Denaturation Enthalpy Research Articles

Role of pulse globulins and albumins in air-water interface and foam stabilization

Pulse protein isolates are promising substitutes for animal protein in foam preparation, but they typically are complex mixtures of multiple proteins, and the contribution of the individual proteins to the behavior of the mixture in air-water interface stabilization is largely unknown. The major protein fractions in isolates are the globulins and albumins, and this study systematically investigated the molecular properties, and interfacial and foaming properties of these two fractions for three different pulses: lentils, faba beans and chickpeas. The key parameters of these pulse proteins in air-water interface and foam stabilization were investigated by correlation analysis. Based on this, low denaturation enthalpy tends to result in both high foamability and foam stability, most likely due to a greater conformational flexibility that allows for a faster adsorption to the air-water interface, and higher degree of structural rearrangement at the interface, which increases interfacial network stiffness. For globulin-rich pulse protein fractions, vicilins and convicilins tend to introduce high surface hydrophobicity, which increases the affinity of the proteins for the interface, and increases protein-protein in-plane interactions through hydrophobic interactions, resulting in the enhancement of interfacial network connectivity and the level of network branching. These factors increase the interfacial resistance to large deformations and increase foam stability. Vicilins and convicilins also tend to have a high value of the surface charge and further promote foam stability by increasing electrostatic repulsion between air bubbles. Legumins tend to reduce foamability since they adsorb to the air-water interface slowly and tend to disrupt the interfacial network structure. These findings provide deeper insights in the role of pulse globulins and albumins in air-water interface and foam stabilization. The proposed key parameters will benefit the predictability of the interfacial and foaming behavior of pulse proteins.

Effect of chitosan on thermal gelling properties of pork myofibrillar protein and its mechanism.

Previous studies have demonstrated that the addition of chitosan can improve the quality and functional properties of meat products. However, the underlying mechanism remains unclear. In this study, the effect and mechanism of the addition of chitosan on the gel properties of myofibrillar protein (MP) were investigated. The results indicated that the gel strength and the water-holding capacity of MP-chitosan gel increased significantly when chitosan was added at 2.5-10 mg mL-1. Myofibrillar protein samples with 10 mg mL-1 added chitosan exhibited the highest elasticity and viscosity during gel formation and strengthening. The addition of chitosan also caused a modification in both the secondary and tertiary structure of MP, resulting in an enhanced exposure of hydrophobic and sulfhydryl groups in comparison with the control. Chitosan inhibited the conversion of immobilized water into free water and the formation of water channels during the thermal gelation process of MP. The denaturation enthalpy (ΔH) of myosin decreased as the concentration of chitosan exceeded 5 mg mL-1. The microstructure showed that the incorporation of chitosan (5-10 mg mL-1) facilitated the formation of compact and well organized MP gel networks. The addition of chitosan can enhance the functional properties of meat protein and facilitate heat-induced gelation, making it a promising ingredient for improving the quality of processed meat products. © 2024 Society of Chemical Industry.

Pomegranate Peel Flour as a Co-encapsulant Improves the Survival of Lactic Acid Bacteria to Thermal Treatment and Simulated Gastrointestinal Conditions

AbstractPomegranate peel flour was employed as a co-encapsulant of two lactic acid bacteria, by alginate emulsion templated microencapsulation, to enhance their resistance to thermal treatment, acidic pHs, and gastric conditions. Samples with pomegranate peel flour increased the tolerance to heat treatment, results consistent with thermal properties related to higher denaturation enthalpy of microcapsules. Co-encapsulated microcapsules also enhanced the survival to low pHs and enhanced almost 60% up the tolerance to bile salts. There was also an increase in survival rate against in vitro gastric acid conditions due to use of the co-encapsulant. In scanning electron microscopy, the incorporation of pomegranate peel flour resulted in a rough and porous structure, probably due to certain interference with the formation of spherical microcapsules, although it presented similar mean diameter, plus higher cell viability as confirmed by confocal laser microscopy. The obtained results indicate that co-encapsulation with a prebiotic ingredient represents a reinforcement of the physical microcapsule integrity to tolerate food process temperatures, besides retarding the adverse effect of acidic, bile salts, and simulated gastrointestinal conditions. The micro alginate co-encapsulation by ionic gelation with a prebiotic as pomegranate peel flour is a suitable alternative to develop thermal processed functional foods.

Divalent metal ion in the active site of purple acid phosphatase modulates substrate binding: Kinetic and thermodynamic properties

The purple acid phosphatase was purified from 5.9-fold to apparent homogeneity from Anagelis arvensis seeds using SP-Sephadex C-50 and Sephadex G-100 chromatography. The results of residual activity tests conducted using different temperature ranges (50–70 °C) were calculated as the activation energy (Ed = 72 kJ/mol), enthalpy (69.31 ≤ (ΔH° ≤ 69.10 kJ/mol), entropy (−122.48 ≤ ΔS° ≤ −121.13 J/mol·K), and Gibbs free energy (108.87 ≤ ΔG° ≤ 111.25 kJ/mol) of the enzyme irreversible denaturation. These thermodynamic parameters indicate that this novel PAP is highly thermostable and may be significant for use in industrial applications. However, it may be confirmed by stopped-flow measurements that this substitution produces a chromophoric Fe3+ site and a Pi-substrate interaction that is about ten times faster. Additionally, these data show that phenyl phosphate hydrolysis proceeds more rapidly in metal form of A. arvensis PAP than the creation of a μ-1,3 phosphate complex. The Fe3+ site in the native Fe3+-Mn2+ derivative interacts with it at a faster rate than in the Fe3+-Fe2+ form. This is most likely caused by a network of hydrogen bonds between the first and second coordination spheres. This suggests that the choice of metal ions plays a significant role in regulating the activity of this enzyme.

Binding and displacement study of gentamicin, 5-fluorouracil, oxytetracycline and rolitetracycline with (BSA: Drug2) complex using spectroscopic and calorimetric techniques: Biophysical approach

Understanding of energetics of interactions between drug and protein is essential in pharmacokinetics and pharmacodynamics study. The binding affinity (K) helps in investigating how tightly or loosely drug is bound to protein. The binding, displacement, conformational change and stability study of drugs- gentamicin (GM), 5-fluorouracil (5FU), oxytetracycline (OTC) and rolitetracycline (RTC) with bovine serum albumin (BSA) has been carried out in presence of each other drug by fluorescence, UV–visible spectroscopy, molecular docking, circular dichroism techniques and thermal denaturation method. The site marker study and docking methods have confirmed that 5FU and GM are able to bind at site 1 and OTC and RTC at site II of BSA. The order of their binding affinities with BSA for the binary system were as GM <5FU < OTC < RTC with the order of 102 < 103 < 105 < 105–6 M−1. The displacement study has shown that higher affinity drug decreases the equilibrium constant of another drug already in bound state with BSA if both these drugs are having the same binding site. Therefore 5FU, GM (binding site 1) drugs were not able to displace OTC and RTC (binding site 2) and vice-versa as they are binding at two different sites. The binding constant values were found to be decreasing with increasing temperature for all the systems involved which suggests static or mixed type of quenching, however can only confirmed with the help of TCSPC technique. The ΔG0 (binding energy) obtained from docking method were in accordance with the ITC method. From molecular docking we have determined the amino acid residues involved in binding process for binary and ternary systems by considering first rank minimum binding energy confirmation. From CD it has been observed that RTC causes most conformational change in secondary and tertiary structure of BSA due to the presence of pyrrole ring. OTC-RTC with higher affinity showed highest melting temperature Tm values while low affinity drugs in (5FU-GM) combination showed lowest Tm value. 5FU showed large endothermic denaturation enthalpy ΔHd0 due to the presence of highly electronegative fluorine atom in the pyridine analogue.

Molecular, interfacial and foaming properties of pulse proteins

Pulses are important protein sources in the current protein transition, but much of the behavior of pulse proteins in food systems (e.g. foam) is still unknown. This study compared the similarities and differences of the proteins from three common pulses: lentil, faba bean, and chickpea, at the molecular, mesoscopic and functionality levels. For each source, the proteins were extracted with a simple one-pot alkaline extraction, resulting in protein extracts with high protein content (67–85%) rich in globulins (68–81%) and albumins (19–32%). All pulse protein fractions were predominantly in a native state with high solubilities (83–91%), high denaturation enthalpies (8.9–10.1 J/(g protein)) and low aggregation levels. Lentil protein showed higher absolute value of the ζ-potential (−18.5 ± 1.2 mV) than faba bean (−13.2 ± 0.8 mV) and chickpea protein (−12.4 ± 1.2 mV). The behavior of all pulse proteins at the air-water interface including adsorption kinetics, interfacial dilatational rheology and interfacial microstructure was investigated and linked to their foaming properties. The pulse protein with the highest vicilin and convicilin content (39.5% in lentil protein) showed the shortest adsorption lag time (300 ms), and demonstrated the highest foam overrun (290 ± 17%). All three pulse protein fractions formed interfaces with disordered solid-like behavior and consisted of heterogeneous network structures. These structures were mostly comprised of intact globulin proteins for lentil and faba bean proteins, while mixtures of intact globulins and unfolded proteins/albumins were observed for chickpea protein. The interfacial stiffness, interfacial density and ζ-potential of these pulse proteins showed a high positive correlation with their foam stabilization properties. Lentil protein has the highest values of those parameters and showed the longest foam half-life time of 115 (± 22) min, while faba bean and chickpea proteins showed comparably lower values of those parameters and shared similarly shorter foam half-life times of 46 (± 19) min and 38 (± 6) min, respectively. These findings can aid to provide clearer directions in screening pulse proteins for desirable performance in aerated food products.

Composition and functionality differences of oat protein concentrates: Potential of less refined concentrates obtained by wet milling

The objective of this study was to determine differences in composition and functionality for oat protein concentrates. This was achieved by comparing preparations extracted at different pH levels using either a twin screw press or alkaline extraction followed by isoelectric precipitation. Extraction by twin screw technology provided a higher protein yield compared to isoelectric precipitation. Analysis by SDS-PAGE revealed similar protein composition regardless of the extraction method or extraction pH except for extraction at pH 6. Extraction at a higher pH led to a higher protein purity and yield, while extraction closer to the isoelectric point of the protein resulted in less pure concentrates. All extracts were freeze-dried, and their composition and functionality were compared. Thermal analysis of the protein concentrates extracted by twin screw pressing showed a higher denaturation enthalpy compared to protein isolates prepared by isoelectric precipitation, suggesting that the native structure of the proteins is preserved to a higher extent. All protein fractions exhibited the typical U-shaped solubility profile, except for the concentrate extracted at pH 6, which showed an increase in solubility with increasing pH. Oat protein concentrates prepared by twin screw pressing had a higher affinity for binding to oil than to water, and this was also higher than for isoelectric precipitated protein extracts. Overall results demonstrate a potential for twin screw technology as a viable alternative to conventional wet extraction methods for producing less refined fractions from oats with tunable functional properties.

Fibrinolytic enzyme from Arthrospira platensis: Kinetic and thermodynamic investigation

Fibrinolytic enzymes from microorganisms have been investigated by their potential application as thrombolytic agents. Previous studies show that the fibrinolytic enzyme from Arthrospira platensis (FEAP) is stable at human physiological temperature (<50 °C) and pH (6.0–10.0). Understanding of the kinetic/thermodynamic characteristics is important to make the advances for industrial applications feasible. Therefore, a kinetic/thermodynamic analysis of FEAP was performed on the fibrin hydrolysis and enzyme thermoinactivation. Results showed two Michaelis-Menten-type profiles with two plateaus, revealing high affinity for the substrate with low Michaelis constant values (0.02 and 6.37 µg∙mL−1). The activation energy of the hydrolysis catalyzed by FEAP and the standard enthalpy variations of reversible enzyme unfolding were 49.65 and 107.01 kJ∙mol−1, respectively. When the temperature increased from 40 to 70 °C, the deactivation rate constant increased from 0.0050 to 0.0134 min−1, while the half-life decreased from 138.62 to 51.72 min. These results allowed to estimate the activation energy (E*d = 27.50 kJ∙mol−1), enthalpy (24.64 ≤ ΔH*d ≤ 24.89 kJ∙mol−1), entropy (−209.86 ≤ ΔS*d ≤ −210.10 J∙mol−1∙K−1), and Gibbs free energy (90.61 ≤ ΔG*d ≤ 96.74 kJ∙mol−1) of thermal denaturation. The data suggest that FEAP is a promising and thermostable biocatalyst that could be exploited for industrial applications.

Combined Sous-Vide and High Hydrostatic Pressure Treatment of Pork: Is the Order of Application Decisive When Using Minimal Processing Technologies?

The aim of using minimal food processing technologies is to preserve the raw material or to achieve a special technological goal with the least possible impact. When several technologies are used together, the intensity of each treatment can be reduced according to Leistner’s hurdle principle. Does the order of application of the treatments result in a detectable difference? This research focuses on the effect of the combination of the sous-vide technology and the high hydrostatic pressure (HHP) treatment. The effect of the pressure level (300 and 600 MPa) and the influence of the treatment order was investigated on pork (longissimus thoracis and lumborum muscles (LTL)). Physico-chemical and microbiological measurements were carried out on day 0 and after 21-day storage at 2 °C and 8 °C. Significant differences were found for both the order of treatment and pressure level in weight loss (p &lt; 0.001), CIELab color parameters a* and b* (p &lt; 0.001), and denaturation enthalpy (p &lt; 0.01). The texture (p &lt; 0.001) and lipid oxidation TBARS values (p &lt; 0.05) were only influenced by the pressure level. In the challenge test, the initial count of 105 CFU/g Listeria monocytogenes dropped below detection limit in all cases. Total aerobic and anaerobic viable numbers were below/near the detection limit in all combined-treated samples on day 0 and showed only slight or more notable growth after 21-day storage at 2 °C and 8 °C, respectively. An additional 300 MPa pressure treatment can increase the safety of sous-vide cooked pork samples while having only a minor effect on physicochemical properties. The 600 MPa pressure treatment results in a stable, albeit not shelf-stable product, but it also affects a considerable number of quality parameters such as color, texture, weight loss, and TBARS values.

Effects of the extraction conditions on functional and structural characteristics of proteins from fenugreek seeds.

The aim of this study is to optimize the extraction process and characterize the proteins found in fenugreek seeds. The water and oil holding capacities, coagulated protein content, foaming and emulsification properties of the isolated proteins at all extraction conditions were investigated. Also, solubility, molecular weights, structural and thermal properties were determined. In the extraction processes carried out at different pHs (pH 6.0-12.0) and solid:solvent ratios (20-60 g/L), it was determined that the highest extraction yield (94.3±0.3%) was achieved when the pH was 11.47 and the solid-solvent ratio was 34.50 g/L. Three distinct bands (46, 59 and 80 kDa) in the range of 22-175 kDa were determined for the fenugreek seed protein isolate obtained at optimum extraction conditions. Protein secondary structures were achieved using Fourier Transform Infrared (FT-IR) spectra and it was determined that β-sheet structures were highly present. In addition, denaturation temperatures and denaturation enthalpy were calculated as ~119°C and 28 mJ/g, respectively.

Response surface optimization, purification, characterization and short-chain chitooligosaccharides production from an acidic, thermostable chitinase from Thermomyces dupontii

Chitin, recovered in huge amounts from coastal waste, may biocatalytically valorized for utilization in food and biotech sectors. Conventional chemical-based conversion makes use of significant volumes of hazardous acid and alkali. Alternatively, enzymes offer better process control and generation of homogeneous products. Process variables were derived to achieve augmented levels of chitinase (3.8809 Ul−1 h−1) productivity from a novel thermophilic fungal strain Thermomyces dupontii, ITCC 9104 following incubation (96 h, 45 °C). An acidic thermostable chitinase TdChiT having molecular mass of 60 kDa has been purified. Optimal TdChiT activity has been demonstrated at 70 °C and pH 5. Notably decreased activity over a broad range of temperature and pH was observed following deglycosylation. Half-life, activation energy, Gibbs free energy, enthalpy and entropy for denaturation of TdChiT at its optimum temperature were 197.40 min, 105.48 kJ mol−1, 100.59 kJ mol−1, 102.64 kJ mol−1 and 5.95 J mol−1 K−1. TdChiT has specificity towards colloidal chitin and (GlcNAc)2–4. Metal ions viz. Mn2+, Ca2+ and Co2+ and nonionic surfactants notably enhanced chitinase activity. Thin layer chromatography analysis has revealed effective hydrolysis of colloidal chitin and (GlcNAc)2–4. TdChiT may potentially be employed for design of better, eco-friendly and less resource-intensive industrial procedures for upcycling of crustacean waste into value-added organonitrogens.

Structural, emulsifying and curcumin-embedded properties of arachin nanoparticles induced by ultrasound and heat

Different types of arachin (one of the major globulins in peanut proteins) nanoparticles were prepared by ultrasound (US) and heat treatments, respectively. The results showed that short-term US treatment induced large nanoparticles (named US200 and US500, ∼267 nm) that maintained a compact globular structure; long-term US treatment induced small nanoparticles (named US500L, ∼197 nm) with a moderately unfolded structure; heat treatment induced medium-sized nanoparticles with an unfolded structure. The large nanoparticles had significantly lower surface hydrophobicity, β-sheet content, and λmax but higher enthalpy of denaturation (ΔH) than other nanoparticles. US500L and US500 exhibited the highest emulsifying activity and stability indices, respectively. As for curcumin-embedded properties, both US and heat treatments enhanced the curcumin encapsulation efficiency (from 88.53 to 94.08–97.88%) and load amount (from 1.77 to 1.88–1.96 μg/mg) of arachin. However, only curcumin in large nanoparticles was effectively protected from damage by heat and light. In simulated digestion tests, curcumin in US500L and heat-induced nanoparticles showed higher stability and bioavailability, which was mainly attributed to the slower digestion of these nanocomplexes. We have established a simple method for the preparation of arachin nanoparticles by US and the nanoparticles have potential applications in the food industry due to their favorable bifunctional properties.

Effects of the Roasting-Assisted Aqueous Ethanol Extraction of Peanut Oil on the Structure and Functional Properties of Dreg Proteins.

The effects of the roasting-assisted aqueous ethanol extraction of peanut oil on the structure and functional properties of dreg proteins were investigated to interpret the high free oil yield and provide a basis for the full utilization of peanut protein resources. The roasting-assisted aqueous ethanol extraction of peanut oil obtained a free oil yield of 97.74% and a protein retention rate of 75.80% in the dreg. The water-holding capacity of dreg proteins increased significantly, and the oil-holding capacity and surface hydrophobicity decreased significantly, reducing the binding ability with oil and thus facilitating the release of oil. Although the relative crystallinity and denaturation enthalpy of the dreg proteins decreased slightly, the denaturation temperatures remained unchanged. Infrared and Raman spectra identified decreases in the C-H stretching vibration, Fermi resonance and α-helix, and increases in random coil, β-sheet and β-turn, showing a slight decrease in the overall ordering of proteins. After the roasting treatment, 62.57-135.33% of the protein functional properties were still preserved. Therefore, the roasting-assisted aqueous ethanol extraction of peanut oil is beneficial for fully utilizing the oil and protein resources in peanuts.

Beef tenderization without exacerbating the cooking loss: The way of enzymatic deamidation

Tenderization of beef using proteolytic enzymes often leads to high water loss due to harsh structural disruption. This study first verified the enzymatic deamidation (protein-glutaminase, PG) in softening grass-fed steak texture without exacerbating the cooking loss. PG deamidation at the deamidation degree (DD) of 5% (d5) or 7% (d7) significantly increased the tenderness and softened the texture whereas they negligibly affected the cooking loss. The muscle bundles were loosed while fibers were thickened probably as the result of charge induced myofibril dissociation (increased myofibril fraction index) and intermolecular repulsion. Compared to papain, the effect of PG deamidation on the water mobility was minor, though it was still seen a slight conversion of bound water into immobilized water in high DD steaks (d5 and d7). PG deamidation hardly hydrolyze individual proteins but partially altered the tertiary structure of muscle proteins, resulting in a slight decrease in denaturation enthalpies of muscle proteins including myosin, collagen and sarcoplasmic protein. These results demonstrated that PG deamidation appeared to be a novel and promising strategy in meat tenderization.

Effects of Wooden Breast Myopathy on Meat Quality Characteristics of Broiler Pectoralis Major Muscle and Its Changes with Intramuscular Connective Tissue.

This study aimed to investigate the effect of wooden breast (WB) myopathy on chemical composition, meat quality attributes and physiochemical characteristics of intramuscular connective tissue (IMCT) of broiler pectoralis major (PM) muscle. Thirty-six fillets were classified into varying degrees of WB condition, including normal, moderate and severe. Results show that WB myopathy altered the collagen profile in PM muscle by increasing total collagen content and decreasing collagen solubility. The composition of macromolecules in IMCT, including hydroxylysyl pyridoxine cross-linking, decorin and glycosaminoglycans, were increased with the severity of WB myopathy. Differential scanning calorimetry analysis indicated higher denaturation temperatures and lower denaturation enthalpy of IMCT for WB. Secondary structures of α-helix and β-sheet in the IMCT of WB were changed to β-turn and random coil. In addition, chemical composition and meat quality attributes showed a correlation with collagen profile and IMCT characteristics. Overall, this study emphasizes the effect of WB myopathy on IMCT and their contributions to meat quality variation.

Production and biochemical and biophysical characterization of fibrinolytic protease of a Mucor subtilissimus strain isolated from the caatinga biome.

Cardiovascular diseases, resulting from the deposition of clots in blood vessels, are the leading cause of death worldwide. Fibrinolytic enzymatic activity can catalyze blood clot degradation. Findings show that 36 fungal isolates recovered from Caatinga soils have the potential to produce fibrinolytic protease under submerged conditions. About 58 % of the isolates displayed fibrinolytic activity above 100 U/mL, with Mucor subtilissimus UCP 1262 being the most active. The protease was biochemically and biophysically characterized, showing that the enzyme had a high affinity for SAApNA substrate and was significantly inhibited by fluoride methyl phenyl sulfonyl-C7H7FO2S, suggesting that it is a chymotrypsin-like serine protease. The highest enzyme activity was detected at pH 5.0 and 28 °C. This fibrinolytic protease's far-UV circular dichroism (CD) showed that its secondary structure was primarily α-helical. The purified fibrinolytic enzyme may represent a novel therapeutic agent for treating thrombosis. At temperatures above 65 °C, the enzyme lost all its secondary structure. Its melting temperature was 58.1 °C, the denaturation enthalpy 85.1 kcal/mol, and the denaturation entropy 0.26 kcal/K∙mol.

Impact of covalent binding with p-coumaric acid on pea protein's structural and functional properties

This study investigated the effects of covalent bonding between pea protein isolate (PPI) and p-coumaric acid (p-CA) on the protein's secondary structure, solubility, foaming properties, emulsifying capacity, and thermal stability. Binding p-CA led to alterations in the secondary structure of PPI, including an increase in α-helix and random coil and a decrease in β-turn. Additionally, it resulted in a reduction in SH and NH groups, as well as a decrease in particle size. As the amount of bound p-CA increased, an increased tendency for aggregation was proposed, resulting in the formation of soluble aggregates through hydrophobic interactions, which was confirmed by a reduction in particle size of proteins after being dissolved in SDS. These structural modifications influenced the protein's functional properties, with the conjugates showing enhanced solubility and emulsifying capacity across various pH levels, but weaker foaming capacity and foam stability. Furthermore, the conjugates exhibited a lower initial denaturation temperature but a higher thermal denaturation enthalpy change (ΔH) compared to PPI, which may be attributed to protein unfolding and the formation of new covalent bonds. This study highlights the potential of p-CA covalent modification of PPI to enhance its functional properties, making it more suitable for food industry applications.

The effect of maltodextrin on properties of sated egg yolk

Salted eggs are mainly produced through salting treatments that taste salty. However, high sodium intake is part of the pathophysiology of hypertension. Thus, this study aimed to develop low-sodium egg yolks with salting treatment using sodium chloride (NaCl) and maltodextrin to reduce salt content in the salting process. Salted egg yolks were produced using methods in the salting process using maltodextrin (10% and 20% supplement) and were compared to salted eggs brined with 20 and 26% sodium chloride (NaCl) solutions. The moisture content, salt content, color, and texture properties of salted egg yolks during salting for up to 35 days were determined. Nevertheless, salted egg yolks produced with the salting solution using maltodextrin supplement had a significant salt content (0.21-3.30 mg/g) that was lower than the amount discovered in commercial salted yolks (2.84-4.15 mg/g). The results revealed that the maltodextrin substitution affected the salted yolks' properties. The salt contents of all salted egg yolk samples gradually increased during the salting process, along with slight decreases in moisture content as salting time and salt solution concentration increased. The lightness (L*) and the yellowness (b*) decreased while the redness (a*) increased. The hardness, adhesiveness, cohesiveness, gumminess, and chewiness of salted egg yolks increased rapidly over the time of salting, while springiness decreased during the initial stages of salting and reached almost constant levels at the end of salting. As the salting time increased to 35 days, the salted yolk gradually became dark reddish. The maximum denaturation temperature (Tmax) and denaturation enthalpy (DH) of egg proteins increased with increasing salting time. These effects were most pronounced due to the high maltodextrin content of the salting solution. This study suggests that this approach with maltodextrin substitution using the shell egg salting protocol can produce low-sodium salted eggs.

Energetics of β-lactoglobulin–flavor compounds interactions

Interaction of bovine β-lactoglobulin (BLG) with several flavor compounds (FC) (2–methylpyrazine, vanillin, 2–acetylpyridine, 2– and 3–acetylthiophene, methyl isoamyl ketone, heptanone, octanone, and nonanone) was studied by high-sensitivity differential scanning calorimetry. The denaturation temperature, enthalpy, and heat capacity increment were determined at different FC concentrations. It was found that the denaturation temperature and heat capacity increment do not depend on the FC concentration, while the denaturation enthalpy decreases linearly with the FC concentration. These thermodynamic effects disclose the preferential FC binding to the unfolded form of BLG. By the obtained calorimetric data, the free energies of FC binding vs. the FC concentrations were calculated. These dependences were shown to be linear. Their slope relates closely to the overall FC affinity for the unfolded BLG in terms of the Langmuir binding model. The overall BLG affinity for FC varies from 20 M–1 (2-methylpyrazine) up to 360 M–1(nonanone). The maximal stoichiometry of the BLG–FC complexes was roughly estimated as a ratio of the length of the unfolded BLG to the molecular length of FC. Using these estimates, the apparent BLG–FC binding constants were determined. They are in the range of 0.3–8.0 M–1 and correlated strictly with the FC lipophilicity descriptor (logP).

Age-related hair denaturation related to protein carbonyls.

Hair ageing is accompanied by hair fibres becoming irregularly shaped causing them to stick out in irregular directions or have more curliness and being spread out. This is believed to be due to changes within the hair fibre structure which occur with ageing, and one of the causes of these changes could be an increase in the number of protein carbonyl groups present in the hair. The aim of this study is to investigate the internal denaturation of hair related to protein carbonyls in attempt to gain new insight into age-related changes that occur in hair. The degree of carbonylation of the hair structural protein as determined by fluorescent labelling and Western blotting analysis was used to investigate the primary structure of hair protein. The amount of helix, a common conformation in the secondary structure of proteins, in hair in groups of women with different ages was also analysed using infrared microscopy coupled with multivariate curve resolution (MCR). From the results of this, an image of the two-dimensional distribution of the α-helices was generated for the hair taken from each age group. Also, high-pressure differential scanning calorimetry (HPDSC) of the hair in water was performed on the hair taken from each age group to determine the peak temperature of endothermic effect and the enthalpy of denaturation. We found that the amino group content in hair proteins decreased and Type II keratin, one of the subunits of intermediate filament, was more carbonylated with age. The results of the MCR indicated eight separate components, including components of the secondary structure of proteins, such as α helices and β sheets. Two-dimensional images of the hair cross-sections revealed that the presence of α helices decreased with age. In addition, data from the HPDSC showed that the enthalpy associated with the denaturing temperature also significantly decreased with age. These results suggest that there is a negative correlation between age and structural integrity of the helix segment in intermediate filament. The results of this study also show that there is a positive correlation between age-related hair denaturation and protein carbonyls.