Protein assays for determining meat protein content in animals
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Preparation of samples The determination of proteins in animal flesh samples involves the question of air-dry samples or fresh samples. After the carcass is slaughtered, the water will dissipate as the body temperature declines, so the test should be taken after the carcass has just been slaughtered. If the other components of the meat sample are to be determined, the sample can be processed according to the method: the animal is sampled immediately after slaughter and crushed, and divided into two parts, one part is put into a brown bottle, and the label is stored cold to store the protein. Content; The other part immediately determines the dry matter content m. The determination of protein with fresh meat samples can reduce the errors in the process of water dispersal and dry matter production, and can reduce the amount of dry matter and reduce the workload. The amount of sample, GB/T14771-93} 2 'in the solid sample 0.2 um 0g, semi-solid sample 2} g, liquid sample 10}-20mlo can be roughly estimated according to the measured sample of its protein, according to the nitrogen content of 30} 40mg determine the sample size.
Sample digestion Weigh a certain amount of sample accurately with a weighing paper and transfer it to a dry digestive tube. Add 0.2 g of copper sulfate and 3 g of potassium sulfate (a certain amount may be weighed in proportion and mixed and ground for later use). It has been suggested to use 0.5g of copper sulfate and potassium sulfate, but the actual operation shows slow digestion, and often caused by excessive use of potassium sulfate and crystallization. Some people tried to increase selenium on the basis of the above two reagents [[3], or used mercury oxide instead of copper sulfate to increase the digestion rate, and proved the feasibility of the method. However, Se powder and mercury oxide are toxic substances, and the gas released during digestion will pollute the environment. Then add 20ml concentrated sulfuric acid, which is the amount required by the national standard law, but the digestion rate is slow, especially for meat foods. Lysine and histidine in meat will increase the digestive speed. According to Shen Jianming et al., the digestive rate of total nitrogen in protein is 7.6 h, and the total nitrogen of pork is about 2.4%. Take 1.500g (about 36mgI) fresh meat for digestion to take 4.7h to complete digestion. Experiments using HZOZ to increase the digestion rate have been confirmed by many people. Through experiments, the author proves that using H202H2S04=32 forest product E, the added amount is 15ml can effectively improve the digestion rate, and the result is accurate.
Install a nitrogen device and place water in the water vapor generator bottle to about 2/3, add a few drops of methyl red indicator solution and a few milliliters of sulfuric acid to keep the water acidic and add a few glass beads to prevent bumping. Pressure controller, and check its airtight h. The boric acid solution was measured in a conical flask for receiving solution. There are many claims about the concentration and amount of boric acid solution. In GB/T 5009.5-1985 [8] is 10 mL. However, this amount is too low and it may not be able to completely absorb the escaped ammonia gas. The amount of boric acid solution should be increased. Experiments have shown that an appropriate increase in the amount of boric acid solution will not affect the results.
The protein analyzer is used to check the precision of the operation steps. There is no requirement for this on the national standard. However, as the scientific research needs and the requirement for accurate results, it is necessary to carry out the recovery test. In addition, Liu Houyuan m used the recovery rate test to calibrate the concentration of hydrochloric acid standard solution, which has the advantages of saving time and standard solution. Accurately weigh 0.5g of sulfated sulphate and replace the sample with the same as above. The calculation formula for nitrogen content is the same as the formula for measuring crude protein, but it is not multiplied by 6.25. The measured amount of sulfuric acid and nitrogen should be 21.19 }.2%. o The recovery rate is calculated according to the formula: R=N/21.19X100%, where R represents the recovery rate and N represents the measured nitrogen content. Two parallel samples were taken for each sample and the arithmetic average was used as the result. When the percentage of crude protein is greater than 25%, the allowable relative deviation is 1%; when the content of crude protein is more than 1% but less than or equal to 25%, the relative deviation is allowed to be 2%; when the content of crude protein is less than or equal to 10%, relative The deviation is 3%.