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  • 1
    Online Resource
    Online Resource
    Determination of the Total Nitrogen Content of Hard, Semihard, and Processed Cheese by the Kjeldahl Method: Collaborative Study
    Oxford University Press (OUP) ; 2002
    In:  Journal of AOAC INTERNATIONAL Vol. 85, No. 2 ( 2002-03-01), p. 445-455
    Details
    In: Journal of AOAC INTERNATIONAL, Oxford University Press (OUP), Vol. 85, No. 2 ( 2002-03-01), p. 445-455
    Abstract: The objective of this collaborative study was to determine interlaboratory performance statistics for a modified and optimized version of AOAC Method 920.123 for the determination of the total nitrogen content of hard, semihard, and processed cheese by Kjeldahl analysis. Details included addressing the issues of material homogeneity, test portion size (1 g), quantitative transfer (weighing on to filter paper), ensuring system suitability (nitrogen recoveries), and using AOAC Method 991.20 as the basis for nitrogen analysis. Fifteen laboratories tested 18 pairs of blind duplicate cheese materials with a crude protein content between 18 and 36%. Materials represented hard, semihard, and processed commercial cheeses with a wide range of composition. Statistical performance parameters expressed as crude protein (nitrogen × 6.38), g/100 g, with invalid and outlier data removed were mean = 26.461, repeatability standard deviation (Sr) = 0.111, reproducibility standard deviation (SR) = 0.153, repeatability relative standard deviation (RSDr) = 0.42%, reproducibility relative standard deviation (RSDR) = 0.58%, repeatability (r) = 0.312, and reproducibility (R) = 0.428. The interlaboratory study results were acceptable and comparable to those for the milk Kjeldahl nitrogen method on a relative nitrogen basis. The Study Directors recommend that this modified method for the determination of total nitrogen in hard, semihard, and processed cheese by Kjeldahl analysis be adopted First Action as an improved method to replace Method 920.123.
    Type of Medium: Online Resource
    ISSN: 1060-3271 , 1944-7922
    URL: Article
    DOI: 10.1093/jaoac/85.2.445
    Language: English
    Publisher: Oxford University Press (OUP)
    Publication Date: 2002
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  • 2
    Online Resource
    Online Resource
    Influence of Milking Three Times a Day on Milk Quality
    American Dairy Science Association ; 1997
    In:  Journal of Dairy Science Vol. 80, No. 3 ( 1997-03), p. 427-436
    Details
    In: Journal of Dairy Science, American Dairy Science Association, Vol. 80, No. 3 ( 1997-03), p. 427-436
    Type of Medium: Online Resource
    ISSN: 0022-0302
    URL: Article
    DOI: 10.3168/jds.S0022-0302(97)75954-X
    Language: English
    Publisher: American Dairy Science Association
    Publication Date: 1997
    detail.hit.zdb_id: 2008548-5
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  • 3
    Online Resource
    Online Resource
    Determination of Fat in Raw and Processed Milks by the Gerber Method: Collaborative Study
    Oxford University Press (OUP) ; 2001
    In:  Journal of AOAC INTERNATIONAL Vol. 84, No. 5 ( 2001-09-01), p. 1499-1508
    Details
    In: Journal of AOAC INTERNATIONAL, Oxford University Press (OUP), Vol. 84, No. 5 ( 2001-09-01), p. 1499-1508
    Abstract: The Gerber method is used worldwide as a simple and rapid method for determining fat in raw and processed milks. However, the volume of the test portion used in the method has not been internationally agreed upon. A collaborative study was conducted to evaluate performance of the Gerber method using either a weighed test portion (11.13 g) or by a 10.77 mL test portion delivered by pipet. For each method, laboratories received 10 test samples: 5 raw and 5 pasteurized homogenized milks, 2 of which were blind duplicate pairs. Eleven and 10 laboratories participated in the evaluation of aliquot addition by weight and pipet, respectively. Mojonnier ether extraction (Method 989.05) was used as the reference method. Interlaboratory study statistics were similar between methods of test portion addition and between raw and processed materials; therefore, summary interlaboratory study statistics were pooled. The fat content of milk samples ranged from 0.96 to 5.48%. Absolute reproducibility and repeatability were not affected by fat level, and pooled statistical performance (invalid and outlier data removed) was (g fat/100 g milk) sr = 0.026, sR = 0.047, r = 0.074, and R = 0.132. Relative standard deviations increased with decreasing fat content, and were summarized by fat level: 1–2% fat milk, mean = 1.437, RSDr = 1.809%, RSDR = 3.271%; 2–6% fat milk, mean = 4.156, RSDr = 0.626%, RSDR = 1.131%. Compared with ether extraction, test results by the Gerber method were slightly lower (0.02% fat) using a weighed test portion and significantly lower (0.06% fat) using a 10.77 mL volume addition by pipet. A trend toward underestimating fat content at lower fat concentrations (1–2% fat) was observed with the weighed test portion but not when a pipet was used. The Associate Referee recommends that the Gerber method using a weighed test portion be adopted as First Action with applicability limited to whole milk.
    Type of Medium: Online Resource
    ISSN: 1060-3271 , 1944-7922
    URL: Article
    DOI: 10.1093/jaoac/84.5.1499
    Language: English
    Publisher: Oxford University Press (OUP)
    Publication Date: 2001
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  • 4
    Online Resource
    Online Resource
    Cheddar Cheese: Influence of Milking Frequency and Stage of Lactation on Composition and Yield
    American Dairy Science Association ; 1997
    In:  Journal of Dairy Science Vol. 80, No. 3 ( 1997-03), p. 437-446
    Details
    In: Journal of Dairy Science, American Dairy Science Association, Vol. 80, No. 3 ( 1997-03), p. 437-446
    Type of Medium: Online Resource
    ISSN: 0022-0302
    URL: Article
    DOI: 10.3168/jds.S0022-0302(97)75955-1
    Language: English
    Publisher: American Dairy Science Association
    Publication Date: 1997
    detail.hit.zdb_id: 2008548-5
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  • 5
    Online Resource
    Online Resource
    Evaluation of Commercially Available Milk Powders for Calibration of Mid-Infrared Analyzers
    Oxford University Press (OUP) ; 1995
    In:  Journal of AOAC INTERNATIONAL Vol. 78, No. 5 ( 1995-09-01), p. 1219-1224
    Details
    In: Journal of AOAC INTERNATIONAL, Oxford University Press (OUP), Vol. 78, No. 5 ( 1995-09-01), p. 1219-1224
    Abstract: The performance of commercially available shelf-stable milk powders that upon reconstitution can be used as calibration samples for mid-infrared (IR) analyzers was evaluated. Twelve reconstituted powders and 7 raw milk samples were sent to each of 7 laboratories. Each laboratory analyzed the reconstituted powders and milk samples by IR and obtained both corrected and uncorrected data. The corrected data reflected the current calibrations (based on calibration with fresh, raw milk) of each instrument. The uncorrected data from the reconstituted powders were used to derive separate calibration equations for each instrument. Two of the 12 reconstituted powers were discarded from the analysis because of poor quality. The abilities of the powder-based and current calibrations to predict accurately the total protein and fat contents of the 7 raw milk samples were compared. For the current and powder-based calibrations, respectively, the mean differences from chemical analysis for total protein were −0.006 and 0.031%, and the standard deviations of the differences (SDD) were 0.029 and 0.029%. For fat, the mean difference for the current calibration was −0.001%, and the SDD was 0.034%. For the powder-based fat calibration, the mean differences were 0.034% (fat A only), −0.047% (fat B only), and −0.061% (fat A and fat B), and SDDs were 0.046% (fat A only), 0.036% (fat B only), and 0.056% (fat A and fat B). The reconstituted powders did not provide as accurate an IR fat calibration for testing raw milk samples as can be obtained with raw milk calibration samples. This is attributed primarily to differences in the characteristics of the fat in the reconstituted powders and in raw milk. For protein, analytical precisions for both types of calibrations were comparable, and the positive bias for the powder-based calibration is relatively easy to correct by basing calibration on true protein nitrogen instead of total nitrogen.
    Type of Medium: Online Resource
    ISSN: 1060-3271 , 1944-7922
    URL: Article
    DOI: 10.1093/jaoac/78.5.1219
    Language: English
    Publisher: Oxford University Press (OUP)
    Publication Date: 1995
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  • 6
    Online Resource
    Online Resource
    Kjeldahl Nitrogen Analysis as a Reference Method for Protein Determination in Dairy Products
    Oxford University Press (OUP) ; 1999
    In:  Journal of AOAC INTERNATIONAL Vol. 82, No. 6 ( 1999-11-01), p. 1389-1398
    Details
    In: Journal of AOAC INTERNATIONAL, Oxford University Press (OUP), Vol. 82, No. 6 ( 1999-11-01), p. 1389-1398
    Abstract: Measurement of total nitrogen by Kjeldahl analysis is the historical reference method for determination of the protein content of dairy products and is used for both calibration and validation of alternative methods for protein determination. Accurate evaluation of alternative methods is not possible if there is large uncertainty regarding the reference values. When Kjeldahl analysis is used to establish reference values, the performance of the Kjeldahl testing must be verified and within established expectations. Advice is given for Kjeldahl system optimization, evaluation of test results, and troubleshooting. Techniques for successful Kjeldahl nitrogen analysis of dairy products other than milk are discussed.
    Type of Medium: Online Resource
    ISSN: 1060-3271 , 1944-7922
    URL: Article
    DOI: 10.1093/jaoac/82.6.1389
    Language: English
    Publisher: Oxford University Press (OUP)
    Publication Date: 1999
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  • 7
    Online Resource
    Online Resource
    Comparison of Babcock and Ether Extraction Methods for Determination of Fat Content of Cream: Collaborative Study
    Oxford University Press (OUP) ; 1996
    In:  Journal of AOAC INTERNATIONAL Vol. 79, No. 4 ( 1996-07-01), p. 907-916
    Details
    In: Journal of AOAC INTERNATIONAL, Oxford University Press (OUP), Vol. 79, No. 4 ( 1996-07-01), p. 907-916
    Abstract: A modified Mojonnier ether extraction method for determination of the fat content of cream was developed based on the method for milk (AOAC Official Method 989.05). The cream Babcock method (AOAC Official Method 920.111 B-C) was modified to harmonize with the milk Babcock method (AOAC Official Method 989.04) and to clarify procedural details. Using the AOAC collaborative study format, 10 laboratories tested 9 pairs of blind duplicate heat-treated cream samples with a fat range of 30-45% using both methods. The statistical performance (invalid and outlier data removed) was as follows: mean % fat = 37.932, sr = 0.125, sR = 0.151, RSDr = 0.330, RSDR = 0.398, r = 0.354, and R = 0.427 for the ether extraction method. For the Babcock method, mean % fat = 38.209, sr = 0.209, SR = 0.272, RSDr = 0.548, RSDR = 0.712, r = 0.592, and R = 0.769. Average test results for fat from the Babcock method were 0.277% (absolute fat) greater than for the Mojonnier ether extraction method. The difference between methods, as a percentage of the average fat content of the samples, was 0.73%. This agrees with differences observed between the 2 methods for milk when 10 to 17 laboratories tested 7 milk samples in blind duplicate at bimonthly intervals over a 4-year period (average difference 0.029% fat, 0.78% as a percentage of average fat content). The Mojonnier ether extraction and Babcock methods for fat in cream have been adopted by AOAC INTERNATIONAL. The new Babcock method replaced the AOAC Official Method 920.111 B-C.
    Type of Medium: Online Resource
    ISSN: 1060-3271 , 1944-7922
    URL: Article
    DOI: 10.1093/jaoac/79.4.907
    Language: English
    Publisher: Oxford University Press (OUP)
    Publication Date: 1996
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  • 8
    Online Resource
    Online Resource
    Effect of Infrared Analyzer Homogenization Efficiency on Repeatability of Uncorrected Fat A and Fat B Signals
    Oxford University Press (OUP) ; 1994
    In:  Journal of AOAC INTERNATIONAL Vol. 77, No. 5 ( 1994-09-01), p. 1217-1223
    Details
    In: Journal of AOAC INTERNATIONAL, Oxford University Press (OUP), Vol. 77, No. 5 ( 1994-09-01), p. 1217-1223
    Abstract: Poor repeatability by infrared milk analyzers may be caused by inefficient homogenization as a result of light scattering and the Christiansen effect. The objectives of this study were to identify instruments with good and poor homogenization efficiency and to determine if a difference exists in repeatability performance between instruments with good vs poor homogenization efficiency. Unhomo-genized and homogenized portions of the same milk were tested 20 times consecutively on 22 instruments. An instrument was considered to have poor homogenization efficiency if the mean difference in the uncorrected signal between unhomo-genized and homogenized portions of the same milk was ≥1.43% of the fat test (i.e., ≥0.05% at 3.5% fat). Instruments were evaluated for repeatability by calculating the sample standard deviation and the range of the latter 19 uncorrected readings for un-homogenized and homogenized milks. When repeatability was evaluated as a function of homogenization efficiency, there was a significant (p = 0.001) correlation between poor homogenization efficiency and poor repeatability when testing unho-mogenized milk but not when testing homogenized milk. Improved homogenizer performance within infrared milk analyzers is needed to improve the repeatability of raw milk testing.
    Type of Medium: Online Resource
    ISSN: 1060-3271 , 1944-7922
    URL: Article
    DOI: 10.1093/jaoac/77.5.1217
    Language: English
    Publisher: Oxford University Press (OUP)
    Publication Date: 1994
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  • 9
    Online Resource
    Online Resource
    Modification of Babcock Method to Eliminate Fat Testing Bias Between Babcock and Ether Extraction Methods (Modification of AOAC Official Methods 989.04 and 995.18): Collaborative Study
    Oxford University Press (OUP) ; 1997
    In:  Journal of AOAC INTERNATIONAL Vol. 80, No. 4 ( 1997-07-01), p. 845-859
    Details
    In: Journal of AOAC INTERNATIONAL, Oxford University Press (OUP), Vol. 80, No. 4 ( 1997-07-01), p. 845-859
    Abstract: The Babcock test for determining fat in milk (AOAC Official Method 989.04) and in cream (AOAC Official Method 995.18) gives consistently higher test results than does the modified Mojonnier ether extraction reference method (AOAC Official Methods 989.05 and 995.19). To decrease the density of material in Babcock columns and thus lower test results, the Babcock method was modified by lowering the temperatures used at various points in the method, from about 57.5° to 48°C. Using the AOAC collaborative study format, 9 laboratories tested 9 pairs of blind duplicate raw milk samples (fat range 2.5–5.7%) and 9 pairs of blind duplicate heat-treated cream samples (fat range 30–45%) using the temperature modified (TM) Babcock method. The ether extraction test was conducted as the reference method. The statistical performance (invalid and outlier data removed) of the TM Babcock method was, for milk: percent fat value of 4.110, repeatability standard deviation (sr) value of 0.037, reproducibility standard deviation (sR) value of 0.047, repeatability relative standard deviation (RSDr) value of 0.901% and reproducibility relative standard deviation (RSDR) value of 1.147%; and for cream: percent fat value of 37.555, sr value of 0.258, sR value of 0.353, RSDr value of 0.687% and RSDR value of 0.940%. The TM Babcock method performance was acceptable but not as good as that achieved in previous studies of the unmodified method. For the TM Babcock and ether methods, respectively, average percentages fat were 4.110 and 4.114 for milk, and 37.555 and 37.485 for cream. Temperature modification statistically eliminated the testing bias between methods. The tem-perature modifications of the Babcock methods for determination of fat in milk and cream (989.04 and 995.18) have been adopted revised first action by AOAC INTERNATIONAL.
    Type of Medium: Online Resource
    ISSN: 1060-3271 , 1944-7922
    URL: Article
    DOI: 10.1093/jaoac/80.4.845
    Language: English
    Publisher: Oxford University Press (OUP)
    Publication Date: 1997
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  • 10
    Online Resource
    Online Resource
    Effectiveness of Temperature Modification in Decreasing the Bias in Milk Fat Test Results Between the Babcock and Ether Extraction Methods
    Oxford University Press (OUP) ; 2003
    In:  Journal of AOAC INTERNATIONAL Vol. 86, No. 4 ( 2003-07-01), p. 768-774
    Details
    In: Journal of AOAC INTERNATIONAL, Oxford University Press (OUP), Vol. 86, No. 4 ( 2003-07-01), p. 768-774
    Abstract: Both the Babcock (AOAC Method 989.04, revised Final Action 2000) and modified Mojonnier ether extraction (AOAC Method 989.05) methods are used in the dairy industry to determine the fat content of milk. Prior to revision in 1997, the Babcock method gave consistently higher fat test results than did the ether extraction. In 1997, a modification of the Babcock method was introduced to bring the results of the Babcock test into closer agreement with the ether extraction. The Babcock method was modified by lowering the temperatures used at various points in the method from about 57.5 to 48°C to increase the density of the material in the Babcock column. A collaborative study of the modification indicated it was successful in bringing the Babcock and ether extraction results into agreement but suggested that performance of the modified method was not as good as that of the unmodified method. In the present study, substantial evidence is presented to validate the success of the Babcock modification in bringing test results into agreement with ether extraction, and to document that temperature modification does not adversely affect method performance. Data were evaluated from an on-going proficiency testing program where 8–15 laboratories tested 7 milk samples in blind duplicate once every 2 months. Laboratories used the unmodified method from 1995 through 1996 and the modified method from 1998 through 1999. Compared with ether extraction, test results from the unmodified Babcock test were consistently higher by an average of 0.022% fat. For the modified Babcock test, average test results were –0.003% fat lower than with ether extraction and not significantly different from zero. AOAC method performance statistics (within-and between-laboratory precision) were equivalent for both the unmodified (Sr = 0.027, SR = 0.041, RSDr = 0.73%, RSDR = 1.08%) and modified (Sr = 0.023, SR = 0.038, RSDr = 0.60%, RSDR = 1.02%) Babcock methods. Modification of the Babcock method was successful in bringing test results into agreement with those of ether extraction.
    Type of Medium: Online Resource
    ISSN: 1060-3271 , 1944-7922
    URL: Article
    DOI: 10.1093/jaoac/86.4.768
    Language: English
    Publisher: Oxford University Press (OUP)
    Publication Date: 2003
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