The rennin-sensitive bond of bovine kappa-casein

Studies on the heat stability of milk protein: II. Effect of exposing milk to light

It was found that the increase in heat stability (coagulation time) that occurs when some milks are stored in light was not caused by changes in pH. These labile milks invariably gave a type A heat-stability curve, had a pH in the range corresponding to the coagulation-time minimum of the curve, and showed the expected abnormal 2-stage type of coagulation. The increase in coagulation time following exposure to light resulted from a delay in the occurrence of the first coagulation, the second coagulation time remaining unaltered. The presence of riboflavin in milk and of O2 in the headspace atmosphere during storage were necessary conditions for milk to be labile. Since light, headspace O2 and riboflavin had similar influences on rennet coagulation time it is suggested that in both instances the causative reaction, as proposed by others to account for the increase in rennet coagulation time of H2O2-treated milk, is stabilization of the heat- and rennin-sensitive methionine-phenylalaninebond in κ-casein by photo-oxidation of the methionine to methionine sulphoxide.

Nomemclature of the proteins of cow's milk: fourth revision

This report reviews the nomenclature of the milk proteins of cow's milk in light of more recent advances in our knowledge. With the establishment of the primary structures of a number of these proteins, we now have a definite identification of alphas1-, kappa-, beta-, and the gamma-caseins as well as beta-lactoglobulin and alpha-lactalbumin. On the basis of new information on their primary structures and relationship to beta-casein polymorphs, changes in nomenclature have been recommended for proteins of the gamma-casein fraction. Although the primary structure serves as the unambiguous definition of proteins for which it is known, a more practical identification is necessary. We recommend that their behavior in gel electrophoresis under suitable conditions be employed for this purpose for all of the "major" milk proteins of raw skim milk except the immunoglobulins where, because of their heterogeneity and molecular genetics, physical parameters are less useful and their identification must be based upon antigenic determinants and their homology with their human counterparts. More work is needed and, with the accumulation of more information, additional changes in nomenclature can be expected for such proteins as the minor components of alphas- and kappa-caseins, alpha-lactalbumin, and the proteose-peptone fraction as well as further confirmation of the presence of immunoglobulins IgE and additional IgG subclasses. Additional components and genetic variants also can be expected.