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

Abstract

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.

Purification and physicochemical characterization of ovine β‐lactoglobulin and α‐lactalbumin

“…This phenomenon can be attributed to the main role of hydrophobic interactions in the stability of proteins and particularly of tyrosyl residues of b-lactoglobulin A in such interactions. Pintado and Malcata [10] have found a good correlation between the pI of whey proteins and the temperature of denaturation (78-97 8C) for pH values in the range 3.5-7.0, in the presence of NaCl. Therefore, ovine b-lactoglobulin B shows a higher temperature of denaturation than ovine b-lactoglobulin A.…”

“…It was also found that heat capacity at pH 2 is lower than at neutral pH for the whole b-lactoglobulin since the unfolded state (prevailing at neutral pH) has a higher heat capacity than the compact denatured state observed at acid pH [31]. The difference observed between the two variants in their temperature of denaturation is dependent on the conditions used in the experiments (pH and ionic strength), which affect the thermal transition of the two b-lactoglobulin variants [10]. This difference in Td at pH 2 shows that b-lactoglobulin A is more heat resistant than the variant B, what agrees with the results of Calavia and Burgos [26] working at a different pH (6.6) but is in disagreement with those reported in the case of the bovine counterpart [32].…”

“…The a-helical domain is composed of three major a-helices (residues 5-11, 23-24, and 86-98) and two short 3 10 helices (residues 18-20 and 115-118). Bovine a-lactalbumin forms high-molecular mass-disulfide oligomers at high pressure (10 kbar, 1000 Mpa) in the presence of low-molecular-mass thiol reducers such as cysteine, mercaptoethanol, and dithiothreitol [9].…”

“…b-Lactoglobulin eluted as a single peak during ion-exchange chromatography by linear gradient of NaCl. Isoelectric focusing showed that a-lactalbumin appears as a single variant, whereas b-lactoglobulin migrates as two bands [10].…”

Major whey proteins in ovine and caprine acid wheys from indigenous greek breeds

“…Studies of caprine whey protein polymorphism and its impact on the properties of caprine milk are even more limited (Pintado & Malcata, 1996;Recio, Pe´rez-Rodrı´-guez, Ramos, & Amigo, 1997;Moioli et al, 1998;Pintado & Malcata, 1999), in contrast to numerous studies that have been carried out on caprine casein polymorphism and its influence on the compositional and technological characteristics of caprine milk. Nucleotide sequence of caprine b-LG cDNA and deduced amino acid sequence of caprine b-LG have been presented by Folch, Coll, and Sa´nchez (1993).…”