Interaction between flavour compounds andβ-lactoglobulin: approach by NMR and 2D/3D-QSAR studies of ligands

Energetics of β-lactoglobulin-flavor compounds interactions

Interaction of bovine β-lactoglobulin (BLG) with several flavor compounds (FC) (2-methylpyrazine, vanillin, 2-acetylpyridine, 2- and 3-acetylthiophene, methyl isoamyl ketone, heptanone, octanone, and nonanone) was studied by high-sensitivity differential scanning calorimetry. The denaturation temperature, enthalpy, and heat capacity increment were determined at different FC concentrations. It was found that the denaturation temperature and heat capacity increment do not depend on the FC concentration, while the denaturation enthalpy decreases linearly with the FC concentration. These thermodynamic effects disclose the preferential FC binding to the unfolded form of BLG. By the obtained calorimetric data, the free energies of FC binding vs. the FC concentrations were calculated. These dependences were shown to be linear. Their slope relates closely to the overall FC affinity for the unfolded BLG in terms of the Langmuir binding model. The overall BLG affinity for FC varies from 20 M-1 (2-methylpyrazine) up to 360 M-1(nonanone). The maximal stoichiometry of the BLG-FC complexes was roughly estimated as a ratio of the length of the unfolded BLG to the molecular length of FC. Using these estimates, the apparent BLG-FC binding constants were determined. They are in the range of 0.3-8.0 M-1 and correlated strictly with the FC lipophilicity descriptor (logP).

β-Lactoglobulin and Glycodelin: Two Sides of the Same Coin?

The two lipocalins, β-lactoglobulin (βLg) and glycodelin (Gd), are possibly the most closely related members of the large and widely distributed lipocalin family, yet their functions appear to be substantially different. Indeed, the function of β-lactoglobulin, a major component of ruminant milk, is still unclear although neonatal nutrition is clearly important. On the other hand, glycodelin has several specific functions in reproduction conferred through distinct, tissue specific glycosylation of the polypeptide backbone. It is also associated with some cancer outcomes. The glycodelin gene, PAEP, reflecting one of its names, progestagen-associated endometrial protein, is expressed in many though not all primates, but the name has now also been adopted for the β-lactoglobulin gene (HGNC, www.genenames.org). After a general overview of the two proteins in the context of the lipocalin family, this review considers the properties of each in the light of their physiological functional significance, supplementing earlier reviews to include studies from the past decade. While the biological function of glycodelin is reasonably well defined, that of β-lactoglobulin remains elusive.

Binding Sites for Oligosaccharide Repeats from Lactic Acid Bacteria Exopolysaccharides on Bovine β-Lactoglobulin Identified by NMR Spectroscopy

Lactic acid bacterial exopolysaccharides (EPS) are used in the food industry to improve the stability and rheological properties of fermented dairy products. β-Lactoglobulin (BLG), the dominant whey protein in bovine milk, is well known to bind small molecules such as fatty acids, vitamins, and flavors, and to interact with neutral and anionic polysaccharides used in food and pharmaceuticals. While sparse data are available on the affinity of EPS-milk protein interactions, structural information on BLG-EPS complexes, including the EPS binding sites, is completely lacking. Here, binding sites on BLG variant A (BLGA), for oligosaccharides prepared by mild acid hydrolysis of two EPS produced by Streptococcus thermophilus LY03 and Lactobacillus delbrueckii ssp. bulgaricus CNRZ 1187, respectively, are identified by NMR spectroscopy and supplemented by isothermal titration calorimetry (ITC) and molecular docking of complexes. Evidence of two binding sites (site 1 and site 2) on the surface of BLGA is achieved for both oligosaccharides (LY03-OS and 1187-OS) through NMR chemical shift perturbations, revealing multivalency of BLGA for EPS. The affinities of LY03-OS and 1187-OS for BLGA gave K D values in the mM range obtained by both NMR (pH 2.65) and ITC (pH 4.0). Molecular docking suggested that the BLGA and EPS complexes depend on hydrogen bonds and hydrophobic interactions. The findings provide insights into how BLGA engages structurally different EPS-derived oligosaccharides, which may facilitate the design of BLG-EPS complexation, of relevance for formulation of dairy products and improve understanding of BLGA coacervation.

Determination of Aroma Compound Partition Coefficients in Aqueous, Polysaccharide, and Dairy Matrices Using the Phase Ratio Variation Method: A Review and Modeling Approach

The partition of aroma compounds between a matrix and a gas phase describes an individual compound's specific affinity toward the matrix constituents affecting orthonasal sensory perception. The static headspace phase ratio variation (PRV) method has been increasingly applied by various authors to determine the equilibrium partition coefficient K in aqueous, polysaccharide, and dairy matrices. However, reported partition coefficients are difficult to relate and compare due to different experimental conditions, e.g., aroma compound selection, matrix composition, equilibration temperature. Due to its specific advantages, the PRV method is supposed to find more frequent application in the future, this Review aims to summarize, evaluate, compare, and relate the currently available data on PRV-determined partition coefficients. This process was designed to specify the potentials and the limitations as well as the consistency of the PRV method, and to identify open fields of research in aroma compound partitioning in food-related, especially dairy matrices.

Modeling bovine serum albumin binding of flavor compounds (alcohols, aldehydes, esters, and ketones) as a function of molecular properties

Interactions between bovine serum albumin (BSA) and 4 classes of flavor compounds (alcohols, esters, aldehydes, and ketones) in aqueous solution were investigated using solid phase microextraction (SPME) of sample headspace and gas chromatography. Alcohols did not bind significantly to BSA. The binding of fixed amounts of individual flavor compounds with each functional group to increasing amounts of BSA was modeled as a function of several descriptors using partial least squares regression (PLSR). Ester binding was modeled as a function of the number of carbon atoms in a molecule and its boiling point (R(2)= 0.954). Aldehyde binding was modeled as a function of the number of hydrogen atoms and boiling point (R(2)= 0.922). Ketone binding was modeled as a function of the numbers of carbon atoms, length of the longer hydrocarbon chain, and degree of branching (R(2)= 0.961).