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beta-Lactoglobulin is the major whey protein in the milk of ruminants and some nonruminants, such as pigs and horses. Although beta-lactoglobulin was first isolated 60 yr ago, no function has been definitely ascribed to beta-lactoglobulin. Recent x-ray crystallographic studies have advanced knowledge of the structure of beta-lactoglobulin, which is homologous with that of retinol-binding protein and lipocalycins; the function of these proteins seems to be participation in the transport of small hydrophobic substances. By analogy, this protein has been suggested as having a role as a transporter of fatty acids and retinol. This review reassesses the function of beta-lactoglobulin in light of the large amount of information that has accrued in the last few years. In particular, this review concentrates upon studies of the binding of retinol and fatty acids to beta-lactoglobulin, including the binding constants and number of binding sites, the location of the binding sites, and the influence of chemical modifications in the interaction of the protein with both ligands. This study also describes studies of the influence of beta-lactoglobulin on several biological processes that may be relevant to the possible biological role of this protein.

Kinetic parameters for heat-induced denaturation of lactoferrin under different conditions were determined over a temperature range 72-85°C. Denaturation of lactoferrin could be described by first-order reaction kinetics. Lactoferrin is denatured more rapidly in its apo form than in the iron-saturated form. Both apolactoferrin and iron-saturated lactoferrin are more heat-sensitive when treated in milk than in phosphate buffer. Values of change in enthalpy of activation of lactoferrin denaturation are high which indicates that a large number of bonds are broken. The association of lactoferrin with 8-lactoglobulin does not significantly influence the change in enthalpy of activation of lactoferrin denaturation.

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beta-Lactoglobulin isolated from milk of cow, sheep, and goat had about 0.5 mol of fatty acids bound per mol of monomer protein. Fatty acids, mainly palmitic and oleic acids, were the major components (about 75% of total lipids). Albumin isolated from the same samples had about 4.5 mol of fatty acids bound per mol of protein. These two proteins were the only whey proteins able to bind labeled fatty acids in vitro. Interaction of beta-lactoglobulin and albumin with insolubilized fatty acids showed some differences, suggesting different structures of the respective fatty acid binding sites.