Some physico-chemical properties of nine commercial or semi-commercial whey protein concentrates, isolates and fractions

The physico-chemical properties are reported for a group of whey protein powders prepared on a commercial or semi-commercial scale by three companies and chemically characterized as described elsewhere (Holt et al., 1999). The dependence of the apparent beta-lactoglobulin % on the recovered % showed that the nine samples could be placed in three distinct groups with beta-lactoglobulin weight % of 70.9 +/- 1.1 (Group 1), 62.0 +/- 3.4 (Group 2) and 39.5 +/- 4.9 (Group 3). Measurements by 1H-NMR spectroscopy, on 3 of the samples confirmed that the native fold still predominated in the beta-lactoglobulin. beta-lactoglobulin could be crystallized from all the powders and the normal space group and cells dimensions were determined for the 8 samples that gave crystals of good enough quality for X-ray studies. Differential scanning microcalorimetry of samples dispersed in a phosphate buffer showed a clear difference between Groups 1 and 2 with a more prominent peak due to alpha-lactalbumin in the Group 2 samples. Light scattering and size exclusion chromatography showed that two types of aggregates were present to a variable extent in all the samples and after a heat treatment, the larger aggregates tended to predominate in Group 2. The rheology measurements, also made in the phosphate buffer, showed a difference of gel stiffness during heat treatment between the Group 1 and Group 2 samples with the exception of the BORCwpc + sample. Within each group, gel stiffness increased with the degree of lactoslylation of the beta-lactoglobulin. Interfacial measurements on samples dispersed in water presented a more complex pattern of behaviour although surface tension measurements at the air water interface of the Group 2 samples showed a two-step pattern of surface tension decrease with time, compared to a single step pattern in the Group 1 samples.