Effects of high hydrostatic pressure (HHP) on protein structure and digestibility of red abalone (Haliotis rufescens) muscle

Effect of UHT Thermal Treatment on the Secondary Structures of Milk Proteins: Insights From FTIR Analysis and Potential Allergenic Activity

Although thermal treatments are beneficial for the preservation and safety of milk, they can also alter its immunogenic activity by affecting its protein components. To achieve precise results, it is essential to identify the specific proteins that cause food allergies. Therefore, investigating the possible alterations of cow's milk proteins (CMPs) resulting from thermal treatments is necessary. In this study, the Fourier transform infrared spectroscopy (FTIR) technique was used to analyze the effect of UHT thermal treatment on the secondary structures of milk casein. Using the second derivative, six characteristic peaks were identified in the Amide I region, ranging from 1700 to 1600 cm-1. It was found that thermal treatments produce shifts in absorption peaks, indicating changes in protein conformation and possibly in allergenic activity. These shifts were clearly identified in the first characteristic peak of samples M8 and M9, from 1621 to 1600 cm-1. The results suggest that thermal treatments may promote protein aggregation by increasing β turns and reducing β sheets and α helices, which could enhance the allergenic potential of the proteins and facilitate the formation of complexes between different milk proteins, such as β-lactoglobulin and κ-casein. Further studies are needed to experimentally validate the allergenic activity of proteins modified by thermal treatments, as only an analytical method (FTIR) was used to evaluate the secondary structures of the proteins.

High-pressure microfluidisation positively impacts structural properties and improves functional characteristics of almond proteins obtained from almond meal

Almond protein isolate (API) obtained from almond meal was processed using dynamic high-pressure microfluidisation (0, 40, 80, 120, and 160 MPa pressure; single pass). Microfluidisation caused significant reductions in the particle size and increased absolute zeta potential. SDS-PAGE analysis indicated reduction in band intensity and the complete disappearance of bands beyond 80 MPa. Structural analysis (by circular dichroism, UV-Vis, and intrinsic-fluorescence spectra) of the API revealed disaggregation (up to 80 MPa) and then re-aggregation beyond 80 MPa. Significant increments in protein digestibility (1.16-fold) and the protein digestibility corrected amino acid score (PDCAAS; 1.15-fold) were observed for the API (80 MPa) than control. Furthermore, significant improvements (P < 0.05) in the functional properties were observed, viz., the antioxidant activity, protein solubility, and emulsifying properties. Overall, the results revealed that moderate microfluidisation treatment (80 MPa) is an effective and sustainable technique for enhancing physico-chemical and functional attributes of API, thus potentially enabling its functional food/nutraceuticals application.

Effect of high-hydrostatic pressure on the digestibility of egg yolk and granule

The impact of high hydrostatic pressure (HHP) on protein digestibility of egg yolk and egg yolk granule was evaluated by static in vitro digestion using the standardized INFOGEST 2.0 method. The degree of hydrolysis (DH) and the phospholipid content were determined during digestion, and the protein and peptide profiles were characterized by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and reverse phase-high pressure liquid chromatography (RP-HPLC). The results showed that HHP induced protein aggregation in egg yolk and granule, mainly by disulfide bridges, which were not disrupted in the oral phase. Proteolysis during the gastric phase improved egg yolk and granule protein solubility, regardless of whether HHP was applied. However, the extent of the samples' digestibility was not affected, with DH values ranging from 15% to 20%. During the intestinal phase, the DH of egg yolk protein (∼40%) was higher than that of the granule (∼25%), probably due to the denser structure of the granule reducing the accessibility of intestinal enzymes. The DH, peptide, and protein profiles of control and HHP-treated egg yolk showed similar protein digestion behaviors for both gastric and intestinal phases. Among the different proteins, only the digestibility of β-phosvitin in HHP-treated granule was enhanced. Consequently, applying HHP to granules represents an interesting process that improves the digestibility of phosvitin with the potential to generate bioactive phosvitin-derived phosphopeptides. PRACTICAL APPLICATION: High hydrostatic pressure, mainly used as a preservation process, did not impair the nutritional quality of the egg yolk and granule proteins but improved the susceptibility of phosvitin (protein contained in egg yolk) proteolysis to produce bioactive phosphopeptides. Consequently, applying HHP to granules represents an interesting process that improves the digestibility of phosvitin.

High hydrostatic pressure induced gastrointestinal digestion behaviors of quercetin-loaded casein delivery systems under different calcium concentration

Casein micelle has a structure of outer hydrophilicity and inner hydrophobicity, its typical digestion characteristic is gastric coagulation. Based on calcium content as the key factor to control this process, high hydrostatic pressure (HHP) was firstly used to modify the micelle structure by mediating the tight connection between casein molecules themselves and with colloidal calcium, then the quercetin-loaded delivery systems were prepared. And in order to investigate the effect of exogenous calcium, calcium chloride was added for digestion. The results indicated that HHP broke the limitation of casein micelles as delivery carriers for hydrophobic components and increased the EE from 51.18 ± 3.07 % to 76.17 ± 3.41 %. During gastric digestion, higher pressure and exogenous calcium synergistically increased the clotting ability and inhibited the release of quercetin. In the small intestine, curds decomposed more slowly under higher pressure and calcium concentration, so the degradation of quercetin was effectively inhibited.

Effects of freeze-thaw cycles on in-vitro digestive properties of myofibrillar protein in mirror carp (Cyprinus carpio L.), based on protein degradation, oxidation, and structural properties

The in-vitro digestive properties of myofibrillar protein (MP) in mirror carp (Cyprinus carpio L.) after freeze-thaw (F-T) cycles were analyzed in terms of the relationship between protein degradation, oxidation, and structural properties. The F-T samples exhibited a significant increase in glucosidase activity, N-acetyl-β-d-glucosidase activity, total protease activity, and non-protein nitrogen content. α-aminoadipate semialdehyde and γ-glutamate semialdehyde contents increased by 23.17% and 123.12%, respectively. Furthermore, 53.97% decrease in the total nitrogen content and changes in the content of different soluble proteins were observed. X-ray diffraction intensity, thermal stability, free amine content, hydrolysis degree, and digestibility of the MP samples decreased, and the 2θ angle and zeta potential were reversed. Besides, changes in the amide band wavenumbers were also detected. Therefore, the protein structure was unfolded and aggregates were formed through degradation and oxidation induced by the F-T cycles, ultimately making the in-vitro digestion of MP difficult.

Comparative structural, digestion and absorption characterization of three common extruded plant proteins

Extruded plant proteins, also known as textured vegetable proteins (TVPs), serve as vital components in plant-based meat analogue, yet their structural and nutritional characteristics remain elusive. In this study, we examined the impact of high-moisture (HM) and low-moisture (LM) extrusion on the structures, digestion and absorption of three types of plant proteins. Extrusion transformed plant proteins from spherical to fibrous forms, and formed larger aggregate particles. It also led to the disruption of original disulfide bonds and hydrophobic interactions within protein molecules, and the formation of new cross-links. Intriguingly, compared to native plant proteins, TVPs' α-helix/β-sheet values decreased from 0.68 to 0.69 to 0.56-0.65. Extrusion increased the proportion of peptides shorter than 1 kD in digesta of TVPs by 1.44-23.63%. In comparison to unextruded plant proteins, TVPs exhibited lower content of free amino acids in cell transport products. Our findings demonstrated that extrusion can modify protein secondary structure by diminishing the α-helix/β-sheet value, and impact protein tertiary structure by reducing disulfide bonds and hydrophobic interactions, promoting the digestion and absorption of plant proteins. These insights offer valuable scientific backing for the utilization of extruded plant-based proteins, bolstering their role in enhancing the palatability and nutritional profile of plant-based meat substitutes.

Contribution of process-induced molten-globule state formation in duck liver protein to the enhanced binding ability of (E,E)-2,4-heptadienal

BACKGROUND

Extracted proteins of alternative animal origin tend to present strong off-flavor perception due to physicochemical interactions of coextracted off-flavor compounds with proteins. To investigate the relationship between absorption behaviors of volatile aromas and the processes-induced variations in protein microstructures and molecular conformations, duck liver protein isolate (DLp) was subjected to heating (65/100 °C, 15 min) and ultra-high pressure (UHP, 100-500 MPa/10 min, 28 °C) treatments to obtain differential unfolded protein states.

RESULTS

Heat and UHP treatments induced the unfolding of DLp to varied degrees, as revealed by fluorescence spectroscopy, ultraviolet-visible absorption, circular dichroism spectra and surface hydrophobicity measurements. Two types of heating-denatured states with varied unfolding degrees were obtained, while UHP at both levels of 100/500 MPa caused partial unfolding of DLp and the presence of a molten-globule state, which significantly enhanced the binding affinity between DLp and (E,E)-2,4-heptadienal. In particular, significantly modified secondary structures of DLp were observed in heating-denatured samples. Excessive denaturing and unfolding degrees resulted in no significant changes in the absorption behavior of the volatile ligand, as characterized by observations of fluorescence quenching and analysis of headspace concentrations.

CONCLUSION

Defining process-induced conformational transition behavior of matrix proteins could be a promising strategy to regulate food flavor attributes and, particularly, to produce DLp coextracted with limited off-flavor components by modifying their interaction during extraction processes. © 2023 Society of Chemical Industry.

Dynamic alterations in protein, sensory, chemical, and oxidative properties occurring in meat during thermal and non-thermal processing techniques: A comprehensive review

Meat processing represents an inevitable part of meat and meat products preparation for human consumption. Both thermal and non-thermal processing techniques, both commercial and domestic, are able to induce chemical and muscle's proteins modification which can have implication on oxidative and sensory meat characteristics. Consumers' necessity for minimally processed foods has paved a successful way to unprecedented exploration into various novel non-thermal food processing techniques. Processing of meat can have serious implications on its nutritional profile and digestibility of meat proteins in the digestive system. A plethora of food processing techniques can potentially induce alterations in the protein structure, palatability, bioavailability and digestibility via various phenomena predominantly denaturation and Maillard reaction. Apart from these, sensory attributes such as color, crispness, hardness, and total acceptance get adversely affected during various thermal treatments in meat. A major incentive in the adoption of non-thermal food processing is its energy efficiency. Considering this, several non-thermal processing techniques have been developed for evading the effects of conventional thermal treatments on food materials with respect to Maillard reactions, color changes, and off-flavor development. Few significant non-thermal processing techniques, such as microwave heating, comminution, and enzyme addition can positively affect protein digestibility as well as enhance the value of the final product. Furthermore, ultrasound, irradiation, high-pressure processing, and pulsed electric fields are other pivotal non-thermal food processing technologies in meat and meat-related products. The present review examines how different thermal and non-thermal processing techniques, such as sous-vide, microwave, stewing, roasting, boiling, frying, grilling, and steam cooking, affect meat proteins, chemical composition, oxidation, and sensory profile.

Effect of Enzymatic Hydrolysis on Solubility and Emulsifying Properties of Lupin Proteins (Lupinus luteus)

Solubility and emulsifying properties are important functional properties associated with proteins. However, many plant proteins have lower techno-functional properties, which limit their functional performance in many formulations. Therefore, the objective of this study was to investigate the effect of protein hydrolysis by commercial enzymes to improve their solubility and emulsifying properties. Lupin protein isolate (LPI) was hydrolyzed by 7 commercial proteases using different E/S ratios and hydrolysis times while the solubility and emulsifying properties were evaluated. The results showed that neutral and alkaline proteases are most efficient in hydrolyzing lupin proteins than acidic proteases. Among the proteases, Protamex® (alkaline protease) showed the highest DH values after 5 h of protein hydrolysis. Meanwhile, protein solubility of LPI hydrolysates was significantly higher (p < 0.05) than untreated LPI at all pH analyzed values. Moreover, the emulsifying capacity (EC) of undigested LPI was lower than most of the hydrolysates, except for acidic proteases, while emulsifying stability (ES) was significantly higher (p < 0.05) than most LPI hydrolysates by acidic proteases, except for LPI hydrolyzed with Acid Stable Protease with an E/S ratio of 0.04. In conclusion, the solubility, and emulsifying properties of lupin (Lupinus luteus) proteins can be improved by enzymatic hydrolysis using commercial enzymes.

High hydrostatic pressure treatment reduces the potential antigenicity of β-conglycinin by changing the protein structure during in vitro digestion

BACKGROUND

High hydrostatic pressure (HHP) treatment has been used to alleviate the allergenicity of soybeans, but there are little data about the potential antigenicity of β-conglycinin after HHP treatment.

RESULTS

We examined the effects of HHP treatment on the antigenicity and structure of β-conglycinin. When the pressure was 300 and 400 MPa, HHP treatment reduced the immunoglobulin (Ig)G binding capacity of β-conglycinin, while its IgE binding capacity did not change significantly. After in vitro digestion, both the IgE and IgG binding of β-conglycinin was obviously inhibited after HHP treatment at 400 MPa and 60 °C, although its binding capacity with linear epitope antibodies increased. Moreover, HHP treatment changed the secondary structure of β-conglycinin, the content of α-helix and random coils increased, while the β-sheet and β-turn decreased. After HHP treatment, the conformational structure was unfolded so that a large number of hydrophobic regions were exposed.

CONCLUSION

HHP treatment alleviated the potential antigenicity of β-conglycinin by modifying its structure, which facilitated in vitro digestion and destroyed epitopes. This research provides a new insight into the mechanism of HHP treatment that affects the sensitization of soy protein allergens. © 2022 Society of Chemical Industry.

Effects of soybean oil on rheological characteristics of dough under high hydrostatic pressure

In order to improve the stability of dough with soybean oil, this paper explored the effect of soybean oil addition on the rheological characteristics of dough under high hydrostatic pressure. The results showed that, compared with the dough without soybean oil, the β-sheet, disulfide bonds content and gauche-ganche-ganche in the dough increased by 4.23%, 0.85 μmol/g and 4.16% respectively when the dough was added with 6% soybean oil, which improved the degree of cross-linking polymerization of gluten protein and the stability of gluten network. Meanwhile, the dough had the highest elastic modulus and the lowest maximum creep compliance (6.85 Pa^-1 ×10^-4 ), indicating that 6% soybean oil significantly increased the elasticity and hardness of the dough. The results of short-range ordered structure and paste properties showed that with the addition of soybean oil, the ordered structure and paste viscosity decreased with the increase of soybean oil.

Application of iTRAQ Technology to Identify Differentially Expressed Proteins of Sauce Lamb Tripe with Different Secondary Pasteurization Treatments

Vacuum-packed sauce lamb tripe was subjected to secondary pasteurization by high-pressure processing (HPP) and heat treatment (HT), and iTRAQ technology was applied to investigate the differentially expressed proteins (DEPs). The analysis revealed 484 and 398 DEPs in the HPP and HT samples, respectively, compared with no treatment. These DEPs were sorted by texture results, and it was revealed that these DEPs acted in different biological processes with many structural proteins and protein subunits related to lamb tripe texture. The results verified by Western blot were consistent with the protein expression changes observed by proteomics. The bioinformatics analysis showed that the hardness and gumminess of the sauce lamb tripe after HT might be related to changes in the expression of CNN1 and FN1. The changes in the expression of TMP, FN1, YWHAG, TTN, collagen isoforms, and ARPC3 might be related to the improved springiness and chewiness of lamb tripe after HPP.

Impact of High-Pressure Treatment on Amino Acid Profile, Fatty Acid Compositions, and Texture of Yellowfin Seabream (Acanthopagrus arabicus) Filets

This work describes the optimization of the pressure–time combination for the inactivation of Listeria monocytogenes in fish medium using a wide range of pressure (225–525 MPa) and holding time (5–30 min). Thereafter, the yellowfin seabream (Acanthopagrus arabicus) filets (100 g each) were subjected to high-pressure (HP) treatment at the optimum pressure/time combination, and the impact of HP on the amino acid profile, fatty acid profiles, color, and texture was assessed. Glycine, glutamic acid, and alanine were recorded as the major amino acids, which did not change significantly after pressurization. Conversely, alanine—the leading free amino acid—dropped significantly after treatment. The fatty acid analysis indicated that oleic acid and palmitic acid accounted for 29.88 and 25.59% of the total fatty acids, respectively. Pressurization did not influence the fatty acid profiles, nutritional quality indices, and hardness of yellowfin seabream fish. The color pigments of filets, measured as a* and b*, changed significantly after the treatment. Overall, this work indicates that HP treatment can be utilized to maintain the nutritional quality of seabream filets; however, further research is needed to maintain the visual color of the fish.

Effects of PEF-Assisted Freeze-Drying on Protein Quality, Microstructure, and Digestibility in Chilean Abalone “Loco” (Concholepas concholepas) Mollusk

The purpose of this study was to apply different pulsed electric field (PEF) conditions as a pretreatment to the freeze-drying (FD) process of Chilean abalone and to assess its effects on protein quality, microstructure, and digestibility of the freeze-dried product. The treatments PEF (0.5, 1.0, and 2.0 kV cm⁻¹) and cooking (CO) were applied at 100°C × 15 min. Then, their performances were subjected to a FD process. PEF + CO pretreated freeze-dried samples showed shorter process times than freeze-dried control samples without PEF + CO, where the treatment PEF at 2.0 kV cm⁻¹ reached the shortest time. In addition, the abovementioned samples presented the best textural parameters but a low protein content. The thermal properties indicate a total denaturation of the proteins, where the amide I region presented greater mobility in the sample pretreated with an electric field of 2.0 kV cm⁻¹. The assay for digestibility shows better hydrolysis for the 2.0 kV cm⁻¹ PEF sample and has a higher Computer-Protein Efficiency Ratio (C-PER). Thereby, variations in thermal behavior and physicochemical parameters in comparison to combined PEF + CO pretreatments were observed. In addition, high protein quality and digestibility of pretreated freeze-dried Chilean abalones were maintained to the desired properties (texture and C-PER) and conditions (FD time).

Release and conformational changes in allergenic proteins from wheat gluten induced by high hydrostatic pressure

The gluten proteins of wheat are major causative agents of harmful immune responses. This study investigated the effects of high hydrostatic pressure (200, 300, 400, and 500 MPa), treatment time (5-25 min) and protein concentration (1%-5% protein weight/volume) on the structures underlying the allergenicity wheat gluten. The results showed that a combination of 400 MPa, 20 min treatment time and 3% protein reduced the wheat gluten allergenicity by 72.2%. Moreover, a Western blotting showed that the allergenicity of 26, 28, 48, 68 kDa and high molecular weight glutenin was sharply reduced. Fourier infrared spectroscopy and surface hydrophobicity indicated that gluten molecules aggregated after HHP treatment. Intermolecular forces indicated that gluten aggregated mainly through hydrophobic interactions and disulfide bonds but not by hydrogen bonds after HHP treatment. These results suggest that structural changes contributed to the reduction of wheat gluten allergenicity and that HHP may enhance safety for susceptible individuals.

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.

Application of nonthermal processing technologies in extracting and modifying polysaccharides: A critical review

Polysaccharides are natural polymer compounds widely distributed in plants, animals, and microorganisms, most of which have a broad spectrum of biological activities to promote human health. They could also be used as texture modifiers in food industry due to their excellent rheological and mechanical properties. Many researchers have shown that nonthermal processing technologies have numerous advantages, such as high extraction efficiency, short extraction time, and environmental friendliness, in the extraction of polysaccharides compared with the traditional extraction methods. Moreover, nonthermal technologies could effectively change the physicochemical properties and structural characteristics of polysaccharides to improve their biological activities or processing properties. Therefore, a comprehensive summary about the extraction and modification of polysaccharides by nonthermal technologies, including ultrasound, high hydrostatic pressure, pulsed electric fields, and cold plasma, was provided in this review. In particular, the underlying mechanisms, processing operations, and current application status of these technologies were discussed. In addition, the applications of combining nonthermal techniques with other technological methods in polysaccharide extraction and modification were briefly introduced.

Effects of High Hydrostatic Pressure on the Conformational Structure and Gel Properties of Myofibrillar Protein and Meat Quality: A Review

In meat processing, changes in the myofibrillar protein (MP) structure can affect the quality of meat products. High hydrostatic pressure (HHP) has been widely utilized to change the conformational structure (secondary, tertiary and quaternary structure) of MP so as to improve the quality of meat products. However, a systematic summary of the relationship between the conformational structure (secondary and tertiary structure) changes in MP, gel properties and product quality under HHP is lacking. Hence, this review provides a comprehensive summary of the changes in the conformational structure and gel properties of MP under HHP and discusses the mechanism based on previous studies and recent progress. The relationship between the spatial structure of MP and meat texture under HHP is also explored. Finally, we discuss considerations regarding ways to make HHP an effective strategy in future meat manufacturing.

Improvement of meat protein digestibility in infants and the elderly

Meat is a valuable protein source with a balanced composition of essential amino acids and various nutrients. This review aims to identify methods to improve digestion of meat proteins, as well as evaluate the digestive characteristics of infants and the elderly. Immature digestive conditions in infants, including a high gastric pH and low protease concentration, can hinder protein digestion, thus resulting in inhibited growth and development. Likewise, gastrointestinal (GI) tract aging and chronic health problems, including tooth loss and atrophic gastritis, can lead to reduction in protein digestion and absorption in the elderly compared with those in young adults. Moderate heating and several non-thermal technologies, such as aging, enzymatic hydrolysis, ultrasound, high-pressure processing, and pulsed electric field can alter protein structure and improve protein digestion in individuals with low digestive capacity.

Effects of high hydrostatic pressure on color, texture, microstructure, and proteins of the tilapia (Orechromis niloticus) surimi gels

The tilapia (Orechromis niloticus) surimi gels were prepared with high hydrostatic pressure (0, 100, 200, 300, and 400 MPa for 15 min) treatments to investigate the changes in water-holding capacity, color, gel strength, microstructure, texture, and proteins of the gels. Compared it with cooked gel (40°C/30 min + 90°C/30 min). The whiteness of heat-induced and HHP-induced gels were significant (p < .05) higher than that of untreated samples. The gels formed by pressurization were dense and flexible, and formed by cross-linking based on hydrogen bonding. SDS-PAGE patterns showed no major change in the actin and tropomyosin protein profiles of gels induced by HHP-300. Raman spectroscopy confirmed disulfide bonds played an important role in gel formation. A lower intensity ratio observed in HHP-induced protein supported the tyrosine residues involved in hydrogen bond formation. The changes of secondary structure suggested decreased α-helix content and increased β-sheet.