maximum temperature 250.2.4 Operation method
Put the receiving bottle in the drying oven and bake at 98-100℃ for 2-3 hours, take it out and put it in the dryer, cool it to room temperature and weigh it. Bake for another half an hour, weigh it again, and repeat the operation until constant weight (the difference between the two weighings should not exceed 0.0004 g). Use filter paper to accurately weigh 2-3 grams of sample on the analytical balance, wrap it and dry it (or use the sample after moisture measurement), tie it tightly with wire, and put it into the extraction tube. Connect the extraction tube to the receiving bottle, pour anhydrous ether along the wall of the extraction tube until it exceeds the upper bend of the siphon tube, and then connect it to the condenser. Connect the condensed water to reflux extraction in a water bath at 60-70℃ (50-60℃ in summer) for 34 hours. After using the extraction tube to recover the anhydrous acetaldehyde, remove the receiving bottle, wipe it clean, put it in a drying oven at 98-100℃ for 2-3 hours, take it out and put it in a dryer to cool to room temperature and weigh it, repeat the operation until constant weight. 2.5 Calculation
Crude fat content X1 (%) Calculate according to formula (1): G
W—crude fat weight, g:
W—sample weight, g.
The difference between two parallel determination results shall not be greater than 0.5%. 3 Determination of crude protein content (Kjær's method) 3.1 Principle
When the sample is heated with sulfuric acid, the organic matter is destroyed, and the nitrogen is converted into ammonium sulfate. Add an excess of sodium hydroxide solution to generate ammonia. Distill ammonia into boric acid solution and titrate with standard hydrochloric acid solution to calculate the total nitrogen content, and then multiply by 6.25 to get the crude protein content.
3.2 Reagents
Sulfuric acid: chemically pure.
30% sodium hydroxide solution.
3% boric acid.
0.1N hydrochloric acid standard solution.
Mixed indicator: 10 ml of 0.2% bromocresol green ethanol solution and 2 ml of 0.2% methyl red ethanol solution. Copper sulfate-potassium sulfate mixture: 6 parts of copper sulfate and 100 parts of potassium sulfate are mixed and ground in a mortar. Set aside. Zinc particles: chemically pure.
3.3 Apparatus
Kjeldahl flask: 500 ml.
Erlenmeyer flask: 250 ml.
Acid dropper: 25 ml.
Electric furnace: 800 watts or 1000 watts.
Nitrogen determination ball.
Condenser.
3.4 Operation method
Accurately weigh 0.8-1.2 g of sample on the analytical balance, put it into a dry Kjeldahl flask, add 3-5 g of copper sulfate-potassium sulfate mixture and 10 ml of sulfuric acid. Heat slowly, increase the fire after the foam disappears, and digest until the solution is clear and green. Cool, add 120 ml of distilled water, and connect to the distillation system. Take a 250 ml conical flask. Add 35 ml of 3% boric acid and 3 drops of mixed indicator. Immerse the condenser mouth in the boric acid absorption solution. Add 23 anti-boiling zinc particles and 40 ml of 30% sodium hydroxide solution to the Kjeldahl flask containing the digestion solution, immediately connect it to the nitrogen determination ball, and distill until the liquid in the flask is reduced by about 2/3. Remove the condenser mouth from the absorption liquid, cut off the power supply, rinse the condenser, and titrate with 0.1N hydrochloric acid standard solution until the gray-red color is the end point. At the same time, make a reagent blank. The crude protein content X2 (%) is calculated according to formula (2): N (V-V0) X 0.014
X 6.25 X 100...
Wherein: N is the equivalent concentration of hydrochloric acid standard solution; V
is the volume of hydrochloric acid standard solution consumed by the sample, milliliter; the volume of hydrochloric acid standard solution consumed by the blank test, milliliter: the weight of the sample, gram:
is the milligram equivalent of nitrogen;
is the coefficient for converting nitrogen into protein.
The difference between two results of parallel determination shall not be greater than 0.3%. 4 Determination of total sugar content (Fehling's volumetric method) 4.1 Principle
When Fehling's solution A and B are mixed, the potassium sodium copper tartrate generated is reduced by reducing monosaccharides to generate red cuprous oxide precipitate. When the end point is reached, a slightly excess of reducing monosaccharides reduces the blue methylene blue chromosome to a colorless leucosome and displays the bright red color of cuprous oxide. 4.2 Reagents
Fehling's solution A: Weigh 69.3 g of chemically pure copper sulfate, dissolve in distilled water, and make up to 1000 ml. Fehling's solution B: Weigh 346 g of chemically pure potassium sodium tartrate and 100 g of sodium hydroxide, dissolve in distilled water, and make up to 1000 ml.
1% methylene blue indicator.
20% sodium hydroxide solution.
6N hydrochloric acid.
Calibration of Fehling's solution: Accurately weigh 0.4 g of analytically pure glucose that has been dried and cooled on an analytical balance, dissolve in distilled water and transfer to a 250 ml volumetric flask, add water to the mark, shake well and set aside. Accurately take 2.5 ml of each Fehling solution A and B, put them into a 150 ml conical flask, add 20 ml of distilled water, heat it on an electric stove until it boils, and titrate it with the prepared glucose solution until the solution turns red. Add 1 drop of methylene blue indicator and continue titrating until the blue disappears and bright red appears as the end point. During the formal titration, first add 0.5 to 1 ml less glucose solution than the preliminary test, boil it on an electric stove for 2 minutes, add 1 drop of methylene blue indicator, and continue titrating with glucose solution to the end point. Calculate its concentration according to formula (3):
Where: A--5 ml of Fehling solution A and B is equivalent to the number of grams of glucose; W--the weight of glucose, grams;
V--the volume of glucose solution consumed during titration, milliliters. 4.3 Instruments Www.bzxZ.net
Conical flask: 150 ml, 250 ml. Volumetric flask: 250 ml.
Sugar dropper: 25 ml.
Beaker: 100 ml.
Centrifuge: 0~4000 rpm.
Industrial balance: sensitivity 0.001 g, maximum weighing 200 g. Electric furnace: 300 watts.
4.4 Operation method
Accurately weigh 1.5~2.5 g of sample on the industrial balance, put it into a 100 ml beaker, and soak it in 50 ml distilled water for 30 minutes (stir several times during soaking). Transfer it to a centrifuge tube, rinse the beaker with 20 ml distilled water, and transfer the washing liquid to the centrifuge tube. Centrifuge at 3000 rpm for 10 minutes on a centrifuge, filter the supernatant through rapid filter paper into a 250 ml conical flask, rinse the original beaker with 30 ml distilled water 2~3 times, and then transfer it to a centrifuge tube to stir and wash the sample residue. Centrifuge at 3000 rpm for 10 minutes, and filter the supernatant through filter paper into a 250 ml conical flask. The sample solution after soaking can also be directly filtered with fast filter paper (add precipitant if necessary). Add 10 liters of 6N hydrochloric acid to the filtrate and place it in a 70℃ water bath for hydrolysis for 10 minutes. Take it out and cool it quickly, add 1 drop of phenolic indicator, neutralize it with 20% sodium hydroxide solution until the solution is slightly red, transfer it to a 250 ml volumetric flask, add water to the scale, shake it well and set aside. Use the method of calibrating Fehling's solution A and B to determine the total sugar in the sample. 4.5 Calculation
Total sugar content X3 (inverted sugar, %) is calculated according to formula (4): A
WXV/250
Wherein: A-5 ml of Fehling's solution A and B is equivalent to the number of grams of glucose: W-sample weight, g;
V-amount of sample solution consumed during titration, ml. The difference between two parallel determination results shall not exceed 0.4%. 5 Determination of water content (normal pressure drying method) 5.1 Instrument
Weighing bottle: diameter 60 mm, height 30 mm. ..4
Industrial balance: sensitivity 0.001 g, maximum weighing 200 g. 5.2 Operation method
Place the weighing bottle in a drying oven at 98-100℃ for 2 hours, cool it in a desiccator, weigh it, dry it for another half an hour, weigh it again, and repeat this operation until the weight is constant (the difference between the two weighings should not exceed 0.004 grams). Use a constant-weight weighing bottle to accurately weigh 4-5 grams of the sample on an industrial balance.Place in a drying oven at 98100℃ for 2~3 hours, cool to room temperature in a desiccator and weigh, repeat the operation until constant weight. 5.3 Calculation
Moisture content X4 (%) Calculate according to formula (5):
—×100..
X4 = -
Where: G—weight loss of sample after drying, g; W—sample weight, g.
The difference between two parallel determination results shall not exceed 0.3%. Additional notes:
This standard was proposed by the Ministry of Commerce of the People's Republic of China. This standard was drafted by the Beijing Food Brewing Research Institute. The main drafter of this standard is Yang Chenjian.
Issued by the National Bureau of Standards on September 17, 1983
Implemented on May 1, 1984
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