Probing the fatty acid binding site of beta-lactoglobulins

Reproducing high mechanical load during industrial processing of UHT milk: Effect on frothing capacity

In this study, possible reasons for an increased level of free fatty acids (FFAs) in Ultra-High Temperature (UHT) treated full fat (3.5% wt/wt) milk and its effect on the frothing properties of milk were investigated. Lipolysis of raw milk from 2 different breeds of cattle (Holstein and Jersey) was induced by mechanical stress and kinetics of lipolysis were compared. Frothing capacity and foam stability of shelf stable milk with different concentrations of FFAs were determined, with a good to medium initial foam volume for up to 4 mEquiv FFA · (100 g fat)-1 fat and poor foam stability with >2 mEquiv FFA · (100 g fat)-1. A combination of mechanical stress and initial condition of fresh raw milk was found to trigger lipolysis and potential sources of mechanical stress during milk processing were identified.

Binding of Per- and Polyfluoroalkyl Substances to β-Lactoglobulin from Bovine Milk

Per- and polyfluoroalkyl substances (PFAS) are known for their high environmental persistence and potential toxicity. The presence of PFAS has been reported in many dairy products. However, the mechanisms underlying the accumulation of PFAS in these products remain unclear. Here, we used native mass spectrometry and molecular dynamics simulations to probe the interactions between 19 PFAS of environmental concern and two isoforms of the major bovine whey protein β-lactoglobulin (β-LG). We observed that six of these PFAS bound to both protein isoforms with low- to mid-micromolar dissociation constants. Based on quantitative, competitive binding experiments with endogenous ligands, PFAS can bind orthosterically and preferentially to β-LG's hydrophobic ligand-binding calyx. β-Cyclodextrin can also suppress binding of PFAS to β-LG owing to the ability of β-cyclodextrin to directly sequester PFAS from solution. This research sheds light on PFAS-β-LG binding, suggesting that such interactions could impact lipid-fatty acid transport in bovine mammary glands at high PFAS concentrations. Furthermore, our results highlight the potential use of β-cyclodextrin in mitigating PFAS binding, providing insights toward the development of strategies to reduce PFAS accumulation in dairy products and other biological systems.

An Atomic and Molecular Insight into How PFOA Reduces α-Helicity, Compromises Substrate Binding, and Creates Binding Pockets in a Model Globular Protein

Per- and polyfluoroalkyl substances (PFAS) pose significant health risks due to their widespread presence in various environmental and biological matrices. However, the molecular-level mechanisms underlying the interactions between PFAS and biological constituents, including proteins, carbohydrates, lipids, and DNA, remain poorly understood. Here, we investigate the interactions between a legacy PFAS, viz. perfluorooctanoic acid (PFOA), and the milk protein β-lactoglobulin (BLG) obtained using a combination of experimental and computational techniques. Circular dichroism studies reveal that PFOA perturbs the secondary structure of BLG, by driving a dose-dependent loss of α-helicity and alterations in its β-sheet content. Furthermore, exposure of the protein to PFOA attenuates the on-rate constant for the binding of the hydrophobic probe 8-anilino-1-naphthalene sulfonic acid (ANS), suggesting potential functional impairment of BLG by PFOA. Steered molecular dynamics and umbrella sampling calculations reveal that PFOA binding leads to the formation of an energetically favorable novel binding pocket within the protein, when residues 129-142 are steered to unfold from their initial α-helical structure, wherein a host of intermolecular interactions between PFOA and BLG's residues serve to insert the PFOA into the region between the unfolded helix and beta-sheets. Together, the data provide a novel understanding of the atomic and molecular mechanism(s) by which PFAS modulates structure and function in a globular protein, leading to a beginning of our understanding of altered biological outcomes.

Prior interaction of protein and lipid affects the formation of ternary complexes with starch

The effects of prior interaction between β-lactoglobulin (βLG) and lauric acid (LA) on their formation of ternary complexes with wheat starch (WS) was studied. Firstly, the interaction between βLG and LA after they were heated at different temperatures between 55 and 95 °C was characterized by fluorescence spectroscopy and molecular dynamics simulation. This showed that a greater degree of βLG-LA interaction occurred after heating at higher temperatures. The WS-LA-βLG complexes formed subsequently were analyzed by differential scanning calorimetry, X-ray diffraction, Raman and FTIR spectroscopy, which showed that as interaction of βLG and LA increased there was an inhibitory action on the formation of ternary complex with WS. Hence, we conclude that there is competition in the ternary systems between the protein and starch to interact with the lipid, and that stronger interaction of the protein and lipid may hinder the formation of ternary complexes with starch.

The Amphoteric Surfactant N,N-Dimethyldodecylamine N-Oxide Unfolds β-Lactoglobulin above the Critical Micelle Concentration

Understanding the interactions between surfactants and proteins is important for the formulation of consumer products as surfactant binding can alter protein activity and stability. Additionally, the structure of the protein-surfactant complex can influence surface activity, which is important for emulsion and foam development. N,N-Dimethyldodecylamine N-oxide (DDAO) is an amphoteric surfactant that is nonionic at high pH. It is often used as a foam booster in detergent formulations and for the extraction of membrane proteins. In this study, a variety of biophysical characterization methods was used to investigate the impact of DDAO at pH 8 on the structure of the globular protein β-lactoglobulin (βLG). Pyrene fluorescence and surface tension studies show that βLG had minimal impact on the critical micelle concentration (CMC) of DDAO, while fluorescence and circular dichroism spectroscopy found unfolding of βLG at concentrations of DDAO greater than the CMC. Small-angle X-ray scattering results confirm changes in the structure of βLG at DDAO concentrations above the CMC. Taken together, DDAO behaves like nonionic and zwitterionic surfactants below its CMC with limited interaction with βLG, while it induces protein unfolding at concentrations higher than the CMC, resulting in a protein-surfactant complex structure that resembles a protein-decorated micelle.

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.

Conjugation reaction with ferulic acid boosts the antioxidant property of arabinogalactan-protein and enhances its ability to form complex with β-lactoglobulin

Ferulic acid was chemically grafted onto the arabinogalactan protein of Aegle marmelos fruit gum using 1,1'-carbonyldiimidazole as coupling reagent. Thus, grafted polysaccharides with different degrees of substitution were prepared and then characterized by gas chromatography/mass spectrometry, size exclusion chromatography, and ultraviolet-visible, infra-red, and nuclear magnetic resonance spectroscopic investigations. Fluorescence spectroscopic investigation showed hydrophobic microdomain formation in grafted polymers. The antioxidant activities of the derivatives, as determined by the 2,2-diphenyl-1-(2,4,6-trinitrophenyl) hydrazyl radical assay, were strong and increases with increasing the degree of feruloylation. Compared to parental arabinogalactan protein (K = 2.38 × 10⁶ M^-1), these grafted polymers bind more strongly with β-lactoglobulin (K = 11.4 × 10⁶ M^-1 and 8.19 × 10⁶ M^-1). Given that gum polysaccharides are valuable component in functional foods, synthesis of antioxidative graft polymer possessing good compatibility with β-lactoglobulin may have important implication.

Conformational changes in bovine α-lactalbumin and β-lactoglobulin evoked by interaction with C18 unsaturated fatty acids provide insights into increased allergic potential

Bovine α-lactalbumin (BLA) and β-lactoglobulin (BLG) are the most common and severe food allergens in milk and they can bind C18 unsaturated fatty acids (UFAs) and their bioactivities were changed. This study aims to determine the effects of C18 UFAs on the structures of BLA and BLG and their allergic properties, such as antigenicity and allergenicity. We reveal that C18 UFAs can efficiently promote the gradual unfolding of the structures of BLA and BLG and increase their hydrophobicity. Moreover, the IgG binding ability and the expression of IgG-dependent activation marker CD200R3 on basophils were remarkably promoted after C18 UFA treatment. Finally, we also observed that C18 UFAs can enhance the IgE binding ability and the degranulation capacity of human basophil KU812 cells (intracellular Ca2+, histamine, β-Hex, and IL-6). Collectively, these results suggested that C18 UFAs changed the structures of BLA and BLG, which contributed to their increased allergic potential.

Beta-lactoglobulin-nutrition allergen and nanotransporter of different nature ligands therapy with therapeutic action

β-lactoglobulin is one of the nutrition allergens present in the milk of many mammals, with the exception of human. This protein belongs to the family of lipocalins, consisting of nine antiparallel β-strands (β-A to β-I) and one α-helix. This structure allows it to serve as a nanotransporter of various nature ligands in a pH dependent manner, which allows us to confidently consider it as a reliable carrier of drugs directly into the intestine, bypassing the destructive acidic environment of the stomach. Based on the latest data, this review describes the currently known methods of reducing the allergenicity of beta-lactoglobulin, as well as the mechanisms and methods of forming complexes of this protein with ligands, which emphasizes its importance and versatility and explains the growing interest in studying its properties in recent decades, and also opens up prospects for its practical application in medicine and pharmaceuticals.

Covalent Adduct Formation Between Flavor Compounds of Various Functional Group Classes and the Model Protein β-Lactoglobulin

The formation of covalent bonds between 47 flavor compounds belonging to 13 different classes of functional groups and β-lactoglobulin (BLG) has been evaluated using electrospray ionization protein mass spectrometry. Covalent bond formation was determined by the appearance of ions in the mass spectra corresponding to BLG + flavor molecule(s). The observed processes for covalent bond formation were Schiff base, Michael addition, and disulfide linkages. Some reactions resulted in protein cross-linking. Aldehydes, sulfur-containing molecules (especially thiols), and functional group-containing furans were the most reactive flavor components. The thiol-containing compounds cleaved one or both electrophilic disulfide linkages in BLG to form disulfide linkages and the sulfides formed covalent bonds with the free cysteine group. Ketones were generally stable, but α-diketones (e.g., diacetyl) were reactive. Some bases (e.g., pyrazines and pyridines) were interactive, while the nucleophilic allylamine was reactive. Hydrocarbons, alcohols, acids, esters, lactones, and pyrans did not give observable levels of adduct formation within the period studied. The formation of covalent bonding (flavor protein) is potentially responsible for the loss of flavor, limiting the shelf-life of many foods.

Effects of Polar Head Nature and Tail Length of Single-Chain Lipids on the Conformational Stability of β-Lactoglobulin

Interaction between β-lactoglobulin and single-chain lipids, differing for either the length of the aliphatic chain or the molecular properties of the headgroup, was investigated at neutral and acidic pH to determine the impact on the thermal stability of the protein. Differential scanning calorimetry results with different fatty acids (from C10:0 to C18:0) show a correlation of both melting temperature and unfolding enthalpy of the protein with the ligand binding affinity, and the maximum effect was found for palmitic acid (PLM). The influence of the lipid polar head was investigated by comparing PLM with lyso-palmitoylphosphatidylcholine (LPC), which possesses the same aliphatic chain. At neutral pH, the stabilizing effect of LPC is less favorable compared to PLM. However, fluorescence results revealed that LPC can bind into the protein calyx even at acidic pH, at variance with fatty acids. Molecular dynamics simulations indicated that this difference is due to the ability of the polar head of LPC to interact with the protein loop that regulates the shift (Tanford transition) between open and closed state of the binding site of β-lactoglobulin. The results provide a rationale for how a ligand has the ability to access the protein active site at acidic conditions by overcoming the Tanford transition, and they demonstrate that β-lactoglobulin can deliver ligands with tailored properties of the polar head in a wide pH range.

Binding behaviors and structural characteristics of ternary complexes of β-lactoglobulin, curcumin, and fatty acids

This study clarified the interaction mechanism and structural characteristics of ternary complexes of β-lactoglobulin, curcumin, and fatty acids.

Effect of supplementation of cows diet with linseed and fish oil and different variants of β-lactoglobulin on fatty acid composition and antioxidant capacity of milk

BACKGROUND

The aim of this study was to determine the influence of polymorphic variants of β-lactoglobulin in cows supplemented with linseed and fish oil on the fatty acid composition and antioxidant capacity of milk. From the herd of 320 Polish Holstein Friesian cows three groups of cows were selected according to the variants of β-LG (β-LGAA, β-LGBB, β-LGAB). During the first 7 days (the initial period) all the cows were fed the same total mixed ration (TMR) diet. From day 8 to 28,150 g fish oil and 250 g linseed (FOL) was added to the TMR diet of each cow.

RESULTS

The results showed that the diet supplemented with FOL was effective in reducing atherogenic and thrombogenic indices. Introducing supplementation improved the antioxidant capacity: higher concentration of C18:2cis-9 trans-11, C20:5 n-3, C22:6 n-3, bioactive whey proteins and vitamin soluble in fat has been recorded. The results showed that β-LGAA was associated with lower levels of atherogenic and thrombogenic indices and higher concentration of C22:5 n-6, phospholipids and β-carotene. β-LGBB favours a higher content of C18:1trans-11, C18:2cis-9 trans-11 and lactoferrin. β-LGAB was associated with higher concentrations of C20:5 n-3, Lysozyme, α-retinol, α-tocopherol and total antioxidant status.

CONCLUSION

Modification of the diet of cows with fish oil and linseed significantly influenced fatty acid composition and antioxidant properties of milk. The effect of β-LG phenotype on the fatty acid composition and antioxidant capacity of milk is variable, which could partly be the result of a β-LG phenotype × diet interaction.

Exploring the heat-induced structural changes of β-lactoglobulin -linoleic acid complex by fluorescence spectroscopy and molecular modeling techniques

Linoleic acid (LA) is the precursor of bioactive oxidized linoleic acid metabolites and arachidonic acid, therefore is essential for human growth and plays an important role in good health in general. Because of the low water solubility and sensitivity to oxidation, new ways of LA delivery without compromising the sensory attributes of the enriched products are to be identified. The major whey protein, β-lactoglobulin (β-Lg), is a natural carrier for hydrophobic molecules. The thermal induced changes of the β-Lg-LA complex were investigated in the temperature range from 25 to 85 °C using fluorescence spectroscopy techniques in combination with molecular modeling study and the results were compared with those obtained for β-Lg. Experimental results indicated that, regardless of LA binding, the polypeptide chain rearrangements at temperatures higher than 75 °C lead to higher exposure of hydrophobic residues causing the increase of fluorescence intensity. Phase diagram indicated an all or none transition between two conformations. The LA surface involved in the interaction with β-Lg was about 497 Ǻ(2), indicating a good affinity between those two components even at high temperatures. Results obtained in this study provide important details about heat-induced changes in the conformation of β-Lg-LA complex. The thermal treatment at high temperature does not affect the LA binding and carrier functions of β-Lg.

The differences in binding 12-carbon aliphatic ligands by bovine β-lactoglobulin isoform A and B studied by isothermal titration calorimetry and X-ray crystallography

Isoforms A (LGB-A) and B (LGB-B) of bovine lactoglobulin, the milk protein, differ in positions 64 (D↔G) and 118 (V↔A). Interactions of LGB-A and LGB-B with sodium dodecyl sulfate (SDS), dodecyltrimethylammonium chloride (DTAC) and lauric acid (LA), 12-carbon ligands possessing differently charged polar groups, were investigated using isothermal titration calorimetry and X-ray crystallography, to study the proton linkage phenomenon and to distinguish between effects related to different isoforms and different ligand properties. The determined values of ΔS and ΔH revealed that for all ligands, binding is entropically driven. The contribution from enthalpy change is lower and shows strong dependence on type of buffer that indicates proton release from the protein varying with protein isoform and ligand type and involvement of LA and Asp64 (in isoform A) in this process. The ligand affinities for both isoforms were arranged in the same order, DTAC < LA < SDS, and were systematically lower for variant B. The entropy change of the complexation process was always higher for isoform A, but these values were compensated by changes in enthalpy, resulting in almost identical ΔG for complexes of both isoforms. The determined crystal structures showed that substitution in positions 64 and 118 did not influence the overall structure of LGB complexes. The chemical character of the ligand polar group did not affect the position of its aliphatic chain in protein β-barrel, indicating a major role of hydrophobic interactions in ligand binding that prevailed even with the repulsion between positively charged DTAC and lysine residues located at binding site entrance.

Bovine β-lactoglobulin/fatty acid complexes: binding, structural, and biological properties

Ligand-binding properties of β-lactoglobulin (β-lg) are well documented, but the subsequent biological functions are still unclear. Focusing on fatty acids/β-lg complexes, the structure-function relationships are reviewed in the light of the structural state of the protein (native versus non-native aggregated proteins). After a brief description of β-lg native structure, the review takes an interest in the binding properties of native β-lg (localization of binding sites, stoichiometry, and affinity) and the way the interaction affects the biological properties of the protein and the ligand. The binding properties of non-native aggregated forms of β-lg that are classically generated during industrial processing are also related. Structural changes modify the stoichiometry and the affinity of β-lg for fatty acids and consequently the biological functions of the complex. Finally, the fatty acid-binding properties of other whey proteins (α-lactalbumin, bovine serum albumin) and some biological properties of the complexes are also addressed. These proteins affect β-lg/fatty acids complex in whey given their competition with β-lg for fatty acids.

Artificial metalloenzymes derived from bovine β-lactoglobulin for the asymmetric transfer hydrogenation of an aryl ketone – synthesis, characterization and catalytic activity

Protein hybrids resulting from the supramolecular anchoring to bovine β-lactoglobulin of fatty acid-derived Rh(iii) diimine complexes catalysed the asymmetric transfer hydrogenation of trifluoroacetophenone with up to 32% ee.

Ligand binding and self-association cooperativity of β-lactoglobulin

Unlike most small globular proteins, lipocalins lack a compact hydrophobic core. Instead, they present a large central cavity that functions as the primary binding site for hydrophobic molecules. Not surprisingly, these proteins typically exhibit complex structural dynamics in solution, which is intricately modified by intermolecular recognition events. Although many lipocalins are monomeric, an increasing number of them have been proven to form oligomers. The coupling effects between self-association and ligand binding in these proteins are largely unknown. To address this issue, we have calorimetrically characterized the recognition of dodecyl sulfate by bovine β-lactoglobulin, which forms weak homodimers at neutral pH. A thermodynamic analysis based on coupled-equilibria revealed that dimerization exerts disparate effects on the ligand-binding capacity of β-lactoglobulin. Protein dimerization decreases ligand affinity (or, reciprocally, ligand binding promotes dimer dissociation). The two subunits in the dimer exhibit a positive, entropically driven cooperativity. To investigate the structural determinants of the interaction, the crystal structure of β-lactoglobulin bound to dodecyl sulfate was solved at 1.64 Å resolution.

Characterization of the covalent binding of allyl isothiocyanate to β-lactoglobulin by fluorescence quenching, equilibrium measurement, and mass spectrometry

Reversible binding of small compounds through hydrophobic interactions or hydrogen bonding to food proteins (e.g. milk proteins) is a thoroughly researched topic. In contrast, covalent interactions are not well characterized. Here, we report a rare form of positive-cooperativity-linear binding of allyl isothiocyanate with β-lactoglobulin, resulting in the cleavage of a disulfide bond of the protein. We compared three methods (i.e. fluorescence quenching, equilibrium dialysis, and headspace-water equilibrium) to characterize the binding kinetics and investigated the molecular binding by mass spectrometry. The methodologies used were found to be comparable and reproducible in the presence of high and low ligand concentrations for fluorescence quenching and equilibrium-based methods respectively.

Interactions of β-lactoglobulin variants A and B with Vitamin A. Competitive binding of retinoids and carotenoids

β-Lactoglobulin (β-Lg) is the major whey protein of bovine milk present at a concentration of 2-3 g L(-1). Its biological role is still not well-known. However, many studies have suggested that β-Lg may play either nutritional or specific transporter role. The high affinity of β-Lg for retinol and other retinoids was reported. The results of interaction studies of β-Lg with carotenoids, that is, β-carotene, β-cryptoxanthin, and α-carotene, which display similar structures are reported in this study. The affinities of β-Lg for binding of retinoids and carotenoids were compared, providing more information about the binding site(s) of these molecules by β-Lg. Interactions were followed by the measurements of quenching of β-Lg tryptophan fluorescence and retinol fluorescence. The obtained results indicate that carotenoids are bound by β-Lg with high affinity of the order of 10(-8) M. Measurement of retinol competition with carotenoids for binding by β-Lg suggests that the binding of these two ligands occurs at two different sites of β-Lg.

β-Lactoglobulin as a molecular carrier of linoleate: characterization and effects on intestinal epithelial cells in vitro

The dairy protein β-lactoglobulin (βlg) is known to bind hydrophobic ligands such as fatty acids. In the present work, we investigated the biological activity in vitro of linoleate once complexed to bovine βlg. Binding of linoleate (C18:2) to bovine βlg was achieved by heating at 60 °C for 30 min at pH 7.4, resulting in a linoleate/βlg molar binding stoichiometry of 1.1, 2.1, and 3.4. Two types of binding sites were determined by ITC titrations. Binding of linoleate induced the formation of covalent dimers and trimers of βlg. The LD(50) on Caco-2 cells after 24 h was 58 μM linoleate. However, cell viability was unaffected when 200 μM linoleate was presented to the Caco-2 cells as part of the βlg complex. The Caco-2 cells did not increase mRNA transcript levels of long chain fatty acid transport genes, FATP4 and FABPpm, or increase levels of the cAMP signal, in response to the presence of 50 μM linoleate alone or as part of the βlg complex. Therefore, it is proposed that βlg can act as a molecular carrier and alter the bioaccessibility of linoleate/linoleic acid.

Dynamics and binding affinity of spin-labeled stearic acids in β-lactoglobulin: evidences from EPR spectroscopy and molecular dynamics simulation

β-Lactoglobulin (β-LG) is a member of the lipocalin protein family involved in the transport of fatty acids and other small hydrophobic molecules. The main binding site is at a central cavity, referred to as "calyx", formed by the protein β-barrel sandwich. Continuous-wave and pulsed Fourier transform electron spin resonance (cw- and FT-EPR) spectroscopy and molecular dynamics (MD) simulation were combined to investigate the interaction of fatty acids with bovine β-LG. Stearic acid bearing the nitroxide label at different positions, n, along the acyl chain (n-SASL, n = 5, 7, 10, 12, 16) were used. The EPR data show that the protein affinity for SASL decreases on going from n = 5 to 16. This behavior is due to the accommodation of the SASL in the protein calyx, which is hampered by steric hindrance of the doxyl ring for n ≥ 10, as evidenced by MD data. Conformation and dynamics of 5-SASL are similar to those of the unlabeled stearate molecule. 5-SASL in the protein binding site undergoes librational motion of small amplitude on the nanosecond time scale at cryogenic temperature and rotational dynamics with correlation time of 4.2 ns at physiological temperature. The results highlight the dynamical features of fatty acids/β-LG interaction.

Effect of gastric conditions on β-lactoglobulin interfacial networks: influence of the oil phase on protein structure

Understanding the effects of digestion conditions on the structure of interfacial protein networks is important in order to rationally design food emulsions which can moderate lipid digestion. This study compares the effect of gastric conditions (pH, temperature, and ionic strength) on β-lactoglobulin films at different fluid interfaces: air-water, tetradecane-water, and olive oil-water. The experiments have been designed to simulate the passage into the stomach media. Hence, preformed interfacial protein (β-lactoglobulin) networks have been exposed to gastric conditions in order to establish generic aspects of the digestion process. The results show that the presence of an oil phase affects both the unfolding of the protein at the interface on adsorption and the subsequent interprotein associations responsible for network formation at the interface. Furthermore, the effects of the physiological conditions characteristic of the stomach also altered differently the preformed protein layer at different fluid interfaces. Initially, the effects of temperature, acid pH, and ionic strength on the dilatational modulus of β-lactoglobulin adsorbed layers at tetradecane-water and olive oil-water interfaces were studied in isolation. The presence of salt was found to have a major effect on the dilatational response at the oil-water interface in contrast to the observations at the air-water interface: it enhanced intermolecular association, hence increasing the packing at the interface causing it to become more elastic. Exposure to acid pH (2.5) also increased the elasticity of the interface, possibly due to the fact that strong electrostatic interactions acting at the interface compensated for the reduced level of intermolecular association. However, the increase in dilatational modulus at the oil-water interface was less noticeable upon exposure to combined changes in acid pH and ionic strength, as would occur in the stomach. This is consistent with previously reported observations at the air-water interface. The quantitative differences in the response of the protein networks to gastric media at different fluid interfaces are discussed in terms of the conformation of β-lactoglobulin within the networks formed at each interface based on detailed theoretical modeling of adsorption data.