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ELUCIDATING THE STRUCTURAL CHANGES OF SOYBEAN BETA-CONGLYCININ AT THE OIL-WATER INTERFACE
No full textSoy proteins are among the most used plant-derived food proteins in human nutrition for their interesting nutritional proprieties. They reportedly exhibit hypocholesterolemic effects and prevent cardiovascular diseases, and their physicochemical proprieties are exploited for their use as food ingredients. beta-conglycinin constitutes 30% of total soybean proteins. Beta-conglycinin is a glycosilated hetero-trimer composed randomly by three different subunits: alpha, alpha’ and beta. The alpha and alpha’subunits are composed by two different domains: the core region and the extension region. The beta subunit only contains the core region. beta-conglycinin readily adsorbs at the interface of an oil-water emulsion with homogenization, but very little is understood yet on the details of the structural changes at the interface. These changes may affect the biological activity of beta-conglycinin, including allergenicity and bioavailability. The aim of this work is to study the structural changes of beta-conglycinin at the oil-water interface.
Fluorescence spectroscopy was used to evaluate tertiary structural changes in beta-conglycinin stabilized emulsions. Mass spectroscopy was utilized for a preliminary identification of the peptides released after tryptic digestion of beta-conglycinin alone and at the emulsion interface.
Beta-conglycinin undergoes a structural change at the oil-water interfaces. In fact, the fluorescence spectra of the protein in beta-conglycinin stabilized emulsion are red-shifted compared with the fluorescence spectra of the native protein. In particular, beta-conglycinin tryptophans seem to increase their exposure to solvent water when the protein interacts with the oil surface. Tryptophans in the mature form of beta-conglycinin are present only in the in the N-terminal extension regions, the least hydrophobic areas, of alpha and alpha’ subunits.
After emulsion digestion with trypsin, some peptides were released into the aqueous phase, including the tryptophan containing regions in the extension domains. Large peptides from the core region are released as well. These peptides come from the least hydrophobic regions of this domain.
In conclusion, it is possible to hypothesize that the core regions of the beta-conglycinin subunits interact with the oil phase, whereas the extension regions of the alpha and alpha’subunits protrude in the aqueous medium. Our proteolysis data also suggest that the core domain is oriented with its least hydrophobic regions exposed to the water
Increasing the association of casein micelles as natural nanodelivery systems with curcumin through static high pressure processing
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Shaping the structure of blends from sunflower press cake and whey proteins through heat treatment and fermentation
No full textThe current food system suffers from the inefficient use of resources, including the generation of side streams of low economic value, but still containing nutritional components. One potential approach to reach a more sustainable food system is to reintroduce such side streams into a circular value chain, and valorise them in novel food products, preferably in an unrefined or minimally refined manner. Moreover, blending side streams from different industries might be a suitable way to exploit functional synergies of structuring components such as proteins and polysaccharides, and to improve the nutritional value of the final food matrix. In this study, we combined the side streams from sunflower oil production (i.e., sunflower seed press cakes) and cheese manufacture (i.e., whey and whey proteins) to obtain novel food matrices containing valuable proteins, structuring polysaccharides, as well as lactose and minerals facilitating the fermentation.
Press cake, whey powder, and whey protein concentrate were dispersed in milk ultrafiltrate to prepare different blends with varying sunflower protein to whey protein ratio (100:0–0:100) but equal dry matter (~26%) and protein content (~10%). Structure formation as a function of heating temperature was studied by heating the blends to 80, 120, or 140 °C in a Rapid Visco Analyser (RVA), either undisturbed or under continuous, moderate shear applied by a paddle rotating at 160 rpm. The bulk viscosity of the unheated blends increased with increasing press cake concentration (0–22.5%) due to the higher polysaccharide to protein ratio. As observed from the torque profiles measured by the RVA, heat treatment at 120 and 140 °C increased the viscosity of the blends. A lower heating temperature, 80 °C, barely affected the sunflower components, but resulted in some denaturation of whey proteins, thereby increasing the viscosity of blends low in press cake and high in whey proteins. Confocal microscopy revealed that undisturbed heating at 120 and 140 °C resulted in the formation of a homogeneous gel network, whereas heating under moderate shear fostered the formation of a more heterogeneous structure, with protein aggregates dispersed in a continuous matrix.
Fermentation trials using three different co-cultures, each comprising one strain of lactic acid bacteria and one yeast strain, were conducted on the blend with the highest press cake content (22.5%) for maximum valorisation of the side stream. The samples were heated in an autoclave at 120 °C for 5 min without agitation prior to inoculation, as a homogeneous structure was assumed favourable for the fermentation. The pH development during fermentation at 26 °C was recorded, and samples were withdrawn for analysis after 12, 24, and 48 h. Small amplitude oscillatory shear rheology showed no significant changes in the storage modulus with fermentation, and confocal microscopy revealed a homogeneous microstructure for the unfermented and all fermented blends. This research provides important insights in the structure formation during processing of biomacromolecule blends and shows the potential of fermentation as a mean to stabilise side stream blends and modulate their sensory properties while only minimally affecting their physical appearance
Turning poop into gold? Fermentation and Extrusion for Increasing the Value of Sunflower Seed Press Cakes and Cheese Whey
No full textPreparation of Side Stream Blends. Fermentation Trials after strains selection. Cell Growth and Acidification. Metabolisation of Sugars & Effect on Proteins. Post-Fermentation Processing Trials. Low Moisture Extrusion. Investigation on Techno-Functional Properties. Extrudates – Structure Formation under Heat. Blends of sunflower seed press cakes and cheese whey were successfully fermented with lactic acid bacteria and yeasts. Fermentation of the blends changed their colour and increased their oil and water binding capacity. Low moisture extrusion barely affected the colour of the blends, but limited heat-induced structure formation
SOY PROTEINS AT OIL-WATER INTERFACE : A FLUORESCENCE STUDY
No full textSoy proteins are one of the most attractive plant food proteins for human and animal nutrition for their good nutritional (they exhibit hypocholesterolemic effect and prevention of cardiovascular diseases) and physicochemical proprieties (such as gel-forming and emulsifying abilities) [1-3].
Glicinin (11S) and-conglycinin (7S) constitute the 65-80% of the total amount of soybean proteins, and they are present in different ratios depending on the cultivar and growing condition [3]. Glycinin is a a heterohexamer with two symmetric trimers stacked on top of one another, with a molecular mass of approximately 300-380 kDa. β-conglycinin, (molecular mass ≈180-200 kDa) is a heterogeneous trimeric glycoprotein, composed by three subunits, , ’, and β with an estimated molecular weight of 67, 71, and 50 kDa, respectively [4-5]. -conglycinin can also form supramolecular aggregates as function of pH and ionic strength [6]. Soy proteins readily adsorb at the interface of an oil water emulsion with homogenization, but very little is yet understood on the details of the structural changes at the interface [7].
The aim of this work is to study the structural changes of soy proteins in solution and compare it to those at the oil-water interface, with focus on heat-induced changes. Fluorescence spectroscopy was applied on solutions and emulsions containing -conglycinin or glycinin in isolation, as well as soy protein isolate (SPI).
Intrinsic fluorescence spectroscopy was used to evaluate tertiary structural changes, along with the binding of fluorescent dyes (ANS), and accessibility of reactive cysteine thiols. Protein conformational changes after interaction with the hydrophobic oil surface were compared with those ensuing from physical (heat) or chemical denaturation (by added chaotropes). Results from solution denaturation experiments indicate that denaturation of -conglycinin solutions by both heat and chaotropes is reversible under appropriate conditions, and results in a rearrangement of the supramacromolecular assembly of the protein structure. On the other hand, glycinin treated under the same conditions underwent irreversible denaturation in solution. Results demonstrated that -conglycinin undergoes partial denaturation after adsorption on the lipid surface. This denaturation is reversible after protein displacement from the interface. Glycinin denaturation at a lipid interface reflected its solution behaviour. Glycinin undergoes a partial denaturation at the surface of hydrophobic droplets, and gave no indication of structural recovery after displacement from the interface
Structural changes of soy proteins at the oil–water interface studied by fluorescence spectroscopy
No full textFluorescence spectroscopy was used to acquire information on the structural changes of proteins at the oil/water interface in emulsions prepared by using soy protein isolate, glycinin, and beta-conglycinin rich fractions. Spectral changes occurring from differences in the exposure of tryptophan residues to the solvent were evaluated with respect to spectra of native, urea-denatured, and heat treated proteins. The fluorescence emission maxima of the emulsions showed a red shift with respect to those of native proteins, indicating that the tryptophan residues moved toward a more hydrophilic environment after adsorption at the interface. The heat-induced irreversible transitions were investigated using microcalorimetry. Fluorescence spectroscopy studies indicated that while the protein in solution underwent irreversible structural changes with heating at 75 and 95 degrees C for 15 min, the interface-adsorbed proteins showed very little temperature-induced rearrangements. The smallest structural changes were observed in soy protein isolate, probably because of the higher extent of protein-protein interactions in this material, as compared to the beta-conglycinin and to the glycinin fractions. This work brings new evidence of structural changes of soy proteins upon adsorption at the oil water interface, and provides some insights on the possible protein exchange events that may occur between adsorbed and unadsorbed proteins in the presence of oil droplets
Denaturation of soy proteins in solution and at the oilewater interface: a fluorescence study
No full textStructural changes ensuing from denaturation of soy proteins in solution or occurring at the oil-water interface were studied by fluorescence spectroscopy. Studies were carried out on solutions and emulsions stabilized with β-conglycinin or glycinin. Tryptophan fluorescence spectroscopy was used to evaluate tertiary structural changes. The binding of fluorescent dyes and the accessibility of reactive cysteine thiols were also used to better identify structural changes of these proteins in solution. Protein conformational changes after interaction with the hydrophobic oil surface were compared with those ensuing from physical (temperature) or chemical denaturation (chaotropes). Results from solution denaturation experiments indicate that structural changes of β-conglycinin by both temperature and chaotropes are reversible under appropriate conditions, and result in a rearrangement of the supramacromolecular assembly of the protein structure. On the other hand, glycinin treated under the same conditions undergoes irreversible denaturation in solution at temperatures well below 90°C. Both proteins undergo partial denaturation after adsorption on the lipid surface, and no further denaturation occurs upon heating of the emulsions prepared with either protein
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