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Per cent nitrogen x 5.7 = per cent crude pro tein of wheat. Per cent nitrogen X 6.25 = per cent protein of other grains. gen found, times a factor of 5.7 ...
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Premiums on high-protein hard red spring wheat has created much interest in the protein test. The Kjeldahl method, a chemical procedure for nitrogen, is still the basic method used for protein analysis. The Kjeldahl method, the Udy dye binding method and the new infrared reflectance method for determining protein are described in this paper. In the analysis of wheat protein by the Kjeldahl method, the moximum amount of variance in results expected between different laboratories and within the same laboratory is larger than the increments of pro tein on which price premiums have been paid. The causes of protein variance and ways of reducing the variance are discussed.
Dr. McDonald is professor, Department of Cereal Chemistry and Technology.
Table 2. Major Steps in Kjeldahl Protein Analysis.
the amount of dye left in solution, the complex is removed by filtering, and the concentration of dye in solution is determined with a color measur ing instrument. The amount of dye left in solution is inversely related to the protein content of the sample.
Variance Expected In Protein Result
Discussion of protein variance will be con fined mostly to the basic Kjeldahl procedure, be cause almost all protein laboratories are still using this method. Protein for samples in the grain trade are obtained from a single analysis on each sam ple. With a single analysis there is probability that occasionally there will be a wide variation from the actual value. More than one analysis on each sample would reduce this number of varia tions.
variance in protein results should be expected between laboratories. Wheat flour samples were analyzed on a monthly basis by some 50 different laboratories in the United States. Wheat grain samples were also analyzed on a monthly basis by 13 different laboratories in the spring wheat area of the United States. The standard deviation, as a measure of deviation from the average value, was
I. R. LIGHT
DETECTOR
Figure 1. Illustration of infrarec:l reflectance method fOl protein analysis.
lower for flour than wheat grain. The step of grinding the wheat sample by each laboratory should have caused at least a part of the higher variation for wheat. Another factor is the uneven distribution of protein found in ground wheat, which will be discussed later.
Table 3. Variance in Protein Results Between Laboratories on Samples Analyzed Monthly.
Average Number (^) Range in standard Sample (^) samples Protein deviationS % % Wheat flour (1975)1 (^12) 11-12 0. Wheat grain (1975)2 10 12-18 (^) 0. '1\1 onthly check sample from the American Association of Cereal Chemists analyzed by some 50 laboratories. 2Monthly check sample of wheat grain from Ingman Laboratories, Inc., analyzed by 13 laboratories. 'Standard Deviation - a measure of the deviation from the average value expressed as percentage protein.
Normal variation expected in protein results where there is a standard deviation of 0.16 per cent is given in Table 4. There would be a 67 per cent probability that a laboratory doing a single protein analysis would obtain a value deviating from the actual value by one ± standard deviation (SD) unit. For example, for a wheat of 14.0 per
(^4) Farm Research
Material Protein content %
Moisture Per^ cent^ of^ dry^ sample^ Protein content water (^) protein nonprotein total wt. content' % % % % (^) % %
'Protein content = Protein as^ %^ of^ dry samEZe^ X 100 Total wt. as % of dry sample
12.2% 16.2% Moisture grain i Moisture grain i Moisture Change of Moisture Change of after protein after protein grinding' content grinding' content Mill used (^) % % % %
I Determined with the Matomco moisture meter. 'Determined by the 1300 C. air-oven method. 3 A 0.5 mm. sieve was used in the mill.
(^6) Farm Research
Table 10. Protein Content of Particles in Ground Hard Red Spring Wheat (Waldron vari ety).
Particle size, micrometers 1 Mill Used >1,000 920 670 398 358 223 < 149
Labconco Burr Mill % Protein 16.6 15.9 14.1 13.7 14.0 14.6 17. % of grain 3.6 9.4 44.4 7.4 11.3 10.1 13. Hobart Burr Mill % Protein 16.2 15.7 14.5 13.7 13.8 14.2 16. % of grain 7.5 11.0 36.3 7.3 13.5 11.4 12. Particle size, micrometers 1 )420 358 237 ( Udy Cyclone Mill % Protein 14.5 14.8 14.6 15. % of grain 13.1 60.8 13.7 12. 1 Particles of different sizes were separated on sieves.
a sampling error can occur when weighing 1 gram of ground sample for the protein test if the right amounts of different size particles are not select ed. The ground sample should be thoroughly mixed before weighing to avoid this type of error.
(Jarnagin ... from Page 2) is true of most scientific research reporting, pro vided that it is accurate and more or less complete. This is not something that has been "granted" to experiment stations, but has been earned over the years through the witness of experience and satis fied customers-the farmers and ranchers who ultimately use the information.
Information from the Experiment Station is believable and believed. It has withstood the ex treme tests of time, experimentation and practical application. It has successfully resisted the efforts of unscientific and non-scientific disbelievers to dent its armor of credibility.
But, we must remember that Experiment Sta tions are composed of people, too. And they suffer through all of the interpersonal communications problems that the rest of us do, too. The principal difference in their messages as reliable sources of information lies in their use of the methods of science in their search for truth. Once their methods uncover new evidence ann new "facts" that indicate what they believe is so, then the
Conclusions
Protein analysis of grain is a complex proce dure with many steps where errors can occur. A sampling error can be introduced prior to analysis when sampling the original grain, when an aliquot of the original sample is obtained for grinding, and when weighing the ground grain for the pro tein test. A change in moisture content of the grain before grinding or during grinding can also introduce an error prior to analysis. High or low protein dockage material in grain can cause a pro tein variance. Therefore, this material should be removed prior to grinding. Many factors can cause errors during the chemical analysis by the Kjel dahl method. To keep these to a minimum, techni cians should be properly trained, and there should be frequent checks made on instruments and glass ware for accuracy. Checks should also be made on all new solutions and chemical reagents used. Check samples should be analyzed daily to test the overall accuracy of the determination. Even with the best technician and equipment, a few results can still vary from the true or correct value.
Literature Cited
communication problem becomes one of penetrat ing the perceptive shields of their intended audi ences with believeable and understandable inter pretations of that evidence.
In this task, they have the support of a group of skilled interpersonal communication craftsmen whose business it is to help create messages that can attract attention and have meaning for those who can make use of that information. This is a fascinating business. The challenges we constantly meet to use all of the skills and techniques at our command to compose effective messages keeps our work filled with interest and variability.
It is the relative success of our working to gether to overcome these challenges that has brought about the large measure of credibility and believability that comes along with information based on Experiment Station research. Our future success lies in our ability to keep up with the new human communication technologies and use them to their fullest as our society continuously expands its interests in and uses of interpersonal communi cation.
May-June, (^1977 )