The Experts below are selected from a list of 324 Experts worldwide ranked by ideXlab platform
Eric A Decker - One of the best experts on this subject based on the ideXlab platform.
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effect of interfacial protein cross linking on the in vitro digestibility of emulsified corn oil by pancreatic lipase
Journal of Agricultural and Food Chemistry, 2008Co-Authors: Sandra Sandra, Eric A Decker, David Julian McclementsAbstract:The objective of this study was to investigate the influence of globular protein interfacial cross-linking on the in vitro digestibility of emulsified lipids by pancreatic lipase. 3% (wt/wt) corn oil-in-water emulsions stabilized by either lecithin or Beta-Lactoglobulin were prepared (pH 7). A portion of the Beta-Lactoglobulin stabilized emulsions was subjected to a heat treatment known to cross-link the adsorbed globular proteins (85 degrees C, 20 min). Pancreatic lipase and bile extract were then added to each emulsion at 37 degrees C (pH 7) and the evolution of the particle charge, particle size, appearance and free fatty acids released were measured over a period of 2 h. The rate and extent of lipid digestion did not differ greatly between lecithin and Beta-Lactoglobulin stabilized emulsions, nor did it differ greatly for unheated (BLG-U) or heated (BLG-H) Beta-Lactoglobulin stabilized emulsions. For example, the initial rate of lipid digestion was found to be 3.1, 3.4, and 2.3 mM fatty acids s(-1) m(-2) of lipid surface for droplets stabilized by BLG-U, BLG-H, and lecithin, respectively. Pancreatic lipase was able to adsorb to the droplet surfaces and access the emulsified lipids, regardless of the initial interfacial composition and the fact that some of the original emulsifier appeared to remain at the oil-water interface during digestion. These results help to explain why the human body is so efficient at digesting dietary triacylglycerols.
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antioxidant mechanisms of enzymatic hydrolysates of beta lactoglobulin in food lipid dispersions
Journal of Agricultural and Food Chemistry, 2006Co-Authors: Ryan J Elias, David Julian Mcclements, J D Bridgewater, R W Vachet, Thaddao Waraho, Eric A DeckerAbstract:The antioxidant activities of aqueous phase Beta-Lactoglobulin (beta-Lg) and its chymotryptic hydrolysates (CTH) were compared in this study. Proteins and peptides have been shown to inhibit lipid oxidation reactions in oil-in-water emulsions; however, a more fundamental understanding of the antioxidant activity of these compounds in dispersed food lipid systems is lacking. CTH was more effective than an equivalent concentration of beta-Lg in retarding lipid oxidation reactions when dispersed in the continuous phase of Brij-stabilized oil-in-water emulsions (pH 7). Furthermore, it was observed that CTH had higher peroxyl radical scavenging and iron-binding values than beta-Lg. Liquid chromatography-mass spectrometry (LC-MS) was used to measure the rate of oxidation of three oxidatively labile amino acid residues (Tyr, Met, and Phe) in certain CTH peptide fragments. Significant oxidation of specific Tyr and Met residues present in two separate 12 amino acid peptide fragments was observed in the days preceding lipid oxidation (39 and 55% of Tyr and Met were oxidized, respectively, by day 4 of the study); however, no significant oxidation of the Phe residue present in a specific 14 amino acid peptide fragment could be observed during the same time period. These data could suggest that Met and Tyr residues are capable of scavenging radical species and have the potential to improve the oxidative stability dispersed food lipids.
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antioxidant activity of cysteine tryptophan and methionine residues in continuous phase β lactoglobulin in oil in water emulsions
Journal of Agricultural and Food Chemistry, 2005Co-Authors: Ryan J Elias, Julian D Mcclements, Eric A DeckerAbstract:Proteins dispersed in the continuous phase of oil-in-water emulsions are capable of inhibiting lipid oxidation reactions. The antioxidant activity of these proteins is thought to encompass both free radical scavenging by amino acid residues and chelation of prooxidative transition metals; however, the precise mechanism by which this occurs remains unclear. In this study, the oxidative stability of cysteine, tryptophan, and methionine residues in continuous phase Beta-Lactoglobulin (beta-Lg) in a Brij-stabilized menhaden oil-in-water emulsion was determined. The presence of low concentrations of continuous phase beta-Lg (250 and 750 microg/mL) significantly inhibited lipid oxidation as determined by lipid hydroperoxides and thiobarbituric acid reactive substances analysis. It was observed that cysteine oxidized before tryptophan in beta-Lg, and both residues oxidized before lipid oxidation could be detected. No oxidation of the methionine residues of beta-Lg was observed despite its reported high oxidative susceptibility. It is conceivable that surface exposure of amino acid residues greatly affects their oxidation kinetics, which may explain why some residues are preferentially oxidized relative to others. Further elucidation of the mechanisms governing free radical scavenging of amino acids could lead to more effective applications of proteins as antioxidants within oil-in-water food emulsions.
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impact of whey protein emulsifiers on the oxidative stability of salmon oil in water emulsions
Journal of Agricultural and Food Chemistry, 2003Co-Authors: Julian D Mcclements, Eric A DeckerAbstract:To obtain a better understanding of how the interfacial region of emulsion droplets influences lipid oxidation, the oxidative stability of salmon oil-in-water emulsions stabilized by whey protein isolate (WPI), sweet whey (SW), Beta-Lactoglobulin (beta-Lg), or alpha-lactalbumin (alpha-La) was evaluated. Studies on the influence of pH on lipid oxidation in WPI-stabilized emulsions showed that formation of lipid hydroperoxides and headspace propanal was much lower at pH values below the protein's isoelectric point (pI), at which the emulsion droplets were positively charged, compared to that at pH values above the pI, at which the emulsion droplets were negatively charged. This effect was likely due to the ability of positively charged emulsion droplets to repel cationic iron. In a comparison of lipid oxidation rates of WPI-, SW-, beta-Lg-, and alpha-La-stabilized emulsions at pH 3, the oxidative stability was in the order of beta-Lg > or = SW > alpha-La > or = WPI. The result indicated that it was possible to engineer emulsions with greater oxidative stability by using proteins as emulsifier, thereby reducing or eliminating the need for exogenous food antioxidants.
J P Simons - One of the best experts on this subject based on the ideXlab platform.
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mammary development and milk secretion in transgenic mice expressing the sheep β lactoglobulin gene
Biochemical Journal, 1992Co-Authors: Colin J Wilde, A J Clark, M A Kerr, Christopher H Knight, M Mcclenaghan, J P SimonsAbstract:Mammary development and milk secretion were studied in transgenic mice which exhibited mammary tissue-specific expression of the sheep Beta-Lactoglobulin gene, and secreted significant quantities of the foreign protein in milk. Mammary development was unaffected by transgenesis. Tissue DNA content and the activities of several key enzyme markers of cell differentiation were similar in transgenic mice and non-transgenic controls. Milk yield, whether estimated by pup weight gain or measured by a 3H2O-dilution method, was unchanged by foreign gene expression. Gross milk composition, including milk protein concentration, was also similar in transgenic and non-transgenic animals, even though Beta-Lactoglobulin accounted for 29% of total milk protein. Therefore the foreign gene product was synthesized at the expense of endogenous milk proteins. However, transgenic mammary tissue in vitro exhibited a significantly higher rate of total protein synthesis than did control tissue. This suggested that a factor limiting milk protein synthesis or secretion in transgenic mice in vivo may have been removed by short-term explant culture of mammary tissue. The results emphasize that the use of transgenesis for manipulating milk composition may depend not only on high-level mammary-specific expression of the foreign gene, but also on the biosynthetic capacity of the mammary gland itself.
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developmental regulation of the sheep β lactoglobulin gene in the mammary gland of transgenic mice
Developmental Genetics, 1991Co-Authors: S E Harris, J P Simons, M Mcclenaghan, A J ClarkAbstract:: Beta-Lactoglobulin (BLG) is the most abundant whey protein in sheep milk but it is not present in mouse milk. We have previously shown that transgenic mice carrying the BLG gene express it specifically in the mammary gland and secrete BLG into milk at high concentrations. Here we demonstrate that BLG transcription is correctly initiated in mice and that BLG synthesis is restricted to the secretory epithelial cells of the mammary gland. We have also determined the temporal pattern of milk protein gene expression and find that the BLG transgene is regulated coordinately with mouse beta-casein and that the patterns of regulation of BLG in mouse and sheep share some similarities.
Yuji Goto - One of the best experts on this subject based on the ideXlab platform.
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solution structure and dynamics of bovine beta lactoglobulin a
Protein Science, 2008Co-Authors: Kazuo Kuwata, Masaru Hoshino, Vincent Forge, Seiichi Era, Carl A Batt, Yuji GotoAbstract:Using heteronuclear NMR spectroscopy, we studied the solution structure and dynamics of bovine Beta-Lactoglobulin A at pH 2.0 and 45 degrees C, where the protein exists as a monomeric native state. The monomeric NMR structure, comprising an eight-stranded continuous antiparallel beta-barrel and one major alpha-helix, is similar to the X-ray dimeric structure obtained at pH 6.2, including betaI-strand that forms the dimer interface and loop EF that serves as a lid of the interior hydrophobic hole. [1H]-15N NOE revealed that betaF, betaG, and betaH strands buried under the major alpha-helix are rigid on a pico- to nanosecond time scale and also emphasized rapid fluctuations of loops and the N- and C-terminal regions.
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cooperative alpha helix formation of beta lactoglobulin and melittin induced by hexafluoroisopropanol
Protein Science, 1997Co-Authors: N Hirota, K Mizuno, Yuji GotoAbstract:Alcohols denature the native state of proteins, and also stabilize the alpha-helical conformation in unfolded proteins and peptides. Among various alcohols, trifluoroethanol (TFE) and hexafluoroisopropanol (HFIP) are often used because of their high potential to induce such effects. However, the reason why TFE and HFIP are more effective than other alcohols is unknown. Using CD, we studied the effects of TFE and HFIP as well as reference alcohols, i.e., methanol, ethanol, and isopropanol, on the conformation of bovine Beta-Lactoglobulin and the bee venom melittin at pH 2. Upon addition of alcohols, Beta-Lactoglobulin exhibited a transformation from the native state, consisting of beta-sheets, to the alpha-helical state, whereas melittin folded from the unfolded state to the alpha-helical state. In both cases, the order of effectiveness of alcohols was shown to be: HFIP > TFE > isopropanol > ethanol > methanol. The alcohol-induced transitions were analyzed assuming a two-state mechanism to obtain the m value, a measure of the dependence of the free energy change on alcohol concentration. Comparison of the m values indicates that the high potential of TFE can be explained by the additive contribution of constituent groups, i.e., F atoms and alkyl group. On the other hand, the high potential of HFIP is more than that expected from the additive effects, suggesting that the cooperative formation of micelle-like clusters of HFIP is important.
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high helical propensity of the peptide fragments derived from beta lactoglobulin a predominantly beta sheet protein
Journal of Molecular Biology, 1995Co-Authors: Daizo Hamada, Yutaka Kuroda, Toshiki Tanaka, Yuji GotoAbstract:Abstract It is generally assumed that peptide fragments derived from globular proteins are either unfolded, or adopt native-like secondary structures, in particular α-helix, which are similar to those occurring in the early stages of protein folding. Since the structured conformations of short peptides are unstable, 2,2,2-trifluoroethanol (TFE) is often used to stabilize them. To examine the folding process of β-proteins, we synthesized three fragments of β-lactoglobulin corresponding to two β-strands and one helix region, and examined their conformation by circular dichroism and nuclear magnetic resonance. These regions were chosen because, according to secondary structure prediction, all three should have high helix propensities. In aqueous solution, the three peptides had only a little ordered structure, but when TFE was added, they exhibited marked helical propensities, as also observed for the whole molecule of β-lactoglobulin. These results indicate that the intrinsic helical propensity of a peptide fragment elucidated by the addition of TFE is not necessarily related to the secondary structure in the native state. The results further suggest a case of non-hierarchical protein folding model, in which non-native structures may be involved in the early stage of folding.
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trifluoroethanol induced stabilization of the alpha helical structure of beta lactoglobulin implication for non hierarchical protein folding
Journal of Molecular Biology, 1995Co-Authors: Kentaro Shiraki, Ken Nishikawa, Yuji GotoAbstract:Trifluoroethanol (TFE) is known to stabilize the alpha-helical structure in proteins and their fragments. However, the relationship between the TFE-induced structures and the native structure is not clear. Here we show that Beta-Lactoglobulin, which consists predominantly of beta-sheets, exhibited a markedly high propensity to form an alpha-helical structure in the presence of TFE, as measured by far-UV circular dichroism. A cooperative transformation from the beta-sheet structure to an alpha-helical structure occurred at a TFE concentration between 10% and 20%. These results were in contrast to a gradual beta-sheet to alpha-helix transition of the constant fragment of the immunoglobulin light chain, which is also a beta-sheet protein. To understand the significance of the high helical propensity of Beta-Lactoglobulin, we measured the TFE-induced conformational transition of more than 20 proteins of various secondary structural types. Whereas the alpha-helical proteins showed a propensity to form an extensive helical structure in TFE, the helical propensity of proteins with a low helical content in the native state varied. The helical content in TFE was correlated more with the helical content predicted by a secondary structure prediction than with the helical content of the native structure, suggesting that the stability of the helical structure in TFE is determined by local interactions between nearby amino acid residues. Our results suggest that an alpha-helical intermediate can accumulate during the refolding process of Beta-Lactoglobulin and that a hierarchical model of protein folding is not necessarily true for some beta-sheet proteins including Beta-Lactoglobulin.
David Julian Mcclements - One of the best experts on this subject based on the ideXlab platform.
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effect of interfacial protein cross linking on the in vitro digestibility of emulsified corn oil by pancreatic lipase
Journal of Agricultural and Food Chemistry, 2008Co-Authors: Sandra Sandra, Eric A Decker, David Julian McclementsAbstract:The objective of this study was to investigate the influence of globular protein interfacial cross-linking on the in vitro digestibility of emulsified lipids by pancreatic lipase. 3% (wt/wt) corn oil-in-water emulsions stabilized by either lecithin or Beta-Lactoglobulin were prepared (pH 7). A portion of the Beta-Lactoglobulin stabilized emulsions was subjected to a heat treatment known to cross-link the adsorbed globular proteins (85 degrees C, 20 min). Pancreatic lipase and bile extract were then added to each emulsion at 37 degrees C (pH 7) and the evolution of the particle charge, particle size, appearance and free fatty acids released were measured over a period of 2 h. The rate and extent of lipid digestion did not differ greatly between lecithin and Beta-Lactoglobulin stabilized emulsions, nor did it differ greatly for unheated (BLG-U) or heated (BLG-H) Beta-Lactoglobulin stabilized emulsions. For example, the initial rate of lipid digestion was found to be 3.1, 3.4, and 2.3 mM fatty acids s(-1) m(-2) of lipid surface for droplets stabilized by BLG-U, BLG-H, and lecithin, respectively. Pancreatic lipase was able to adsorb to the droplet surfaces and access the emulsified lipids, regardless of the initial interfacial composition and the fact that some of the original emulsifier appeared to remain at the oil-water interface during digestion. These results help to explain why the human body is so efficient at digesting dietary triacylglycerols.
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formation of hydrogel particles by thermal treatment of beta lactoglobulin chitosan complexes
Journal of Agricultural and Food Chemistry, 2007Co-Authors: Younho Hong, David Julian McclementsAbstract:Molecular complexes based on proteins and ionic polysaccharides have considerable potential for encapsulation of functional food components, but their widespread utilization is limited because their structure is highly sensitive to pH and ionic strength. We have investigated the possibility of creating stable hydrogel particles by thermal treatment of protein (Beta-Lactoglobulin) and cationic polysaccharide (chitosan) mixtures. Mixed solutions of Beta-Lactoglobulin (0.5 wt %) and chitosan (0.1 wt %) were prepared at various pH's (3-8) and were heated (80 degrees C for 20 min). Prior to heating, the biopolymer mixtures formed molecular complexes at pH values where there was an electrostatic attraction between the protein and the polysaccharide: soluble complexes at pH 4.5; complex coacervates at pH 5.0 and 5.5; precipitates at pH>5.5. After heating, relatively small (d approximately 140 nm) and cationic (zeta>+20 mV) hydrogel particles were formed at pH 4.5, but much larger aggregates were formed at pH 5.0 and higher (d>1000 nm). The thermally treated hydrogel particles formed at pH 4.5 maintained their initial particle size when the pH was subsequently adjusted within the range pH 3-5, but they aggregated when the pH was adjusted to >pH 5 because of a reduction in the magnitude of their electrical charge. This study suggests that hydrogel particles can be formed by heating mixed protein-polysaccharide systems under controlled conditions. These hydrogel particles may be useful for encapsulation of functional food components.
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antioxidant mechanisms of enzymatic hydrolysates of beta lactoglobulin in food lipid dispersions
Journal of Agricultural and Food Chemistry, 2006Co-Authors: Ryan J Elias, David Julian Mcclements, J D Bridgewater, R W Vachet, Thaddao Waraho, Eric A DeckerAbstract:The antioxidant activities of aqueous phase Beta-Lactoglobulin (beta-Lg) and its chymotryptic hydrolysates (CTH) were compared in this study. Proteins and peptides have been shown to inhibit lipid oxidation reactions in oil-in-water emulsions; however, a more fundamental understanding of the antioxidant activity of these compounds in dispersed food lipid systems is lacking. CTH was more effective than an equivalent concentration of beta-Lg in retarding lipid oxidation reactions when dispersed in the continuous phase of Brij-stabilized oil-in-water emulsions (pH 7). Furthermore, it was observed that CTH had higher peroxyl radical scavenging and iron-binding values than beta-Lg. Liquid chromatography-mass spectrometry (LC-MS) was used to measure the rate of oxidation of three oxidatively labile amino acid residues (Tyr, Met, and Phe) in certain CTH peptide fragments. Significant oxidation of specific Tyr and Met residues present in two separate 12 amino acid peptide fragments was observed in the days preceding lipid oxidation (39 and 55% of Tyr and Met were oxidized, respectively, by day 4 of the study); however, no significant oxidation of the Phe residue present in a specific 14 amino acid peptide fragment could be observed during the same time period. These data could suggest that Met and Tyr residues are capable of scavenging radical species and have the potential to improve the oxidative stability dispersed food lipids.
Sangeeta Prakash - One of the best experts on this subject based on the ideXlab platform.
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antigenicity of β lactoglobulin reduced by combining with oleic acid during dynamic high pressure microfluidization multi spectroscopy and molecule dynamics simulation analysis
Journal of Dairy Science, 2019Co-Authors: Junzhen Zhong, Hongda Yu, Lei Zhou, Shanlin Fu, Sangeeta PrakashAbstract:Some food components can modulate the antigenicity of Beta-Lactoglobulin (beta-LG). This study investigated the role of oleic acid (OA) in reducing the antigenicity of beta-LG. The results indicate the antigenicity of beta-LG gradually decreased from 15 (sample with no OA) to 9.86, 7.51, and 6.01 mu g/mL when interacting with OA during dynamic high-pressure rnicrofluidization treatment at 0.1, 80, and 160 MPa. Although binding sites (n) of beta-LG combined with OA at 0.1, 80, and 160 MPa decreased from 0.79 to 0.5 and 0.66, 3-LG had a higher binding affinity (K-a) to OA than that of untreated beta-LG. The values of K-a for beta-LG/OA at 0.1, 80, and 160 MPa were 5.51 x 10(6), 17.43 x 10(6), and 49.75 x 10(6)/12(-1), respectively. The molecule dynamic simulation showed that the OA molecules located at both beta-barrel (site 1) interacted with Lys60, Glu62, and Lys69 and outer surface site 2 consisting of Tyr20, Tyr42, Ser21, Glu157, and His161. Additionally, when binding with OA during the dynamic high-pressure microfluidization treatment, the conformation of beta-LG changed, reflected by the decrease of fluorescence intensity and total sulfhydryl group content, the increase of surface sulfhydryl group content, and secondary structure changes of beta-LG. These results deduce that some epitopes may be masked by OA or modified by the conformational changes, resulting in the decline of antigenicity of beta-LG molecules.