Studies on genetic variants of α‐lactalbumin and β‐lactoglobulin from milk of native Portuguese ovine and caprine breeds

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Summary α‐Lactalbumin (α‐La) and β‐lactoglobulin (β‐Lg) fractions were obtained from Portuguese native breeds of ewes and goats by preparative gel filtration and further purified by ion exchange; their genetic variants were characterized by isolectric focusing, and β‐Lg isolated was further characterized by differential scanning calorimetry. Separation of β‐Lg and α‐La by molecular exclusion from native whey was relatively easy, whereas β‐Lg from both breeds accounted for a single peak via ion exchange under various gradients of NaCl. Isoelectric focusing has indicated that α‐La from ovine and caprine wheys appears as a single variant in each case, as well as β‐Lg from caprine whey; however, β‐Lg from ovine whey appears as two peaks, tentatively denoted as β‐Lg A and B. Further comparison with bovine whey made it possible to rank whey proteins by increasing value of pI as follows: bovine β‐Lg A, bovine α‐La, bovine β‐Lg B, ovine and caprine α‐La, ovine β‐Lg A, and finally ovine β‐Lg B and caprine β‐Lg. β‐Lg from goat's whey showed the highest onset temperature of denaturation in the presence (78–97 °C) or absence (90–100 °C) of NaCl for every pH tested; when NaCl was present, a good correlation between pI and onset temperature of denaturation was obtained for pH values in the range 3.5–7.0.