Denaturation Enthalpy Research Articles

Preparation and Characterization of an Ancient Aminopeptidase Obtained from Ancestral Sequence Reconstruction for L-Carnosine Synthesis.

As a biologically active peptide, L-carnosine has been widely used in the pharmaceutical, cosmetic and health care industries due to its various physiological properties. However, relatively little research is available regarding L-carnosine’s enzymatic synthesis function. In this study, a potential enzyme sequence with the function of carnosine synthesizing was screened out using the ancestral sequence reconstruction (ASR) technique. Identified with L-carnosine synthesis activity, this enzyme was further confirmed using autoproteolytic phenomenon via Western blot and N-terminal sequencing. After purification, the enzymatic properties of LUCA–DmpA were characterized. The melting temperature (Tm) and denaturation enthalpy (ΔH) of LUCA–DmpA were 60.27 ± 1.24 °C and 1306.00 ± 26.73 kJ·mol−1, respectively. Circular dichroism (CD) spectroscopy results showed that this ancestral enzyme was composed of α-helix (35.23 ± 0.06%), β-sheet (11.06 ± 0.06%), β-turn (23.67 ± 0.06%) and random coil (32.03 ± 0.06%). The enzyme was characterized with the optimal temperature and pH of 45 °C and 9.0, respectively. Notably, LUCA–DmpA was also characterized with remarkable pH tolerance based on the observation of more than 85% remaining enzymatic activity after incubation at different pH buffers (pH = 6–11) for 12 h. Additionally, rather than being improved or inhibited by metal ions, its enzymatic activity was found to be promoted by introducing organic solvent with a larger log P value. Based on these homology modeling results, the screened LUCA–DmpA is suggested to have further optimization potential, and thereafter to be offered as a promising candidate for real industrial applications.

Mechanisms of inulin addition affecting the properties of chicken myofibrillar protein gel

This paper studied the effects of inulin addition (0–20 mg mL −1 ) on the properties of chicken myofibrillar protein (MP) heat-induced gel. The molecular forces to maintain the gel structure, gelling formation process and gel microstructure were studied to explore the influencing mechanism of inulin on gel properties of MP. The results showed that the springiness and hardness of MP-inulin gel significantly increased when inulin was added at 5–20 mg mL −1 , while the water holding capacity (WHC) significantly enhanced at 5–10 mg mL −1 inulin addition ( P < 0.05). The most appropriate inulin addition to improve the properties of MP mixed gel was 10 mg mL −1 . The addition of 20 mg mL −1 inulin decreased the cooking loss of mixed gel. Inulin promoted the exposure of more hydrophobic groups and the formation of disulfide bonds. Inulin addition significantly decreased the I850/I830 in Raman spectrometry, indicating an increase in the formation of hydrogen bonds with MP molecules. However, inulin had little effect on electrostatic interaction between MP molecules. During the heating process, the highest storage modulus (G′) value was observed in MP samples added with 15 mg·mL −1 inulin at gel forming and strengthening stage. The denaturation enthalpy (ΔH) value of myosin decreased when inulin exceeded 10 mg mL −1 . The microstructure showed that MP composite gel with 10 mg mL −1 inulin had a dense and well-aggregated network structure. These results indicated that inulin addition could make MP denaturation easier during heating, strengthen the molecular forces of MP and the gel network structure, thus improving the MP gel properties. • Inulin addition improved the gel properties and microstructure of myofibrillar protein. • Inulin strengthened the molecular forces of myofibrillar protein in gels. • Inulin addition made myofibrillar protein more prone to thermal denaturation. • Mechanisms of inulin addition affecting properties of myofibrillar protein gel was revealed.

Physicochemical and functional properties of buckwheat (Fagpopyrum esculentum Moench) albumin

Buckwheat albumin is a promising functional food material that can suppress postprandial blood glucose elevation. Here, we studied the physicochemical and functional properties of buckwheat albumin such as thermal resistance, solubility, and emulsifying and foaming properties to evaluate its potential for application in various foods such as mayonnaise, ice cream, meringues and sponge cake. The denaturation temperature of buckwheat albumin was measured using Differential Scanning Calorimetry (DSC) with and without the addition of dithiothreitol (DTT), and solubility in the pH range of 3.0–6.0 was measured as protein concentration in supernatant before and after heating. Emulsifying and foaming properties of buckwheat albumin were also evaluated before and after hydrolysis by protease. Buckwheat albumin exhibited high thermal resistance with a denaturation temperature of 148.4 °C. However, the peak temperature of DSC thermogram decreased and denaturation enthalpy increased with DTT addition. High solubility was observed at pH 3.0–6.0, which was retained even after heating at 80 °C for 20 min. Furthermore, buckwheat albumin showed high emulsifying and foaming properties in the pH range 3.0–6.0. Although its emulsifying property was decreased on protease treatment, high foaming capacity was maintained even after hydrolysis. These findings suggested that buckwheat albumin can be widely used in various functional foods.

Identifying changes in soybean protein properties during high-moisture extrusion processing using dead-stop operation

To provide additional evidence and better understand the high-moisture texturing extrusion process of soybean protein isolate (SPI), the physico-chemical changes of SPI during extrusion were investigated. SPI in the extruder feeding zone, barrel zones 1 (80 °C) to 4 (135 °C), and the cooling die (80 °C) were obtained from a dead-stop operation. The lowest values associated with the denaturation enthalpy and the extractable protein occurred in zone 3 (150 °C). The minimum level of the protein subunit content was identified in zone 4. The highest value of the average protein molar mass occurred in zone 3. The β-sheet ratio in the protein increased, and the unordered ratio decreased after extrusion. The surface hydrophobicity of the protein decreased with water injection in zone 1; however, it increased in zone 2 (110 °C). Overall, SPI undergoes swelling, denaturation, aggregation, and depolymerization due to water injection, heating, and shearing during high-moisture extrusion.

A Possible Way to Relate the Effects of SARS-CoV-2-Induced Changes in Transferrin to Severe COVID-19-Associated Diseases.

SARS-CoV-2 infections are responsible for the COVID-19 pandemic. Transferrin has been found to explain the link between diseases associated with impaired iron transport and COVID-19 infection. The effect of SARS-CoV-2 on human whole blood was studied by differential scanning calorimetry. The analysis of the thermal transition curves showed that the melting temperature of the transferrin-related peak decreased in the presence of SARS-CoV-2. The ratio of the under-curve area of the two main peaks was greatly affected, while the total enthalpy of the heat denaturation remained nearly unchanged in the presence of the virus. These results indicate that SARS-CoV-2, through binding to transferrin, may influence its Fe3+ uptake by inducing thermodynamic changes. Therefore, transferrin may remain in an iron-free apo-conformational state, which depends on the SARS-CoV-2 concentration. SARS-CoV-2 can induce disturbance in erythropoiesis due to toxicity generated by free iron overload.

Effect of microwave heating time on the gel properties of chicken myofibrillar proteins and their formation mechanism

SummaryThe present work was conducted to illustrate the mechanism of gel formation of myofibrillar proteins (MPs) under different microwave heating times. The results showed that the denaturation enthalpy (ΔH) of the MPs significantly decreased when the heating time increased from 3 to 9 s and then completely disappeared as the heating time progressed, indicating that the MPs gradually denatured and subsequently aggregated with increasing heating time, which was further verified by the changes in the secondary structure, electrophoretic bands, and gel properties (e.g., water holding capacity and textural profiles) of the MPs. Microstructural images indicated that the MP gel formed under 12 s had the most compact network, indicating that extended microwave heating time could induce quality deterioration of MP gels. Moreover, the hydrophobic forces, electrostatic forces, and disulphide bonds of the MPs gradually intensified with increasing microwave heating time, suggesting that both non‐covalent and covalent bonds could promote molecular denaturation and subsequent aggregation of MPs. In addition, correlation analysis revealed that the changes in the molecular conformation of MPs induced by different microwave heating times could effectively regulate the formation of MP gels and their related properties.

Modulation of the Structure and Stability of Novel Camel Lens Alpha-Crystallin by pH and Thermal Stress.

Alpha-crystallin protein performs structural and chaperone functions in the lens and comprises alphaA and alphaB subunits at a molar ratio of 3:1. The highly complex alpha-crystallin structure challenges structural biologists because of its large dynamic quaternary structure (300–1000 kDa). Camel lens alpha-crystallin is a poorly characterized molecular chaperone, and the alphaB subunit possesses a novel extension at the N-terminal domain. We purified camel lens alpha-crystallin using size exclusion chromatography, and the purity was analyzed by gradient (4–12%) sodium dodecyl sulfate–polyacrylamide gel electrophoresis. Alpha-crystallin was equilibrated in the pH range of 1.0 to 7.5. Subsequently, thermal stress (20–94 °C) was applied to the alpha-crystallin samples, and changes in the conformation and stability were recorded by dynamic multimode spectroscopy and intrinsic and extrinsic fluorescence spectroscopic methods. Camel lens alpha-crystallin formed a random coil-like structure without losing its native-like beta-sheeted structure under two conditions: >50 °C at pH 7.5 and all temperatures at pH 2.0. The calculated enthalpy of denaturation, as determined by dynamic multimode spectroscopy at pH 7.5, 4.0, 2.0, and 1.0 revealed that alpha-crystallin never completely denatures under acidic conditions or thermal denaturation. Alpha-crystallin undergoes a single, reversible thermal transition at pH 7.5. The thermodynamic data (unfolding enthalpy and heat capacity change) and chaperone activities indicated that alpha-crystallin does not completely unfold above the thermal transition. Camels adapted to live in hot desert climates naturally exhibit the abovementioned unique features.

β-Lactoglobulin–fucoidan nanocomplexes: Energetics of formation, stability, and oligomeric structure of the bound protein

Interaction of β-lactoglobulin (BLG) with a sulfated polysaccharide isolated from the brown alga Fucus vesiculosus (fucoidan, FVF), was studied by nephelometry, high-sensitivity differential scanning calorimetry, and sedimentation velocity as a function of pH and the polysaccharide/protein ratio. FVF–BLG complexes were found over the pH 2.5–6.0 range. The complexation was accompanied by the decrease in the conformational stability of BLG at pH < pI 5.2 of the protein where FVF and BLG were oppositely charged. Near pI of the protein and at the pH values larger a bit than pI, where BLG has a large dipole moment or carries a small negative charge, the complexation appeared as changes in the oligomeric state of the protein. Binding curves of BLG to FVF were obtained at pH 3.0 and 6.0 according to the DSC and sedimentation velocity data. Binding constants were evaluated: 3.6 × 103 M−1 at pH 3.0 and 2 × 104 M−1 at pH 6.0. Correlations between the denaturation enthalpy and temperature for the free and bound protein in terms of Kirchhoff's law indicated that the denaturation of both forms of the protein is associated with comparable changes in the accessible surface area of the BLG molecule. It means that the binding of BLG to FVF does not perturb the hydrophobic core of the protein.

How hydrocolloids can control the viscoelastic properties of acid-swollen collagen pastes

The interactions between proteins and polysaccharides are of considerable importance in the food industry. In this study, the effect of adding non-charged methylcellulose (MC), hydroxypropylmethylcellulose (HPMC), medium (GM) and high (GH) molecular weight guar gum and negatively charged sodium carboxymethylcellulose (CMC) was investigated on the rheological and thermal properties of acid-swollen collagen pastes, as a function of collagen concentration. Dynamic frequency sweeps showed that the addition of the hydrocolloids, except for CMC, increased the storage modulus (G′) and loss modulus (G″) of collagen pastes at all collagen levels investigated. MC, HPMC, GH, and GM increased the collagen pastes' storage modulus to a similar extent. In contrast, the values of the loss moduli were found to be markedly different for each hydrocolloid. The loss factor (tan δ) showed that incorporating the hydrocolloids made the pastes less elastic than pure collagen pastes. The phase transition temperature of collagen measured during the temperature sweep tests was not affected by MC, HPMC, GH, and GM. However, CMC shifted the transition temperature of collagen to higher temperatures. Micro Differential scanning calorimeter (microDSC) results showed that the presence of MC, HPMC, and guar gums did not affect the denaturation temperature (Td) and enthalpy (ΔH). In contrast, the addition of CMC increased the denaturation temperature and denaturation enthalpy of collagen pastes. By fixing the hydrocolloids' viscosifying power and changing the collagen concentration, collagen pastes with different hydrocolloids show different viscoelastic properties.

Influence of konjac glucomannan on thermal and microscopic properties of frozen wheat gluten, glutenin and gliadin

The effects of different konjac glucomannan (KGM) concentrations (0.5%, 1.5%, 2.5%, 3.5%, 4.5%, w/w) on the thermal and microscopic properties of the frozen wheat gluten, glutenin and gliadin were investigated in this study. KGM exerted a positive effect on the denaturation temperature and denaturation enthalpy of frozen gluten and gliadin, while KGM decreased those of frozen glutenin. Such effects induced by KGM were resulted from the interaction between KGM and frozen wheat gluten, glutenin and gliadin. The underlying mechanism was discussed from the perspective of protein structure. Specifically, the addition of KGM increased the α-helix structure of frozen gluten and gliadin, while decreased the α-helix of frozen glutenin. Furthermore, β-turn of frozen gluten and gliadin presented a decreasing trend with increasing amount of KGM. Scanning electron microscopy confirmed that there was stronger interaction between wheat protein and KGM. These results provide fundamental knowledge for better application of KGM in frozen protein-based foods.

Gelation of chicken batters during heating under high pressure

The gelling process of chicken meat batters, which were heated (75 °C) under atmospheric pressure or high pressure (200/400 MPa), was investigated by determining the hardness of batter, residual denaturation enthalpy, microstructure, and protein secondary structure. The results showed that meat batters heated at 200 MPa showed a similar increase in hardness to heat-only samples, but meat batters heated at 400 MPa showed a texture decreasing tendency after a limited increase. High pressure disrupted the myofibrils, promoted protein denaturation and aggregation in the first stage of heating under pressure treatment. In the second stage of treatment, heating was the main driving force for protein gelation, which was disturbed by hindering the structural transformation of proteins in the presence of high pressure during heating. The effect of 200 MPa on muscle proteins was relatively gentle and had a less negative effect. Excessive high pressure should be avoided when applying heating under pressure for gel-type meat products processing. Industry relevanceHigh-pressure processing is increasingly applied in the meat industry. By combining high pressure with heating, their effects on texture improvement and microbial inactivation can be maximized. In this study, the influence of high pressure on the texture of meat products was analyzed, which showed that excessive pressure would significantly interfere with the thermal denaturation of the protein, thus adversely affecting the formation of the gel structure. High pressure at 400 MPa and above should be avoided when applying heating under pressure for gel-type meat products processing.

Protein, thermal and functional properties of α-, γ- and ω-gliadins of wheat and their effect on bread making characteristics

The study investigated the rheological, microstructural and functional properties of α-, γ- and ω-gliadins. Crude gliadin was subjected to cation exchange fast protein liquid chromatography and eluted individual gliadins in 17 peaks. NanoLC Electrospray ionization coupled MS-MS analysis revealed the identity of polypeptides from selected peaks as α-, α/β-, and γ-gliadins with high PLGS (ProteinLynx Global SERVER™) score. Inclusion of 1% (w/w) total gliadin containing, α-, γ- and ω-gliadins to base flour decreased dough development time and stability, while increased peak resistance and dough softening. The addition of gliadins improved the loaf volume of bread. DSC revealed multiple peak denaturation temperatures (Tp) for gluten, α- and γ-gliadins whereas, single peak for gliadins and ω-gliadins. The enthalpies of denaturation (ΔH) for gliadin and its purified α-, γ-, and ω-gliadin fraction were higher than gluten. Scanning electron micrographs (SEM) displayed collateral relationship among dough microstructure and mixing characteristics of these elements. These findings provided insight into the functionality of purified gliadins and potential use in the development of different food products.

Peracetic Acid-Ethanol Processed Human Tendon Allograft: A Morphological, Biochemical, and Biomechanical Study In Vitro.

To clarify the morphological, biochemical, and biomechanical effects of peracetic acid-ethanol sterilization processing to human hamstring tendon allografts for different time periods. Thirty-two fresh-frozen human hamstring tendon allografts obtained from an allograft supplier were prepared and incubated in peracetic acid-ethanol solution (PES) containing 1% v/v peracetic acid and 24% v/v ethanol. Specimens were randomly classified into four groups according to the PES processing time (untreated as the control group, 30 min as the PES30 group, 120 min as the PES120 group, and 240 min as the PES240group). Light microscopy with hematoxylin-eosin and toluidine blue were performed, along with transmission electron microscopy (TEM) to measure the collagen fibril diameters and their distributions, from which the collagen fibril index (CFI) and mass average diameter (MAD) were calculated. The thermal stability and collagen denaturation were analyzed by differential scanning calorimetry (DSC) and collagen denaturation test by α-chymotrypsin. Cyclic loading and failure testing were applied on five tendons from each group, from which the cyclic creep strain, elastic modulus, maximum stress, maximum strain, and strain energy density were calculated. Tendons in the control, PES30, PES120 groups showed similar regularly aligned collagen fibers in light microscopy images, while the images from the PES240 group revealed relatively disordered and heterogeneous collagen bundles with larger interfiber spaces. TEM analysis showed that the mean diameter (F = 3.09, P = 0.04) was lower in the PES120 group (87.15 ± 4.76 nm) than it was in the control group (99.39 ± 9.19 nm) but not statistically (P = 0.05). Moreover, the CFI value in the PES30 group (65.37 ± 4.14%) was the lowest among groups (all P ≤ 0.01), while no variance existed in density and MAD among groups (F = 2.09, P = 0.13, and F = 0.27, P = 0.85, respectively). The onset temperature (H = 8.74, P = 0.03) and peak temperature (H = 9.97, P = 0.02) were decreased in the PES30 group compared to the control group (P = 0.02 and P = 0.01, respectively), but there were no differences in enthalpy of denaturation among groups (F = 2.20, P = 0.17). The collagen denaturation test revealed lower hydroxyproline concentrations in PES-treated specimens with no statistical differences among groups (H = 8.86, P = 0.07). The maximum stress showed variance (F = 10.52, P < 0.01) that it was higher in PES30 group (68.29 ± 10.86 MPa) compared to the PES120 and the PES240 group, while it was lower in the PES120 group (19.40 ± 4.94 MPa) compared to the control and the PES30 group (all P < 0.05). The strain energy density (F = 7.34, P < 0.01) was over 4 times higher in the PES30 group (7.39 ± 2.51 MPa) than it was in the PES120 group (1.56 ± 0.64 MPa, P < 0.01). PES treatment for 30 min has no adverse effect on the properties of human hamstring tendon allografts, longer processing time could not promise better properties preservation.

English

In this experiment, effect of lead (Pb) + chromium (Cr) mixture on superoxide dismutase (SOD) in the liver of Labeo rohita at a concentration of 11.1 mgL-1 was observed. The ammonium sulphate precipitation and ion exchange chromatography techniques were successfully used to purify SOD. After purification, SOD activity of control and Pb+Cr treated fish was noted as 581.00 and 645.45 UmL-1, respectively while the specific activity was 1383.33 and 1613.62 Umg-1, respectively. The fold purification value of SOD was 2.75 and 2.45 for control and stressed fish, respectively. The recovery was calculated as 77.06 and 57.43% for control and stressed fish, respectively. The results of kinetic characterization showed that SOD form control and exposed fish had maximum activity at pH 6.5 and 7.0. Temperature also had a significant effect on activity of SOD. The SOD activity was measured maximum at 30°C for both control and Pb+Cr exposed fish. The Km value of liver SOD for control and Pb+Cr treated L. rohita was calculated as 1.48 and 0.62 mM, respectively. The value of Vmax for SOD from liver of control and Pb+Cr exposed fish was 1000 and 570 U mL-1, respectively. The enthalpy of denaturation (∆H*) for liver SOD from control and Pb+Cr exposed L. rohita was computed as 3.492 and 2.802 KJ mol-1 at 40°C, respectively and these values were dropped off with increasing the temperature until it remains 3.251 and 2.561 KJ mol-1 at 70°C, respectively. The free energy of thermal denaturation (ΔGº) of liver SOD was slightly increased with increasing temperature until 75°C which shows its resistance against heat. The values of ΔGº was observed as 58.03 and 57.95 KJ mol-1 for control and exposed fish at 40°C, respectively while the same was increased upto 62.37 and 62.00 KJ mol-1 at 70°C, respectively. It was concluded from negative value of ΔS* (entropy of inactivation) that the SOD is stable thermodynamically.

Sous Vide Cook Temperature Alters the Physical Structure and Lipid Bioaccessibility of Beef Longissimus Muscle in TIM-1.

Changes in the physical states, induced with different sous vide cooking temperatures, significantly (P < 0.05) altered lipid bioaccessibility measured in the TNO-simulated gastrointestinal tract model-1 of AAA boneless beef striploin, containing the longissimus lumborum muscle. The denaturation of actin significantly correlates with the total cumulative free fatty acid (FFA) bioaccessibility, whereby the striploin cooked to 60 °C presents the maximum lipid bioaccessibility (15.8 ± 1.0%), rate constant (ka) for FFA hydrolysis (0.087 ± 0.003 min-1), and greatest actin denaturation enthalpy (-0.57 ± 0.06 ΔH). Thus, thermal treatments above 60 °C significantly decrease the kinetics of lipolysis (70 °C = 0.042 ± 0.002 min-1 and 80 °C = 0.047 ± 0.002 min-1) and the resultant total lipid bioaccessibility (70 °C = 8.6 ± 0.7 and 80 °C = 8.3 ± 0.5%). This research highlights the potential to manipulate the physical food structure to alter digestion kinetics, supporting the need to understand supramolecular structures in food and their nutritional outcomes.

Comparison of the characteristics of prolamins among foxtail millet varieties with different palatability: Structural, morphological, and physicochemical properties

Recently, there are considerable interests in the influence of prolamins on eating quality of grains. To inquire the potential effect of prolamins on the palatability of foxtail millet, prolamin characteristics under its raw (PR) and post-cooked (PC) state among three typical varieties with high (Zhonggu, ZG), medium (Zhaonong, ZN), and low (Hongmiao, HM) palatability were compared. The distinctive differences in amino acid composition, molecular structure, physicochemical properties were found in PRs and PCs, especially for HM variety. HM-PR recorded the lowest hydrophobic amino acids and surface hydrophobicity while having the superior hydration properties. The lowest denaturation temperature was found in HM-PR, which also had the highest denaturation enthalpy (ΔH). Nevertheless, HM-PR exhibited irregularly spherical protein body with the largest mean diameter. Evidenced by the highest random coil and lower α-helix and β-sheet content, a less stable secondary structure of HM-PR was found, corresponding to the most intensified disulfide cross-linking and protein aggregations in HM upon cooking. Overall, HM-PR was presumed to greatly affect the hydro-thermal utilization efficiency of starch granules during cooking, given the steric-hindrance effect of prolamins on granules in endosperm. The Present study provided new insights into the role of prolamins on foxtail millet palatability.

Blood serum denaturation profile examined by differential scanning calorimetry reflects the effort put into ultramarathon by amateur long-distance runners

The impact of participation in the ultramarathon on the health and mental and physical condition is very complex. Undoubtedly, exercise brings many benefits but also involves health risks. Especially such an extreme effort as the one associated with finishing the ultramarathon run, can be dangerous to the health of the runner. With the variety of possible biomarkers of excessive fatigue that threaten health and life, a question arises which of them are the best and which should be considered in amateur long-distance runners showing particularly high individual variability. In this study differential scanning calorimetry (DSC) has been applied to show the overall effect of the 12-h run on blood sera of participants. Serum samples were obtained from the blood of ten male amateur long-distance runners, collected before and immediately after the run. Distinct changes in the shape of DSC curves have been observed for serum after finishing the run relative to pre-race serum. Statistically significant differences between stages "before" and "after" ultramarathon running have been found for parameters of the endothermic transition associated with denaturation of serum proteins. An increase in the temperature (from 70.9±0.9 to 75.8±2.9°C) and excess heat capacity (from 0.859±0.201 to 1.102±0.226 Jg-1 °C-1) at peak maximum, the enthalpy of serum denaturation (from 18.55±6.52 to 22.08±5.61 Jg-1) and the first moment of the thermal transition with respect to the temperature (from the value of 67.0±2.1 to 72.6±2.1°C) has been observed. These results show a clear impact of running an ultramarathon on the participant's blood serum.

Effect of cryogenic freezing on the rheological and calorimetric properties of pasteurized liquid egg yolk

The egg yolk undergoes an irreversible gelation process when freezing to –6 °C or lower. In this experiment, liquid egg yolk (LEY) was frozen in liquid nitrogen and stored at –18 °C for 150 days. The measurement of pH and colour of LEY were performed. The examination of the rheological and calorimetric properties of samples was also carried out. The results indicated that the pH of LEY changed significantly during frozen storage, increasing from 6.37 ± 0.02 to 6.58 ± 0.03 over five months. The colour of the samples also showed a significant change compared to the fresh sample. The rheological properties of the LEY also changed significantly after 1 day of freezing and during frozen storage, with a clear increasing trend of the yield stress. The results of the calorimetric study showed that freezing and frozen storage did not affect the denaturation temperature, however, the denaturation enthalpy was reduced by about half after five months of frozen storage.

Ultrasound-induced structural modification and thermal properties of oat protein

The objective of this study was to characterize the solubility, structural, thermal, and aggregation properties of oat protein under high-intensity ultrasound (HIU) treatment. Suspensions of oat protein isolate (OPI) at pH 2.0–8.0 were subjected to HIU for 5 min at 70% amplitude; solubility, particle size, surface attributes, UV–Vis absorption, intrinsic fluorescence, polypeptide profiles, calorimetric properties, and thermal aggregation were determined. The HIU treatment significantly reduced particle size (up to 37%) and increased surface charge of OPI leading to solubility increases (up to 48%, P < 0.05) at pH 2.0–3.0 and pH 5.5–8.0. However, HIU did not alter the protein profile nor disrupt disulfide linkages between α and β subunits. Reduced enthalpy of denaturation with no shift in thermal transition temperature were observed in HIU samples unless disulfide bonds were pre-cleaved. While control OPI displayed variable changes in particle size upon heating from 20 to 95 °C, the HIU sample maintained a relatively uniform and smaller particle size. The findings indicate that protein particle disruption and weakening of intermolecular forces by HIU improved physicochemical and thermal properties of OPI, which are of value to processing oat protein-based beverages and other food products.

Assessment of impact of pulsed electric field on functional, rheological and structural properties of vital wheat gluten

Pulsed electric field (PEF) was efficient in inactivating lipase in wheat grains. To understand the modification in wheat components, the functional, rheological, and structural properties of vital wheat gluten (VWG) were evaluated after PEF treatment. The results showed that the PEF parameters, electric field intensity (EFI), pulse frequency, pulse width, and material residence time significantly (P < 0.01) affected the solubility, water-holding capacity, oil-holding capacity, foaming capacity, foam stability, and emulsion stability to different extents. The transition temperature and denaturation enthalpy of gluten protein decreased significantly (P < 0.01). The elastic modulus, viscous modulus, tanδ of the wet gluten protein, and the apparent viscosity of VWG changed slightly; however, they changed significantly (P < 0.05) with the increase in EFI. Larger EFIs resulted in a more homogeneously condensed and evenly distributed wet gluten pore. The proportion of α-helices and β-sheets had decreased and increased with the increase in EFI, respectively, while the proportion of random coils changed insignificantly (P > 0.05). The amount of free and total sulfhydryl increased and decreased significantly (P < 0.01) with an increase in EFI, respectively. Surface hydrophobicity was significantly reduced (P < 0.01).