Cleavage Of Κ-casein Research Articles

Allergy to Goat/Sheep’s Milk with Good Tolerance to Cow’s Milk but Not to Cow’s Milk Cheese: Identification of 1-105 Peptide from -Casein as the Molecular Basis of Reactivity toward Cow’s Milk Cheese for Two Patients

In Europe, a new population of patients developing anaphylaxis to goat’s/sheep’s milk associated to tolerance to cow’s milk has recently appeared. Nevertheless, among these patients, some show allergic reactions to cow’s milk cheeses but these reactions are less severe than those directed against goat’s/sheep’s milk. The objective of the study was to the molecular determinants of the reactivity of this category of patients toward goat’s/sheep’s milk and cow’s milk cheese. Western blots with either monoclonal antibodies specific of each casein or patients sera were performed. We confirmed that goat caseins are the main allergen recognized by patients with goat’s/sheep’s milk anaphylaxis. Patients IgE recognized also strongly and mainly bovine κ-casein 1-105 peptide which is present in cow’s milk cheese but not in cow’s milk. This peptide is generated by cleavage of κ-casein by chymosin during cheese fabrication. The reactivity of patients with anaphylaxis to goat’s/sheep’s milk toward cow’s milk cheese is due to the presence of an epitope in bovine κcasein 1-105 peptide, epitope absent or not accessible in full-length bovine κ-casein.

Effect of storage time and temperature of milk protein concentrate (MPC85) on the renneting properties of skim milk fortified with MPC85

This study investigated the effect of storage temperature (20–50 °C) and time (0–60 days) on the renneting properties of milk protein concentrate with 85% protein (MPC85). Reconstituted skim milk was fortified with the MPC85 (2.5% w/w) and the renneting properties of the skim milk/MPC85 systems were investigated using rheology. It was found that the final complex modulus (final G∗) and the yield stress of the rennet-induced skim milk/MPC85 gels decreased exponentially with storage time of the MPC85 for storage temperatures greater than 20 °C, with a greater effect at the higher storage temperatures. Changes in the solubility of MPC85 with storage time were correlated with the rheological properties. The primary phase of renneting (cleavage of κ-casein) was not affected by the storage of the MPC85; hence the effect was related to the secondary stage of renneting (aggregation/coagulation of rennet-treated casein micelles). Using a temperature–time superposition method, a master curve was formed from the final G∗, yield stress and solubility results. This suggested that the same physical processes affected the solubility and rennet gelation properties of the milks. It is proposed that the MPC85 protein in rennet-treated skim milk/MPC85 solutions may transform from an interacting material, when solubility is high, to an inert or weakly interacting material, when solubility is low, and that this results in the reduced final G∗ and yield stress of the rennet gels when MPC85 is stored at elevated temperatures for long periods.

Immunogenicity of κ-Casein and Glycomacropeptide

Glycomacropeptide (GMP), arising from the cleavage of κ-casein by chymosin or pepsin, has been correlated with a wide variety of biological activities including immunosuppression capacity, inhibition of pathogen invasion, and induction of satiety. Due to the interest in exploiting such potential of GMP, we aimed at characterizing the immunogenic properties of GMP as an indication of its potential allergenicity. Immunogenicity of κ-casein and GMP were investigated using 2 animal models based on different routes of immunization: 1) mice immunized intraperitoneally or subcutaneously with either κ-casein, polymerized GMP, GMP coupled to the immunogenic carrier ovalbumin, or GMP alone; 2) mice coadministered κ-casein or GMP and cholera toxin. The specific antibody response to GMP was evaluated as well as the antigen-specific T-cell response. The results demonstrated that immunization or feeding with κ-casein induced GMP-specific antibodies, whereas GMP per se lacked immunogenicity independently of the mode of presentation. The size of the presented form of GMP did not influence its immunogenicity. Because the results showed that GMP did not induce a specific T-cell response, we postulate that GMP lacks the ability to stimulate antigen-specific T cells.

Comparison of conformations of κ-casein, para-κ-casein and glycomacropeptide

The conformation of κ-casein was compared with those of para-κ-casein and glycomacropeptide formed by the cleavage of κ-casein with chymosin. Para-κ-casein is insoluble in water at room temperature, but is slightly soluble in 0.07 M NaCl (pH 7.0) at 3°C. The secondary structure of κ-casein, para-κ-casein and glycomacropeptide was estimated from CD spectra measured at 3°C by the method of Yada and that of Provencher and Glockner. The surface hydrophobicity of these molecules was estimated by the fluorometric method. It was concluded that the secondary structures of para-κ-casein and glycomacropeptide segments were changed slightly by cleavage with chymosin. Para-κ-casein was estimated to have more β-sheet structure than glycomacropeptide. Para-κ-casein had larger hydrophobic regions on the molecular surface compared with the corresponding part in κ-casein.