In Vitro Pepsin Digestion Characteristics of Silver Carp (Hypophthalmichthys molitrix) Surimi Gels with Different Degrees of Cross-Linking Induced by Setting Time and Microbial Transglutaminase

Postmortem Muscle Proteome Characteristics of Silver Carp (Hypophthalmichthys molitrix): Insights from Full-Length Transcriptome and Deep 4D Label-Free Proteomic

The coverage of the protein database directly determines the results of shotgun proteomics. In this study, PacBio single-molecule real-time sequencing technology was performed on postmortem silver carp muscle transcripts. A total of 42.43 Gb clean data, 35,834 nonredundant transcripts, and 15,413 unigenes were obtained. In total, 99.32% of the unigenes were successfully annotated and assigned specific functions. PacBio long-read isoform sequencing (Iso-Seq) analysis can provide more accurate protein information with a higher proportion of complete coding sequences and longer lengths. Subsequently, 2671 proteins were identified in deep 4D proteomics informed by a full-length transcriptomics technique, which has been shown to improve the identification of low-abundance muscle proteins and potential protein isoforms. The feature of the sarcomeric protein profile and information on more than 30 major proteins in the white dorsal muscle of silver carp were reported here for the first time. Overall, this study provides valuable transcriptome data resources and the comprehensive muscle protein information detected to date for further study into the processing characteristic of early postmortem fish muscle, as well as a spectral library for data-independent acquisition and data processing. This batch of muscle-specific dependent acquisition data is available via PRIDE with identifier PXD043702.

Insight into Ionic Strength-Induced Solubilization of Myofibrillar Proteins from Silver Carp (Hypophthalmichthys molitrix): Structural Changes and 4D Label-Free Proteomics Analysis

In this study, changes in the physical, structural, and assembly characteristics of silver carp myofibrillar proteins (MPs) at different ionic strength (I) values were investigated. Moreover, the differential proteomic profile of soluble MPs was analyzed using 4D proteomics based on timsTOF Pro mass spectrometry. Solubility of MPs significantly increased at high I (>0.3), and the increase in I enhanced the apparent viscosity, fluorescence intensity, surface hydrophobicity, and α-helix content of MPs solution. Particle size and sodium dodecyl sulfate-polyacrylamide gel electrophoresis patterns also supported the solubility profiles. Transmission electron microscopy and atomic force microscopy observations revealed the morphological assembly and disassembly of MPs under different I conditions. Finally, proteomic analysis revealed the evolution law of salt-induced solubilization of MPs and the critical molecular characteristics in different I environments. The number of differentially abundant proteins (DAPs) decreased with the increase of I, and most DAPs related to the muscle filament sliding, contraction and assembly, actinin binding, and actin filament binding. The soluble abundance of myosin and some structural proteins was dependent on I, and structural proteins in the Z-disk and M-band might contribute to the solubilization of myosin. Our findings provide insightful information about the impact of common I on the solubility pattern of MPs from freshwater fish.

Chickpea protein hydrolysate as a novel plant-based cryoprotectant in frozen surimi: Insights into protein structure integrity and gelling behaviors

Chickpea protein (CP) and its enzymatic hydrolysates are one of the most widely consumed pulse ingredients manifesting versatile applications in food industry, such as binders, emulsifiers, and meat protein substitutes. Other than those well-known functionalities, however, the use of CP as a cryoprotectant remained unexplored. In this study, we prepared the chickpea protein hydrolysate (CPH) and investigated its cryoprotective effects to frozen surimi in terms of the protein structure integrity and gelling behaviors. Results indicated that CPH could inhibit myofibrillar protein (MP) denaturation and oxidation during the freeze-thaw cycling, as evidenced by their increased solubility, Ca²⁺-ATPase activity, sulfhydryl concentration, and declined content of disulfide bonds, carbonyl concentration and surface hydrophobicity. Freezing-induced changes on MP secondary structures were also retarded. Moreover, gels prepared from CPH-protected frozen surimi demonstrated more stabilized microstructure, uniform water distribution, enhanced elasticity, gel strength and water holding capacity. The CPH alone, at a reducing addition content of 4% (w/w), exhibited comparable cryoprotective performance to that of the commercial formulation (4% sucrose and 4% sorbitol). Therefore, this study provides scientific insights for development of pulse proteins as novel and high-performance food cryoprotectants.

Unrinsed Nemipterus virgatus surimi provides more nutrients than rinsed surimi and helps recover immunosuppressed mice treated with cyclophosphamide

BACKGROUND

The rinsing process in the production of surimi can cause the loss of some important nutrients. To investigate the differences in nutritional properties between rinsed surimi (RS) and unrinsed surimi (US), this study compared the elemental composition, amino acid composition, fatty acid composition, proteomics, and an immunosuppression mouse model of surimi before and after rinsing, and analyzed the nutritional and immunological properties of RS and US.

RESULTS

The results showed that the protein, fat, and ash contents of RS were decreased compared with those of US; specifically, the contents of essential amino acids, semi-essential amino acids, non-essential amino acids, saturated fatty acids, monounsaturated fatty acids, and polyunsaturated fatty acids were decreased. In the non-labeled quantitative proteomics analysis, three high-abundance quantifiable protein contents and 68 low-abundance quantifiable protein contents were found in RS (P-values < 0.05, ratio > 2). Immune function experiments in mice revealed that both RS and US contributed to the recovery of immunity in immunocompromised mice. The effect of US was better than that of RS.

CONCLUSION

The rinsing process in surimi processing leads to the loss of nutrients in surimi. US promotes the recovery of immunity in immunocompromised mice more effectively than RS. © 2023 Society of Chemical Industry.

Changes in Myosin from Silver Carp (Hypophthalmichthys molitrix) under Microwave-Assisted Water Bath Heating on a Multiscale

To further prove the advantages of microwave-assisted water bath heating (MWH) in low-value fish processing, the effects of different heating methods (two heating stage method, high temperature section respectively using MWH1, MWH2, MWH3, WH—water heating, MH—microwave heating) on secondary and tertiary myosin structures, SDS-PAGE, surface morphology, scanning electron microscopy (SEM), and particle size distribution were compared and analyzed. The findings revealed that MH and MWH aided in the production of gel formations by promoting myosin aggregation. Myosin from silver carps demonstrated enhanced sulfhydryl group and surface hydrophobicity after MWH treatment, as well as a dense network structure. The distribution of micropores becomes more uniform when the microwave time is increased. Actually, the total effect of microwave time on myosin is not substantially different. The correlation between particle size distribution and protein aggregation was also studied, in terms of time savings, the MWH of short microwave action is preferable since it not only promotes myosin aggregation but also avoids the drawbacks of a rapid warming rate. These discoveries give a theoretical foundation for understanding silver carp myosin under microwave modification, which is critical in the food industry.

Identification and release kinetics of peptides from tilapia skin collagen during alcalase hydrolysis

Collagen from tilapia skin was extracted and confirmed as type I collagen. Collagen was then hydrolyzed with alcalase for 4 h and the released peptides were identified. The structure-activity relationship of collagen-released peptides showed that proline at position C3 played a key role in improving ACE inhibitory activity, while proline at position C2 had a negative effect. Collagen peptide release kinetics showed that with the extension of time, the number of peptides increased dramatically at first, decreased, and then tended to be stable. This indicated that collagen peptides mainly originated from primary enzymolysis at the first stage and began to undergo secondary hydrolysis in the second stage. Afterwards, secondary enzymolysis was dominant at the third stage and finally remained stable at final two stages. Understanding the pattern of collagen peptide release kinetics might offer a powerful approach in the collagen-peptide food processing industry to better control food safety and quality.

Peptidomic analysis of digested products of surimi gels with different degrees of cross-linking: In vitro gastrointestinal digestion and absorption

To investigate the cross-linking degree on the in vitro gastrointestinal digestion and absorption properties of surimi gel, three types of surimi gels with low, moderate, and high cross-linking degrees were prepared, and then in vitro digestion models (static and dynamic) and a Caco-2 cell monolayer model combined with LC-MS/MS were used to do peptidomic analysis of digestive and absorbed juices. The results showed that an increase in cross-linking degree promoted the release of peptides after gastrointestinal digestion. These peptides originated from the myosin head and rod, the rod was the main digestion region. More potential bioactive peptides from intestinal digestive juice could be transported through the intestinal epithelium. Compared with static digestion, dynamic digestion digested surimi gels more thoroughly, especially during gastric digestion. This study provides a theoretical basis and guidance for the production of surimi products with higher nutritional value and the in vitro digestion methods of gelatinous foods.

Protein-polyphenol conjugates: Preparation, functional properties, bioactivities and applications in foods and nutraceuticals

Protein is a crucial nutritional ingredient in the daily human diet. Polyphenols (PPNs) are the abundant phytochemicals in plants, which are associated with health promotion as well as affect functionality in food systems. Both ingredients possess different types of functionalities (crosslinking, gelling, emulsifying, film-forming, etc.) and bioactivities (antioxidant, antimicrobial, anti-inflammatory, etc.). In the past decade, various methods have been implemented to enhance the functionalities and bioactivities of foods. Conjugation or grafting methods has been introduced widely. Conjugations of PPNs with proteins through various methods have been performed for the synthesis of the protein-polyphenol conjugate. Those potential grafting methods are alkaline associated, free-radical mediated, enzyme catalyzed, and chemical coupling methods. Several factors such as reaction conditions, type of proteins, and PPNs also influenced the conjugation efficiency. Various technologies, e.g., mass spectroscopy, fluorescence spectroscopy, UV spectroscopy, Fourier transform infrared spectroscopy, circular dichroism, and sodium dodecyl sulfate polyacrylamide gel electrophoresis have been used to elucidate conjugation and structural alternation of proteins and some properties of resulting conjugates. The prepared protein-PPN conjugates have been documented to enhance the bioactivities and functional properties of an initial protein. Moreover, conjugates have been employed in emulsions or as nanoparticles for nutraceutical delivery. Edible-films for food packaging and hydrogels for controlled drug release have been developed using protein-PPN conjugates. This chapter focuses on the methodologies and characteristics of protein-PPN conjugates and their applications in various food systems and nutraceutical field.

In vitro trypsin digestion and identification of possible cross-linking sites induced by transglutaminase (TGase) of silver carp (Hypophthalmichthys molitrix) surimi gels with different degrees of cross-linking

Surimi gels with different cross-linking degrees (18.52%, 34.67%, 62.87% and 79.11%) were prepared to identify the numbers and locations of lysine residues involved in TGase-induced cross-linking, and to reveal the quantity and location relationships among cross-linking degrees, cross-linking sites and digestion sites by using trypsin digestion, SDS-PAGE and LC-MS/MS methods. The results showed that with the increase in cross-linking degree from 18.52% to 79.11%, 1) the quantity of cross-linking sites gradually increased from 25 sites to 47 sites, 2) the main possible cross-linking domain moved from myosin head to rod, 3) the numbers of digestion sites first decreased from 1262 sites to 1194 sites, and then increased to 1302 sites, 4) the changes in the values of digestion sites were mainly concentrated in myosin rod and it was also the main region of digestion. This study can help exploring the relationship between enzymatic cross-linking and nutritional properties of food.

Proteomic profiling and oxidation site analysis of gaseous ozone oxidized myosin from silver carp (Hypophthalmichthys molitrix) with different oxidation degrees

Ozone is used to in surimi production and affects the conformation of myosin and gelling properties. Amino acid analysis, SDS-PAGE, in-gel trypsin hydrolysis and LC-MS/MS were used to investigate the effect of the ozone treatment time on the oxidation principle of amino acids to identify the oxidation site and oxidation mechanism of myosin with different oxidation degrees. The results showed that the order of ozonation of amino acids from easy to difficult was tyrosine > cysteine > histidine > proline. The protein structure near the SH1-SH2 region initially changed when the ozone treatment time was 50 s. Prolonging the oxidation to 80 s leads to an irregular distribution of oxidation sites. Ten min of ozone treatment resulted in the aggregation from the SH1 helical region and myosin rod. This study helped to clarify the mechanism of ozone oxidation, thus providing a theoretical basis for producing surimi products of improved quality.

Effect of Psyllium (Plantago ovata Forks) Husk on Characteristics, Rheological and Textural Properties of Threadfin Bream Surimi Gel

Effects of psyllium (Plantago ovata) husk powder (PHP) at various concentrations (0, 1, 2, 3 and 4%, w/w) on gelling properties of surimi from threadfin bream (Nemipterus sp.) were investigated. The addition of 1% PHP resulted in the highest increase (50%) in the breaking force (BF) of surimi gel (S), compared to that of the control gel (CON; without PHP). Lower BF was obtained for gel incorporated with PHP at the higher levels (2–4%) (p < 0.05). On the other hand, deformation (DF) was decreased with the addition of PHP at all levels compared to the CON gel. The whiteness and expressible moisture content of gels were decreased with augmenting levels of PHP (p < 0.05). Protein patterns revealed that PHP at all concentrations did not affect the polymerization of the myosin heavy chain. A loss in the elasticity of the gel was attained with the addition of PHP as indicated by decreased storage modulus (G’). A finer and more compact network was detected in gels containing 1 and 2% PHP than that found in the CON. FTIR spectra suggested that the addition of PHP influenced the secondary structure as well as functional groups of myofibrillar proteins. Based on the sensory evaluation, the surimi containing PHP at 1–3% showed a similar overall likeness score to the CON. Therefore, PHP at the optimum level could improve the gelling properties of the threadfin bream surimi with high acceptability.

Temperature-dependent in vitro digestion properties of isoelectric solubilization/precipitation (ISP)-isolated PSE-like chicken protein

The effects of various heating strategies (72 °C-20 min, 100 °C-60 min) on the digestibility of isoelectric solubilization/precipitation (ISP)-isolated pale, soft, exudative (PSE)-like chicken protein in an in vitro simulated gastrointestinal model were studied. Untreated PSE-like meat protein was used as the control. The hydrophobic groups were much more exposed in ISP-isolated protein than in the control protein, and the difference diminished after heating. The results of SDS-PAGE analyses and digestion kinetic parameters show the ISP isolates had higher digestibility than the control group when heated at 72 °C for 20 min (P < 0.05), but there was no significant difference between the 100 °C heated groups (P > 0.05). Additionally, all ISP-isolated groups showed higher peptide abundance than the control groups. In summary, heating at 72 °C for 20 min is beneficial to increase the digestion properties of ISP-isolated PSE-like chicken protein, but its gel properties are weaker than those of protein heated at 100 °C for 60 min.