Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “LACTOGLOBULINS”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,351 records · Page 75Linked to original sources
PubMed2000

Comparison of heat and pressure treatments of skim milk, fortified with whey protein concentrate, for set yogurt preparation: effects on milk proteins and gel structure.

Heat (85 degrees C for 20 min) and pressure (600 MPa for 15 min) treatments were applied to skim milk fortified by addition of whey protein concentrate. Both treatments caused > 90 % denaturation of beta-lactoglobulin. During heat treatment this denaturation took place in the presence of intact casein micelles; during pressure treatment it occurred while the micelles were in a highly dissociated state. As a result micelle structure and the distribution of beta-lactoglobulin were different in the two milks. Electron microscopy and immunolabelling techniques were used to examine the milks after processing and during their transition to yogurt gels. The disruption of micelles by high pressure caused a significant change in the appearance of the milk which was quantified by measurement of the colour values L*, a* and b*. Heat treatment also affected these characteristics. Casein micelles are dynamic structures, influenced by changes to their environment. This was clearly demonstrated by the transition from the clusters of small irregularly shaped micelle fragments present in cold pressure-treated milk to round, separate and compact micelles formed on warming the milk to 43 degrees C. The effect of this transition was observed as significant changes in the colour indicators. During yogurt gel formation, further changes in micelle structure, occurring in both pressure and heat-treated samples, resulted in a convergence of colour values. However, the microstructure of the gels and their rheological properties were very different. Pressure-treated milk yogurt had a much higher storage modulus but yielded more readily to large deformation than the heated milk yogurt. These changes in micelle structure during processing and yogurt preparation are discussed in terms of a recently published micelle model.

Animals↗
PubMed2000

Angiotensin I-converting enzyme inhibitory properties of whey protein digests: concentration and characterization of active peptides.

The aim of this study was to identify whey-derived peptides with angiotensin I-converting enzyme (ACE) inhibitory activity. The bovine whey proteins alpha-lactalbumin and beta-lactoglobulin were hydrolysed with pepsin, trypsin, chymotrypsin, pancreatin, elastase or carboxypeptidase alone and in combination. The total hydrolysates were fractionated in a two step ultrafiltration process, first with a 30 kDa membrane and then with a 1 kDa membrane. Inhibition of ACE was analysed spectrophotometrically. The peptides were isolated by chromatography and identified by mass and sequencing analysis. The most potent inhibitory peptides were synthesized by the 9-fluorenylmethoxycarbonyl solid phase method. Inhibition of ACE was observed after hydrolysis with trypsin alone, and with an enzyme combination containing pepsin, trypsin and chymotrypsin. Whey protein digests gave a 50% inhibition (IC50) of ACE activity at concentration ranges within 345-1733 micrograms/ml. The IC50 values for the 1-30 kDa fractions ranged from 485 to 1134 micrograms/ml and for the < 1 kDa fraction from 109 to 837 mg/ml. Several ACE-inhibitory peptides were isolated from the hydrolysates by reversed-phase chromatography, and the potencies of the purified peptide fractions had IC50 values of 77-1062 microM. The ACE-inhibitory peptides identified were alpha-lactalbumin fractions (50-52), (99-108) and (104-108) and beta-lactoglobulin fractions (22-25), (32-40), (81-83), (94-100), (106-111) and (142-146).

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1993

Retinol uptake from retinol-binding protein (RBP) by liver parenchymal cells in vitro does not specifically depend on its binding to RBP.

The uptake characteristics of both the retinol and retinol-binding protein (RBP) moieties of the retinol-RBP complex by liver parenchymal cells (PC) in vitro were studied to assess whether retinol uptake is mediated by a cell-surface receptor for RBP. At 37 degrees C as well as 4 degrees C, [3H]retinol uptake from [3H]retinol-RBP showed a time-dependent increase, and was not saturable at concentrations exceeding the physiological concentration by more than a factor of 2 (3 microM). Uptake of [3H]retinol was not inhibited by a 10-fold molar excess of unlabeled retinol-RBP. Cell association of 125I-RBP at 37 and 4 degrees C was low and showed no time dependence. In addition, the association of 125I-RBP was not saturable at concentrations up to 3 microM. These data do not support the existence of a cell-surface receptor for RBP on rat liver PC. The uptake of [3H]retinol from RBP was also compared to the uptake of retinol from cellular retinol-binding protein (CRBP) and lactoglobulin. Uptake characteristics of [3H]retinol from CRBP and lactoglobulin were similar to that of [3H]retinol from RBP. Furthermore, a similar percentage of the [3H]retinol taken up by PC was metabolized into retinyl esters, irrespective of its carrier. These data suggest that the uptake of retinol and its subsequent metabolic processing do not depend on binding to RBP. The low level of cell association of 125I-binding proteins was not due to uptake, degradation, and secretion of ligand by PC. This suggests that retinol is dissociated from its binding protein before uptake by PC.

Animals↗
PubMed1985

Mechanism of poly(ethylene glycol) interaction with proteins.

Poly(ethylene glycol) (PEG) is one of the most useful protein salting-out agents. In this study, it has been shown that the salting-out effectiveness of PEG can be explained by the large unfavorable free energy of its interaction with proteins. Preferential interaction measurements of beta-lactoglobulin with poly(ethylene glycols) with molecular weights between 200 and 1000 showed preferential hydration of the protein for those with Mr greater than or equal to 400, the degree of hydration increasing with the increase in poly(ethylene glycol) molecular weight. The preferential interaction parameter had a strong cosolvent concentration dependence, with poly(ethylene glycol) 1000 having the sharpest decrease with an increase in concentration. The preferential hydration extrapolated to zero cosolvent concentration increased almost linearly with increasing size of the additive, suggesting steric exclusion as the major factor responsible for the preferential hydration. The poly(ethylene glycol) concentration dependence of the preferential interactions could be explained in terms of the nonideality of poly(ethylene glycol) solutions. All the poly(ethylene glycols) studied, when used at levels of 10-30%, decreased the thermal stability of beta-lactoglobulin, suggesting that caution must be exercised in the use of this additive at extreme conditions such as high temperature.

Guanidine↗
PubMed1987

Thermal stability of proteins in the presence of poly(ethylene glycols).

Thermal unfolding of ribonuclease, lysozyme, chymotrypsinogen, and beta-lactoglobulin was studied in the absence or presence of poly(ethylene glycols). The unfolding curves were fitted to a two-state model by a nonlinear least-squares program to obtain values of delta H, delta S, and the melting temperature Tm. A decrease in thermal transition temperature was observed in the presence of poly(ethylene glycol) for all of the protein systems studied. The magnitude of such a decrease depends on the particular protein and the molecular size of poly(ethylene glycol) employed. A linear relation can be established between the magnitude of the decrease in transition temperature and the average hydrophobicity of these proteins; namely, the largest observable decrease is associated with the protein of the highest hydrophobicity. Further analysis of the thermal unfolding data reveals that poly(ethylene glycols) significantly effect the relation between delta H degrees of unfolding and temperature for all the proteins studied. For beta-lactoglobulin, a plot of delta H versus Tm indicates a change in slope from a negative to a positive value, thus implying a change in delta Cp in thermal unfolding caused by the presence of poly(ethylene glycols). Results from solvent-protein interaction studies indicate that at high temperature poly(ethylene glycol) 1000 preferentially interacts with the denatured state of protein but is excluded from the native state at low temperature. These observations are consistent with the fact that poly(ethylene glycols) are hydrophobic in nature and will interact favorably with the hydrophobic side chains exposed upon unfolding; thus, it leads to a lowering of thermal transition temperature.

Chymotrypsinogen↗
PubMed1999

Formation of domains of cationic or anionic lipids in binary lipid mixtures increases the electrostatic coupling strength of water-soluble proteins to supported bilayers.

The electrostatic binding strength of water-soluble proteins having either an excess positive (cytochrome c) or negative (beta-lactoglobulin) electric charge to oppositely charged supported planar bilayers (SPBs) was studied as a function of the bilayer phase state (fluid or gel phase) by IR-ATR spectroscopy. The bilayer consisted of mixtures of zwitterionic DEPC with either cationic DMTAP or anionic DMPG. We observed drastic differences in the binding strength of both proteins for the two bilayer phase states, with the gel phase exhibiting a higher binding strength than the fluid phase, under conditions where the two lipid components had different hydrophobic chain lengths resulting in a nonideal mixing behavior. In addition, for beta-lactoglobulin we observed a strong binding to a gel phase SPB comprising DEPC/DMTAP, while raising the temperature of the SPB above the chain melting transition temperature of the mixture resulted in a complete unbinding of the protein. In contrast, for DMPC/DMTAP having the same cationic charge content but no hydrophobic chain mismatch, no phase-dependent coupling strength of the protein to the SPB was observed. Our results suggest that the formation of charge-enriched domains by partial demixing of the bilayer lipids at the transition to the gel state is crucial for modulation of the protein binding strength to the SPB, while the intrinsic charge of the solid support surface is of minor importance.

Animals↗
PubMed2006

Shear flow induces amyloid fibril formation.

Shear flow is indirectly implicated in amyloid formation in vitro. Despite the association between amyloid fibrils and disease, and the prevalence of flow in physiological systems, the effect of this parameter is uncharacterized. We designed a novel Couette cell to quantitatively investigate shear exposure during fibrillogenesis. Amyloid formation by beta-lactoglobulin was monitored in situ with real-time fluorescence measurements across a range of shear rates. We demonstrate shear-induced aggregation of spheroidal seed-like species. These seeds enhance fibril formation in native beta-lactoglobulin, thereby demonstrating that shear flow generates an amyloidogenic precursor. Furthermore, preformed fibrils are degraded by exposure to high shear rates. Our results have implications for the mechanism of amyloid formation in physiological flow conditions.

Amyloid↗
PubMed2000

Mechanism and characteristics of protein release from lactitol-based cross-linked hydrogel.

Lactitol-based cross-linked hydrogel was synthesized, and model proteins (alpha-chymotrypsin, beta-lactoglobulin, bovine serum albumin (BSA), and gamma-globulin) were incorporated into the cross-linked hydrogel. The larger-molecular-weight proteins have lower diffusivity (D(e)) in the hydrogel. Increasing temperature accelerated the diffusion rate of proteins; however, the diffusion did not follow the Arrhenius equation at temperatures above 37 degrees C. The swelling ratio of the hydrogel was slightly decreased after heating for 2 h at 37 and 45 degrees C, and significantly reduced after 1 h at 60 degrees C. Therefore, diffusion of beta-lactoglobulin and BSA may be decreased by hydrogel shrinking at temperature over 37 degrees C. The model proteins have high affinities to buffer solution compared to the hydrogel network structure, resulting in high partition coefficients (K > 1) which do not affect the calculation of D(e) values. Incorporated protein release follows the theory of hindered diffusion.

Animals↗
PubMed2002

Transfer of aroma compounds through the lipidic-aqueous interface in a complex system.

The transfer kinetics of aroma compounds from the aqueous phase to the lipidic phase (miglyol) and from miglyol to the aqueous phase have been studied in the presence or absence of a protein, beta-lactoglobulin, and at different pH values. In the presence of beta-lactoglobulin, the transfer at the interface from the aqueous to the lipidic phase decreases, with a greater effect of the presence of the protein at pH 3 than at pH 6. This barrier effect of the protein plays a role in the transfer of the aroma compounds between the different phases of the matrix.

Aldehydes↗
PubMed2002

Physical and chemical interactions in cold gelation of food proteins.

pH-Induced cold gelation of whey proteins is a two-step process. After protein aggregates have been prepared by heat treatment, gelation is established at ambient temperature by gradually lowering the pH. To demonstrate the importance of electrostatic interactions between aggregates during this latter process, beta-lactoglobulin aggregates with a decreased iso-electric point were prepared via succinylation of primary amino groups. The kinetics of pH-induced gelation was affected significantly, with the pH gelation curves shifting to lower pH after succinylation. With increasing modification, the pH of gelation decreased to about 2.5. In contrast, unmodified aggregates gel around pH 5. Increasing the iso-electric point of beta-lactoglobulin via methylation of carboxylic acid groups resulted in gelation at more alkaline pH values. Comparable results were obtained with whey protein isolate. At low pH disulfide cross-links between modified aggregates were not formed after gelation and the gels displayed both syneresis and spontaneous gel fracture, in this way resembling the morphology of previously characterized thiol-blocked whey protein isolate gels (Alting, et al., J. Agric. Food Chem. 2000, 48, 5001-5007). Our results clearly demonstrate the importance of the net electric charge of the aggregates during pH-induced gelation. In addition, the absence of disulfide bond formation between aggregates during low-pH gelation was demonstrated with the modified aggregates.

Chemical Phenomena↗
PubMed2003

Headspace solid-phase microextraction method for the study of the volatility of selected flavor compounds.

Changes in the volatility of selected flavor compounds in the presence of nonvolatile food matrix components were studied using headspace solid-phase microextraction (HS-SPME) combined with GC-MS quantification. Time-dependent adsorption profiles to the SPME fiber and the partition coefficients between different phases were obtained for several individual volatiles, showing that HS-SPME analysis with a short sampling time can be used to determine the "true" headspace concentration at equilibrium between the headspace and a sample matrix. Equilibrium dialysis followed by HS-SPME/GC-MS was carried out to confirm the ability of HS-SPME extraction for monitoring the free volatile compounds in the presence of proteins. In particular, a short sampling time (1 min) avoided additional extraction of volatiles bound to the protein. Interactions between several selected flavor compounds and nonvolatile food matrix components [beta-lactoglobulin or (+)-catechin] were also studied by means of HS-SPME/GC-MS analysis. The volatility of ethyl hexanoate, heptanone, and hexanal was significantly decreased by the addition of beta-lactoglobulin compared to that of isoamyl acetate. Catechin decreased the volatility of ethyl hexanoate and hexanal by 10-20% and increased that of 2-heptanone by approximately 15%. This study indicates that HS-SPME can be a useful tool for the study of the interactions between volatile compounds and nonvolatile matrix components provided the kinetic and thermodynamic behavior of the volatiles in relation to the fiber chosen for the studies is carefully considered.

Adsorption↗
PubMed2004

Heat-induced changes in the ultrasonic properties of whey proteins.

The physical aggregation of commercial whey protein isolate (WPI) and purified beta-lactoglobulin was studied by ultrasound spectroscopy. Protein samples were dialyzed to achieve constant ionic strength backgrounds of 0.01 and 0.1 NaCl, and gelation was induced in situ at constant temperatures (from 50 to 75 degrees C) or with a temperature ramp from 20 to 85 degrees C. Changes in the ultrasonic properties were shown in the early stages of heating, at temperatures below those reported for protein denaturation. During heating, the relative ultrasound velocity (defined as the difference between sample velocity and reference velocity) decreased continuously with temperature, indicating a rearrangement of the hydration layer of the protein and an increase in compressibility of the protein shell. At temperatures <50 degrees C the ultrasonic attenuation decreased, and <65 degrees C both velocity and attenuation differentials showed increasing values. A sharp decrease in the relative velocity and an increase in the attenuation at 70 degrees C were indications of "classical" protein denaturation and the formation of a gel network. Values of attenuation were significantly different between samples prepared with 0.01 and 0.1 M NaCl, although no difference was shown in the overall ultrasonic behavior. WPI and beta-lactoglobulin showed similar ultrasonic properties during heating, but some differences were noted in the values of attenuation of WPI solutions, which may relate to a less homogeneous distribution of aggregates caused by the presence of alpha-lactalbumin and other minor proteins in WPI.

Chemical Phenomena↗
PubMed1999

Raman spectral analysis in the C-H stretching region of proteins and amino acids for investigation of hydrophobic interactions.

Raman spectra of amino acids showed complexity in the C-H stretching region (2800-3100 cm(-)(1)) attributed to diversity of CH, CH(2), and CH(3) groups in the side chains, ionization state, and microenvironment. The involvement of specific amino acids in the C-H stretching region of selected proteins, namely, lysozyme, alpha-lactalbumin, beta-lactoglobulin, and their binary mixtures, was investigated by deconvolution using maximum likelihood techniques. The main protein band near 2940 cm(-)(1) was attributed not only to aromatic and aliphatic amino acids but also to many other amino acids. A band near 3065 cm(-)(1) was assigned to aromatic residues, whereas bands near 2880 and 2900 cm(-)(1) corresponded primarily to aliphatic amino acids. Heating at 90 degrees C increased relative intensity near 2940 cm(-)(1) and decreased relative intensity at 2895-2902 cm(-)(1) for lysozyme and its mixtures with alpha-lactalbumin or beta-lactoglobulin. Additional bands at 2812 or 2838 and 3003 cm(-)(1) were observed after heating or in 8 M deuterated urea, reflecting changes upon denaturation.

Amino Acids↗
PubMed1999

Enhancement of the foaming properties of protein dried in the presence of trehalose.

Surface tension, foamability, and foam stability kinetics have been measured for the pure proteins bovine serum albumin (BSA) and beta-lactoglobulin, before and after aqueous solutions of the proteins had been subjected to different drying conditions, and also for whey protein concentrate (WPC). Pure proteins were air-dried, at 78 or 88 degrees C, in the presence and absence of sucrose or trehalose, at a mass ratio of 5:1 sugar/protein. WPC was spray-dried in the presence of various sugars: trehalose, sucrose, lactose, and lactitol. Spray-drying WPC without sugars resulted in a dramatic decrease in the foam stability, whereas drying in the presence of sugars gave better retention of the original foaming properties. Trehalose in particular resulted in almost complete retention of the foam stability observed for the nondried WPC. Pure beta-lactoglobulin showed similar behavior, but trehalose did not seem to afford the same protection to BSA.

Animals↗
PubMed2004

Depletion-flocculation in oil-in-water emulsions using fibrillar protein assemblies.

This paper shows that low concentrations of beta-lactoglobulin fibrils can induce depletion-flocculation in beta-lactoglobulin-stabilized oil-in-water emulsions. The minimum required fibril concentration for flocculation was determined experimentally for fibril lengths of about 3 and 0.1 microm. The minimum fibril concentration for flocculation is two orders of magnitude higher for the short fibrils than for the long ones. These experimental results correspond well with a theoretical prediction based on a model of spinodal decomposition. In addition, rheological measurements were performed, verifying that flocculation was induced by a depletion mechanism. The results of this study show that the minimum concentration required for depletion-flocculation can be tuned by varying the length of the fibrils.

Emulsions↗
PubMed2007

Chemical nature of stochastic generation of protein-based carbonyls: metal-catalyzed oxidation versus modification by products of lipid oxidation.

An assessment of 2,4-dinitrophenylhydrazine (DNPH)-detectable protein-based carbonyls is one of the most common assays used to quantify oxidative stress in vitro and in vivo. In this study, we compared, for the lipid-binding protein beta-lactoglobulin, the extent to which carbonyl reactivity could be introduced by adventitious metal-catalyzed oxidation (MCO) in the absence and presence of a polyunsaturated lipid or by treatment with various individual bifunctional lipid oxidation products capable of introducing carbonyls into proteins by adduction to nucleophilic side chains. With metal ions and either O2/reductant or H2O2 as the terminal oxidant, the maximal level of DNPH-detectable carbonyl generation obtainable in several hours was 0.1-0.2 mol carbonyl per mol protein monomer, with Cu(II) being more effective than Fe(II). Exposure instead to bifunctional lipoxidation-derived aldehydes (1-2 mM) generated in some cases in excess of 1 mol carbonyl per mol protein. The rank order of carbonyl incorporation reactivity was acrolein > 4-oxo-2-nonenal > 4-hydroxy-2-nonenal > 2,4-decadienal > malondialdehyde. Protein cross-linking ability followed a somewhat different rank order. Parallel studies on reductively methylated beta-lactoglobulin revealed that His and Cys residues are intrinsically more responsible than Lys residues for carbonyl appearance and that the availability of Lys residues accounts for the reduction of carbonyl content at later time (presumably reflecting cross-linking chemistry) that occurs for acrolein and 4-oxo-2-nonenal. Overall, these results suggest that DNPH reactivity observed physiologically on nonmetalloproteins may arise more from the attachment of lipid-derived products of oxidative stress than from adventitious MCO of side chains. Additional studies carried out to clarify the potential use of DNPH derivatization to tag peptide-based carbonyls for mass spectrometric analysis revealed that DNPH derivatization can reverse under the conditions used for proteolysis.

Catalysis↗
PubMed2003

Milk protein polymorphism in Kangayam cattle.

This paper reports the milk protein polymorphism, the allele frequencies of variants and the possible linkages among various combinations of milk protein phenotypes in the Kangayam cattle of south India. Milk samples from 156 Kangayam cows were typed by starch gel and polyacrylamide gel electrophoresis for caseins and whey proteins, respectively. All the four milk protein components studied, alpha(s)1-casein. beta-casein, beta-lactoglobulin and alpha-lactalbumin, exhibited polymorphism with high allele frequencies of 0.9231 +/- 0.0151 for alpha(s)1-casein C, 0.9263 +/- 0.0148 for beta-casein A, 0.9135 +/- 0.0159 for beta-lactoglobulin B and a relatively high frequency of 0.6218 +/- 0.0275 for alpha-lactalbumin A. The mean heterozygosity estimated over all the four milk protein loci was 0.2420. Genetic equilibrium was observed among all the loci studied, except alpha-lactalbumin. Linkage analysis confirmed the non-independence between alpha(s)1- and beta-caseins and between caseins and alpha-lactalbumin phenotypes.

Animals↗
PubMed1992

Rescuing transgene expression by co-integration.

To test whether foreign gene expression can be improved in transgenic mice by manipulating the site of integration, we co-integrated the efficiently expressed sheep beta-lactoglobulin gene with two poorly expressed beta-lactoglobulin-derived hybrid genes encoding human proteins. In each case, we observed a significant improvement in the frequency and level of expression of the hybrid gene. "Rescuing" transgene expression by co-integration may provide a general solution for improving the efficiency of heterologous gene expression in transgenic animals.

Animals↗