Evaluation of automated dye binding determination of protein in milk
Park, D.L.; King, R.L.
Journal - Association of Official Analytical Chemists 57(1): 42-47
1974
ISSN/ISBN: 0004-5756 PMID: 4814325 Document Number: 79974
The Technicon AutoAnalyzer Orange G dye binding system for protein determination in milk was compared with the Kjeldahl and Udy methods. Individual cow and mixed herd milk samples were analysed, including such variables as effect of ageing, 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. Ageing 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-Friesian 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 dialysing time, decreased dye concentration, and decreased sampling rate. Instrument performance was also influenced by dialysis membrane replacement.