Characterisation of the casein fraction of Ibérico cheese by electrophoretic techniques

The physicochemical characteristics of Ibérico cheese, a semi‐hard Spanish variety manufactured from mixtures of cow's, ewe's and goat's milk, were studied. The casein fraction and breakdown products of 6‐month‐old cheeses were characterised by various electrophoretic techniques: urea polyacrylamide gel electrophoresis (urea‐PAGE) at alkaline pH, isoelectric focusing (IEF) and two‐dimensional polyacrylamide gel electrophoresis (2DE). Proteins were separated in 2DE according to their charge/mass ratio by urea‐PAGE at alkaline pH in the first dimension and according to their isoelectric point by IEF in the second dimension. Some individual bands considered homogeneous by urea‐PAGE at alkaline pH (ie different grades of phosphorylation of α_s1‐casein and α_s2‐casein) or by IEF (ie overlapping of several bands of α_s2‐casein with γ‐casein bands) were found to be complex mixtures of casein components by 2DE. The two‐dimensional electrophoretic pattern was characteristic of the milk of each animal species included in Ibérico cheese. Capillary electrophoresis (CE) was also used to study the Ibérico cheeses. The high resolution of this technique allowed the identification of the main caseins of the different species (ie para‐κ‐casein, β‐casein, γ₂‐casein and γ₃‐casein). © 2002 Society of Chemical Industry