Fluorescence spectroscopy and molecular modeling investigations on the thermally induced structural changes of bovine β-lactoglobulin

Regioselective analysis of heat-induced conformational changes of β-lactoglobulin by quantitative liquid chromatography-mass spectrometry analysis of chemical labeling kinetics

β-Lactoglobulin is a main allergen in cow's milk; its allergenicity is strongly impacted by processing. To understand heat-induced epitope-specific effects, the present study analyzed regiospecific conformational changes of heated native β-lactoglobulin variant A (BLG-A). Complementary fluorescence spectroscopy methods indicated two denaturation phases comprising minor sequential conformational changes (25-75 °C) and complete transitions (80-90 °C). Regioselective conformational changes of BLG-A in the native state (25 °C), sequential (70 °C) and complete transition (90 °C) were determined by quantitative liquid chromatography-mass spectrometry analysis of chemical labeling kinetics covering 14 lysine residues and the N-terminus. Conformational changes in two phases were observed for N-terminus, K8 (both N-terminal chain), K60 (β-sheet C), K75 (β-sheet D), K77 (DE loop), K83 (β-sheet E), K100 and K101 (FG loop). The residues K14 (β-sheet A1), K47 (β-sheet B), K69, K70 (both β-sheet D), and K91 (β-sheet F) were not involved in conformational changes.

Heat Stability Assessment of Milk: A Review of Traditional and Innovative Methods

It is important to differentiate milk with different thermostabilities for diverse applications in food products and for the appropriate selection of processing and maintenance of manufacturing facilities. In this review, an overview of the chemical changes in milk subjected to high-temperature heating is given. An emphasis is given to the studies of traditional and state-of-the-art strategies for assessing the milk thermostability, as well as their influencing factors. Traditional subjective and objective techniques have been used extensively in many studies for evaluating thermostability, whereas recent research has been focused on novel approaches with greater objectivity and accuracy, including innovative physical, spectroscopic, and predictive tools.

Investigating the synergistic effects of high-pressure homogenization and pH shifting on the formation of tryptophan-rich nanoparticles

A combined treatment of high-pressure homogenization (HPH) and pH-shifting on the mixture of α-lactalbumin (α-LA) and tryptophan (Trp) was used to fabricate nanoparticles (α-LA-Trp-NP). The optimal α-LA/Trp ratio (5:1), HPH pressure (206.8 MPa), and recirculation time (40 min) was found to produce small α-LA-Trp-NP (243.0 ± 7.2 nm) with a narrow particle size distribution. Comparing the size and morphology of α-LA-NPs with α-LA-Trp-NPs indicated that the presence of Trp significantly affected the size and morphology of the NPs in the dry form. The stability of the α-LA-Trp-NPs was improved by using the combination of HPH and pH-shifting. The α-LA-Trp-NPs showed better freeze-thaw stability and retained the particle characteristics with heat treatment at 63 °C, 30 min after the freeze-thaw cycle. α-LA-Trp-NPs were also observed to have remarkable stability against pH changes and thermal treatments at 63 °C, 30 min, and 90 °C, 2 min.

Spectroscopy and dynamics of beta-lactoglobulin complexed with rifampicin

In this paper, we report the binding interaction of milk protein, beta-lactoglobulin (BLG), with an antibiotic against tuberculosis, rifampicin (RIF). BLG intrinsic fluorescence from tryptophan (Trp) amino acids was monitored to understand protein-drug interactions. Binding parameters and stoichiometry were estimated with the help of fluorescence spectral changes. Synchronous fluorescence spectroscopy was employed to exclusively monitor the Trp and Tyrosine (Tyr) environment in the presence of RIF. With the help of steady state fluorescence at different temperatures supported by time-resolved fluorescence, we confirmed that the protein forms a static complex with RIF. Thermodynamic parameters, ΔH and ΔS values, showed the involvement of hydrophobic forces between the RIF and BLG. Competitive displacement assay with ANS confirmed the BLG calyx as the binding site for RIF. Energy transfer mechanism from Trp to RIF was attributed to the fluorescence changes in protein upon complexation. The Förster resonance energy transfer (FRET) was used to find distance, energy transfer efficiency and rate of energy transfer between donor (BLG) and acceptor (RIF). Fourier-transform infrared (FTIR) spectroscopy was utilized for estimating changes in the secondary structure of BLG induced by RIF. Molecular docking was used to visualise the binding location of RIF on BLG. Molecular dynamics (MD) simulation studies showed a consistent binding interactions between BLG and RIF during the 100 ns simulation period and this well supported the increased beta sheet content in FTIR. Overall our results establish the potential of intrinsic fluorescence of BLG in combination with biophysical tools to rationalize drug-protein interactions.Communicated by Ramaswamy H. Sarma.

Effect of Preheating Whey Protein Concentrate on the Stability of Purple Sweet Potato Anthocyanins

Anthocyanins (ANs) have strong antioxidant activities and can inhibit chronic diseases, but the instability of ANs limits their applications. The conservation of preheating whey protein concentrate (WPC) on the stability of purple sweet potato ANs was investigated. The retention of ANs in WPC-ANs was 85.88% after storage at 25 °C for 5 h. WPC-ANs had higher retention of ANs in heating treatment. The retention rates of ANs in WPC-ANs exposed to light and UV lamps for 6 h were 78.72% and 85.76%, respectively. When the concentration of H2O2 was 0.50%, the retention rate of ANs in the complexes was 62.04%. WPC-ANs' stability and antioxidant activity were improved in simulated digestive juice. The WPC-ANs connection was static quenching, and the binding force between them was a hydrophobic interaction at one binding site, according to the fluorescence quenching spectroscopy. UV-visible absorption spectroscopy and Fourier transform infrared spectroscopy (FTIR) analysis further indicated that the secondary structure and microenvironment of amino acid residues in WPC can be impacted by the preheating temperature and preheating times of WPC. In conclusion, preheating WPC can successfully preserve the stability of purple sweet potato ANs by binding to them through a non-covalent interaction.

Modification and oxidative degradation of β-lactoglobulin by UVB irradiation

Ultraviolet (UV) B irradiation induces protein modification, especially the conformational rearrangement of proteins, and is therefore promising as a non-thermal and non-chemical functionalization technique. Nevertheless, UVB irradiation introduces radicals and oxidizes side chains resulting in the loss of food quality. Thus, assessing the UVB irradiation-based functionalization of β-lactoglobulin (BLG) versus its oxidative degradation is of interest. UVB irradiation of up to 8 h was successfully applied to loosen the rigid folding of BLG and increase its flexibility. Thereby, the cysteine at position 121 and hydrophobic regions became surface-exposed as indicated by the increase in accessible thiol groups and increased surface hydrophobicity. Furthermore, we demonstrated the cleavage of the "outer" disulfide bond C⁶⁶-C¹⁶⁰ by LC-MS/MS after tryptic digestion of BLG. The 2-h-irradiated BLG showed adequate conformational rearrangement for protein functionalization while being minimally oxidized.

Understanding molecular interaction between thermally modified β-lactoglobulin and curcumin by multi-spectroscopic techniques and molecular dynamics simulation

This study elucidated the binding of curcumin (CUR) onto preliminary thermally modified β-lactoglobulin (β-LG). β-LG at pH 8.1 was heated at 75 °C, 80 °C and 85 °C for 10 min to construct denatured proteins (β-LG75, β-LG80, β-LG85). Steady and time-resolved fluorescence studies uncovered that CUR quenched proteins in simultaneous static and dynamic mode. Pre-heating β-LG improved its binding with CUR and the strongest affinity occurred in β-LG80. Fluorescence resonance energy transfer (FRET) analysis indicated that binding distance between CUR and β-LG80 was the smallest and energy transfer was the most efficient. β-LG80 had the highest surface hydrophobicity. Fourier-transform infrared (FT-IR) spectroscopy and differential scanning calorimeter (DSC) confirmed that CUR transferred from crystal to amorphous state after association with protein and revealed the contribution of hydrogen bonds. Combination of β-LG80 with CUR retained the antioxidant capacity of each component. Molecular dynamics simulation demonstrated enhanced hydrophobic solvent accessible surface area of β-LG80 compared with native protein. Data obtained from this study may provide useful information for comprehensively understanding the ability of β-lactoglobulin to bind hydrophobic substances under different environmental conditions like high temperature and alkaline medium.

Fabrication of a novel antioxidant emulsifier through tuning the molecular interaction between soy protein isolates and young apple polyphenols

Soy protein isolates (SPI) exhibit weaker emulsifying properties than those of animal proteins, thereby limiting their wide applicability. In this study, a novel plant-based antioxidant emulsifier was developed using SPI and young apple polyphenols (YAP), and its underlying interaction mechanisms were discovered using multispectral technology and molecular docking. YAP physically bound to SPI through hydrogen bonds and hydrophobic interactions, which significantly enhanced the free radicals scavenging, reducing, and metal ion chelating abilities of SPI by introducing free hydroxyl groups. Moreover, SPI modified by YAP exerted better emulsifying performance owing to a looser protein structure, reflected by a higher random coil and a lower α-helix content. In addition, YAP may bridge adjacent SPI molecules, promoting the adsorption and anchoring of SPI at the oil-water interface. SPI-YAP complexes are promising antioxidant emulsifiers that can be used to nano-deliver functional oils and nutrients, thereby broadening SPI and YAP applications in the food industry.

High-temperature glycosylation modifies the molecular structure of ovalbumin to improve the freeze-thaw stability of its high internal phase emulsion

In this study, ovalbumins (OVAs) were glycosylated with fructo-oligosaccharide (FO) at different temperatures (80 °C, 100 °C, 120 °C, and 140 °C) and durations (1 h and 2 h) via wet-heating. The glycosylated OVAs (GOVAs) were characterized by the degree of glycosylation (DG), particle size, zeta potentials, and structural changes. GOVAs-stabilized high-internal-phase emulsions (HIPEs) were then prepared to compare their macro- and microstructure and freeze-thaw stability. The results showed that the DG of GOVAs increased with the increase in glycosylation temperature and the protein structure unfolded with it. Glycosylation decreased the particle size, zeta potential, and α-helical structures and increased the β-sheets and surface hydrophobicity (H₀) of GOVAs compared with unmodified OVAs. Moreover, GOVAs-stabilized HIPEs exhibited smaller particle sizes, zeta potentials, agglomeration indexes, oil loss rates, and freezing points and higher viscoelasticity, centrifugal stabilities, flocculation indexes, and freeze-thaw stabilities. Notably, HIPEs prepared by GOVAs (glycosylated higher than 120 °C) showed the least changes in macro- and microscopic appearances after freeze-thawing. These findings will provide a novel method for improving and broadening the functionalities of OVAs and potentially develop HIPEs with enhanced freeze-thaw stabilities.

Improvement in Emulsifying Capacity of Goose Liver Protein Treated by pH Shifting with Addition of Sodium Tripolyphosphate and Its Proteomics Analysis

Goose liver isolate treated by pH shifting and pH shifting/non-enzyme phosphorylation with goose liver isolate was used as a control. The functional property differences in the protein and proteins involved in the interfacial layer treated with pH shifting and non-enzyme phosphorylation were studied. Compared with the goose protein isolates (GPIs) at pH 7.0, the GPIs treated by pH shifting was not a good choice to be an emulsifier in a neutral environment, and non-enzyme phosphorylation inhibited the negative effects of pH shifting treatment and improved protein properties. The results of proteomics showed that the identified proteins in the interfacial layer belong to hydrophilic proteins. Non-enzyme phosphorylation increased the abundances of most proteins due to ion strength, including some phosphorylated proteins. Correlation analysis indicated that protein solubility was highly positively related with S₀, intrinsic fluorescence, total sulfhydryl, free sulfhydryl, A0A0K1R5T3, R0KA48, R0KFP7, U3J1L1, P01989, R0JSM9, and R0LAD1, and was also highly negatively related with particle size and R0M210, R0M714, and R0LFA3. The emulsifying activity index (EAI) demonstrated highly positive correlation with protein solubility, and was correlated with R0JKI4, R0KK84, R0L1Y3, R0LCM7, A0A068C605, and U3IW62.

Effect of chitosan oligosaccharide glycosylation on the emulsifying property of lactoferrin

There is fast increasing interest in the development of alimentary protein stabilized emulsions due to their potential applications in functional food fields. This work studied the effect of glycation degree with chitosan oligosaccharide (COS) on the emulsifying properties of lactoferrin (LF) through Maillard reaction. In the present study, SDS-PAGE and FT-IR were used to confirm LF and COS covalently binding together successfully. Intrinsic fluorescence showed that glycation with COS led more hydrophobic groups exposed to the surface of the structure and particle size increase of LF. Emulsions with 50% (v/v) oil phase and protein concentration of 2% (w/v) was fabricated through one-step shear method. Compared with native LF, emulsions stabilized by LF-COS conjugates showed smaller droplet size and lower creaming index (CI). Among these samples, LF-COS conjugates under 4 h had the best emulsifying efficiency and stability, the emulsion droplet size and the CI of which decreased 39.66% and 28.55% compared with LF, respectively. Furthermore, glycation with COS enhanced the interfacial activity of LF leading to more adsorbing amount and forming thicker layer on the droplets and gel network in the emulsions. This finding would make sense to further understand the modification of emulsifying properties of alimentary proteins through glycosylation with saccharides and develop novel protein-based emulsifiers.

Aggregation and conformational change of mushroom (Agaricus bisporus) polyphenol oxidase subjected to atmospheric cold plasma treatment

Atmospheric cold plasma (ACP) is a novel nonthermal technology with potential applications in maintaining and improving food quality. The effect of ACP on the activity and structure of mushroom (Agaricus bisporus) polyphenol oxidase (PPO) was evaluated. Results demonstrated that the dielectric barrier discharge (DBD) based plasma technology could inactivate PPO (up to 69%) at 50 kV with the increased concentrations of H₂O₂ and NO_x. An obvious enhancement of surface hydrophobicity was observed, whereas a gradual reduction of total sulfhydryl content was recorded with the increasing exposure time. Data from circular dichroism, atomic force microscopy, particle size distribution and fluorescence spectra displayed the rearrangement of secondary structure and disruption of the tertiary structure. Red shifts of fluorescence spectra showed positive correlations with the inactivation rate of PPO. Therefore, ACP treatment could be served as an alternative approach to inactivate undesirable enzymes to minimize the loss of food nutrition and quality.

Analyzing the Interaction between Anthocyanins and Native or Heat-Treated Whey Proteins Using Infrared Spectroscopy

The color stability of anthocyanins (ACN) has been shown to be improved by interaction with whey proteins (WP). In this study, we explore the ACN–WP interaction using Fourier transform infrared spectroscopy (IR). ACN from purple corn, grape, and black carrot (50 μM) were evaluated. IR spectra (4000–700 cm⁻¹) were collected for native and preheated (40–80 °C) WP (5 mg/mL) and ACN–WP mixtures at pH 7.4. Soft independent modeling of class analogy was used to analyze the IR data. The WP secondary structure changed after heat treatments and after interaction with ACN. As expected, the WP α-helices decreased, and β-sheet increased after heat treatment. The intensities of the WP amide I and II bands decreased after ACN addition, revealing a decrease in the WP α-helix content. Higher preheating temperatures (70–80 °C) resulted in a more disordered WP structure that favored stronger WP–ACN interactions related to amide III changes. Addition of ACN stabilized WP structure due to heat denaturation, but different ACN structures had different binding affinities with WP. WP structure had less change after interaction with ACN with simpler structures. These results increase our understanding of ACN–WP interactions, providing a potential strategy to extend anthocyanin color stability by WP addition.

The interactions between anthocyanin and whey protein: A review

Anthocyanins (ACN) are natural pigments that produce bright red, blue, and purple colors in plants and can be used to color food products. However, ACN sensitivity to different factors limits their applications in the food industry. Whey protein (WP), a functional nutritional additive, has been shown to interact with ACN and improve the color, stability, antioxidant capacity, bioavailability, and other functional properties of the ACN-WP complex. The WP's secondary structure is expected to unfold due to heat treatment, which may increase its binding affinity with ACN. Different ACN structures will also have different binding affinity with WP and their interaction mechanism may also be different. Circular dichroism (CD) spectroscopy and Fourier transform infrared (FTIR) spectroscopy show that the WP secondary structure changes after binding with ACN. Fluorescence spectroscopy shows that the WP maximum fluorescence emission wavelength shifts, and the fluorescence intensity decreases after interaction with ACN. Moreover, thermodynamic analysis suggests that the ACN-WP binding forces are mainly hydrophobic interactions, although there is also evidence of electrostatic interactions and hydrogen bonding between ACN and WP. In this review, we summarize the information available on ACN-WP interactions under different conditions and discuss the impact of different ACN chemical structures and of WP conformation changes on the affinity between ACN and WP. This summary helps improve our understanding of WP protection of ACN against color degradation, thus providing new tools to improve ACN color stability and expanding the applications of ACN and WP in the food and pharmacy industries.

Computational strategies for the discovery of biological functions of health foods, nutraceuticals and cosmeceuticals: a review

Scientific and consumer interest in healthy foods (also known as functional foods), nutraceuticals and cosmeceuticals has increased in the recent years, leading to an increased presence of these products in the market. However, the regulations across different countries that define the type of claims that may be made, and the degree of evidence required to support these claims, are rather inconsistent. Moreover, there is also controversy on the effectiveness and biological mode of action of many of these products, which should undergo an exhaustive approval process to guarantee the consumer rights. Computational approaches constitute invaluable tools to facilitate the discovery of bioactive molecules and provide biological plausibility on the mode of action of these products. Indeed, methodologies like QSAR, docking or molecular dynamics have been used in drug discovery protocols for decades and can now aid in the discovery of bioactive food components. Thanks to these approaches, it is possible to search for new functions in food constituents, which may be part of our daily diet, and help to prevent disorders like diabetes, hypercholesterolemia or obesity. In the present manuscript, computational studies applied to this field are reviewed to illustrate the potential of these approaches to guide the first screening steps and the mechanistic studies of nutraceutical, cosmeceutical and functional foods.

The effect of whey protein concentration and preheating temperature on the color and stability of purple corn, grape and black carrot anthocyanins in the presence of ascorbic acid

Our objective was to explore the effects of whey protein (WP) concentration and preheating temperature on anthocyanin color expression and stability over time in the presence of ascorbic acid. Anthocyanins from purple corn, grape or black carrot were mixed with native WP or preheated WP (40-80°C) in various concentrations (0-10 mg/mL) in pH 3 buffer containing 0.05% ascorbic acid and stored in the dark at 25 °C for 5 days. WP addition increased anthocyanin absorbance and protected anthocyanin from ascorbic acid-mediated degradation. Increasing WP concentration resulted in lower lightness and higher chroma, hue angle and color stability. The color loss of anthocyanin solutions decreased by 40%-50% when 10 mg/mL WP was added. Native WP showed more color enhancement and protection than thermally-induced WP. Increasing the WP preheating temperature resulted in less absorbance increase and more absorbance loss. Anthocyanin' half-life was improved by addition of WP in a dose dependent manner. Native WP addition (10 mg/mL) extended anthocyanin half-life by about 2 times for purple corn and grape, and 1.31 times for black carrot anthocyanin solutions. Preheating temperature did not significantly affect anthocyanin protection by WP. WP addition might enhance anthocyanin stability in beverages containing ascorbic acid, expanding anthocyanin application in foods.

Whey protein addition and its increased light absorption and tinctorial strength of model solutions colored with anthocyanins

Anthocyanins (ACN) are pigments with vivid colors, but their application as food colorants is restricted by their limited stability and color expression. Anthocyanins exhibit higher stability in dairy systems than in buffers at similar pH, suggesting that pigments may be able to interact with dairy components such as proteins, resulting in improved performance as colorants. Our objective was to determine the type of interaction between whey proteins (WP) and ACN leading to color enhancements and to determine the role of the ACN chemical structure in this interaction. Model solutions colored with semipurified pigments from sources with different ACN profiles (Berberis boliviana, grape skin, purple corn, black carrot, and red cabbage) were mixed with different concentrations of whey protein isolate (WPI) in pH 3 buffer. Absorption spectra of these solutions were acquired using an absorbance microplate reader, and color parameters were calculated from spectral data. Isolated ACN 3-glucosides were used to determine the role of the aglycone structure in the WP-ACN interaction using visible and fluorescence spectroscopy. In silico modeling was used to visualize potential differences in the interaction between β-lactoglobulin and ACN. Addition of WPI resulted in hyperchromic shifts at the wavelength of maximum absorption in the visible range (λ_vis-max) of up to 19%, and a significant increase in tinctorial strength for all ACN sources (ΔE > 5). Moreover, ACN acylation did not seem to play a significant role in the WP-ACN interaction. When using isolated ACN, WPI addition resulted in hyperchromic shifts at the λ_vis-max only for methoxylated ACN such as petunidin-3-glucoside (up to 24%), and malvidin-3-glucoside (up to 97%). The bimolecular quenching constant values (K_q > 10¹⁰M^-1s^-1) strongly suggested that the predominant type of quenching interaction was static. Analysis of enthalpy, entropy, and Gibbs free energy showed that this binding was spontaneous; depending on the chemical structure of the ACN, the predominant binding forces could be hydrophobic interactions or hydrogen bonding. Modeling suggested that methoxylations in the B ring of the aglycon structure promoted interactions with electron acceptor amino acids. Overall, WP could be used to enhance the tinctorial strength of select ACN depending on their structural characteristics. Therefore, ACN source selection may play a key role for specific applications in dairy products.

Monitoring the Interaction between Thermally Induced Whey Protein and Anthocyanin by Fluorescence Quenching Spectroscopy

The color stability of anthocyanins was shown to improve with addition of whey proteins (WP). The goal of this study was to investigate the binding mechanisms of purple corn, grape and black carrot anthocyanin extracts to native and preheated WP (40-80 °C, 3.6 μM) at a pH of 3 using fluorescence quenching spectroscopy. The fluorescence spectra were collected with an excitation wavelength of 280 nm at 25 °C, 35 °C and 45 °C. The quenching data were analyzed by using the Stern-Volmer equation. The fluorescence intensity of WP decreased (up to 73%) and its λmax increased (by ~5 nm) with increasing anthocyanin concentration (0-100 μM). The quenching data showed that the interaction between anthocyanin extracts and WP was a static quenching process. Thermodynamic analysis showed their binding was mainly through hydrophobic interactions. Their binding affinity was higher for preheated WP than native WP and decreased gradually with increasing preheating temperature. Black carrot anthocyanin extract had the lowest binding affinity with WP, likely due to the larger molecular structure. These results help better understand the protection mechanism of native and preheated WP on anthocyanin color stability, expanding the application of anthocyanins as food colorants that better withstand processing and storage.

Effect of preheated milk proteins and bioactive compounds on the stability of cyanidin-3-O-glucoside

Native and preheated whey protein isolates (WPI) and casein (at 55 °C-90 °C) were used as protective carriers. Three bioactive compounds, including (-)-Epigallocatechin-3-gallte (EGCG), gallic acid, and vitamin C, were added to enhance the stability of cyanidin-3-O-glucoside (C3G). Under acidic (pH 3.6) and neutral (pH 6.3) conditions, both native and preheated milk proteins showed significant protective effect on C3G. WPI preheated at 85 °C presented the best protective effect on C3G under neutral condition by reducing its thermal, oxidation, and photo degradation rates 25.0%, 38.0%, and 41.1%, respectively. The addition of vitamin C into the protein-anthocyanin solutions accelerated the color loss of C3G, whereas EGCG and gallic acid improved its thermal stability. Among the bioactive compounds, gallic acid provided the most significant protective effect on C3G by further decreasing the thermal degradation rate of C3G 44.6% as a result of the formation of 85 °C preheated WPI-gallic acid-C3G complexes.

Interactions between gluten and water-unextractable arabinoxylan during the thermal treatment

This study aimed to investigate the interactions between gluten and water-unextractable arabinoxylan (WUAX), which changed the conformation and aggregation of gluten during the thermal treatment. In this work, the interactions between water-unextractable arabinoxylan and wheat gluten during thermal treatment were extensively evaluated by different techniques. The results showed that the extra WUAX could impair the viscoelasticity as well as weaken the thermal properties of gluten. The fluorescence spectra revealed the extra WUAX changed the conformation of gluten molecules. Besides, chemical interaction measurement indicated that the extra WUAX prevented the formation of partial disulfide bonds and had a major effect on the hydrophobic interaction of gluten. In summary, these results indicated that WUAX disrupted the covalent crosslinking by affecting disulfide bonds between gluten proteins, and dominated the folding/unfolding process of gluten via the competition with gluten for water, resulting in the poor quality of whole wheat-based foods.

Structural and functional changes of the protein β-lactoglobulin under thermal and electrical processing conditions

In the present study we have tried to explore the effect of static external electric field of strength 3.0 V/nm on the conformational changes adopted by the protein β-lactoglobulin. We have chosen different temperatures viz. 300 K, 400 K and 450 K to evaluate the temperature dependent effect of electric field. We have observed that combined effect of high temperature and static external electric field show significant changes on the structural conformation of the protein which in turn may affect the functional properties of the protein. Calculations of root mean square deviations reveal that both helical and β-sheet regions of the protein are noticeably affected at high temperature. We have used solvent accessible surface area (SASA) and dipole moment values to explain that there is changes in hydrophobicity of the protein surface due to presence of external electric field. The study reveals that electric field in combination with high temperature can be used to alter the conformation of the protein and the effect of external electric field is more pronounced at high temperature than that of low temperature. The study provides a better understanding of the conformational changes adopted by the protein under the stress of external electric field and high temperature and provide guidance to choose optimum conditions for processing without loss of nutritional properties.

The Interaction of Bovine β-Lactoglobulin with Caffeic Acid: From Binding Mechanisms to Functional Complexes

In this study, the interaction of native and transglutaminase (Tgase) cross-linked β-lactoglobulin (β-LG) with caffeic acid (CA) was examined, aiming to obtain functional composites. Knowledge on the binding affinity and interaction mechanism was provided by performing fluorescence spectroscopy measurements, after heating the native and cross-linked protein at temperatures ranging from 25 to 95 °C. Regardless of the protein aggregation state, a static quenching mechanism of intrinsic fluorescence of β-LG by CA was established. The decrease of the Stern–Volmer constants with the temperature increase indicating the facile dissociation of the weakly bound complexes. The thermodynamic analysis suggested the existence of multiple contact types, such as Van der Waals’ force and hydrogen bonds, between β-LG and CA. Further molecular docking tests indicated the existence of various CA binding sites on the β-LG surface heat-treated at different temperatures. Anyway, regardless of the simulated temperature, the CA-β-LG assemblies appeared to be unstable. Compared to native protein, the CA-β-LG and CA-β-LG_Tgase complexes (ratio 1:1) exhibited significantly higher antioxidant activity and inhibitory effects on α-glucosidase, α-amylase, and pancreatic lipase, enzymes associated with metabolic syndrome. These findings might help the knowledge-based development of novel food ingredients with valuable biological properties.

Molecular Dynamics Simulation for Mechanism Elucidation of Food Processing and Safety: State of the Art

Molecular dynamics (MD) simulation is a useful technique to study the interaction between molecules and how they are affected by various processes and processing conditions. This review summarizes the application of MD simulations in food processing and safety, with an emphasis on the effects that emerging nonthermal technologies (for example, high hydrostatic pressure, pulsed electric field) have on the molecular and structural characteristics of foods and biomaterials. The advances and potential projection of MD simulations in the science and engineering aspects of food materials are discussed and focused on research work conducted to study the effects of emerging technologies on food components. It is expected by showing key case studies that it will stir novel developments as a valuable tool to study the effects of emerging food technologies on biomaterials. This review is useful to food researchers and the food industry, as well as researchers and practitioners working on flavor and nutraceutical encapsulations, dietary carbohydrate product developments, modified starches, protein engineering, and other novel food applications.

Structural Assessment and Catalytic Oxidation Activity of Hydrophobized Whey Proteins

Chemical modification of whey proteins allows manipulation of their characteristics, such as surface charge and hydrophobicity. Herein, we report the influence of hydrophobization accomplished by a preacetylation stage and a subsequent combined acetylation-heating process on some characteristics of whey proteins. Hydrophobization extensively (≥90%) acetylated the available free amino groups of whey proteins. The produced protein particles were nanoscaled (75 nm) and had a significantly low isoelectric point (3.70). Hydrophobization increased the β-sheet content of whey proteins and significantly decreased the solvent exposure of tyrosine residues. It also conferred a less compact tertiary structure to the proteins and decreased the extent of disulfide-bond formation by heating. The mobility of α-lactalbumin in nonreducing electrophoresis gel increased as a consequence of hydrophobization. Then, the ability of whey proteins to catalyze hydroquinone autoxidation was examined, and it was found that the activity decreased as a result of hydrophobization. The catalytic activity of the proteins was associated with the free-amino-group content, which determined the extent of cation-π attractive interactions; ζ-potential, which determined the extent of anion-π repulsive interactions; and π-stacking between hydrophobic residues and the electron cloud of the quinone ring.

Effect of heat treatments on the structure and emulsifying properties of protein isolates from cumin seeds ( Cuminum cyminum)

The effect of heat treatments (65, 75, 85, and 95 ℃, 30 min) on the structure and the emulsifying properties of cumin protein isolates were investigated. The fluorescence spectra analysis showed that the conformations were remarkably influenced by heat treatments. An increase in the ratio of α-helix in the secondary structure of heated cumin protein isolates was observed from the result of circular dichroism. Thermal treatments at different temperatures led to an increase in the surface hydrophobicity ( H_o) and a decrease in zeta potential ( ζ) of cumin protein isolates. Emulsifying activity index and emulsion stability index of heated cumin protein isolates were reduced at different protein concentrations (0.1, 0.5, and 1.0%), while the protein absorption in emulsions stabilized by heated cumin protein isolates gradually increased with heating temperature increasing. Moreover, both emulsions stabilized by native and heated cumin protein isolates showed pseudo-plastic fluid behavior and exhibited a decrease in their viscosities with proteins concentration increasing. But thermal treatments produced different effects on the flow behavior of emulsions formed by various protein concentrations, the flow index for heated cumin protein isolates emulsions increased at protein concentrations of 0.5 and 1.0%, but decreased at a concentration of 0.1%. These results might provide reference for the cumin protein processing and its application in food industry.

Effect of preheat treatment of milk proteins on their interactions with cyanidin-3-O-glucoside

In this study, the binding of cyanidin-3-O-glucoside (C3G) to preheated milk proteins β-lactoglobulin (β-Lg) and β-casein (β-CN) at 55-90 °C under pH 3.6 and pH 6.3 was investigated using multi-spectral techniques. Fluorescence quenching spectroscopy data showed C3G quenched milk proteins' fluorescence strongly. Thermodynamic analysis revealed that C3G bound to β-Lg mainly through hydrogen bonding and hydrophobic interactions, and that their binding affinity increased gradually with increasing preheating temperature at pH 6.3, whereas it decreased at pH 3.6. Hydrogen bonding and van der Waals forces played the major roles in the interaction of β-CN with C3G, their affinity decreasing with increasing preheating temperature at both pH values. The combination of C3G and preheated β-Lg at 85 °C had the strongest binding affinity, with a K_A of 14.10 (±0.33) × 10⁵ M^-1 (pH 6.3, 298 K). Preheating of milk proteins did not change their major forces with C3G. Fourier transform infrared spectra (FT-IR) results showed that C3G binding altered the secondary structures of β-Lg and β-CN by reducing the proportion of α-helix and β-sheet structures and increasing the proportion of random coil and turn structures. The structural changes of preheated β-Lg upon C3G binding were more pronounced than that of native β-Lg, while there was little difference between preheated and native β-CN in their structural changes upon C3G binding. These results will be helpful in better understanding the relevance of native and preheated milk protein-C3G interactions to the stability of C3G, and in promoting its application in the food industry as a natural pigment.

Controlling Agglomeration of Protein Aggregates for Structure Formation in Liquid Oil: A Sticky Business

Proteins are known to be effective building blocks when it comes to structure formation in aqueous environments. Recently, we have shown that submicron colloidal protein particles can also be used to provide structure to liquid oil and form so-called oleogels ( de Vries , A. J. Colloid Interface Sci. 2017 , 486 , 75 - 83 ) . To prevent particle agglomeration, a solvent exchange procedure was used to transfer the aggregates from water to the oil phase. The aim of the current paper was to elucidate on the enhanced stability against agglomeration of heat-set whey protein isolate (WPI) aggregates to develop an alternative for the solvent exchange procedure. Protein aggregates were transferred from water to several solvents differing in polarity to investigate the effect on agglomeration and changes in protein composition. We show that after drying protein aggregates by evaporation from solvents with a low polarity (e.g., hexane), the protein powder shows good dispersibility in liquid oil compared to powders dried from solvents with a high polarity. This difference in dispersibility could not be related to changes in protein composition or conformation but was instead related to the reduction of attractive capillary forces between the protein aggregates during drying. Following another route, agglomeration was also prevented by applying high freezing rates prior to freeze-drying. The rheological properties of the oleogels prepared with such freeze-dried protein aggregates were shown to be similar to that of oleogels prepared using a solvent exchange procedure. This Research Article provides valuable insights in how to tune the drying process to control protein agglomeration to allow for subsequent structure formation of proteins in liquid oil.

Thermal stability of the complex formed between carotenoids from sea buckthorn (Hippophae rhamnoides L.) and bovine β-lactoglobulin

Sea buckthorn has gained importance as a versatile nutraceutical, due to its high nutritive value in terms of carotenoids content. β-Lactoglobulin (β-LG) is a natural carrier for various bioactive compounds. In this study, the effect of thermal treatment in the temperature range of 25 to 100°C for 15min on the complex formed by β-LG and carotenoids from sea buckthorn was reported, based on fluorescence spectroscopy, molecular docking and molecular dynamics simulation results. Also, the berries extracts were analyzed for their carotenoids content. The chromatographic profile of the sea buckthorn extracts revealed the presence of zeaxanthin and β-carotene, as major compounds. The Stern-Volmer constants and binding parameters between β-LG and β-carotene were estimated based on quenching experiments. When thermally treating the β-LG-carotenoids mixtures, an increase in intrinsic and extrinsic fluorescence intensity up to 90°C was observed, together with blue-shifts in maximum emission in the lower temperature range and red-shifts at higher temperature. Based on fluorescence spectroscopy results, the unfolding of the protein molecules at high temperature was suggested. Detailed information obtained at atomic level revealed that events taking place in the complex heated at high temperature caused important changes in the β-carotene binding site, therefore leading to a more thermodynamically stable assembly. This study can be used to understand the changes occurring at molecular level that could help food operators to design new ingredients and functional foods, and to optimize the processing methods in order to obtain healthier food products.

pH and heat induced structural changes of chicken ovalbumin in relation with antigenic properties

Ovalbumin is the major egg white protein known to induce allergic reactions in humans. A comprehensive evaluation of the structural and antigenicity features of ovalbumin subjected to different pH and heat treatments was performed by combining fluorescence spectroscopic measurements, ELISA and in silico prediction. The intrinsic fluorescence spectra indicated modification of the ovalbumin tertiary structure depending on pH and applied temperature. The heat treatment caused the alteration of ovalbumin structure, which exhibited gradual hydrophobic exposure. The in depths check of ovalbumin molecular model, after performing molecular dynamics simulations, indicated the slight transition toward a typical β-strand dominant structure with the temperature increase. Moreover the immunoenzymatic test was employed to estimate the effect of the pH and thermal treatment on the stability of ovalbumin epitopes. Only a 5.5% reduction of the residual antigenicity was observed when heat treating the ovalbumin samples at pH 7.0, whereas a significant reduction (over 82%) of the antigenicity was obtained at pH 9.5 and temperatures over 80°C. Both pH and thermal treatment affected the conformation of ovalbumin. The reduced recognition of the modified native ovalbumin by specific antibodies at alkaline pH is most probably a consequence of significant changes in the local conformation of the epitopes.