Decrease In Α-helix Content Research Articles

Investigation of the Interaction between Mechanosynthesized ZnS Nanoparticles and Albumin Using Fluorescence Spectroscopy.

In this paper, ZnS nanoparticles were bioconjugated with bovine serum albumin and prepared in a form of nanosuspension using a wet circulation grinding. The stable nanosuspension with monomodal particle size distribution (d50 = 137 nm) and negative zeta potential (-18.3 mV) was obtained. The sorption kinetics and isotherm were determined. Interactions between ZnS and albumin were studied using the fluorescence techniques. The quenching mechanism, describing both static and dynamic interactions, was investigated. Various parameters were calculated, including the quenching rate constant, binding constant, stoichiometry of the binding process, and accessibility of fluorophore to the quencher. It has been found that tryptophan, in comparison to tyrosine, can be closer to the binding site established by analyzing the synchronous fluorescence spectra. The cellular mechanism in multiple myeloma cells treated with nanosuspension was evaluated by fluorescence assays for quantification of apoptosis, assessment of mitochondrial membrane potential and evaluation of cell cycle changes. The preliminary results confirm that the nontoxic nature of ZnS nanoparticles is potentially applicable in drug delivery systems. Additionally, slight changes in the secondary structure of albumin, accompanied by a decrease in α-helix content, were investigated using the FTIR method after analyzing the deconvoluted Amide I band spectra of ZnS nanoparticles conjugated with albumin. Thermogravimetric analysis and long-term stability studies were also performed to obtain a complete picture about the studied system.

Hydration effect of whey protein treated by glow discharge plasma

Glow discharge plasma (GP) was used to study the hydration mechanism of whey protein with different moisture content (10%, 20%, 30%). When the moisture content was 20%, the effect was most obvious. Strong hydration effect was confirmed by Fourier transform infrared spectroscopy (FTIR) results with sharper, narrower and blue-shifted from 3283.49 cm−1 to 3286.26 cm−1, indicating the enhanced hydrogen bond. More flexible protein structure with a significant decrease in α-helix content (from 18.50% to 14.62%), β-sheet content (from 29.67% to 19.38%) and crystallinity degree (from 6.18% to 0.81%) was introduced. Whey protein underwent oxidation reactions of CC to C–O–C(H) and further to COOH, C–OH to C–O–C and sulfhydryl to disulfide bonds. The scanning electron microscopy (SEM) results showed that the treated whey protein was highly aggregated (from 55.40 μm to 226.87 μm) and formed porous and rough polymers. Additionally, the treated whey protein exhibited higher anti-oxidation activity, with DPPH, ABTS and OH free radicals increased by 14.55%, 11.08% and 15.56%. The water/oil holding capacity and light transmittance of whey protein was improved by 18.18%, 22.05% and 35.69%, respectively.

Effects of ultrahigh magnetic field on the structure and properties of whey protein

Whey protein is an important protein supplement and its physical properties are being modified to meet various food and other related applications needs. In this study, we investigated changes of the physical and chemical properties of whey protein after treatment with ultrahigh magnetic fields (UMF) (5, 10, 15 and 20 T). We found UMF treatment induced more ordered structures with significant decrease in α-helix content (from 18.73% to 15.77%) and increase in β-sheet content (from 11.70% to 17.49%). UMF treatment caused the C–C bonds to be oxidized to C–O–C(H) and further oxidized to COOH, the N–CO groups to be oxidized to COOH, and the SH groups to be oxidized to SS. When the UMF strength was 10 T, these effects were the most significant. After treatment with UMF at 10 T, highly aggregated polymers were formed, which were 36 times larger in particle size (37.92 μm in diameter) than that of the untreated sample. The crystallinity degree of whey protein was increased to 28.78 ± 0.47. Additionally, the treated polymer exhibited higher anti-oxidation activity, better foaming capacity/stability, enhanced water/oil absorption capacity and higher emulsification capability. Therefore, UMF treatment of whey protein showed great potential in food processing and treatment.

Non-thermal plasma modulation of the interaction between whey protein isolate and ginsenoside Rg1 to improve the rheological and oxidative properties of emulsion

Molecular interaction forces regulate the interfacial properties of oil-in-water emulsion and play a key role in the rheology and stability of the emulsion in the food industry. In this study, the effects of non-thermal plasma (NTP) treatment on the structural and functional properties of whey protein isolate (WPI) and its binding interaction with ginsenoside Rg1 (GR1) were investigated. The results based on surface hydrophobicity, infrared spectroscopy and fluorescence spectroscopy test showed that the NTP treatment induced the unfolding of the structure of WPI and promoted the binding affinity between WPI and GR1. By comparing with untreated WPI (an α-helix content of 19.63 % and a β-sheet content of 31.66 %), there was a greater decrease in α-helix content and an increase in β-sheet content of WPI in N20-WPI (α-helix = 9.63 %, β-sheet = 39.63 %) and N20-WPI-GR1 (α-helix = 4.98 %, β-sheet = 48.66 %) groups. Importantly, the NTP treatment increased the interfacial adsorption and antioxidant capacity of the WPI-GR1 complexes, which contributed to the improvement of the rheological properties and oxidation stability of the emulsion. As a result, the NTP treatment could markedly improve the rheological and antioxidative properties of the WPI-GR1 complexes and the NTP-treated WPI-GR1 emulsions was more stable than that untreated. The present research indicated that NTP-treated formation of protein-saponin complexes could enhance the functional properties of the proteins, thus expanding their application as functional ingradients in nutritionally fortified food.

Novel sous-vide pressure technique affecting properties of local beef muscle

The low-temperature, long-time method of cooking known as sous-vide was used with increased pressure to enhance the tenderness and cook yield of local Thai beef round. The cooking was done in specialized equipment at 60 °C and 101, 200 or 300 kPa for 0–4 h. Beef treated with pressure was slightly lighter in color, and samples cooked for 2 h at 200 kPa had greater red saturation. Cooking at 200 kPa improved cook yield while reducing cook loss, with values of 78% after 4 h at 200–300 kPa versus 67% at 101 kPa. Cooking at 200–300 kPa resulted in more tender beef than at 101 kPa after 2 h. Sensory evaluation showed sous-vide pressure beef had higher ranking scores for tenderness and juiciness compared to control. SEM showed connective tissue of sous-vide pressure-cooked beef was diffuse and with looser muscle fibers than boiled or raw beef. Electrophoretic profiles showed that thick and thin filament bands decreased with cooking time. However, myosin heavy chain was sensitive to both heat and pressure. Reducing conditions showed pressure and heat induced disulfide bonding. Studies by FTIR showed cooking at 200 kPa caused the greatest decrease in α-helix content and increase in β-structures than non-treated and boiled beef.

A novel hydrophobin encoded by hgfII from Grifola frondosa exhibiting excellent self-assembly ability.

Hydrophobins are small proteins from filamentous fungi, which have remarkable self-assembly properties of great potential, e.g., as drug carriers and as anti-bacterial agents, but different hydrophobins, with improved properties, are needed. HGFI (a hydrophobin from Grifola frondosa) is a class I hydrophobin, which can self-assemble into rodlet structures with a length range 100–150 nm. In this study, we identified a new hydrophobin gene (hgfII) from the mycelium of G. frondosa with a much higher transcriptional level than hgfI. Heterologous expression of hgfII was accomplished in the Pichia pastoris. X-ray photoelectron spectroscopy and water contact angle assay measurements revealed that HGFII can self-assemble into a protein film at the air–solid interface, with circular dichroism and thioflavin T fluorescence studies showing that this effect was accompanied by a decrease in α-helix content and an increase in β-sheet content. Using atomic force microscopy, it was shown that HGFII self-assembled into rodlet-like structures with a diameter of 15–30 nm, showing that it was a class I hydrophobin, with self-assembly behavior different from HGFI. The surface hydrophobicity of HGFII was stronger than that of HGFI, meanwhile, in emulsification trials, HGFII displayed better dispersive capacity to the soybean oil than HGFI, producing a more stable and durable emulsion.

A novel anti-browning agent S-furfuryl thioacetate for fresh-cut potato screened from food-derived sulfur compounds

This research aimed to screen out safe and effective inhibitors of enzymatic browning from food-derived sulfur-containing compounds. Among eighteen candidate compounds, three were found to reduce the browning of fresh potato mashes. One of these compounds, S-furfuryl thioacetate (S-Ft) at only 0.04 and 0.07 mM inhibited the browning of fresh potato sticks, for over 10 d at 4 °C with an efficacy close to sodium bisulfite at 2.40 mM. S-Ft also reduced the browning of eggplant and asparagus lettuce slices. S-Ft retarded the browning occurrence of potato mashes and tyrosine solutions, but it did not cause the brown pigments colorless. Both the decrease in tyrosine contents and the increase in quinone contents were slowed by S-Ft in potato mashes. Compared with control, S-Ft at 0.04 and 0.07 mM reduced polyphenol oxidase (PPO) activity by 91.22 % and 91.77 %, and addition of copper acetate recovered the PPO activities to 55.62 % and 59.45 % of control, respectively. Kinetics results showed S-Ft inhibited PPO activity in a reversible mixed-type manner. The data of circular dichroism analysis and fluorescence emission spectra indicated S-Ft treatment caused the decrease in α-helix content, the increase in β-sheet content and the change in secondary structure of PPO. Molecular docking results illustrated S-Ft could act with Cu2+ and amino acid residues of PPO. By comparison with other anti-browning inhibitors, S-Ft has the characteristics of low dosage and long shelf-life extension. These results demonstrated that S-Ft could be a novel and promising enzymatic browning inhibitor by chelating Cu2+ and changing the conformation of enzyme to reduce PPO activity.

Ultrasound Improved the Non-Covalent Interaction of β-Lactoglobulin with Luteolin: Regulating Human Intestinal Microbiota and Conformational Epitopes Reduced Allergy Risks

The present study aims to investigate the effects of ultrasound on the non-covalent interaction of β-lactoglobulin (β-LG) and luteolin (LUT) and to investigate the relationship between allergenicity and human intestinal microbiota. After treatment, the conformational structures of β-LG were changed, which reflected by the decrease in α-helix content, intrinsic fluorescence intensity and surface hydrophobicity, whereas the β-sheet content increased. Molecular docking studies revealed the non-covalent interaction of β-LG and LUT by hydrogen bond, van der Walls bond and hydrophobic bond. β-LG-LUT complex treated by ultrasound has a lower IgG/IgE binding ability and inhibits the allergic reaction of KU812 cells, depending on the changes in the conformational epitopes of β-LG. Meanwhile, the β-LG-LUT complex affected the composition of human intestinal microbiota, such as the relative abundance of Bifidobacterium and Prevotella. Therefore, ultrasound improved the non-covalent interaction of β-LG with LUT, and the reduction in allergenicity of β-LG depends on conformational epitopes and human intestinal microbiota changes.

Antibacterial mechanism of ultrasound combined with sodium hypochlorite and their application in pakchoi (Brassica campestris L. ssp. chinensis).

In order to prolong the storage and inhibit microorganisms of pakchoi, the antibacterial activity and mechanism of ultrasound combined with sodium hypochlorite (NaClO-US), the efficiency of NaClO-US in reducing Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa as well as preserving quality of pakchoi were investigated. Ultrasound treatment could significantly reduce the usage of NaClO solution from 800 ppm to 500 ppm. NaClO-US decreased the counts of E. coli, S. aureus and P. aeruginosa, which disrupted the bacterial cell membrane with cytoplasmic leakage. In addition, NaClO-US significantly increased cell membrane permeability, while cell membrane integrity decreased, the secondary structure of bacterial proteins showed several obvious changes, such as the increase of random coil content, as well as the decrease of α-helix content. The bacterial counts, E. coli, S. aureus and P. aeruginosa population in pakchoi treated with NaClO-US reduced by 1.89, 1.40, 1.60, 1.72 log CFU g-1 , respectively compared to control sample after storage for 15 days. NaClO-US resulted in minimum chlorophyll depletion, flavor and sensory deterioration. NaClO-US solution treatment inhibited microorganisms and prolonged storage of pakchoi. © 2022 Society of Chemical Industry.

The interaction of allicin with bovine serum albumin and its influence on the structure of protein

The interaction of allicin with bovine serum albumin (BSA) and the effect of allicin binding on the structure of protein were investigated. The BSA fluorescence displayed decreased fluorescence strength after binding with allicin, which quenched BSA fluorescence in a concentration-dependent manner. The number of binding sites and binding constants were measured by fluorescent quenching method. The result of reverse phase HPLC showed that the peak of BSA shifted to higher retention time, which indicated that allicin had bound to BSA. 88.4 % of total free thiol groups of BSA have bound to allicin at the allicin/BSA molar ratio of 0.1. Allicin could destabilize the secondary and tertiary structure of BSA. At the allicin/BSA ratio of 0.1, the BSA's circular dichroism spectrum showed that allicin caused a decrease of α-helix content and a significant increase of the β-sheet content (p < 0.05). Changes in surface hydrophobicity indicated that more hydrophobic groups were exposed due to the action of allicin. These results provide important insight into the study of prevailing role of protein in drug pharmacokinetics and pharmacodynamics.

Camellia nitidissima Chi leaf as pancreatic lipase inhibitors: Inhibition potentials and mechanism.

In this study, Camellia nitidissima Chi leaf extract was investigated for its compounds and pancreatic lipase inhibitory potentials. The interaction was determined using ultraviolet (UV) spectroscopy, circular dichroism (CD), fluorescence spectroscopy (FS), and molecular docking to understand the inhibiton, kinetic, and conformation of extraction-pancreatic lipase complex. C. nitidissima Chi leaf extraction inhibited the pancreatic lipase activity in a dose-dependent manner at the concentration of 1-12mg/ml. The Lineweaver-Burk plots indicated that the inhibition on pancreatic lipase by extraction was noncompetitive. In addition, the decrease in α-helix contents, increase in β-sheet and β-turn, and decrease in fluorescence intensity after extraction treatment indicated that the conformation of pancreatic lipase was changed. This work revealed that C. nitidissima Chi leaf extraction played a significant role in inhibiting pancreatic lipase activity and brought out a solution of delay fat accumulation. PRACTICAL APPLICATIONS: This study reports the components in the extract of C. nitidissima Chi leaf and its inhibitory effect and mechanism of pancreatic lipase. C. nitidissima Chi leaf is a good source of bioactive components, including multiflorin B, kaempferol-3-O-rutinoside, vicenin-2, apigenin-6-C-pentosyl-8-C-hexosyl, vitexin, kaempferol, and other ingredients. It can inhibit pancreatic lipase and be used to control obesity and treat hyperlipidemia. This study also revealed the structure changes of C. nitidissima Chi leaf extract on pancreatic lipase, and further revealed the inhibitory mechanism of C. nitidissima Chi leaf extract on lipase, which provides a theoretical basis for C. nitidissima Chi leaf as a lipase inhibitor.

Heat sensitive protein-heat stable protein interaction: Synergistic enhancement in the thermal co-aggregation and gelation of lactoferrin and α-lactalbumin

The synergistic enhancement in the thermal co-aggregation and gelation of lactoferrin (LF), a heat sensitive protein, and α-lactalbumin (ALA), a heat stable protein, was investigated at pH 7.0. Heating temperatures (70 °C and 90 °C; 30 min) and ALA concentrations (0–0.5 mM) significantly affected the structural characteristics of the resultant thermal aggregates and gels. The turbidity and size of LF-ALA thermal aggregates were increased with increasing ALA concentration; at a low total protein concentration of 0.57 mM, LF-ALA gels can be formed. The presence of ALA led to some hydrophobic residues originally located in the interior of LF to be exposed further during heating. New intermolecular disulfide bonds, mainly unstable ones, were formed between LF molecules and/or ALA molecules during co-heating. The aggregation of LF and ALA was a gradual denaturation process, accompanied by an increase in β-sheet content and decrease in α-helix content. Random spherical aggregates with large size (1–5 μm) were observed by transmission electron microscopy, clearly confirming the nucleation and growth of LF with ALA. There existed strong rheological synergism between LF and ALA, thereby leading to a large reduction in gelation times (4–11 min) with increasing ALA concentration and heating temperature. Considering these data, LF and ALA played different and indispensable roles in thermal aggregation and gelation: LF engaged readily in thermal aggregation, while ALA mainly assisted the LF thermal aggregation. Three types of mechanisms (co-fusion, nucleation and growth) involved in the aggregation and gelation processes. In all, the data of the current study has enhanced the comprehension of heat sensitive protein-heat stable protein thermal aggregation and gelation, and may help to design LF-based new ingredients for the control of food textures and delivery systems for food and pharmaceutical applications.

Studying the interaction mechanism between bovine serum albumin and lutein dipalmitate: Multi-spectroscopic and molecular docking techniques

Bovine serum albumin (BSA) is a natural protein commonly used to prepare nanoparticle to encapsulate food ingredients. The interaction between lutein dipalmitate and BSA was investigated using fluorescence, UV–vis absorption, circular dichroism (CD) spectroscopies and molecular docking. The fluorescence quenching study suggested the quenching process of BSA by lutein dipalmitate was static, which was consistent with the results of UV–vis absorption. The binding parameters proved that the binding stoichiometry between BSA and lutein dipalmitate was 1:1. Molecular docking revealed that lutein dipalmitate bound to site I on BSA, which was confirmed by site competitive experiments. Moreover, thermodynamic study and molecular docking suggested lutein dipalmitate spontaneously bound to BSA by hydrogen bond, van der Waals force, and hydrophobic interaction. The synchronous and three-dimensional fluorescence showed that the microenvironment of Tyr and Trp was changed and the protein skeleton got loosened in the presence of lutein dipalmitate. According to CD, a decrease in α-helix content of BSA was observed upon the addition of lutein dipalmitate.

H-Bonding-mediated binding and charge reorganization of proteins on gold nanoparticles.

Once introduced into the human body, nanoparticles often interact with blood proteins, which in turn undergo structural changes upon adsorption. Although protein corona formation is a widely studied phenomenon, the structure of proteins adsorbed on nanoparticles is far less understood. We propose a model to describe the interaction between human serum albumin (HSA) and nanoparticles (NPs) with arbitrary coatings. Our model takes into account the competition between protonated and unprotonated polymer ends and the curvature of the NPs. To this end, we explored the effects of surface ligands (citrate, PEG-OMe, PEG-NH2, PEG-COOH, and glycan) on gold nanoparticles (AuNPs) and the pH of the medium on structural changes in the most abundant protein in blood plasma (HSA), as well as the impact of such changes on cytotoxicity and cellular uptake. We observed a counterintuitive effect on the ζ-potential upon binding of negatively charged HSA, while circular dichroism spectroscopy at various pH values showed an unexpected pattern in the reduction of α-helix content, as a function of surface chemistry and curvature. Our model qualitatively reproduces the decrease in α-helix content, thereby offering a rationale based on particle curvature. The simulations quantitatively reproduce the charge inversion measured experimentally through the ζ-potential of the AuNPs in the presence of HSA. Finally, we found that AuNPs with adsorbed HSA display lower toxicity and slower cell uptake rates, compared to functionalized systems in the absence of protein. Our study allows examining and explaining the conformational dynamics of blood proteins triggered by NPs and corona formation, thereby opening new avenues toward designing safer NPs for drug delivery and nanomedical applications.

The Inhibition of Polysialyltranseferase ST8SiaIV Through Heparin Binding to Polysialyltransferase Domain (PSTD)

The polysialic acid (polySia) is a unique carbohydrate polymer produced on the surface Of Neuronal Cell Adhesion Molecule (NCAM) in a number of cancer cells, and strongly correlates with the migration and invasion of tumor cells and with aggressive, metastatic disease and poor clinical prognosis in the clinic. Its synthesis is catalyzed by two polysialyltransferases (polySTs), ST8SiaIV (PST) and ST8SiaII (STX). Selective inhibition of polySTs, therefore, presents a therapeutic opportunity to inhibit tumor invasion and metastasis due to NCAM polysialylation. Heparin has been found to be effective in inhibiting the ST8Sia IV activity, but no clear molecular rationale. It has been found that polysialyltransferase domain (PSTD) in polyST plays a significant role in influencing polyST activity, and thus it is critical for NCAM polysialylation based on the previous studies. To determine whether the three different types of heparin (unfractionated hepain (UFH), low molecular heparin (LMWH) and heparin tetrasaccharide (DP4)) is bound to the PSTD; and if so, what are the critical residues of the PSTD for these binding complexes? Fluorescence quenching analysis, the Circular Dichroism (CD) spectroscopy, and NMR spectroscopy were used to determine and analyze interactions of PSTD-UFH, PSTD-LMWH, and PSTD-DP4. The fluorescence quenching analysis indicates that the PSTD-UFH binding is the strongest and the PSTD-DP4 binding is the weakest among these three types of the binding; the CD spectra showed that mainly the PSTD-heparin interactions caused a reduction in signal intensity but not marked decrease in α-helix content; the NMR data of the PSTD-DP4 and the PSTDLMWH interactions showed that the different types of heparin shared 12 common binding sites at N247, V251, R252, T253, S257, R265, Y267, W268, L269, V273, I275, and K276, which were mainly distributed in the long α-helix of the PSTD and the short 3-residue loop of the C-terminal PSTD. In addition, three residues K246, K250 and A254 were bound to the LMWH, but not to DP4. This suggests that the PSTD-LMWH binding is stronger than the PSTD-DP4 binding, and the LMWH is a more effective inhibitor than DP4. The findings in the present study demonstrate that PSTD domain is a potential target of heparin and may provide new insights into the molecular rationale of heparin-inhibiting NCAM polysialylation.

Biological Response of and Blood Plasma Protein Adsorption on Silver-Doped Hydroxyapatite.

Hydroxyapatite (HAP) is an extensively used orthopedic biomaterial because of its high biocompatibility and osteoconductivity. Implant-related infection is a major cause of orthopedic device failure. Previous research showed that silver-doped hydroxyapatite nanoparticles (Ag-HAP NPs) have prominent antimicrobial activity, but their biocompatibility and plasma protein response remained unexplored. Here we investigated the effects of synthesis conditions on Ag-HAP NP antimicrobial (E. coli and S. epidermidis) activity, biocompatibility, and the adsorption of two blood plasma proteins, human serum albumin (HSA) and fibrinogen (Fib). It was found that synthesis pH affected the Ag content of Ag-HAP NPs and subsequent Ag+ release from the NPs in solution. This, in turn, affected antimicrobial efficiency and cytotoxicity to murine preosteoblast cells (MC3T3-E1). More HSA than Fib was adsorbed on a molar basis. The conformation of HSA changed drastically from predominantly α-helix and minor β-sheet content in solution to greater β-sheet than α-helix content when adsorbed. Correspondingly, the melting temperature Tm of HSA changed significantly from 76 °C in solution to ∼65-66 °C when adsorbed. Fib exhibited a modest decrease in α-helix content while theβ-sheet content increased modestly upon adsorption and its Tm remained unchanged at ∼60 °C. These differences in behavior of HSA and Fib are ascribed to the much smaller size of HSA, which allows a greater molecular packing density on the surface, which induces greater conformational changes. The protein adsorption behavior on Ag-HAP was similar to that on pure HAP. Thus, we show that Ag-HAP NPs have antimicrobial activity without deleterious effects on biocompatibility and blood plasma protein adsorption.

The effects of insoluble dietary fiber on myofibrillar protein gelation: Microstructure and molecular conformations

The effects of insoluble dietary fiber (IDF) on heat-induced gelation properties, such as microstructural changes and the molecular conformation of myofibrillar proteins (MP), were analyzed by image analyses and Raman spectroscopy. Scanning electron microscopy revealed that pure MP gelation contained a loose and dispersed network with interconnected water channels. With IDF addition, the lacunarity and the particle size of water pores both significantly decreased (P < 0.05) and fractal dimension significantly increased (P < 0.05), which indicated the formation of a homogenous and compact three-dimensional network. Through Raman spectra, IDF addition resulted in modification of amide I and III regions, by a significant decrease in α-helix content, accompanied by an increase of β-sheets, β-turns, and random coil content (P < 0.05); the intensity of CU+005CH stretching vibrations bending vibrations bands were significantly decreased (P < 0.05). Principal component analyses showed significant correlations between textual property, microstructure and molecular conformations. Cluster analyses indicated IDF improved the functionality of MP gel by 1): IDF stable the moisture phase 2) “concentrated” MP promoted structural integrity and compact gelation.

Effect of pH-shifting treatment on structural and functional properties of whey protein isolate and its interaction with (−)-epigallocatechin-3-gallate

Effect of pH-shifting on structural and functional properties of whey protein isolate and its interaction with (−)-epigallocatechin-3-gallate were investigated. Circular dichroism spectra showed that pH-shifting induced the decrease in α-helix content by 12.18% and β-sheet content by 3.24%, but β-turn and random coil content increased by 4.26% and 5.91%, respectively. Increase of fluorescence intensity and red-shift of maximum emission wavelength indicated the structural unfolding and exposure of tyrosine. The treatment also significantly increased the surface hydrophobicity, disulfide bonds content, solubility, emulsifying activity and emulsion stability of whey protein isolate at P < 0.05 level. Fluorescence quenching analysis revealed that treated whey protein isolate have a stronger binding affinity to (−)-epigallocatechin-3-gallate, resulting a better protection against the degradation of (−)-epigallocatechin-3-gallate and its antioxidant activity. This study confirmed that pH-shifting treatment can improve functional properties of whey protein isolate and its potential as a protective carrier for polyphones.

Effects of selected phosphate salts on gelling properties and water state of whole egg gel

The aim of this study was to verify the influence of selected phosphate salts (sodium diphosphate and trisodium phosphate) on the gelling properties and water state of whole egg gel. As shown by the results, the gel and water holding properties of whole egg was effectively improved after the addition of sodium diphosphate and trisodium phosphate, possibly through affecting the solubility, surface hydrophobicity, z-average particle size and pH of liquid egg dispersions. The difference in the viscoelastic properties of whole egg gels brought by two phosphate salts was related to their obvious difference in calculated ionic strength and pH. As the addition level of phosphate salts increased, the protein secondary structure after gelation was changed remarkably, characterized by the decrease of α-helix content and the increase of β-sheet content. The gel β-sheet content was positively correlated with fracture strain and percentage of bound water and immobilized water, while the α-helix content was negatively correlated with fracture strength. The scanning electron microscope (SEM) results showed that the addition of phosphate salts would facilitate the formation of a fine high strength stranded structure. Moreover, the color characteristics of whole egg gels can be more effectively improved by sodium diphosphate in comparison with trisodium phosphate.

Effect of gamma irradiation on structural, molecular, thermal and rheological properties of sunflower protein isolate

Protein isolates were prepared from sunflower meal using alkaline extraction technique and were irradiated at different doses (0, 10, 20, 30, 40 and 50 kGy). Sunflower protein isolates were evaluated for structural, molecular, thermal and rheological properties. Secondary structure of proteins was disrupted with decrease in α-helix content and concomitant increase in β-sheet content. The change in fluorescence spectra was observed indicating the alteration in tertiary structure of protein molecules mainly due to the conformational changes especially aggregation and crosslinking of protein molecules. Increase in thermal stability of protein after irradiation was found as determined by differential scanning calorimetry and thermal gravimetric analysis. Molecular weight of protein was increased in a dose dependent manner due to protein-protein crosslinking. Development of cracks on the surface of protein particle after irradiation was observed by scanning electron microscopy. Storage (G′) and loss modulus (G″) of protein dispersion was increased after gamma irradiation.