Bovine Milk Beta-lactoglobulin Research Articles

Beta-Lactoglobulin as a Model Food Protein: How to Promote, Prevent, and Exploit Its Unfolding Processes.

Bovine milk beta-lactoglobulin (BLG) is a small whey protein that is a common ingredient in many foods. Many of the properties of BLG relevant to the food industry are related to its unfolding processes induced by physical or chemical treatments. Unfolding occurs through a number of individual steps, generating transient intermediates through reversible and irreversible modifications. The rate of formation of these intermediates and of their further evolution into different structures often dictates the outcome of a given process. This report addresses the main structural features of the BLG unfolding intermediates under conditions that may facilitate or impair their formation in response to chemical or physical denaturing agents. In consideration of the short lifespan of the transient species generated upon unfolding, this review also discusses how various methodological approaches may be adapted in exploring the process-dependent structural modifications of BLG from a kinetic and/or a thermodynamic standpoint. Some of the conceptual and methodological approaches presented and discussed in this review can provide hints for improving the understanding of transient conformers formation by proteins present in other food systems, as well as when other physical or chemical denaturing agents are acting on proteins much different from BLG in complex food systems.

Stabilization of beta-lactoglobulin by polyols and sugars against temperature-induced denaturation involves diverse and specific structural regions of the protein

Temperature sensitivity of bovine milk beta-lactoglobulin (BLG) was assessed in the presence/absence of non-reducing sugars (sucrose and trehalose) and polyols (glycerol and sorbitol). None of them affected the structural features of the protein at room temperature, where the only observed effect was an increased affinity towards hydrophobic probes in the presence of all co-solutes but glycerol. Although most of the observed effects in temperature-ramp experiments are due to entropic effects (fitting within the “preferential exclusion” theory of protein stabilization), this study indicates that each co-solute exhibit different efficacy at stabilizing specific regions of BLG, suggesting that each of them acts in a specific way on the solvent/protein system. The relevance of these observations with respect to systems of practical relevance is discussed, given the widespread use of heat-polymerizing proteins – such as BLG – in many food formulations that very often include significant amounts of sugars and/or polyols.

Intestinal uptake of retinol: enhancement by bovine milk beta-lactoglobulin

The effect of bovine milk beta-lactoglobulin (BLG) on intestinal uptake of retinol was examined in suckling rats with the everted sac technique. Uptake of 0.06 mumol retinol/L bound to BLG (BLG-retinol) was significantly (p less than 0.01) higher than that of 0.06 mumol free retinol/L both in the jejunum and the ileum. The enhancing effect of BLG on retinol uptake was specific because equimolar concentrations of bovine serum albumin and lactoferrin had no effect on retinol uptake. However, serum retinol-binding protein (RBP), which shares structural and conformational similarities with BLG, also enhanced retinol uptake. BLG, BLG-retinol, and RBP-retinol all inhibited the uptake of retinol from BLG-[3H]retinol in a concentration-dependent manner. Uptake of retinol from BLG-retinol was saturable (apparent Km = 5.6 mumol/L, Vmax = 22.7 nmol.g-1.5 min-1), not affected by metabolic inhibitors, and partially temperature dependent (Q10 = 2.77). BLG also significantly (p less than 0.01) enhanced retinol uptake in the intestine of adult rats. These results demonstrate that BLG specifically enhances intestinal uptake of retinol and suggest the possibility of a receptor for BLG-like proteins at the brush border membrane of the enterocyte.