Bovine ␤-lactoglobulin (␤-Lg) has been studied extensively in both the isolated and the naturally occurring states. It is a commercially important whey protein of obvious nutritional value but, so far, one that has no clearly identified biological function.

Bovine b-lactoglobulin~BLG! in vivo has been found complexed with fatty acids, especially palmitic and oleic acid. To elucidate the still unknown structure-function relationship in this protein, the interactions between 13 C enriched palmitic acid~PA! and BLG were investigated by means of one-, two-, and three-dimensional NMR spectroscopy in the pH range 8.4-2.1. The NMR spectra revealed that at neutral pH the ligand is bound within the central cavity of BLG, with the methyl end deeply buried within the protein. The analysis of 13 C spectra of the holo protein revealed the presence of conformational variability of bound PA carboxyl end in the pH range 8.4-5.9, related to the Tanford transition. The release of PA starts at pH lower than 6.0, and it is nearly complete at acidic pH. This finding is relevant in relation to the widely reported hypothesis that this protein can act as a transporter through the acidic gastric tract. Ligand binding and release is shown to be completely reversible over the entire pH range examined, differently from other fatty acid binding proteins whose behavior is analyzed throughout the paper. The mode of interaction of BLG is compatible with the proposed function of facilitating the digestion of milk fat during the neonatal period of calves.Keywords: bovine b-lactoglobulin; lipocalin binding sites; nuclear magnetic resonance; palmitic acid; T 1 measurements; Tanford transition Bovine b-lactoglobulin~BLG! is a 18 kDa protein belonging to the lipocalin superfamily, a big family of proteins with a variety of biological functions related to the binding and transport of metabolites. Although lipocalins show low sequence similarity, they share a common b-barrel topology, as the major structural motif. Structure determination of bovine BLG has been performed by X-ray and NMR at neutral and low pH, respectively~Brownlow et al

Analytical results are given for whey powders prepared on a commercial or semi-commercial scale by three companies. Altogether, five preparations enriched in ␤-lactoglobulin, four whey protein isolates and a fraction enriched in ␣-lactalbumin were analyzed for protein composition, including % ␤-lactoglobulin, ␣-lactalbumin, bovine serum albumin, casein (glyco) macropeptide and the main triglycerides. Protein composition was determined by high pressure gel permeation and reversed phase liquid chromatography and by capillary zone electrophoresis. The extent of modification of the native ␤-lactoglobulin structure was also measured through the degree of lactosylation and the fraction of accessible free sulphydryl groups. One significant finding was that the calculated recovery of protein following quantitation of the chromatogram or electropherogram was seldom above 90% and occasionally below 60% of that loaded onto the column or capillary, raising doubts as to the reliability of the analytical results. Extrapolation by linear regression to 100% recovery allowed estimates to be made of the true ␤-lactoglobulin composition of the samples. The nine samples could be placed into three distinct groups with estimat-ed true ␤-lactoglobulin weight % of 70.9 Ϯ 1.1, 62.0 Ϯ 3.4 and 39.5 Ϯ 4.9. Physico-chemical properties of the group of samples are reported elsewhere (Holt et al., 1999).The inter-laboratory comparisons involved the Royal Veterinary and Agricultural University (KVL), two laboratories of BDI (Lab1 and Lab2), NIZO food research (NIZO) and the Composition of whey protein isolates and fractions C. Holt et al. Figure 2 RP-HPLC analysis of commercial whey protein samples using the LRTL method. A. MDFwpi-1, B. MDFwpi-1a, C. MDFwpi-1b.Figure 3 Capillary zone electropherograms of selected samples as obtained by the KVL method. Within the b-Lg region, lactosylated forms have longer migration times than the native forms. on the Molecular Basis of the Aggregation, Denaturation, Gelation and Surface Activity of Whey Proteins (MADGELAS), CT96-1202. All other members of the MADGELAS group are thanked for their co-operation in the sample survey, of which this paper forms a part. The HRI work was supported by the Scottish Office Composition of whey protein isolates and fractions C. Holt et al.

The effect of heat on lactoperoxidase activity in bovine milk was studied over a range of 68 to 76 °C. Values of residual enzymatic activity after different treatments were studied by kinetic analysis, obtaining D-values and the Z-value (3.1 °C). Denaturation of lactoperoxidase, measured by loss in activity, can be described as a 1st-order reaction. Rate constants were calculated, as was the energy of activation, which was 737.69 kJ/mol. Thermodynamic parameters were also calculated. The high value obtained for the variation in enthalpy of activation indicates that a high amount of energy is required to initiate denaturation, probably due to the molecular conformation of lactoperoxidase.

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