Structural features of myofibrillar fish protein interacting with phosphatidylcholine liposomes

Effect of supercritical carbon dioxide on protein structure modification and antimicrobial peptides production of Mongolian cheese and its in vitro digestion

The aim of this research was to investigate the effects of supercritical carbon dioxide (SC-CO2) treatment on protein structure in Mongolian cheese. The peptides during the digestive process of the SC-CO2 treated cheese were also studied. SC-CO2 technology was utilized to treat Mongolian cheese at three temperatures (45, 55 and 65 °C) and three pressures (7.5, 12.5 and 17.5 MPa). The results of fluorescence, ultraviolet-visible, Fourier transform infrared spectroscopy and free sulfhydryl groups showed that SC-CO2, particularly at 65 °C and 17.5 MPa, modified the protein structure in Mongolian cheese effectively. The data of LC-MS/MS-based peptidomics showed that the content of antimicrobial peptides found in the SC-CO2 treated Mongolian cheese was 1.55 times that of the untreated Mongolian cheese; the content of unique antimicrobial peptides in the digested SC-CO2 treated Mongolian cheese was 1.46 times that of the digested untreated Mongolian cheese, which proved that SC-CO2 could help produce antimicrobial peptides in cheese not only during the process of SC-CO2 treatment but during subsequent simulated gastrointestinal digestion as well. In conclusion, SC-CO2 could be considered a promising method to develop cheese products with potential health benefits.

Cryoprotective effect of soluble soybean polysaccharides and enzymatic hydrolysates on the myofibrillar protein of Nemipterus virgatus surimi

Cryoprotective effect and potential mechanism of soluble soybean polysaccharides (SSPS) and enzymatic hydrolysates on surimi was investigated. After hydrolysis, the molecular weight of SSPS significantly decreased, and the hydrolysates prepared by endo-polygalacturonase (EPG-SSPS) was the lowest (154 kDa). Infrared spectrum analysis revealed that enzymatic hydrolysis didn't alter the functional groups of SSPS, but it did augment the exposure to hydroxyl groups. Surimi containing 5 % EPG-SSPS had the lowest freezable water after 20 days of frozen storage. Furthermore, the 5 % EPG-SSPS group manifested the highest metrics in total sulfhydryl (8.0 × 10-5 mol/g), active sulfhydryl content (6.7 × 10-5 mol/g), Ca2+-ATPase activity, and exhibited the lowest level in carbonyl content, surface hydrophobicity (153 μg). Notably, the 5 % EPG-SSPS maintained the stability of protein structure. Conclusively, SSPS enzymatic hydrolysate using endo-polygalacturonase imparted superior cryoprotective effect on the myofibrillar protein of surimi, and the mechanism might be a decrease in molecular weight and exposure of hydroxyl groups.

Insight into the effect of large yellow croaker roe phospholipids on the physical properties of surimi gel and their interaction mechanism with myofibrillar protein

BACKGROUND

The present study aimed to investigate the effects of large yellow croaker roe phospholipids (LYCRPLs) on the physical properties of surimi gels and to clarify their interaction mechanism with myofibrillar proteins (MPs) in terms of chemical forces and the spatial conformation.

RESULTS

LYCRPLs could improve the gel strength, textural properties, rheological properties and water-holding capacity of surimi gels. Moreover, the interaction mechanism between LYCRPLs with MPs was revealed through intermolecular forces, Fourier transform infrared spectroscopy and ultraviolet visible absorption spectroscopy. The findings demonstrated that LYCRPLs enhanced the surface hydrophobicity and particle size of MPs, facilitating expansion and cross-linking of MPs.

CONCLUSION

These results provide a theoretical basis for improving the characteristics of surimi gels and thus facilitate the application of LYCRPLs in the aquatic food industry. © 2023 Society of Chemical Industry.

Probing the interaction between encapsulated ethoxyquin and its β-cyclodextrin inclusion complex with bovine serum albumin

Ethoxyquin (EQ) is a synthetic antioxidant that is derived from quinolines and found in many meat products. EQ is strictly regulated in feed due to its potential health implications. An investigation of the interaction mechanism between EQ and transporter protein before and after β-cyclodextrin (β-CD) encapsulation was conducted with the use of multi-spectroscopy, cyclic voltammetry, and molecular docking. EQ formed complexes with bovine serum albumin (BSA), and affected secondary structure and microenvironment polarity of BSA. However, at 298 K, EQ's fluorescence quenching constants decreased from (9.81 ± 0.05) × 103 L mol-1 to (4.94 ± 0.09) × 103 L mol-1, binding constants decreased from (10.28 ± 0.02) × 103 L mol-1 to (2.08 ± 0.07) × 103 L mol-1, after encapsulation in β-CD as well as the binding distance increased. β-CD contains part of EQ in its hydrophobic cavity, inhibiting its binding to BSA. β-CD inclusion complex prevented adverse effects of EQ on BSA conformation. However, β-CD encapsulation had no effect on EQ's antioxidant activity.

Interaction between liposome and myofibrillar protein in surimi: Effect on gel structure and digestive characteristics

This study investigated the effects of the interaction between liposomes and myofibrillar protein (MP) on tilapia surimi. The strong interaction between liposomes and MP was primarily mediated through hydrogen bonding and hydrophobic interaction. Liposomes caused the unfolding of MP structure, resulting in the decrease of α-helix content and transformation of spatial structure. Notably, the appropriate ratio of liposomes improved the gel properties of tilapia surimi. The water distribution, microstructure, and texture characteristics further confirmed that liposomes strengthened the structure of surimi gel through non-covalent bonds. However, excessive liposomes (1.0 %) weakened gel characteristics and texture. Moreover, the proper ratio of liposomes enhanced the stability of surimi gels during digestion, reducing protein digestibility from 66.0 % to 54.8 %. Curcumin-loaded liposomes in gel matrix notably delayed digestion and improved bioavailability. This delay in digestion was attributed to the ability of liposomes to decrease the interaction between MP and digestive enzymes. This study provides new insight into the application of liposomes in protein-rich food matrixes.

Investigation on the quality regulating mechanism of antifreeze peptides on frozen surimi: From macro to micro

Freeze denaturation of protein caused by ice crystals is the main motivation for the quality deterioration of surimi during circulation and storage. This investigation aimed to cryoprotect surimi by adding antifreeze peptides from Takifugu obscurus skin (TsAFP) which can inhibit ice recrystallization, and to elucidate regulating mechanism. The comprehensive results showed that 4% TsAFP, half dosage of commercial cryoprotectant, had good cryoprotection on surimi by reducing the moisture variation and maintaining protein solubility of surimi at macro level, as well as inhibiting the degeneration and structure changes of myofibrillar proteins at micro level. Meanwhile, TsAFP could directly bind to the structural cavity of myosin, inhibit protein freezing-induced oxidation, maintain the spatial structure of myosin and water retention ability to preserve the surimi quality. This study helped better comprehend the protective mechanisms of antifreeze peptides in frozen surimi and was expected to provide a promising cryoprotectant for low-sweetness and low-calorie surimi.

The Spatial Distribution Patterns, Physicochemical Properties, and Structural Characterization of Proteins in Oysters (Crassostrea hongkongensis)

Protein content, a vital component determining the nutritional quality of oysters, is unevenly distributed in different parts of oyster. In this study, the spatial distribution (visceral mass, mantle, gill, and adductor) patterns and structural characteristics of proteins, including water–soluble proteins (WSP), salt–soluble proteins (SSP), acid–soluble proteins (ASP) and alkali–soluble proteins (ALSP) of oysters (Crassostrea hongkongensis) were investigated with the amino acid analyzer, circular dichroism spectroscopy (CD), fourier transform infrared spectroscopy (FTIR), and fluorescence spectroscopy. The results showed that oyster proteins were mainly distributed in the visceral mass and mantle. The protein composition was WSP, SSP, ALSP, and ASP in descending order, which conformed to the ideal amino acid pattern. Variations in secondary structure, molecular weight distribution, and thermal denaturation temperatures of the oyster proteins were observed. SSP had wider bands (16–270 kDa) than those of ASP (30–37 kDa) and ALSP (66–270 kDa). Among the four proteins, the SSP of the mantle showed the highest thermal stability (87.4 °C), while ALSP of the adductor muscle had the lowest the lowest the peak denaturation temperature (Tm) (53.8 °C). The proportions of secondary structures in oyster proteins were different, with a higher proportion of solid protein β–folds, and the exposure of aromatic amino acid residues and disulfide bonds and the microenvironment in which they were located were also different.

Improving the solubility of myofibrillar proteins in water by destroying and suppressing myosin molecular assembly via glycation

Filamentous myosin is a self-assembling polymer that prevents myofibrillar proteins (MPs) from functioning in low ionic strength media. This study was aimed at investigating if glycation has the potential to improve the solubility of MPs in water. MPs were conjugated with monosaccharides, oligosaccharides, and polysaccharides under wet reaction conditions at 37 °C. The conjugation was verified by SDS-PAGE, FT-IR and amino acid analyses. MPs conjugated with dextran (DX) exhibited a higher solubility and dispersion stability in water, which corresponded to smaller particle size and more uniform distribution (P < 0.05). According to secondary and tertiary structure analyses, the loss of α-helix structures and unfolding of the MPs appear to be the main reasons for MP solubilization. Additionally, according to the zeta-potential, confocal laser scanning microscopy, and atomic force microscopy observation results, glycation can provide electrostatic repulsion or steric hindrance to disintegrate existing filamentous myosin aggregates and inhibit further self-assembly behavior.

Surface characteristics and emulsifying properties of whey protein/nanoliposome complexes

The surface characteristics and emulsifying properties of whey proteins (WP) after complexation with nanoliposomes (NL) were investigated. WP surface hydrophobicity enhanced after complexation with NL, and it indicated the exposure increase of WP hydrophobic groups. WPNL interfacial tension significantly decreased compared with that of WP. The interfacial protein content of WPNL-stabilized emulsions was slightly different from that of WP-stabilized emulsions. WP emulsifying properties were significantly improved after complexation with NL. The mean sizes and polydispersity indexes of WPNL-stabilized emulsion droplets were smaller than those of WP-stabilized emulsion droplets. The absolute zeta-potential values of WPNL-stabilized emulsions were greater than those of WP-stabilized emulsions. Electrostatic repulsion played a vital role in WPNL-stabilized emulsion stability. Moreover, surface and emulsifying properties of WPNL were changed by exterior factor-induced alteration of protein advanced structures. The emulsifying properties of WP after complexation with NL were improved due to the modification of WP surface characteristics.

High-intensity ultrasound improves the physical stability of myofibrillar protein emulsion at low ionic strength by destroying and suppressing myosin molecular assembly

The specific molecular behavior of myofibrillar proteins (MPs) in low-salt media limits the development of muscle protein-based emulsions. This study aimed to evaluate the potential of high-intensity ultrasound (HIU; 150, 300, 450, and 600 W) to improve the physical stability of MP emulsion at low ionic strength and decipher the underlying mechanism. According to the physical stability analysis, HIU pretreatment, especially at 450 W power, significantly improved the physical stability of MP emulsions, as evidenced by the reduced particle size, enhanced inter-droplet interactions, and increased uniformity of the droplet size distribution (p < 0.05). The results of interfacial protein composition, Fourier transform infrared spectroscopy analysis, and microscopic morphology observation of the aqueous MP suspension suggested that HIU induced the depolymerization of filamentous myosin polymers and inhibited the subsequent self-assembly behavior. These effects may facilitate protein adsorption and molecular rearrangement at the oil-water interface, forming a complete interfacial layer and, thus, droplet stabilization. Confocal laser scanning microscopy observations further confirmed these results. In conclusion, these findings provide direct evidence for the role of HIU in improving the physical stability of MP emulsions at low ionic strength.

DMPC Phospholipid Bilayer as a Potential Interface for Human Cystatin C Oligomerization: Analysis of Protein-Liposome Interactions Using NMR Spectroscopy

Studies revolving around mechanisms responsible for the development of amyloid-based diseases lay the foundations for the recognition of molecular targets of future to-be-developed treatments. However, the vast number of peptides and proteins known to be responsible for fibril formation, combined with their complexity and complexity of their interactions with various cellular components, renders this task extremely difficult and time-consuming. One of these proteins, human cystatin C (hCC), is a well-known and studied cysteine-protease inhibitor. While being a monomer in physiological conditions, under the necessary stimulus—usually a mutation, it tends to form fibrils, which later participate in the disease development. This process can potentially be regulated (in several ways) by many cellular components and it is being hypothesized that the cell membrane might play a key role in the oligomerization pathway. Studies involving cell membranes pose several difficulties; therefore, an alternative in the form of membrane mimetics is a very attractive solution. Here, we would like to present the first study on hCC oligomerization under the influence of phospholipid liposomes, acting as a membrane mimetic. The protein–mimetic interactions are studied utilizing circular dichroism, nuclear magnetic resonance, and size exclusion chromatography.