Free Sulfhydryl Group Content Research Articles

Properties, digestion and peptide release of heat-induced duck egg white

In this study, moisture content, textural properties, microstructure, free sulfhydryl group content, the secondary structure of heat-induced duck egg white gels (DEWG) under different heating temperatures of 80 °C, 90 °C, 100 °C and times of 10, 15, 20, and 25 min were investigated. Enzymolysis efficiency and peptide mapping were determined to clarify the linkage mechanism in gel properties, digestion behavior and peptide release of DEWG. Results indicated that with the increasing temperature and time, a gel with harder texture and less moisture was formed. Related gel exhibited a more compact form of aggregation in the environmental scanning electron microscopy (ESEM) and transmission electron microscope (TEM), as well as an increase in the amount of free sulfhydryl group and β-sheet. The in vitro digestibility and the number of peptides produced were affected by protein aggregation morphology. The gel with low induction temperature and shorter induction time showed a loose structure, resulting in a higher digestibility and more quantity of peptides released. In conclusion, heat induced changes in gelation behavior of duck egg white protein, and thus exhibited critical effects on protein digestion and peptide released.

Impact of germination on structural, functional properties and in vitro protein digestibility of sesame (Sesamum indicum L.) protein

To enhance the functional properties and utilization of sesame protein, the impact of different germination treatments (0 d, 2 d, and 4 d) on the structural and functional properties of sesame protein was investigated in this study. The results showed that germination significantly increased the content of free sulfhydryl groups and the surface hydrophobicity of sesame protein, indicating that the protein molecular structure was unfolded. The high molecular weight protein bands gradually disappeared, and the secondary structure of the sesame protein was changed after germination. Moreover, germination led to changes in the foaming and emulsifying properties of sesame protein. The in vitro protein digestibility and solubility of sesame protein were also increased after germination. These results suggested that germination treatment can improve the structural and functional properties of sesame protein and can be used as an effective approach to enhance the nutritional properties and processing value of plant seed protein.

Photo‐protective effect of cuttlefish ink melanin on human hair

AbstractThe photoprotective properties of exogenous melanin extracted from cuttlefish ink on human hair was assessed. Melanin extracted from cuttlefish ink was applied on black hair and irradiated using a solar simulator. The extent of photodegradation was determined by microstructural, morphological and mechanical testing. The UV–Vis spectra of melanin extracted from cuttlefish ink indicated strong absorption at UV region and moderate absorption in visible region. The melanin‐coated samples indicated significant protection to hair cuticle against UV radiations, as indicated by microscopic images (SEM). Conversely, visible cracks were evident on uncoated hair shafts, when exposed to UV‐radiations. Also, the melanin‐coated hair samples indicated negligible alterations in disulfide linkages, free sulfhydryl group content, water retention index and swelling index on UV exposure, as compared to that of uncoated samples. Similarly, the mechanical strength of the uncoated hair fibers was far compromised by UV irradiation compared to that of melanin‐coated hair fibers. The observations of the present study postulate cuttlefish melanin as a potential photoprotective agent in hair‐care formulations, which is otherwise considered as a process discard from cephalopod processing industry.

Free radical grafting of whey protein isolate with tea polyphenol: Synthesis and changes in structural and functional properties

Free radical grafting is a green and expeditious tool that was used to modify whey protein isolate (WPI) to synthesize WPI-(−)-epigallocatechin-3-gallate (EGCG) and WPI-catechin (C) antioxidant emulsifier and improve its functional and interfacial properties. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and matrix assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF–MS) were used to verify the covalent bonding between polyphenols and WPI. Results revealed that at least two EGCG molecules and three catechin molecules were grafted onto WPI. Meanwhile, the grafting of tea polyphenols, especially EGCG, with WPI decreased their fluorescence intensity; α-helix content; and free amino, sulfhydryl, and tyrosine group contents. A lycopene nanoemulsion constructed with the WPI-EGCG conjugate had smaller changes in size and ζ-potential than that constructed with WPI during 30-day storage, which was attributed to its enhanced emulsifying activity, emulsification stability, and ability to reduce the interfacial tension of conjugates. The improvement in oxidation resistance and interfacial adsorption layer thickness helped the WPI-EGCG conjugate to significantly reduce the lycopene degradation rate during storage. Thus, WPI modified with polyphenol by free radical grafting can be used to construct an emulsion delivery system for functional nutrients with a stable interface and high retention rate.

Self-Assembled Pea Protein Isolate Nanoparticles with Various Sizes: Explore the Formation Mechanism.

Pea protein isolate nanoparticles (PPINs) were successfully prepared by potassium metabisulfite (K2S2O5). The disulfide bonds were disrupted by K2S2O5, and then the PPINs were formed through self-assembly. The average diameter of PPINs increased from 124.7 to 297.5 nm as the concentration of K2S2O5 was increased from 2 to 8 mM, and the PPINs showed higher ζ-potentials (-32.2 to -35.8 mV) and unimodal distribution. The content of free sulfhydryl groups first increased and then decreased with the fracture and reformation of disulfide bonds. Subsequently, the increase of the β-sheet, which has considerable hydrophobicity, promoted the formation of PPINs. The formation mechanism of PPINs was explored by dissociation tests: hydrophobic interactions maintained the basic skeleton of PPINs, disulfide bonds stabilized the internal structure, and hydrogen bonds existed on the exterior of the particles. This study provided a simple and economical method to fabricate nanoparticles.

Effects of different dietary polyphenols on conformational changes and functional properties of protein–polyphenol covalent complexes

In this study, conjugates of whey protein isolate (WPI) and four polyphenols (epigallocatechin gallate [EGCG], quercetin [QC], apigenin [AG], and naringenin [NG]) were prepared through free-radical grafting. The results for polyphenol binding equivalents and content of free amino and sulfhydryl groups as well as those from sodium dodecyl sulfate–polyacrylamide gel electrophoresis confirmed the covalent interaction between WPI and the polyphenols. Fourier transform infrared spectroscopy and fluorescence spectrum analysis identified the potential binding sites of the complexes and determined changes in the protein structure. The particle size distribution and scanning electron microscopy data demonstrated increases in conjugate particle sizes and surface changes in the complexes. The conjugation process significantly increased the polyphenols’ antioxidant properties and thermal stabilities, whereas surface hydrophobicity was substantially reduced. WPI-EGCG had the best functional properties, followed by WPI-QC, WPI-AG, and WPI-NG.

Effect of ultrasound pretreatment on structural, physicochemical, rheological and gelation properties of transglutaminase cross-linked whey protein soluble aggregates

A solution (10%, w/v) of whey protein soluble aggregates (WPISA) was pretreated with high-intensity ultrasound (HUS, 20 kHz) for different durations (10–40 min) before incubation with transglutaminase (TGase) to investigate the effect of HUS on the structural, physicochemical, rheological, and gelation properties of TGase cross-linked WPISA. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) results showed that HUS increased the amounts of high-molecular-weight polymers/aggregates in WPISA after incubation with TGase. HUS significantly increased (P < 0.05) the degree of TGase-mediated cross-linking in WPISA, as demonstrated by a reduction in free amino group contents. HUS significantly increased (P < 0.05) the particle size, intrinsic fluorescence intensity, and surface hydrophobicity of TGase cross-linked WPISA, but had no significant impact (P > 0.05) on the zeta-potential or total free sulfhydryl group content of TGase cross-linked WPISA. The apparent viscosity and the consistency index of TGase cross-linked WPISA were significantly increased by HUS (P < 0.05), which indicated that HUS facilitated the formation of more high-molecular-weight polymers. HUS significantly increased (P < 0.05) the water holding capacity and gel strength of glucono-δ-lactone (GDL)-induced TGase cross-linked WPISA gels. The results indicated that HUS could be an efficient tool for modifying WPISA to improve its degree of TGase-mediated cross-linking, which would lead to improved rheological and gelation properties.

Depolymerization of chicken egg yolk granules induced by high-intensity ultrasound

The effects of high-intensity ultrasound (HIU) treatment-induced depolymerization of chicken egg yolk granules were investigated. The results showed that the yolk granules were depolymerized after HIU treatment, and the average particle size was significantly reduced from 289.4 nm (untreated) to 181.4 nm (270-W HIU treatment). All contents of dry matter, protein, calcium and phosphorus in the supernatant of the HIU-treated yolk granule solution increased, which suggests that HIU treatment increases the dissolution of yolk granule components. Spectroscopic analysis showed that HIU treatment increased the polarity of the microenvironment and enhanced the hydrogen bond force of yolk granules. These changes induced by HIU treatment collectively enhanced the zeta potential, decreased the free sulfhydryl group content, and slightly improved the emulsifying activity index of yolk granules. The present study reveals the depolymerization effect of HIU treatment on egg yolk granules and can inspire new potential applications of egg yolk granules.

Effects of ultrasound emulsification on the properties of pork myofibrillar protein-fat mixed gel

This work was aimed to explore the effects of ultrasound as an emulsification method on the properties of pork myofibrillar protein (MP) and fat mixed gel under different ratios (w/v, 15:1, 10:1, 5:1, 1:1, 1:5, 1:10 and 1:15). Results indicated that sonication decreased the hardness, springiness and water holding capacity of gels with the ratios higher than 5:1, while increased these properties with the ratio at 1:15. Sonication also increased the storage modulus value of samples with the ratios lower than 1:10 during 58 to 80 ℃. The effects of ultrasound emulsification on ultrastructure, surface hydrophobicity and free sulfhydryl group contents of samples were different with the changes of ratios. The absolute zeta potential value was increased of all samples after sonication. MP were combined with fat particles after sonication. Our results demonstrate that ultrasound emulsification can be used to improve the properties of higher fat MP gel.

Consequences of dynamic high-pressure homogenization pretreatment on the physicochemical and functional characteristics of citric acid-treated whey protein isolate

This study investigated the physicochemical and functional characteristics of citric acid (CA)-treated whey protein isolate (WPI) by dynamic high-pressure homogenization (DHPH) at different pressure levels (0, 25, 50, 75, and 100 MPa, 3 cycles). The number of macromolecular polymers increased in CA-treated WPI with DHPH at 0–100 MPa by the analysis of molecular size distributions. DHPH can reduce the particle size of WPI and CA-treated WPI. Additionally, the content of free sulfhydryl groups and surface hydrophobicity of WPI and CA-treated WPI increased after DHPH treatment (p < 0.05). Also, DHPH promoted gel formation in the CA-treated WPI, with the gel hardness increased by 43.66% after DPHP pretreatment at 100 MPa (p < 0.05). Meanwhile, after DPHP pretreatment at 100 MPa, emulsifying activity index (EAI) of CA-treated WPI and WPI increased by 13.15% and 27.36%, respectively (p < 0.05). Thus, DHPH pretreatment could enhance the degree of crosslinking of the CA-treated WPI and improve its gel and emulsifying properties, broaden the application of WPI in food processing.

Effects of short-term fermentation with lactic acid bacteria on the characterization, rheological and emulsifying properties of egg yolk

Lactic acid bacteria fermentation is a safe and green technology that can modify the function of food ingredients (including proteins). In this article, egg yolks were subjected to fermentation with commercial lactic acid bacteria for 0, 3, 6 and 9 h, respectively. After fermentation treatment, the microbial composition has changed obviously (Streptococcus thermophilus increased significantly). The free sulfhydryl group (SH) contents and surface hydrophobicity of egg yolk proteins were significantly reduced. The rheological results indicated that the treated egg yolks possessed a decreased apparent viscosity. Correspondingly, the emulsifying activity of egg yolk was enhanced from 9.07 to 19.55, 23.40 and 24.61 m2/g for 3, 6 and 9 h of fermentation, respectively. And the emulsifying stability reached the maximum after 3 h of fermentation. This study investigated the relationship between structure and properties of yolk proteins, and showed that lactic acid fermentation endued egg yolk with better emulsifying properties.

Impact of milk thistle (Silybum marianum) on the mycotoxin caused redox-homeostasis imbalance of ducks liver

The Fusarium mycotoxins deoxynivalenol (DON) and zearalenone (ZEA) frequently contaminate grain crops, especially maize, the basis of poultry's feed. Mycotoxins enter the food chain and induce pathological changes in edible tissues. Milk thistle (Silybum marianum) has been used for the treatment of liver disease in humans because of its antioxidant and hepatoprotective effects, but its utility in veterinary use is poorly examined. To investigate possible protective properties against mycotoxin caused oxidative stress in poultry, pressed form of milk thistle seed (0.5%) was tested in white, female, Hungarian ducks over a feeding period of 47 days. Ducks were separated into 3 groups. The first group was fed with normal diet. The second group was fed with normal diet contaminated with DON (4.9 mg/kg) and ZEA (0.66 mg/kg). The third group received mycotoxin contaminated feed with milk thistle supplementation. Histological examination, markers of the redox status and metal element concentration measurements were carried out. The results showed alterations in the histological examination and in the redox homeostasis markers as a short-term effect by strengthening the antioxidant system. Acute exposure of mycotoxins caused an oxidative stress, which induced an effective antioxidant defensive response of the organism indicated by the free sulfhydryl group content (from 0.72 ± 0.06 to 0.77 ± 0.11) and the reducing power (0.49 ± 0.06 to 0.52 ± 0.08) elevation. The short-term free radical injury may be compensated by the liver resulting in decreased lipid peroxidation markers (malondialdehyde concentration: from 16.86 ± 0.49 to 0.94 ± 0.15, conjugated diene concentration: from 0.21 ± 0.07 to 0.17 ± 0.03). Silymarin further strengthtened the antioxidant defense by the elevation of sulfhydryl groups concentration and reducing power property resulted in decreased total scavenger capacity. However the concentration of lipid peroxidation markers were further elevated by the used antioxidant treatment (MDA: 5.2 ± 0.35, DC: 0.26 ± 0.08). In conclusion, the mycotoxin-contamination activated effectively the antioxidant system. The milk thistle supplementation has cytoprotective effects according to the histological findings, activated the antioxidant system, however the elevation of lipid peroxidation products need further explanation.

Molecular structural modification of duck egg white protein conjugates with monosaccharides for improving emulsifying capacity

Glycosylation is considered to be an effective method to improve the emulsifying property of proteins, and this work investigates and discusses the correlation between the molecular structure of glycosylated egg white protein (EWP) and its emulsifying capacity. Three types of monosaccharides, including glucose, d-galactose and d-xylose, were utilized to conjugate with EWP in a wet glycosylation environment. Molecular structural properties of EWP, involving surface hydrophobicity, secondary and tertiary structures, protein flexibility, and free sulfhydryl group content, were determined. The results showed that the degree of grafting (DG), browning intensity and apparent viscosity increased significantly (P < 0.05) with the monosaccharides proportion improved, and the intrinsic fluorescence intensity and surface hydrophobicity of EWP decreased obviously during glycosylation, and the absolute value of zeta potential, protein flexibility and free sulfhydryl content improved remarkably (P < 0.05). Emulsifying capacity results showed that glycosylation improved emulsifying activity and emulsifying stability of EWP, especially after the addition of d-xylose. The particle size analysis exhibited that the D4,3 and D3,2 declined obviously (P < 0.05) as DG increased. Correlation analysis revealed the improvement of the emulsifying capacity of glycosylated EWP showed in a DG-dependent manner, as remarkably influenced by molecular flexibility, surface hydrophobicity, tertiary structure changes and free sulfhydryl. The work provides a deep insight into the molecular conformation−emulsifiability relationship of EWP−monosaccharides conjugates.

Mechanism of change of the physicochemical characteristics, gelation process, water state, and microstructure of okara tofu analogues induced by high-intensity ultrasound treatment

The effects of high-intensity ultrasound treatment on the physicochemical characteristics, gelation process, water state, and microstructure of okara tofu analogues were evaluated. Suspensions composed of okara and SPI were treated with ultrasound at different power settings (0, 500, 600, 700, or 800 W) for 20 min, and then, the physicochemical characteristics of the suspensions and okara tofu analogues gelation were determined. After ultrasound treatment at different power settings, the mean particle size of the suspension samples decreased, whereas the surface hydrophobicity and free sulfhydryl group contents of the suspension samples increased. The suspension samples exhibited different gelation behaviors, resulting in distinct water-holding capacities, textural properties, and microstructures in the final treated okara tofu analogues. With increasing ultrasound power from 500 W to 800 W, the water-holding capacity and gel yield of the okara tofu analogues first increased and then decreased. When the ultrasound power was set to 600 W, maximum values of the water-holding capacity and gel yield of 73.95% and 97.48%, respectively, were reached. The textural properties were as follows: hardness, 656.75 g; springiness, 1.203 mm; cohesiveness, 0.435 g mm; gumminess 285.75 g; and chewiness, 343.76. The overall acceptability score increased to the highest. Compared with that of the control sample, the T21 relaxation time of okara tofu analogues decreased to 45.43 ms and its peak area increased to 94.97%; the okara tofu analogues showed a more uniform and denser gel network with filamentous and homogeneous pores; and the okara fibers were embedded more uniformly in the network. Therefore, high-intensity ultrasound changed the microstructure and physicochemical properties of okara fibers and proteins, producing a firm and uniform okara tofu analogues gel network. This study can provide a thorough understanding of the gelling properties of okara tofu analogues.

Effect of pH-shifting treatment on structural and heat induced gel properties of peanut protein isolate

Modifying proteins with new methods to improve their functional properties is essential to extend their application in food related field. In this study, the effect of pH-shifting treatment on structural and heat induced gel properties of peanut protein isolate (PPI) were investigated. PPI was subject to different pH conditions (pH 2, pH 4, pH 10, and pH 12) for 1 h, then adjusted back to pH 7 and they were marked as PPI2, PPI4, PPI10, and PPI12, respectively. It was found that the breaking force (BF) and water holding capacity (WHC) of PPI10 gel were significantly improved due to the decreased particle size, increased solubility, free sulfhydryl group content and surface hydrophobicity of PPI10. While PPI2 or PPI12 lost their gel ability due to the formation of large protein aggregates. These results indicated that pH-shifting treatment might be a convenient and economical method to prepare PPI with different gel and structural properties.

Effect of Na2CO3 on quality and volatile compounds of steamed bread fermented with yeast or sourdough

The effects of Na2CO3 on the quality, change of protein subunits and volatile compounds of sourdough leavened Chinese steamed bread (sourdough-CSB) and yeast leavened CSB (yeast-CSB) were investigated. Results suggested that, low Na2CO3 level endowed both CSB with softer crumb and little change of surface color. Besides, Na2CO3 addition improved the overall aroma profile by inhibiting the production of aroma-negative compounds (butanoic acid, 1-octen-3-ol, hexanal and heptanal). Sodium dodecyl sulfate polyacrylamide gel electrophoresis analysis showed an obvious increase in intensity of protein bands with low molecular weight, consistent with the result of size-exclusion high-performance liquid chromatography analysis and free sulfhydryl group (SH) content, indicating the hydrolysis of glutenin macropolymer (GMP) under alkaline condition in yeast-CSB. While in sourdough-CSB, GMP and SH content firstly decreased at low Na2CO3 level (0–0.2%) and then increased at high Na2CO3 level (0.3%–0.5%).

Behavioral Changes in Glutenin Macropolymer Fermented byLactobacillus plantarumLB-1 to Promote the Rheological and Gas Production Properties of Dough

Glutenin macropolymer (GMP) plays a pivotal role in improving dough quality. In this study, a novel Lactobacillus plantarum LB-1 (LB-1) on the fermentation characteristics of dough were investigated from the perspective of GMP. The results showed that the ordered secondary structure (α-helices and β-sheets) content of GMP in dough synergistically fermented by yeast and LB-1 (DYLB-1) was 20.5% more than that in dough fermented by yeast (DY), and the average particle size was 2.46 μm smaller. Moreover, the higher level of total free amino acids and lower free sulfhydryl group (SHf) content in the DYLB-1 indicated that the network structure strength was enhanced. Furthermore, the protein and starch in the DYLB-1 were uniformly and closely connected, which endows the DYLB-1 with excellent rheological and gas production properties. Therefore, the method used to produce the DYLB-1 was recommended as a new strategy for producing high-quality dough.

Effect of alkaline extraction pH on structure properties, solubility, and beany flavor of yellow pea protein isolate

In the current study, the impact of alkaline extraction pH (8.5, 9.0, and 9.5) on chemical composition, molecular structure, solubility and aromatic profile of PPI was investigated by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), the quantification of free sulfhydryl group and disulfide bond contents, size exclusion chromatography with multi-angle static light scattering and refractive index (SEC-MALS-RI), circular dichroism (CD) spectroscopy, and headspace solid phase micro extraction gas chromatography-mass spectroscopy (HS-SPME-GC–MS). We found that protein recovery yield increased from 49.20% to 57.56% as the alkaline extraction pH increased from 8.5 to 9.5. However, increasing the extraction pH promoted the formation of protein aggregates which decreased the percent protein solubility although there was no influence on protein secondary structure. PPI extracted at pH 9.0 possessed the lowest beany flavor as revealed by the selected six beany flavor markers including alcohols, aldehydes, ketones and pyrazine. The lowest lipoxygenase activity at pH 9.0 may contribute to the least beany flavor in PPI. Therefore, pH 9.0 was found to be the optimal condition for preparing premium PPI in terms of yield, functionality, and aromatic profile using alkaline extraction-isoelectric precipitation process. The findings could have fundamental implications for the preparation and utilization of pea proteins in food applications.

Influence of Na2CO3 on the quality of dough with rice wine sourdough and steamed bread

SummaryThe potential use of Na2CO3 in the dough with rice wine sourdough and steamed bread was studied in the processing steamed bread, by looking at the effects of Na2CO3 addition on the dough and steamed bread quality. The relationship between Na2CO3 concentration and pH was linear. Increasing the added Na2CO3 levels from 0.10% to 0.30% resulted initially in a lower content of free sulfhydryl groups (SH), but this eventually increased. Na2CO3 addition resulted in increased glutenin macropolymer (GMP) content in the dough and reduced the softness of the dough. Dough with 0.20% Na2CO3 had significantly lower Jmax and a values compared to the other Na2CO3 concentrations tested, indicating this concentration to be ideal for reduced dough softness and appropriate interaction between molecules in dough structure. The addition of 0.20% and 0.25% Na2CO3 was also beneficial to the extension of gluten and the formation of a proper and uniform gluten network, making the dough more fine and smooth. Additionally, significant correlations were found between the creep–recovery of dough and the specific volume and hardness of steamed bread. Finally, the addition of 0.20% Na2CO3 in dough resulted in improved specific volume, whiteness and the sensory score of rice wine sourdough steamed bread.

Physicochemical properties of caprine and commercial bovine whey protein concentrate

Whey protein from caprine milk, a by-product of cheese manufacturing, was recovered by ultrafiltration technology and dried by lyophilization. A caprine whey protein concentrate (WPCc) with 64.60% of protein content was prepared. The physicochemical properties of WPCc samples under different solutions (water or 0.1 M NaCl aqueous solution) and thermal conditions (25 °C and treatment at 90 °C for 30 min) were evaluated and compared with commercial bovine whey protein concentrate (WPCb). The chemical composition and the amino acid profiles were also determined. Both WPCc and WPCb showed high solubility in 0.1 M NaCl (almost 100%) and low solubility (38%) under heat treatment and at pH 5 (close to the isoelectric point). WPCc had a greater content of free sulfhydryl groups and higher positive and negative zeta potentials at extreme pH values than WPCb; however, the surface hydrophobicity of WPCc was lower. With respect to bovine whey protein concentrate, the caprine whey proteins presented higher amounts of basic amino acid and also of isoleucine, methionine, glycine and histidine. Results obtained in this work indicated that the caprine whey protein concentrate presents good and similar physicochemical properties to those observed for bovine whey protein concentrate and that it could be used for the same food applications.