Rafael Berrocal

Tryptic phosphopeptides from whole casein. II. Physicochemical properties related to the solubilization of calcium

Casein phosphopeptides (CPP) were produced by tryptic hydrolysis of sodium caseinate and further purified by precipitation and chromatography on QAE-Sephadex A-25. Their physico-chemical properties were compared with the properties of an enzymically dephosphorylated equivalent preparation (DPP). Binding of Ca2+ to the peptides was measured using a Ca selective electrode and was found to increase with pH and to show 1/1 stoicheiometry Ca/Porg in CPP at pH 6.5 and 7.6. Klotz plots indicated equivalent binding sites at these two pH values, but some heterogeneity was seen at pH 3.5. In contrast, DPP did not bind significant amounts of Ca2+. CPP effectively inhibited the formation of insoluble calcium phosphates at different Ca/P ratios. The effective CPP concentration was 10 mg/l and complete stability of calcium phosphate solutions was obtained at about 100 mg/l. This stabilizing effect was dependent on the presence of organic P.

Powdered Milk Micellar Casein Prevents Oral Colonization by Streptococcus sobrinus and Dental Caries in Rats: A Basis for the Caries–Protective Effect of Dairy Products

Three animal studies were performed to investigate the influence of the macromolecular structure of milk casein on caries incidence and the possible ecological changes of the oral microbiota by such casein fractions. Towards this end, rats were infected with mixed bacterial suspensions of Streptococcus sobrinus OMZ 176 and Actinomyces viscosus Ny1. Various milk protein fractions were incorporated into carefully balanced powdered cariogenic diets to constitute the sole major protein component. Diets containing micellar casein had a pronounced and highly significant effect on almost all clinical and microbiological parameters examined. Both the formation of advanced dentinal fissure (B) and smooth surface (E) caries lesions was inhibited by diets containing micellar casein; this caries–inhibiting effect appeared to be due mainly to modifications within the plaque microbiota. The proportion of S. sobrinus in the oral cavity of rats was reduced (73–80%) by micellar casein–containing preparations, whereas the A. viscosus population was increased. Both these microbiological parameters were always negatively correlated. This appears to be the first example of a food component other than dietary sugars, selectively modifying the composition of the dental plaque microbiota of rats in such a way as to reduce its pathogenic potential. It also demonstrates the importance of establishing a molecular basis for the role of food components, which prove to be beneficial to oral health.

Low resolution NMR spectroscopy: a tool to study protein denaturation: I. Application to diamagnetic whey proteins

A method using low resolution NMR spectroscopy is described for investigating whey protein thermal denaturation. The method is based on measuring at 20 °C changes in water proton transverse (T 2 ) relaxation parameter following the denaturing treatment. This parameter is shown to be sensitive to protein denaturation and not to other phenomena such as gelation. Examples are given for the qualitative study of protein thermal denaturation in whey protein concentratc, β-lactoglobulin, α-lactalbumin, bovine serum albumin and immunoglobulins aqueous solutions and for the quantitative determination of thermal denaturation in whey protein concentrate solutions.

Low-field nuclear magnetic resonance relaxation study of thermal effects on milk proteins

A recently described nuclear magnetic resonance (NMR) method was evaluated for its usefulness in studying thermal effects on milk proteins. The increase in water proton T 2 relaxation rate observed during thermal treatment of aqueous whey protein solutions above the denaturing onset temperature paralleled results obtained with the standard Rowland (1938) method. The influence of milk constituants on NMR characteristics was analysed. The NMR response increased with the ionic strength and the addition of caseinate or casein micelles. The relevance of the T 2 relaxation probe for studying thermal modifications of milk proteins is discussed. It is proposed to apply the NMR method for determining either reversible or irreversible thermal denaturation of whey proteins in model Systems.