Effects of high hydrostatic pressure on the conformational structure and the functional properties of bovine serum albumin

Combined application of high pressure and ultrasound in fig paste: effect on bioactive and volatile compounds

The combined impact of high-hydrostatic pressure (HHP) and ultrasound (US) on the cyanidin-3-O-rutinoside (C3R), quercetin-3-O-rutinoside (Q3R), and volatile compounds from fig (Ficus carica) paste was investigated. The HHP increased the content of C3R and Q3R, from 70 to 133 mg/kg fw and 31 to 44 mg/kg fw, respectively. The combination of HHP and US further enhanced the extraction of these bioactive compounds. Specifically, processing fig paste with US for 5 min at 40 °C yielded approximately 250 mg of C3R/kg fw and 45 mg of Q3R/kg fw, after 20 min. More than 25 volatile compounds were identified, with benzaldehyde being the predominant compound, accounting > 75%. Trace amounts of hydroxymethylfurfural (< 0.36 mg/100 g fw) were detected in HHP-processed fig paste. The application of HHP at mild temperatures and short time, combined with US, effectively promotes the content of bioactive compounds present in fig paste without adversely affecting the fruit's volatile compounds.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10068-023-01410-1.

Transglutaminase-induced soybean protein isolate cold-set gels treated with combination of ultrasound and high pressure: Physicochemical properties and structural characterization

Soybean protein isolate (SPI) was treated by the combined exposure to ultrasound and high pressure and then subjected to transglutaminase (TGase)-catalyzed cross-linking to prepare SPI cold-set gels. The effects of combined treatments on physicochemical and structural properties of TGase-induced SPI cold-set gels were investigated. The combination of ultrasound and high pressure promoted the covalent disulfide bonds and ε-(γ-glutaminyl) lysine isopeptide bonds as well as non-covalent hydrophobic interactions, which further improved the gelation properties of SPI compared to ultrasound or high pressure alone. In particular, the 480 W ultrasound followed by high pressure treatment of gels led to higher strength (120.53 g), water holding capacity (95.39 %), immobilized water (93.92 %), lightness (42.18), whiteness (51.03), and elasticity (G' = 407 Pa), as well as more uniform and compact microstructure, thus resulting in the improved gel network structure. The combination of two treatments produced more flexible secondary structure, tighter tertiary conformation and higher denaturation degree of protein in the gels, leading to more stable gel structure. The structural modifications of SPI contributed to the improvement of its gelation properties. Therefore, the combined application of ultrasound and high pressure can be an effective method for improving the structure and properties of TGase-induced SPI cold-set gels.

A comparative study of the impacts of preparation techniques on the rheological and textural characteristics of emulsion gels (emulgels)

A subtype of soft solid-like substances are emulsion gels (emulgels; EGs). These composite material's structures either consist of a network of aggregated emulsion droplets or a polymeric gel matrix that contains emulsion droplets. The product's rheological signature can be used to determine how effective it is for a specific application. The interactions between these structured system's separate components and production process, however, have a substantial impact on their rheological imprint. Therefore, rational comprehension of interdependent elements, their structural configurations, and the resulting characteristics of a system are essential for accelerating our progress techniques as well as for fine-tuning the technological and functional characteristics of the finished product. This article presents a comprehensive overview of the mechanisms and procedures of producing EGs (i.e., cold-set and heat-set) in order to determine the ensuing rheological features for various commercial applications, such as food systems. It also describes the influence of these methods on the rheological and textural characteristics of the EGs. Diverse preparation methods are the cause of the rheological-property correlations between different EGs. In many ways, EGs can be produced using various matrix polymers, processing techniques, and purposes. This may lead to various EG matrix structures and interactions between them, which in turn may affect the composition of EGs and ultimately their textural and rheological characteristics.

Modifications to structural, techno-functional and rheological properties of sesame protein isolate by high pressure homogenization

In this study, we aimed to determine the effect of high pressure homogenization (HPH) at a pressure up to 150 MPa on microstructural, techno-functional and rheological properties of sesame protein isolate (SPI). HPH treatment caused a partial change in the secondary structure of SPI, however, the changes in surface hydrophobicity and free -SH groups, indicating HPH had significant effect on the tertiary structure. After the HPH treatment, the particles dispersed homogeneously with more rougher surface. Sesame proteins had the smallest particle size (0.79 μm) and highest zeta potential (38.83 mV) at 100 MPa pressure. The most developed water/oil holding capacity, emulsification and foaming properties were achieved at 100 MPa pressure. However, the maximum stable foam formation (83.33 %) was determined at 150 MPa pressure. When the shear rate is fixed as 50 1/s, an increase in the viscosity value of the samples treated with 100 and 150 MPa pressure was detected compared to the control sample, while the lowest viscosity was determined the ones treated at 50 MPa. In all samples except 50 MPa pressure-treated proteins, viscoelastic character became dominant with increasing frequency (G' > G″). Modification with HPH resulted in a decrease of about 15 °C in the gelation temperature of SPI.

Effects of high pressure synergistic enzymatic physical state and concentration on the denaturation of polyphenol oxidase

The synergistic effect of the initial state of the enzyme and pressure level on the denaturation of PPO has not been clear yet, but it significantly affects the application of high hydrostatic pressure (HHP) in the enzyme-containing food processing. Solid (S-) and low/high concentration liquid (LL-/HL-) polyphenol oxidase (PPO) was used as the study object, and the microscopic conformation, molecular morphology and macroscopic activity of PPO under HHP treatments (100-400 MPa, 25 °C/30 min) were investigated by spectroscopic techniques. The results show that the initial state has a significant effect on the activity, structure, active force and substrate channel of PPO under pressure. The effec can be ranked as follows: physical state > concentration > pressure, S-PPO > LL-PPO > HL-PPO. High concentration has a weakening effect on the pressure denaturation of the PPO solution. Under high pressure, the α-helix and concentration factors play a crucial role in stabilizing the structure.

Structural Characteristics and Emulsifying Properties of Soy Protein Isolate Glycated with Galacto-Oligosaccharides under High-Pressure Homogenization

This study explored the Maillard reaction process during the glycation of soy protein isolate (SPI) with galacto-oligosaccharides (GOSs) under high-pressure homogenization (HPH) and its effects on the emulsifying properties of SPI. SPI-GOS glycation under moderate pressure (80 MPa) significantly inhibited the occurrence and extent of the Maillard reaction (p < 0.05), but homogenization pressures in the range of 80−140 MPa gradually promoted this reaction. HPH caused a decrease in the surface hydrophobicity of the glycated protein, an increase in the abundance of free sulfhydryl groups, unfolding of the protein molecular structure, and the formation of new covalent bonds (C=O, C=N). Additionally, the particle size of emulsions created with SPI-GOS conjugates was reduced under HPH, thus improving the emulsifying properties of SPI. A reduction in particle size (117 nm), enhanced zeta potential (−23 mV), and uniform droplet size were observed for the emulsion created with the SPI-GOS conjugate prepared at 120 MPa. The conformational changes in the glycated protein supported the improved emulsification function. All results were significantly different (p < 0.05). The study findings indicate that HPH provides a potential method for controlling glycation and improving the emulsifying properties of SPI.

Effect of high hydrostatic pressure processing on the structure, functionality, and nutritional properties of food proteins: A review

Proteins are important food ingredients that possess both functional and nutritional properties. High hydrostatic pressure (HHP) is an emerging nonthermal food processing technology that has been subject to great advancements in the last two decades. It is well established that pressure can induce changes in protein folding and oligomerization, and consequently, HHP has the potential to modify the desired protein properties. In this review article, the research progress over the last 15 years regarding the effect of HHP on protein structures, as well as the applications of HHP in modifying protein functionalities (i.e., solubility, water/oil holding capacity, emulsification, foaming and gelation) and nutritional properties (i.e., digestibility and bioactivity) are systematically discussed. Protein unfolding generally occurs during HHP treatment, which can result in increased conformational flexibility and the exposure of interior residues. Through the optimization of HHP and environmental conditions, a balance in protein hydrophobicity and hydrophilicity may be obtained, and therefore, the desired protein functionality can be improved. Moreover, after HHP treatment, there might be greater accessibility of the interior residues to digestive enzymes or the altered conformation of specific active sites, which may lead to modified nutritional properties. However, the practical applications of HHP in developing functional protein ingredients are underutilized and require more research concerning the impact of other food components or additives during HHP treatment. Furthermore, possible negative impacts on nutritional properties of proteins and other compounds must be also considered.

Factors affecting the modification of bovine milk proteins in high hydrostatic pressure processing: An updated review

High hydrostatic pressure (HHP) treatment induces structural changes in bovine milk proteins depending on factors such as the temperature, pH, concentration, decompression rate, cycling, composition of the medium and pressure level and duration. An in-depth understanding of the impact of these factors is important for controlling HHP-induced modification of milk proteins and the interactions within or between them, which can be applied to prevent undesired aggregation, gelation, and precipitation during HHP processing or to obtain specific milk protein modifications to attain specific protein properties. In this regard, understanding the influences of these factors can provide insight into the modulation and optimization of HHP conditions to attain specific milk protein structures. In recent years, there has been a great research attention on HHP-induced changes in milk proteins influenced by factors such as pH, temperature, concentration, cycling, decompression condition, and medium composition. Hence, to provide insight into how these factors control milk protein structures under HHP treatment and to understand if their effects depend on HHP parameters and environmental conditions, this review discusses recent findings on how various factors (pH, temperature, cycling, decompression rate, medium composition, and concentration) affect HHP-induced bovine milk protein modification. Practical Application: The information provided in this review will be very useful to anticipate the challenges related to the formulation and development of pressure-treated milk and dairy products.

Impact of holder, high temperature short time and high hydrostatic pressure pasteurization methods on protein structure and aggregation in a human milk protein concentrate

This work evaluated the impact of high temperature short time (HTST, 72 °C, 15 s), high hydrostatic pressure (HHP, 400-600 MPa at 5 and 10 min) and Holder pasteurization (HoP, 62.5 °C, 30 min) on protein profile and aggregation in a human milk protein concentrate (HMPC). The structural changes induced in milk proteins were investigated in HMPC as well as in sedimentable and non-sedimentable fractions recovered after ultracentrifugation. The results showed that heat treatments induced more protein denaturation and aggregation than did HHP treatments. Indeed, heat-induced protein aggregates observed in HMPC and the sedimentable fraction were mainly composed of lactoferrin and α-lactalbumin. More specifically, the concentration of lactoferrin in HMPC decreased by 86% after HTST and HoP whereas no effect was observed after HHP treatment. These results show the potential of HHP processing as a pasteurization method for HMPC since it minimizes the impact on protein structure, which generally correlates to protein quality and bioactivity.

Fabrication and Characterization of Ultra-High-Pressure (UHP)-Induced Whey Protein Isolate/κ-Carrageenan Composite Emulsion Gels for the Delivery of Curcumin

The emulsion gels have attracted extensive interests due to their unique physical characters, remarkable stability, and control release properties of flavor and functional components compared to emulsions in liquid. In the current work, whey protein isolate (WPI)/κ-carrageenan (κ-CG) composite emulsion gels were fabricated based on the ultra-high-pressure (UHP) technology, in replacement of the traditional thermal, acid, or enzyme processing. Uniform composite emulsion gels could be fabricated by UHP above 400 MPa with minimum WPI and κ-CG concentrations of 8.0 and 1.0 wt%, respectively. The formation of UHP-induced emulsion gels is mostly attributed to the hydrophobic interaction and hydrogen bonding. The emulsion gels with different textures, rheology properties, and microstructures could be fabricated through adjusting the formulations (WPI concentration, κ-CG concentration, and oil phase fraction) as well as processing under different conditions (pressure and time). Afterward, curcumin-loaded emulsion gels were fabricated and subjected to an in vitro simulated gastrointestinal digestion in order to investigate the gastrointestinal fate of curcumin. In vitro simulated digestion results demonstrated that the UHP treatment significantly retarded the release of curcumin but had little impact on the bioaccessibility of curcumin. The results in this work provide useful information for the construction of emulsion gels through a non-thermal process, which showed great potential for the delivery of heat-sensitive bioactive components.

Effects of High Hydrostatic Pressure Pretreatment on the Functional and Structural Properties of Rice Bran Protein Hydrolysates

Rice bran protein (RBP) hydrolysis was conducted after high hydrostatic pressure (HHP) pretreatment. The structural and functional properties of HHP-pretreated rice bran protein hydrolysates (RBPH) were investigated. HHP pretreatments were conducted at 100, 200, and 300 MPa; then, enzymatic hydrolysis at atmospheric pressure was performed using trypsin. An RBPH sample that had not been pretreated by HHP was used as a control. Free sulfhydryl (SH) content, SDS-PAGE profiles, high-performance size exclusion chromatography (HPSEC), Fourier transform infrared (FTIR) spectrum, scanning electron microscopy (SEM), intrinsic fluorescence spectrum, solubility, and emulsifying and foaming properties were evaluated. Changes in particle size and ζ-potential were monitored. Compared with the control, the results of solubility, the emulsifying activity index (EAI) and the emulsifying stability index (ESI) increased significantly (p < 0.05) at 200 MPa. The content of free SH increased significantly (p < 0.05) at 100 MPa. FTIR spectrum and fluorescence analysis confirmed the changes in the secondary and tertiary structures. The experimental results indicated that the structural and functional properties of HHP-pretreated RBPH improved.

Physicochemical properties of seed protein isolates extracted from pepper meal by pressure-assisted and conventional solvent defatting

Pepper seed is one by-product in pepper processing, rich in protein, fat, and fiber, and is a new plant-based protein source. In this paper, the physicochemical and functional properties of pepper seed protein isolates (PSPIs) extracted from pepper meal by pressure-assisted defatting (PAD) and conventional solvent defatting (CSD) were investigated. The yields of SPIs extracted by CSD and PAD were 22.8% and 20.5%, respectively. Compared with the PSPIs obtained by CSD, the solubility, water-holding and oil-holding capacities, and emulsifying and foaming abilities of the PSPIs obtained by PAD were significantly increased by 11.22%, 29.17%, 40%, 160%, and 100%, respectively. Additionally, UV-visible, intrinsic fluorescence and infrared spectroscopic characterization revealed the tertiary and secondary conformation changes of the PSPIs, which might contribute to the improvement of their functional properties. Overall, PAD significantly improved the functional properties of the PSPIs. The PSPIs extracted by this innovative technology would be a new plant protein alternative for food formulations with better functional properties.

Investigation of the consequences of ultrasound on the physicochemical, emulsification, and gelatinization characteristics of citric acid-treated whey protein isolate

The effect of ultrasound (US) pretreatment (0, 200, 400, 600, and 800 W) on the physicochemical, emulsification, and gelatinization characteristics of citric acid (CA)-treated whey protein isolate (WPI) was investigated. Size exclusion chromatography demonstrated that when compared with untreated WPI, US pretreatment promoted production of more molecular polymers in the CA-treated WPI. There was a reduction in particle size of CA-treated WPI with the increase of US power (0-800 W), whereas its free sulfhydryl content, surface hydrophobicity, and intrinsic fluorescence strength increased. Furthermore, compared with untreated WPI, emulsifying ability index and emulsifying stability index of CA-treated WPI were increased by 14.04% and 10.10%, respectively, at 800 W. Accordingly, US pretreatment promoted the gel formation of CA-treated WPI, and its gel hardness was increased by 28.0% with US power ranging from 0 to 800 W. Therefore, US and CA treatment can be considered as an effective way to improve the emulsifying and gelatinization characteristics of WPI.

Investigation on the interaction of acrylamide with soy protein isolate: Exploring the binding mechanism in vitro

Acrylamide (AA), which is a carcinogen in humans, has been a research focus in terms of food risk assessment. However, few published studies have explored protein strategies to reduce the health risks of AA. The objective of this study was to investigate the binding of AA with soy protein isolate (SPI) and elucidate the binding mechanism. The results showed that AA could bind with nontreated, heat-treated, high-pressure homogenization-treated, and ultrasound-treated SPI in vitro. Fourier-transform infrared spectroscopy suggested that secondary structure of SPI changed significantly after binding with AA in the nontreated and different treated groups. Moreover, fluorescence quenching experiments suggested that the quenching of SPI by AA was static quenching and hydrogen bonds, hydrophobic interactions, and van der Waals forces were involved in this process. PRACTICAL APPLICATION: The study of SPI and AA binding could provide a new perspective for reducing the bioaccessibility of AA in human body by using protein. The results showed that SPI could potentially be used as a novel health strategy to reduce the harm of AA in the human body.

Stability improvement of reduced-fat reduced-salt meat batter through modulation of secondary and tertiary protein structures by means of high pressure processing

This study investigated the effect of high-pressure processing (HPP) at 100 to 400 MPa for 2 min on the stability of reduced-fat reduced-salt (RFRS) meat batter. Total expressible fluid (TEF) of RFRS batter reached its minimum value at 200 MPa. The results of Raman spectra revealed that α-helix reached its random coils increased as the pressure level was increased, and pressure up to 200 MPa remarkably increased protein unfolding but 400 MPa increased aggregation. Finally, Raman spectra and magnetic resonance imaging (MRI) revealed that 200 MPa significantly increased tryptophan, tyrosine doublet, CH₃ and/or CH stretching and proton intensities related to water and fats; but decreased β structures, SS stretching (475) and (g-g-t or t-g-t, 540), as compared with the control. RFRS batter treated at 200 MPa is beneficial for the meat industry from the technological point of view and for consumers from the health point of view, as the improved emulsion stability contributed by the modified secondary and tertiary structures.

Biological and conventional food processing modifications on food proteins: Structure, functionality, and bioactivity

Food proteins are important nutrients for human health and thus make significant contributions to the unique functions of different foods. The modification of proteins through physical and biological processing could improve the functional and nutritional properties of food products; these changes can be attributed to modifications in particle size, solubility, emulsion stability, secondary structure, as well as the bioactivities of the proteins. Physical processing treatments might promote physical phenomena, such as combined friction, collision, shear forces, turbulence, and cavitation of particles, and lead to changes in the particle sizes of proteins. The objective of this review is to illustrate the effect of physical and biological processing on the structure, and physical and chemical properties of food-derived proteins and provide insights into the mechanism underlying structural changes. Many studies have suggested that physical and biological processes, such as ultrasound treatment, high pressure homogenization, ball mill treatment, and enzymatic hydrolysis could affect the structure, physical properties, and chemical properties of food-derived proteins. Some important applications of food-derived proteins are also discussed based on the relationships between their physical, chemical, and functional properties. Perspectives from fundamental or practical research are also brought in to provide a complete picture of the currently available relevant data.

Effects of High Pressure Modification on Conformation and Digestibility Properties of Oyster Protein

To expand the utilization of oyster protein (OP), the effects of high pressure (100 to 500 MPa) on chemical forces, structure, microstructure, and digestibility properties were investigated. High pressure (HP) treatment enhanced the electrostatic repulsion (from -13.3Control to -27.8HP200 mV) between protein molecules and avoided or retarded the formation of protein aggregates. In addition, the HP treated samples showed uniform distribution and small particle size. The changes in electrostatic interaction and particle size contributed to the improvement of solubility (from 10.53%Control to 19.92%HP500 at pH 7). The stretching and unfolding of protein were modified by HP treatment, and some internal hydrophobic groups and -SH groups were exposed. HP treatment modified the secondary structure of OP. The treated samples contained less α-helix and β-sheet structures, whereas the proportions of β-sheet and random coil structures were increased. The treated samples have high digestibility in the stomach (from 26.3%Control to 39.5%HP500) and in the total digestive process (from 62.1%Control to 83.7%HP500). In addition, the total digestive production showed higher percentages of small peptides (<1 kDa) after HP treatment. The protein solubility and digestibility were increased after HP treatment, and high solubility and high digestibility might increase the chance that OP become a kind of protein supplement.

Modeling counterion partition in composite gels of BSA with gelatin following high pressure treatment

We examine the morphology of hydrogels made of bovine serum albumin and gelatin following high pressure processing at 300 MPa for 15 min at 10 and 80 °C. Emphasis is on the distribution of added calcium counterions between the polymeric phases seen in changes in the structural properties of the composite gel. Protocol includes thermal and HPP treatments, dynamic oscillation rheology, ESEM, and modeling from the "synthetic polymer approach" to rationalize results. Pressurization at 10 °C produced continuous gelatin networks with dispersed BSA inclusions whereas pressurization at 80 °C yielded an inverse dispersion of BSA as the continuous phase supporting liquid gelatin inclusions. Lewis and Nielsen equations were adapted to predict the counterion distribution between the polymeric phases that profoundly affected the structural properties of the pressurized gels. The concept of counterion partition (p_c) is introduced to the literature to follow the phase behavior of the composites in the presence of added calcium counterions.

Surface Hydrophobicity and Functional Properties of Citric Acid Cross-Linked Whey Protein Isolate: The Impact of pH and Concentration of Citric Acid

The effects of citric acid-mediated cross-linking under non-acidic conditions on the surface hydrophobicity, solubility, emulsifying, and foaming properties of whey protein isolate (WPI) were investigated. In this research, citric acid-mediated cross-linking could not only increase the surface hydrophobicity of whey proteins at pH 7.0 and 8.0, but it also improved its emulsifying and foaming properties. The emulsifying activity and foaming ability of WPI reached a maximum under the condition of 1% citric acid and pH 7.0. However, the solubility of WPI-CA gradually decreased with pH and the content of citric acid increased. Therefore, the cross-linking mediated by citric acid under non-acidic aqueous conditions, markedly altered the surface hydrophobicity and enhanced emulsifying and foaming properties of WPI.