Validation of capillary electrophoresis in the analysis of ewe's milk casein

Recent investigations have shown that capillary electrophoresis (CE) can be an alternative to other techniques such as polyacrylamide gel electrophore sis (PAGE) or sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SD S-PAGE) in the qualitative analysis and separation of the different casein fractions in cow's and ewe's milk. However, past work has not yet clarified whether that method can achieve good quantifications. The present study ha s used a commercial whole ovine casein standard and a mixture of the standa rd and whole casein extracted from ewe's milk cheese to test the reliabilit y of the technique. The results show that CE was able to quantify the ewe's milk caseins. The areas under four of the most representative peaks on the electrophoretogram for two alpha and two beta-caseins (designated alpha-ca sein1(CE), alpha-casein2(CE), beta-casein1(CE), and beta-casein2(CE) in ord er of elution) were used to validate the method. In relation to Linearity, coefficient of determination (r(2)) values greater than 99% were obtained f or the regressions of each of the caseins. Moreover, each casein yielded re sponse factors with a relative standard deviation (R.S.D.) of less than or equal to 5. The coefficients obtained in the day-to-day reproducibility ana lysis were higher than those for the same-day repeatability, but all the va lues were within acceptable limits. In the study of accuracy, the percentag e recovery rates for the alpha-casein fractions were higher than those for the beta-casein fractions, hence quantification of the latter using this te chnique would appear to be more accurate under the conditions employed. (C) 1999 Elsevier Science B.V. All rights reserved.