Simultaneous separation and quantitation of the major bovine whey proteins including proteose peptone and caseinomacropeptide by reversed-phase high-performance liquid chromatography on polystyrene-divinylbenzene.

A precise, sensitive and reliable RP-HPLC method was developed to enable not only unequivocal determination of alpha-lactalbumin and beta-lactoglobulin in bovine whey samples, but also simultaneous measurement of proteose peptone, caseinomacropeptide, bovine serum albumin and immunoglobulin G. The optimised method on the Resource RPC column allowed separation of the proteins in 30 min and could be applied to the analysis of soluble proteins in a variety of commercial and laboratory whey products. Furthermore, some qualitative information on protein heterogeneity and quality could be derived from the RP-HPLC analyses with additional data available from on-line electrospray mass spectrometry. Within- and between-day repeatability over a wide range of concentrations was excellent (RSD< or =5%) for all proteins except immunoglobulin G and bovine serum albumin where RSD was 7-10%. Analysis of grouped data from whey protein concentrate and whey protein isolate samples gave a limit of detection of < or =0.3% powder mass and a limit of quantitation of < or =1.0% powder mass for all proteins except immunoglobulin G. Limits of detection and quantitation were 0.6% and 2.0%, respectively, for this protein. Quantitative data obtained by the RP-HPLC method compared very favourably with data obtained by alternative methods of whey protein analysis.

Acid-polyacrylamide gel electrophoresis of lysozyme-estrone glucuronide conjugates.

Acid-polyacrylamide gel electrophoresis (acid-PAGE) was used for analysis of lysozyme-estrone glucuronide conjugates. The resolution of the system allowed the identification of individual conjugate families which differed only in the position of acylation or in the number of estrone glucuronide units. Acid-PAGE was a good alternative to denaturing cation-exchange chromatography for the analysis, separation, and small-scale purification of lysozyme-estrone glucuronide conjugates. It revealed the true order of the relative degree of positive charge on the lysozyme-estrone glucuronide conjugates.

Comparative study of methods for the isolation and purification of bovine kappa-casein and its hydrolysis by chymosin.

kappa-Casein was purified from a single batch of whole acid casein (kappa-A variant) using different methods in order to compare their merits in producing a purified material with a carbohydrate and phosphate heterogeneity representative of the whole kappa-casein complement in milk. Ion-exchange methods of purification gave products of higher purity than precipitation techniques involving final purification by ethanol fractionation, but all methods resulted in kappa-caseins of apparently similar heterogeneity and chemical composition. The purified kappa-caseins were hydrolysed with chymosin and the derived macropeptides isolated. These were all virtually identical as determined by reversed-phase chromatography and gel electrophoresis. Some observations on chymosin hydrolysis of kappa-casein were made. In addition to formation of the major para-kappa-casein (Glu1-Phe105) and macropeptide (Met106-Val169), chymosin hydrolysis at pH 6.6 also resulted in two minor para-kappa-caseins with N-termini corresponding to Phe18 and Ser33 of kappa-casein. At pH 5.5 and 4.5 para-kappa-casein was rapidly hydrolysed into at least six fragments, one of which had an N-terminus corresponding to Trp76 of kappa-casein. At pH 6.6, 5.5 and 4.5 the kappa-casein macropeptide was stable to chymosin, but at pH 2.3 it was hydrolysed by chymosin into fragments with N-termini corresponding to Met106, Ile125, Ala138, Val139, Thr145 and Glu147 of kappa-casein.