Collaborative Study of the Pro-Milk Method for the Determination of Protein in Milk

1975 ◽  
Vol 58 (4) ◽  
pp. 770-772
Author(s):  
John W Sherbon
Keyword(s):  
Protein Content ◽  
Collaborative Study ◽  
Good Precision ◽  
Milk Samples ◽  
Solution Studies ◽  
Dye Solutions

Abstract Seven milk samples and 2 standard dye solutions were analyzed for protein content by the Pro-Milk method by 6 collaborating laboratories. Interlaboratory variations, although small, were significant, probably because of extremely good precision. Blind duplicates (2 sets) did not differ from each other. Tests of dilute dye solutions, involving only the colorimeters, showed interlaboratory variation, which indicates the need to carefully calibrate each instrument. The magnitudes of the variations encountered in the milk and dye solution studies were sufficiently small to allow adoption of the Pro-milk method as official first action.

Collaborative Study of the Kjeldahl Method for Determination of Protein Content of Milk

1969 ◽  
Vol 52 (1) ◽  
pp. 126-130
Author(s):  
D R Strang ◽  
J W Sherbon
Keyword(s):  
Statistical Analysis ◽  
Standard Deviation ◽  
Protein Content ◽  
Analysis Of Variance ◽  
Collaborative Study ◽  
Protein Analysis ◽  
Average Standard Deviation ◽  
Milk Samples ◽  
Kjeldahl Method

Abstract Nitrogen in 12 milk samples was measured in 19 laboratories by the Kjeldahl method. Three of the 19 laboratories were excluded from statistical analysis because the nitrogen values they reported differed markedly from those reported by the remaining 16 laboratories. The average standard deviation for the determinations was 0.012% nitrogen, which is equal to 0.077% protein. Analysis of variance indicated that the error due to the laboratories effect was significant when 16 laboratories were considered. When the laboratories were sorted according to various experience criteria, the variations due to laboratories were significant. When the laboratories were blocked according to catalyst used, the variation among laboratories was not significant.

Cryoscopy of Milk: Effect of Variations in the Method

1966 ◽  
Vol 49 (3) ◽  
pp. 511-515 ◽  
Author(s):  
R W Henningson
Keyword(s):  
Statistical Analysis ◽  
Sample Size ◽  
Freezing Point ◽  
Collaborative Study ◽  
Sample Temperature ◽  
Milk Samples ◽  
Two Samples ◽  
Temperature Rate

Abstract Bath level, sample temperature, rate of stirring, degree of supercooling, sample size, sample isolation, and refreezing of the sample were the variables in the thermistor cryoscopic method for the determination of the freezing point value of milk chosen for study. Freezing point values were determined for two samples of milk and two secondary salt standards utilizing eight combinations of the seven variables in two test patterns. The freezing point value of the salt standards ranged from –0.413 to –0.433°C and from –0.431 to –0.642°C. The freezing point values of the milk samples ranged from –0.502 to –0.544°C and from –0.518 to –0.550°C. Statistical analysis of the data showed that sample isolation was a poor procedure and that other variables produced changes in the freezing point value ranging from 0.001 to 0.011°C. It is recommended that specific directions be instituted for the thermistor cryoscopic method, 15.040–15.041, and that the method be subjected to a collaborative study.

Collaborative Study Using a ZDBT Colorimetric Method for the Determination of Copper in Alcoholic Products

1967 ◽  
Vol 50 (2) ◽  
pp. 334-338
Author(s):  
Duane H Strunk ◽  
A A Andreasen
Keyword(s):  
Sulfuric Acid ◽  
Carbon Tetrachloride ◽  
Collaborative Study ◽  
Colorimetric Method ◽  
Good Precision ◽  
Determination Of Copper

Abstract Results are given on a collaborative study in which a zinc dibenzyldithiocarbamate (ZDBT) colorimetric method is used to measure copper in alcoholic products such as high wine, spirits, gin, whisky, brandy, rum, and wine. In this method, the sample is made ca 0.SN with sulfuric acid, and carbon tetrachloride containing 0.2% ZDBT is added. The colored copper-ZDBT complex is extracted in the carbon tetrachloride and measured at 438 mμ against a similar carbon tetrachloride extract of a blank. Data show good precision, and it is recommended that the ZDBT method be adopted as official, first action.

Collaborative Study of the Gas-Liquid Chromatographic Method for Determination of Stereochemical Composition of Amphetamine

1972 ◽  
Vol 55 (1) ◽  
pp. 146-148
Author(s):  
Clyde E Wells
Keyword(s):  
Column Chromatography ◽  
Chromatographic Method ◽  
Collaborative Study ◽  
Good Precision ◽  
Liquid Chromatographic Method ◽  
Precision And Accuracy ◽  
Standard Deviations ◽  
Liquid Chromatographic ◽  
Amphetamine Sulfate

Abstract Eight laboratories collaboratively studied a method for the quantitative GLC determination of d- and l-amphetamine in tablets. The drugs are separated from tablet excipients by column chromatography and reacted with Ntrifluoroacetyl-( 0-prolyl chloride, and the resulting derivatives are analyzed by GLC. The samples consisted of commercial d-amphetamine sulfate tablets (with and without butabarbital), dl-amphetamine sulfate tablets, and a mixed d- and l-amphetamine sulfate standard. Recoveries were acceptable, and the standard deviations never exceeded 0.64%. The results demonstrate that the method gives good precision and accuracy, and the method is recommended for adoption as official first action.

Collaborative Study Using Atomic Absorption Spectrophotometry for the Determination of Copper in Alcoholic Products

1967 ◽  
Vol 50 (2) ◽  
pp. 338-339
Author(s):  
Duane H Strunk ◽  
A A Andreasen
Keyword(s):  
Atomic Absorption ◽  
Spectrophotometric Method ◽  
Collaborative Study ◽  
Atomic Absorption Spectrophotometry ◽  
Good Precision ◽  
Absorption Method ◽  
Standard Curve ◽  
Absorption Spectrophotometry ◽  
Determination Of Copper

Abstract A collaborative study was conducted on the 'atomic absorption spectrophotometric method for measuring the concentration of copper in alcoholic products. In this method, the samples are aspirated directly into the burner of the instrument, and the absorhance values are converted to ppm copper by reference to a standard curve. Data show good precision and are comparable to those obtained by the ZDBT method. It is recommended that the atomic absorption method be adopted as official, first action.

Collaborative Study of the Milko-Tester Method for Measuring Fat in Homogenized and Unhomogenized Milk

1975 ◽  
Vol 58 (3) ◽  
pp. 572-575
Author(s):  
W Frank Shipe ◽  
Gary F Senyk
Keyword(s):  
Collaborative Study ◽  
Calibration Standards ◽  
Milk Samples ◽  
Automated Method ◽  
Standard Deviations

Abstract The Mark III Industrial Model Milko-tester was evaluated to determine its reliability for testing both unhomogenized and homogenized milk samples. Six laboratories participated in 2 trials. In the first trial, the range among laboratories for homogenized milk was 0.29% and unhomogenized milk 0.34%. This variation was apparently due to inaccurate calibrations. In the second trial, 2 calibration standards were used for each type of milk and the range was reduced to 0.04% for homogenized milk and 0.05% for unhomogenized milk. The standard deviations for unhomogenized and homogenized milk were 0.008 and 0.010 for trial 1 and 0.005 and 0.005 for trial 2, respectively. The official first action automated method I for the determination of fat in raw, unhomogenized milk has been expanded to include the determination of fat in homogenized milk by the use of the Mark III Industrial Model Milko-tester.

Direct and Indirect Determination of True Protein Content of Milk by Kjeldahl Analysis: Collaborative Study

1991 ◽  
Vol 74 (2) ◽  
pp. 281-288 ◽  
Author(s):  
David M Barbano ◽  
Joanna M Lynch ◽  
J Richard Fleming
Keyword(s):  
Nitrogen Content ◽  
Protein Content ◽  
Total Nitrogen ◽  
Collaborative Study ◽  
Total Nitrogen Content ◽  
Nonprotein Nitrogen ◽  
Protein Nitrogen ◽  
Nitrogen Determination ◽  
True Protein

Abstract Currently, the reference procedure for determination of the "protein" content of milk is based on measurement of the total nitrogen content of milk by the Kjeldahl method (AOAC method, 920.105). About 6% of the total nitrogen content of milk Is nonprotein nitrogen. Therefore, total nitrogen multiplied by the conversion factor 6.38 overestimates the true protein content of milk on average by about 6%. In the present study, new direct and Indirect methods were developed for measurement of the true protein content of whole milk by Kjeldahl nitrogen determination. Both new methods are sample preparation procedures used to fractionate the nitrogen-containing compounds In milk prior to measurement of the nitrogen content of these fractions by Kjeldahl analysis. The collaborative study consisted of 9 pairs of blind duplicate milk samples that were analyzed for total nitrogen, nonprotein nitrogen, and protein nitrogen by each of 10 laboratories. Both methods for true protein measurement (direct and Indirect) gave acceptable statistical performance characteristics and good agreement between methods. The new direct method requires about half the laboratory analysis work of the indirect method (i.e., total minus nonprotein nitrogen). The methods have been adopted official first action by AOAC as (1) a new method for nonprotein nitrogen determination in milk, (2) a new method (direct) for determination of protein nitrogen content of milk, and {3) an alternative method (indirect) for determination of protein nitrogen content of milk.

scholarly journals Analysis of Fat and Protein Content in Milk Using Laser Polarimetric Scatterometry

Agriculture ◽  
2021 ◽  
Vol 11 (11) ◽  
pp. 1028
Author(s):  
Alexey V. Shkirin ◽  
Dmitry N. Ignatenko ◽  
Sergey N. Chirikov ◽  
Nikolai F. Bunkin ◽  
Maxim E. Astashev ◽  
...  
Keyword(s):  
Protein Content ◽  
Dairy Production ◽  
Size Distributions ◽  
Fat Percentage ◽  
Milk Samples ◽  
Quantitative Content ◽  
Scattering Matrices ◽  
Control Milk ◽  
Dairy Cow Nutrition

Monitoring the composition of milk products is an important factor in the management of dairy farms and industry. Information on the quantitative content of milk components is necessary to control milk quality, as well as to optimize dairy cow nutrition and diagnose their clinical condition. The content of fat and protein is considered the main criterion for determining the market value of milk. Increasing the efficiency of dairy production requires the use of inexpensive and compact devices that are capable of performing multicomponent analysis of milk both directly on the farm and in technological lines. We investigated the possibility of fast simultaneous determination of fat and protein content in milk by laser polarimetric scatterometry. The block-diagonal elements of the scattering matrix were measured for a series of commercially produced milk samples with the indicated fat percentage, which were diluted by volume with water. From the measured scattering matrices, the size distributions of fat droplets and casein aggregates were reconstructed. Using the size histograms, the content of fat and protein and protein-to-fat ratio in the studied milk samples are estimated.

Collaborative Study on the GLC and AOAC Methods for the Quantitative Determination of Lactic and Succinic Acids in Egg

1970 ◽  
Vol 53 (1) ◽  
pp. 28-35
Author(s):  
Walter F Staruszkiewicz
Keyword(s):  
Lactic Acid ◽  
Standard Deviation ◽  
Succinic Acid ◽  
Collaborative Study ◽  
Good Precision ◽  
Three Samples ◽  
Egg Extracts ◽  
Aoac Method ◽  
Whole Egg

Abstract Nine laboratories collaboratively studied a method for the quantitative GLC determination of lactic and succinic acids in eggs. Four of the laboratories also analyzed samples by the official AOAC method (16.037–16.042). Samples of frozen whole egg, some passable and some decomposed, were analyzed. The organic acids were extracted by the present AOAC procedures, the acids were then esterified with BF2-l-propanol, and the esters were quantitated by GLC. A collaborative report already published on the GLC determination of standard lactic and succinic acids added to egg extracts established that the method gives accurate results over a broad range of acid concentrations. The samples in the present study contained 4–30 mg lactic acid/100 g egg and 0–20 mg succinic acid/100 g egg. Each collaborator analyzed three samples in duplicate and one sample in triplicate. Using the GLC method, the standard deviation was never greater than 0.6 mg for samples containing less than 16 mg lactic acid/100 g egg, while the standard deviation was 0.2 mg for 7 mg or less succinic acid/100 g egg. The results demonstrate that the method gives good precision when it is applied to passable and to decomposed egg and the method is recommended for adoption as official first action.

Evaluation of Automated Dye Binding Determination of Protein in Milk

1974 ◽  
Vol 57 (1) ◽  
pp. 42-47
Author(s):  
Douglas L Park ◽  
Raymond L King
Keyword(s):  
Protein Content ◽  
Mercuric Chloride ◽  
Sampling Rate ◽  
Protein Determination ◽  
Binding System ◽  
Milk Samples ◽  
Instrument Performance ◽  
Dye Binding ◽  
Herd Milk

Abstract The Technicon AutoAnalyzer dye binding system for protein determination in milk was compared with the Kjeldahl and Udy methods. Individual cow and mixed herd milk samples were analyzed, including such variables as the effect of aging, chemical preservation, laboratory manipulation of protein content, and experimental changes in instrumental parameters. The Udy and Kjeldahl methods showed better agreement than the Technicon procedure in all treatments. Aging resulted in slight decreases in apparent protein content by both dye binding methods. Variation due to treatment with formaldehyde and mercuric chloride was considerable for the Technicon system (+ 0.72 and +0.20% protein, respectively). Individual cow milks varied more than herd milks and Guernsey more than Holstein milk. Milk samples standardized for protein content showed a high correlation with the Kjeldahl results. Replication by the Technicon system was superior to both the Udy and Kjeldahl methods. Performance of the Technicon system improved with increased dialyzing time, decreased dye concentration, and decreased sampling rate. Instrument performance was also influenced by dialysis membrance replacement.

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