Denaturation Enthalpy Research Articles

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).

Enzymatic and extrusion pretreatments of defatted rice bran to improve functional properties of protein concentrates

SummaryThis study evaluated effects of enzymatic, extrusion and combined pretreatments on functional and thermal properties of protein concentrates from defatted rice bran to improve their applicability to food formulations. After the pretreatments, protein concentrates were recovered by alkaline solubilisation and isoelectric point precipitation. Water absorption capacity, oil absorption capacity, emulsifying and foaming properties, and thermal stability were determined in protein concentrates. Yields of each pretreatment were above 62% protein. Enzymatic hydrolysis increased all functional properties studied, mainly for emulsifying activity index (an increase of 71.1%) and foaming capacity (an increase of 60.3%). The extrusion affected positively the oil absorption capacity, emulsifying activity index and foaming capacity. The combined process was able to raise the functional properties. The principal component analysis confirmed that 95.5% improvement in functional properties of concentrates had a strong positive correlation with the pretreatments. However, the pretreatments affected thermal stability and the enthalpy of denaturation negatively.

Extraction and Characterization of Proteins from Pachyrhizus ahipa Roots: an Unexploited Protein-Rich Crop.

Pachyrhizus ahipa is an unexploited crop known to be rich in proteins compared to other edible roots and tubers. These proteins are not prolamins, thus ahipa represents an interesting new source of ingredients for gluten-free foods. In this work, ahipa proteins (AP) were extracted and partially characterized in pursuit of their use as food ingredients. The effect of ultrasound treatment on protein extraction efficiency was evaluated. AP were characterized by their size, amino acid composition, surface hydrophobicity, intrinsic fluorescence, FTIR spectra, solubility, and thermal and emulsifying properties. AP were efficiently removed from the vegetal tissue using PBS or water, regardless of the use of ultrasound, but not easily recovered by precipitation. This protein fraction was composed of small proteins, with sizes ranging from 9 to 30kDa, and highly polar. AP resulted particularly rich in aspartic acid (59% of the total amino acid content), for which they can be classified as Asp-rich proteins. Their elevated content of acidic groups was evidenced in the ATR-FTIR spectrum. The amide I band deconvolution as well as the low surface hydrophobicity and denaturation enthalpy indicated that these proteins are mainly unordered structures. The emulsifying properties of AP were enhanced when the concentration was increased from 0.1 to 1% (w/v) but resulted lower than those of soy protein. The high polarity, small size, and low isoelectric point make AP particularly suitable for acidic food matrices.

Effect of heat treatment on the structure and digestion properties of oat globulin

AbstractBackground and objectivesThe heat treatment required for deactivation of enzymes was carried out in crop species such as oats to retain its desirable shelf life, but it may lead to a reduction in nutritive value and denaturation of globulin. This study compared the effect of two heat treatments, stirring roasting (240°C, 15 min; OFG) and kiln roasting (140°C, 45 min; OMG), on structure and digestion properties of oat globulins.FindingsThe results showed that compared with control oat globulin (OCG), both heat treatments decreased the content of amino acid in the oat globulins. The increase in roasting temperature (from 140°C to 240°C) led to the change in the secondary structure in oat globulins, with a decrease in β‐sheet and β‐turn contents, and an increase in α‐helix and random coil contents. Scanning electron microscopy showed that the structure of OFG was fragmented into small clumps. Compared with kiln roasting (140°C), stirring roasting (240°C) decreased average molecular weight, peak viscosity, and denaturation enthalpy but increased viscosity and in vitro digestibility of oat globulin.ConclusionsCompared with kiln roasting, stirring roasting increased in vitro digestibility of oat globulin and contributed to the taste, but the nutritional loss was greater.Significance and noveltyTwo heat treatment methods for enzymatic inactivation were compared regarding the effect on the structure and in vitro digestibility of oat globulin, indicating that higher temperature increased digestibility of oat globulin.

Pea Protein Extraction Assisted by Lactic Fermentation: Impact on Protein Profile and Thermal Properties.

Although pea protein has been widely explored, its consumption is still limited by undesirable sensory characteristics and low solubility. All these properties can be modified during protein extraction process. Besides, previous studies showed that lactic acid bacteria (LAB) have a positive effect on legume protein ingredients in terms of flavor and functional properties. Hence, the objective of this work was to explore an alternative extraction method based on alkaline extraction/isoelectric precipitation (AEIEP) resulting in globulin-rich and residual albumin-rich fractions. Here, the decrease in pH was achieved by lactic fermentation instead of mineral acid addition. Different bacteria strains (Streptococcus thermophilus, Lactobacillus acidophilus and Bifidobacterium lactis) have been used alone or in co-culture, and the results were compared with the usual acidification. The extraction assisted by fermentation led to the increase by 20–30% in protein content/yield of the albumin fraction, meaning that the solubility of the extracted pea protein was increased. This result could be explained by the proteolytic activity of bacteria during lactic fermentation. Therefore, the thermal denaturation properties of the isolated protein fractions measured by differential scanning calorimetry could be mainly ascribed to differences in their polypeptide compositions. In particular, higher denaturation enthalpy in globulin fractions after fermentation compared to AEIEP (~15 J/g protein vs. ~13 J/g protein) revealed the relative enrichment of this fraction in pea legumins; a higher part of 7S globulins seemed to be consumed by lactic acid bacteria.

The effect of extraction and isoelectric pH values on functional and thermal properties of tahini meal protein

ABSTRACT - Tahini is an important product of peeled sesame. As a byproduct of oil extraction from tahini, tahini meal (TM) is a valuable protein source. However, it is only used to feed livestock. TM can be used as an affordable protein source in human diet. In this research work, the effects of extraction pH (10, 11 and 12) and isoelectric pH (4.5, 5.5 and 6.5) on functional and thermal properties of proteins isolated from TM were studied. Functional properties of extracted proteins including water and oil absorption, foaming capacity and foam stability as well as thermal properties were measured. The results showed that the highest protein extraction efficiency (87%) was obtained in extraction pH at pH≥11 and isoelectric pH 6.5. In addition, the highest levels of water and oil absorption capacity were obtained in proteins precipitated at pH 6.5 (p ≤0.05). The highest level of foaming capacity and stability was observed in proteins extracted at pH11 and precipitated at pH6.5. On the other hand, thermal properties of TM protein including onset denaturation temperature (Tm), denaturation peak temperature (Td) and denaturation enthalpy (ΔHd) were affected by sediment pH and pH 6.5 led to the highest thermal characteristics. Since the optimum characteristics of proteins isolated from TM were obtained at isoelectric pH 6.5 and extraction pH 11, these pH values are recommended for the extraction and precipitation of TM proteins, respectively.

Comparison of different thawing methods effect on the calorimetric and rheological properties of frozen liquid egg yolk

AbstractEggs are commonly used in the food industry because of their excellent nutrient value and also for their coagulating, foaming, emulsifying, colouring and flavouring properties. Manufacturers substitute shell eggs with processed egg products, such as liquid whole egg, liquid egg yolk or albumin. They have a shelf life of a few weeks, but freezing can increase it to 1 year. However, freezing causes gelation in case of egg yolk. This process is highly dependent on the conditions of freezing and thawing.In our study, raw liquid egg yolk was frozen and stored for 14 days at −18 °C. On days 1, 7 and 14 samples were thawed by two different methods. Denaturation temperature and enthalpy were investigated by differential scanning calorimetry. Besides, rheological properties were examined at 20 °C, Herschel–Bulkley model was fitted to flow curves of the examined samples. The dry matter content was also recorded during the experiment. Two-way ANOVA was used to analyse data.The results of the study showed that method of thawing had no significant effect on calorimetric and rheological properties and dry matter content. In contrast, freezing and frozen storage had a significant effect on denaturation enthalpy and rheological properties.

Heat denaturation of ribonuclease under high pressure: Differential scanning microcalorimetry study

Scanning microcalorimetry was used to study heat denaturation of ribonuclease A at high pressure. The pressure dependences of temperature and enthalpy of denaturation were measured at two levels of pH. It was shown that pressure destabilizes the RNase structure and significantly reduces the enthalpy of denaturation. Pressure does not affect the cooperativity of transition. The results allowed estimating of the partial increment of volume ΔVm as well as increments of isothermal compressibility and thermal expansibility associated with denaturation. Increasing pressure increases the magnitude of the volume increment ΔVm. The second-order pressure derivatives of ΔVm must be taken into account to retrieve dependencies between temperature / enthalpy of denaturation vs. pressure. Proportional change of ΔVm and its partial derivatives with respect to pressure and temperature provides a basis for approximation of experimental data. The nature of the volume increment decrease accompanying the denaturation of proteins and the driving mechanism of the change of denaturation enthalpy with increasing pressure are discussed.

The effect of prolonged intense physical exercise of special forces volunteers on their plasma protein denaturation profile examined by differential scanning calorimetry.

The human blood plasma proteome profile has been an area of intensive investigation and differential scanning calorimetry (DSC) has come forward as a novel tool in analyzing plasma heat capacity changes to monitor various physiological responses in health and disease. This study used DSC to assess potential alterations in the plasma heat capacity profile of albumin and globulins during extremely demanding physical exercise. We monitored the changes in denaturation profiles of those plasma proteins for five consecutive days of an extraordinary exercise training schedule in 14 young male Special Forces volunteers, as well as after a 30-day recovery period. The major effect of the prolonged intense exercise was the continuous upward shift of the albumin peak by 2°-3°C on the initial days of exercise, with a tendency to plateau circa the 5th day of exercise. In addition, some redistribution of the denaturational enthalpy was observed upon exercise, where the globulins peak increased relative to the albumin peak. Noteworthy, the alterations in the plasma proteome denaturational profiles were not persistent, as virtually full recovery of the initial status was observed after 30 days of recovery. Our findings indicate that 5 days of exhaustive physical exercise of highly trained individuals enhanced the thermal stability of plasma albumin shifting its denaturational transition to higher temperatures. We surmise that these effects may be a result of increased blood oxygenation during the prolonged intense exercise and, consequently, of albumin oxidation as part of the overall adaptation mechanisms of the body to extreme physical and/or oxidative stress.

Rheological, structural and thermal characteristics of protein isolates obtained from album (Chenopodium album) and quinoa (Chenopodium quinoa) seeds

This study was carried out to examine the structural, rheological and thermal characteristics of protein isolates extracted from album and quinoa seeds. The results showed that surface hydrophobicity, free and total sulfhydryl groups were found significantly (p≤0.05) higher in quinoa protein isolates. Rheological parameters showed that both G' (storage modulus) and G" (loss modulus) were higher in quinoa protein isolates than album protein isolates. Enthalpy of denaturation (∆H) was found significantly (p≤0.05) higher in quinoa protein isolates, however, denaturation temperature (Td) was found higher in album protein isolates. Thermal gravimetric analysis showed that album protein isolates were degraded much faster than quinoa protein isolates with increasing temperature. Both quinoa and album protein isolates had two diffraction peaks at 2θ=10° and 2θ=20° respectively, but the peaks were more intense in album protein isolates. Circular dichroism showed α-helical structure and a more dominant negative peak in album protein isolates. FTIR showed characteristic peaks at 1200, 1500, 1700 and 3100-3300 cm−1 for both album and quinoa seed proteins respectively. SDS-PAGE results confirmed the presence of globulins in quinoa and album protein isolates.

Effects of HHP’s Holding Time on Proteins of Liquid Egg Products

Today’s consumers require food products with fresh, or fresh-like characteristics. Minimal processing technologies are indicated as technologies with a gentle impact on sensorial and techno-functional properties. High Hydrostatic Pressure (HHP) is a widely used minimal technology considered as a cold pasteurization method in food preservation. The effect of applied pressure of HHP is well understood, but the holding time of HHP treatment is not extensively investigated in topic of proteins. One of the most important attribute of liquid egg products are the great foaming ability, foaming stability as well as emulsifying properties. These techno-functional properties are highly influenced by the protein structures of egg products. In our study, liquid egg products were pressurized at 400 MPa, for 1, 3, 5 7 and 10 minutes. The protein structures of liquid egg white (LEW), liquid egg yolk (LEY) and liquid whole egg (LWE) were investigated using Differential Scanning Calorimetry (DSC).Our study pointed out that after HHP treatment at 400 MPa, for 10 minutes 12% decrease in denaturation enthalpy of LWE was observed. In LEY 30% decrease was detected after 10 minutes HHP treatment. The highest impact of HHP treatment (35% decrease in denaturation enthalpy) in LWE was noted. The changes in protein structures of liquid egg products were smaller, than the effects of higher pressure applied for preservation. In aspects of techno-functional properties applying a longer holding time is more favourable, than applying a higher pressure.

Effects of thermal treatment on collagen present in bovine M. Semitendinosus intramuscular connective tissue. Analysis of the chemical, thermal and mechanical properties

Abstract There is still interest in understanding how the collagen characteristics of the intramuscular connective tissue (IMCT)-perimysium contributes to the tenderness and tenacity in different meat cuts after the cooking process. In the present work, the analysis of the changes in IMCT after thermal treatments is proposed. The study of the thermal treatment (1 h) at different temperatures (25−65 °C) was designed to focus on the chemical, mechanical and thermal properties of the collagen present in isolated IMCT-perimysium. Collagen degradation degree (Deg), the solubility of collagen and proteoglycan components, thermal properties and mechanical stress were studied on treated-IMCT-perimysium. The results showed that collagen Deg increased significantly at 65 °C. The soluble proteoglycan fraction did not show changes among treatments. Thermal properties presented notorious and significant changes at 65 °C. Enthalpies of denaturation (ΔH) increased and denaturation peak temperatures (Tp) decreased in relation with lower thermal-treatments. Finally, there were not significant differences in mechanical properties and load-stress among treatments. Deg at 65 °C might indicate chemical changes in total collagen; labile populations were solubilized while the stable population remained in IMCT-perimysium. The effects of thermal treatment at higher temperatures and the presence of meat enzyme should be investigated in the future.

Thermophysical Properties of Beef Steaks of Varying Thicknesses Cooked With Low and High Grill Surface Temperatures

The objective of this study was to determine the thermodynamic and physical properties of beef strip loin steaks of varying thicknesses and USDA quality grades cooked with high and low grill surface temperatures. Thermal characteristics described by changes in the denaturation temperature (between 55°C – 60°C) and enthalpies of protein denaturation (70°C – 75°C) both differed (P = 0.031 and P = 0.001, respectively) among thick steaks, with thick steaks cooked on a high grill surface temperature having a lower denaturation temperature and enthalpy compared with thick steaks cooked on a low grill surface temperature. No differences (P &amp;gt; 0.05) were observed among thin steaks for denaturation temperature or enthalpy. The elastic behaviors of the surface and center of the steaks were analyzed to determine how the microstructure of the beef responded to applied stress. The elastic behavior of steak centers was influenced in a three-way interaction (P = 0.029) between quality grade, steak thickness, and grill surface temperature. The elastic behavior of the surface of steaks was influenced by the interaction of quality grade and steak thickness (P = 0.031). These interactions, along with the differences in the thermal characteristic of proteins, suggest that the microstructure of steaks was affected by each cooking treatment group. Hardness, resilience, and chewiness were each influenced by a three-way interaction (P = 0.023; 0.014; and 0.030; respectively). Thin steaks possessed greater cohesiveness (P = 0.038) and shear force ( P = 0.007) values. Meanwhile, thin steaks exhibited lower springiness (P = 0.002). The measured alterations in thermal and physical proper- ties in the beef steaks suggest that the composition, thickness, and cooking regiments impact the microstructure of beef, and this was ultimately confirmed through textural measurements. The results of this research can be used in the design of cooking processes that match beef characteristics.

Raw and cooked meat emulsion stability as affected by starches determined by principal component analysis

This work aimed to study the relationship between meat emulsion in both raw and cooked states employing two different types of starch, potato, and wheat, in meat batters formulated with different fat percent. Emulsion stability as related to water retention capacity, thermal denaturation temperature, and enthalpy plus thermal diffusivity were determined in the raw and cooked state. There was an inherent difference in potato starch functionality, with higher emulsion stability and yield, but the Pearson correlation analysis and PCA demonstrated that water holding capacity and the denaturation enthalpy resulted in higher cook yield as a consequence of lower expressible moisture. This results in establishing the importance to maintain meat extensors as starches functionality before and during mixing and thermal processing to obtain better yield and less water release in fat-reduced meat products, both important quality parameters, related to sensory (juiciness) and texture (hardness) properties of comminuted meat products.

Changes in myoglobin content in pork Longissimus thoracis muscle during freezing storage

In this study, pork Longissimus thoracis muscle was used, which was frozen in a chamber and thawed under controlled conditions. The color profile and the surface myoglobin were evaluated. A thermal analysis was performed by modulated differential scanning calorimetry (MDSC), and Fourier-transform infrared spectroscopy with attenuated total reflection (FTIR-ATR). It was found that there were important effects in myoglobin due to the freeze-thawing process in parameters such as pH, luminosity (L*), and chroma values, as well as in activation energies (Ea) and denaturation enthalpy (ΔH) between myoglobin forms. In raw meat, it was found that there was a greater proportion of deoxymyoglobin, and in frozen-thawed samples, metmyoglobin was the most abundant form, indicating that are significant effects which are correlated with the changes in tri-stimulus coordinates and with the thermal and chemical parameters in pork meat.

Physicochemical Properties of Mucin Extracted from &lt;i&gt;Misgurnus mizolepis&lt;/i&gt; Epidermal Mucus

The purpose of this study was to investigate the extraction yield and physicochemical characteristics of mucin from the epidermal mucus of Misgurnus mizolepis. Ninety percent ethanol produced the highest yield of mucin. At higher concentrations, mucin had more elastic properties, as revealed by dynamic viscoelasticity measurements. Differential scanning calorimetry (DSC) demonstrated that mucin is a thermostable glycoprotein. Denaturation enthalpy increased as mucin concentration increased. Mucin inhibited the growth of both Escherichia coli and Bacillus cereus, but had better antimicrobial activity in the former. Mucin also exhibited antioxidant activity, equivalent to 66.64% of that of L-cysteine. Mucin inhibited elastase activity and MMP-1 & MMP-2 expression activity, and induced hyaluronic acid expression. It is indicating that mucin is effective in moisturizing and anti-aging the skin. Thus, mucin from the epidermal mucus of Misgurnus mizolepis could have great potential as a non-food material in various industries.

High-pressure thawing of pork: Water holding capacity, protein denaturation and ultrastructure

The effects of high-pressure thawing at 70 MPa (35 min), 140 MPa (29 min), and 210 MPa (25 min) were studied for their affect on the water holding capacity, protein denaturation and ultrastructure of porcine longissimus dorsi muscle that was frozen for 24 h at −18 °C. For comparison, water thawing at 20 °C and air thawing at 4 °C were used as control groups. The results showed that thawing losses at 140 MPa were significantly lower (P < 0.05) than those for atmospheric water thawing and the other two high-pressure conditions. However, pressing losses at 70 and 210 MPa were higher. The cooking losses and the degree of protein denaturation increased as the pressure increased. At 210 MPa, the endothermic transition temperature was higher, and the enthalpy of myosin protein denaturation was lower (P < 0.05) than the other treatment groups. At this pressure, the actin peak disappeared. Shrinkage of the sarcomere was observed in the high-pressure thawing groups, and the greatest sarcomere shrinkage was observed at 210 MPa. The H band began to appear blurry at 70 MPa and almost disappeared at 140 and 210 MPa. At the same time, the Z lines became coarser and the I band became considerably wider and white at 210 MPa.

Quercetin loaded gelatin films with modulated release and tailored anti-oxidant, mechanical and swelling properties

Quercetin, a flavonoid widely diffused in fruits and vegetables, is known for its good pharmacological qualities, such as anti-oxidant and anti-inflammatory properties. In this work, we loaded quercetin on gelatin films with the aim to develop materials with tailored anti-oxidant, mechanical and stability properties. To this purpose, gelatin films at increasing flavonoid content were prepared using two different solvents, namely H2O/EtOH (EtOH films) and DMSO (DMSO films). Quercetin content increased up to about 3.8 and 1.8 wt% in DMSO and EtOH films, respectively. The use of DMSO as solvent prevents the partial regain of collagen triple helix structure during gelling of gelatin sols and results in remarkable extensibility of the films. At variance, EtOH films display X-ray diffraction patterns and DSC plots in agreement with the presence of triple helix structure, and exhibit reduced swelling and increasing mechanical properties on increasing quercetin content. Moreover, their values of denaturation enthalpy indicate the presence of chemical interaction between the flavonoid and gelatin, which can be responsible of their lower quercetin release in PBS in comparison to DMSO films. The flavonoid release is sustained for both series of films and occurs through anchorage to gelatin nanoparticles. Moreover, both DMSO and EtOH functionalized films exhibit relevant anti-oxidant properties, in agreement with their RSA levels, which are comparable to that of pure quercetin.

Chemical and flavor profile changes of cocoa beans (Theobroma cacao L.) during primary fermentation.

This survey reports for the first time the changed of quality of fermented cocoa (Theobroma cacao L.) beans. The quality evaluation and simultaneous detection of amino acids, flavor, procyanidin, color, fat, protein, antioxidant activity, and enthalpy were obtained for different fermentation stages of cocoa beans. The results showed that total essential amino acids contents ranged from 2.64 g/100 g to 3.68 g/100 g. A total of 88 compounds identified at the end of the fermentation belonged to alcohols, acids, esters, ketones, pyrazines, aldehydes, and terpenoids. One of the chemical groups that were present in highest abundance in the consummation treatments was acids, representing 56.04% of the total extracted area, followed by alcohols (22.95%) and ketones (9.40%). The colors of the beans in different fermentation stages were different, from deep purple to deep red‐brown. Fermented cocoa beans were shown to be 53.45% and 13.51% bean butter and protein content, respectively. The value of denaturation enthalpy (ΔH) ranged from 30.4 (J/g) to 43.38 (J/g). The 3‐day fermented sample had the highest ΔH (43.38 J/g). When the fermentation process was complete, the procyanidin concentration of the beans decreased, with the final yield of procyanidin at 6.2%. During fermentation, the antioxidant capacity of beans gradually reduced. The fermenting of cocoa beans had a significant effect on the quality formation. The findings of this study constitute a basis for further investigations on the quality formation of cocoa during fermentation.