Study On The Method For Determination Of Protein In Food And Animal Feed

The protein contributes substantially to human and the animal's growth and development, and it plays an irreplaceable role. In order to reduce costs, some manufactures producing feed or food add excessive non-essential nitrogen-containing chemical substances. The determination result seem to be the sample protein actual content, but it is actually higher than their product's protein content. These kind of low-protein products not only hinder the animal's growth, but also do harm to the anmials'health and even human food safety.At present, the national standard method Kjeldahl is used to determine protein content in food and feed as well as grains. According to its theory, the determination result is obviously higher than that of the sample protein actual content if samples include non-protein nitrogen-containing chemical substances. This shortcoming results in a wrong valuation of these products'qualities. The way to solve the problem is to establish a method, which can't be interrupted when determine the samples even if they contain non-protein nitrogen-containing chemical substances. At last, we can take this method as a supplement or replacement of Kjeldahl.In this study, by comparing the current methods of protein content determination, the author establishes a simple, sensitive and accurate determination of protein in food and feed as well as grains. These study aspects are as follows: The identification of stability and linear range; Interference to determination method; The impact factors on sample pre-treatment and the best digestive conditions; interference of the sample protein determination; verify establishment method using Kjeldahl.The author has identified the the best digestive conditions of different samples ,such as rice, corn, soybean, wheat flour, corn straw, alfalfa hay, ham, fresh meat. The digestive conditions include the temperature, NaOH concentration, time, samples dilution etc. When samples weight 0.3 g, the best digestive conditions: water bathing temperature are 50℃; NaOH concentration 1.0 mol / L expect for wheat flour 0.25mol/L ,digestive time for flour 0.5 h, rice, maize flour, Meat, ham for 1 h, soy flour 2 h, alfalfa hay, corn stalks 4 h respectively; Samples are diluted 500 times expect for soybeans 1000 times. In accordance with the above conditions, Lowry method issued in the actual samples determination. Compared with Kjeldahl determination, the result is basically consistent. The percentage of soybean is 95.2% , maize flour is 110% ,and other types of samples is close to 100% repectively. Interference tests showed that non-protein nitrogen, such as melamine, ammonium sulfate, urea, isobuty ildene diurea have no impacts on the results even the additive concentration is 333.3 g / kg. A Biuret concentration 66.7 g / kg is without interference. Sodium chloride, sugar, sodium citrate, vitamin C, vitamin B1, inositol, a variety of amino acids except for tyrosine adding conventional dosage even several times have not clear interference.The results showed that, Lowry method has high sensitivity, more accurate results, little interference and it is also a convenient method for determination of a large number of samples.The establishment of the Lowry method to determinate samples such as food, feed and grain produce ideal results, especially on preventing non-protein product instead of real product entry the market.