Apparent chemical composition of nine commercial or semi-commercial whey protein concentrates, isolates and fractions

Analytical results are given for whey powders prepared on a commercial or semi-commercial scale by three companies. Altogether, five preparations enriched in beta-lactoglobulin, four whey protein isolates and a fraction enriched in alpha-lactalbumin were analyzed for protein composition, including % beta-lactoglobulin, alpha-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 beta-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 beta-lactoglobulin composition of the samples. The nine samples could be placed into three distinct groups with estimated true beta-lactoglobulin weight % of 70.9 +/- 1.1, 62.0 +/- 3.4 and 39.5 +/- 4.9. Physico-chemical properties of the group of samples are reported elsewhere (Holt et al., 1999).