A comprehensive review of the mechanisms on fish stress affecting muscle qualities: Nutrition, physical properties, and flavor.

Fish inevitably face numerous stressors in growth, processing, and circulation. In recent years, stress-related change in fish muscle quality has gradually become a research hotspot. Thus, the understanding of the mechanism regarding the change is constantly deepening. This review introduces the physiological regulation of fish under stress, with particular attention devoted to signal transduction, gene expression, and metabolism, and changes in the physiological characteristics of muscular cells. Then, the influences of various stressors on the nutrition, physical properties, and flavor of the fish muscle are sequentially described. This review emphasizes recent advances in the mechanisms underlying changes in muscle quality, which are believed to be involved mainly in physiological regulation under stress. In addition, studies are also introduced on improving muscle quality by mitigating fish stress.

Comparative analysis of soluble and insoluble dietary fiber on improving the gelation performance and fishy odors of silver carp surimi.

This work investigated the effects and mechanisms of soluble and insoluble dietary fiber (SDF and IDF) on the gelation performance and fishy odors of silver carp surimi. The results showed that the gel properties of surimi increased and then decreased with increasing SDF content, and the best gel properties were achieved at 1 wt% SDF. The gel strength, elasticity and deformation resistance of surimi increased in a dose-dependent manner as affected by IDF, but its effect on viscosity and recovery ratio was similar to SDF. Moreover, 2 wt% SDF and 1 wt% IDF reduced the content and odor activity value (OAV) of most fishy compounds in surimi, and the latter was superior to the former. The rheological characteristics indicated that SDF affected the thermal gelation properties of surimi mainly through filling, concentration and volume exclusion, and IDF mainly through filling, concentration and intermolecular interactions between IDF and myofibrillar protein. Additionally, SDF and IDF inhibited the release of fishy odors by improving the gel network structure and their adsorption, but more SDF (2 wt%) promoted the formation of escape channels for odors release. In summary, 1 wt% IDF could simultaneously improve the gelation performance and fishy odors of silver carp surimi.

Insights into the potential mechanism of liquid nitrogen spray freezing's influence on volatile compounds in surimi gels with different cross-linking degrees: Focus on oxidation, protein structure, intermolecular force and free amino acid alterations.

This study revealed the variations in odor characteristics and underlying mechanisms of different cross-linked surimi gels under liquid nitrogen (LN) spray freezing. The results demonstrated that LN spray freezing had an essential effect on the gels' odor. The odor changes in the -80 °C LN spray freezing group were closer to the control group, while -35 °C LN spray freezing treatment had the greatest impact on the aroma quality of gels. Freezing reduced gels' texture properties, intensified lipid and protein oxidation, altered protein conformation, increased surface hydrophobicity and hydrophobic interactions. These changes affected the gels' odor characteristics, leading to a reduction in fish aroma and an increase in fishy and oil odors after freezing. These tendencies were more pronounced at -35 °C LN spray freezing with lower cross-linking degrees, and reducing the freezing temperature to -80 °C and increasing the cross-linking degree to 62.99% mitigated the extent of deterioration in gel flavor quality.

Covalent and non-covalent interaction of myofibrillar protein and cyanidin-3-O-glucoside: focus on structure, binding sites and in vitro digestion properties.

BACKGROUND: The aim of this study was to investigate the effects of covalent and non-covalent interactions between myofibrillar protein (MP) and cyanidin-3-O-glucoside (C3G) on protein structure, binding sites, and digestion properties. Four methods of inducing covalent cross-linking were used in the preparation of MP-C3G conjugates, including tyrosinase-catalyzed oxidation, alkaline pH shift treatment, free radical grafting, and ultrasonic treatment. A comparison was made between MP-C3G conjugates and complexes, and the analysis included sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), C3G binding ratio, liquid chromatography-tandem mass spectrometry (LC-MS/MS), protein side-chain amino acids, circular dichroism spectroscopy, three-dimensional fluorescence, particle size, and in vitro simulated digestion. RESULTS: Covalent bonding between C3G and amino acid side chains in MP was confirmed by LC-MS/MS. In covalent bonding, tryptophan residues, free amino groups and sulfhydryl groups were all implicated. Among the 22 peptides covalently modified by C3G, 30 modification sites were identified, located in lysine, histidine, tryptophan, arginine and cysteine. In vitro simulated digestion experiments showed that the addition of C3G significantly reduced the digestibility of MP, with the covalent conjugate showing lower digestibility than the non-covalent conjugate. Moreover, the digestibility of protein decreased more during intestinal digestion, possibly because covalent cross-linking of C3G and MP further inhibited trypsin targeting sites (lysine and arginine). CONCLUSION: Covalent cross-linking of C3G with myofibrillar proteins significantly affected protein structure and reduced protein digestibility by occupying more trypsin binding sites. © 2023 Society of Chemical Industry.

Flavor and sensory profile of Chinese traditional fish noodles produced by different silver carp (hypophthalmichthys molitrix) mince ingredients.

This study employs sensory evaluation, headspace gas chromatography-ion mobility spectrometry (HS-GC-IMS), and headspace solid-phase microextraction gas chromatography-mass spectrometry (HS-SPME-GC-MS) techniques to investigate the effect of different pretreatment of fresh silver carp mince (running water rinsing 0, 1, or 2 times) and commercially frozen surimi on the odor characteristics of fish noodles. The free choice profiling (FCP) and check all that apply (CATA) sensory analysis methods were utilized to identify 10 characteristic descriptors, which include "grass, fish fragrance, unpleasant fishy, fatty, roast, ammonia, caramel, warmed-over, earthy, and mushroomy". HS-GC-IMS and HS-SPME-GC-MS detected 80 and 37 volatile compounds (VCs) in fish noodles. The 1-Penten-3-ol, (E)-2-pentenal-D, hexanal-D, pentanal-D, (E,E)-2, 4-heptadienal-D contents were significantly correlated with "fish fragrance" and "unpleasant fishy", and octanal, nonanal, heptanal, 2-methylpyrazine contents were significantly correlated with "warmed-over" flavor. The results of this study can be helpful for fish noodle quality improvement and industrial production.

Effect of raw material frozen storage on physicochemical properties and flavor compounds of fermented mandarin fish (Siniperca chuatsi).

Frozen mandarin fish (MF) is utilized for preparation fermented MF. However, how raw material (RM) affects the quality and flavor of fermented MF is unclear. This study investigated the impact and mechanism of RM frozen storage on the microstructure, texture, water distribution, and flavor of fermented MF by light microscopy, texture profile analysis, low-field nuclear magnetic resonance, gas chromatography-ion mobility spectrometry, and multivariate analysis. With increasing RM frozen storage time, both frozen MF and frozen-based fermented MF decreased in muscle fiber density while increased in muscle fiber diameter. Additionally, RM frozen storage exhibited a significant impact on the water distribution of frozen MF, while no obvious effect on that of frozen-based fermented MF. Seven odorant (2-methyl-1-propanol, 3-hydroxy-2-butanone, 2,3-butanedione, hexanal-D, ethyl acetate-D, 3-pentanone, and acetone) were shown as potential markers to distinguish fermented MF. This study could provide a theoretical basis for the production of high-quality frozen-based fermented MF.

Effects of Phenolics on the Physicochemical and Structural Properties of Collagen Hydrogel.

In the current era, the treatment of collagen hydrogels with natural phenolics for the improvement in physicochemical properties has been the subject of considerable attention. The present research aimed to fabricate collagen hydrogels cross-linked with gallic acid (GA) and ellagic acid (EA) at different concentrations depending on the collagen dry weight. The structural, enzymatic, thermal, morphological, and physical properties of the native collagen hydrogels were compared with those of the GA/EA cross-linked hydrogels. XRD and FTIR spectroscopic analyses confirmed the structural stability and reliability of the collagen after treatment with either GA or EA. The cross-linking also significantly contributed to the improvement in the storage modulus, of 435 Pa for 100% GA cross-linked hydrogels. The thermal stability was improved, as the highest residual weight of 43.8% was obtained for the hydrogels cross-linked with 50% GA in comparison with all the other hydrogels. The hydrogels immersed in 30%, 50%, and 100% concentrations of GA also showed improved swelling behavior and porosity, and the highest resistance to type 1 collagenase (76.56%), was obtained for 50% GA cross-linked collagen hydrogels. Moreover, GA 100% and EA 100% obtained the highest denaturation temperatures (Td) of 74.96 °C and 75.78 °C, respectively. In addition, SEM analysis was also carried out to check the surface morphology of the pristine collagen hydrogels and the cross-linked collagen hydrogels. The result showed that the hydrogels cross-linked with GA/EA were denser and more compact. However, the improved physicochemical properties were probably due to the formation of hydrogen bonds between the phenolic hydroxyl groups of GA and EA and the nitrogen atoms of the collagen backbone. The presence of inter- and intramolecular cross-links between collagen and GA or EA components and an increased density of intermolecular bonds suggest potential hydrogen bonding or hydrophobic interactions. Overall, the present study paves the way for further investigations in the field by providing valuable insights into the GA/EA interaction with collagen molecules.

Development and Identification of Novel α-Glucosidase Inhibitory Peptides from Mulberry Leaves.

The mulberry leaf is a botanical resource that possesses a substantial quantity of protein. In this study, alcalase hydrolysis conditions of mulberry leaf protein were optimized using the response surface method. The results showed that the optimum conditions were as follows: substrate protein concentration was 0.5% (w/v), enzymatic hydrolysis temperature was 53.0 °C, enzymatic hydrolysis time was 4.7 h, enzyme amount was 17,800 U/g, and pH was 10.5. Then mulberry leaf peptides were separated by ultrafiltration according to molecular weight. Peptides (<3 kDa) were screened and subsequently identified using LC-MS/MS after the evaluation of α-glucosidase inhibition across various fractions. Three novel potential bioactive peptides RWPFFAFM (1101.32 Da), AAGRLPGY (803.91 Da), and VVRDFHNA (957.04 Da) with the lowest average docking energy were screened for molecular dynamics simulation to examine their binding stability with enzymes in a 37 °C simulated human environment. Finally, they were prepared by solid phase synthesis for in vitro verification. The former two peptides exhibited better IC50 values (1.299 mM and 1.319 mM, respectively). These results suggest that the α-glucosidase inhibitory peptides from mulberry leaf protein are potential functional foods or drugs for diabetes treatment, but further in vivo studies are needed to identify the bioavailability and toxicity.

Effect of material temperatures on quality of fish vermicelli, a noodle-shaped surimi product.

The study investigated the effect of material temperatures (15°C, 20°C, 25°C, 30°C, 35°C, and 40°C) on the quality of fish vermicelli (FV) in terms of morphological, cooking, textural, microstructural, and water distribution properties. Results showed that as the material temperatures increased, the surface smoothness, cooking characteristics, and textural properties of FV significantly increased, followed by a decrease. Especially, when the material temperatures were 25°C and 30°C, the FV samples exhibited denser and more continuous gel networks with more embedded starch particles, resulting in decreased cooking loss and improved tensile strength. However, at material temperatures above 35°C, the continuity of the protein phase was disrupted by overswelling starch granules, leading to the worst cooking characteristics and textural properties. Especially at material temperatures of 40°C, the water holding capacity, hardness, and springiness of FV decreased by 25.59%, 73.48%, and 47.98%, respectively, compared to the samples at 25°C. Additionally, the cooking loss increased by 91.40%. In conclusion, the critical material temperature for the quality deterioration of FV was 35°C, and it was recommended to produce FV below this temperature.

Correction: Dietary L-tryptophan alleviated LPS-induced intestinal barrier injury by regulating tight junctions in a Caco-2 cell monolayer model.

Correction for 'Dietary L-tryptophan alleviated LPS-induced intestinal barrier injury by regulating tight junctions in a Caco-2 cell monolayer model' by Mengdie Chen et al., Food Funct., 2019, 10, 2390-2398, https://doi.org/10.1039/C9FO00123A.

Comparative Study on Hydrolysis, Physicochemical and Antioxidant Properties in Simulated Digestion System between Cooked Pork and Fish Meat.

Pork and grass carp are commonly consumed animal protein sources, classified as red meat and white meat, respectively. This study aimed to better understand the differences in digestive behavior, nutrition, and functionality during digestion between these two types of meat after fat removal. The results showed that grass carp was more easily digested than pork, with a higher degree of hydrolysis, a smaller protein particle size, and a greater release of oligopeptides and amino acids (p < 0.05). During gastric digestion, all α-helix structures were destroyed, and the effect of the whole digestion process on the secondary and tertiary structure of pork protein was greater than that of grass carp. The antioxidant properties of the digestive fluids from the two types of meat showed different strengths in various assays, but the correlation analysis revealed that TCA-soluble peptides, random coil content, and particle size significantly influenced both types of meat. These findings provide new insights into the structural state and antioxidant properties of protein in meat digestion, which contribute to our understanding of the nutritional value of pork and grass carp.

Investigation of the effect of chemical composition of surimi and gelling temperature on the odor characteristics of surimi products based on gas chromatography-mass spectrometry/olfactometry.

This study investigated the effects of chemical composition of surimi (prepared by 0, 1, or 2 times of rinsing) and gelling temperature (90 °C and 100 °C) on the odor characteristics of surimi products and the relationship between the chemical composition of surimi and the aroma of surimi products. The once- and twice-rinsed surimi showed a decrease (p < 0.05) of 71.32%, 74.60%, 42.79% and 61.12% in the contents of total amino acids and total fatty acids, respectively. The surimi products prepared with un-rinsed surimi at 90 °C had the highest fish-fragrance score, while those prepared with once-rinsed surimi at 100 °C showed the strongest warmed-over flavor (WOF) and the lowest fish-fragrance score.Gly, Phe, and most of the saturated fatty acids were associated with WOF formation in surimi products, while Leu, Ile, Val, Asp, and unsaturated fatty acids were positively related to their fish-fragrance note.

Insight into the spatial distribution and interaction model of heat-induced micro- and nano-starch/myofibrillar protein blends.

This work investigated the gelatinizing and hydration properties of raw and milled tapioca starches at micron and nano scale as well as their effects on gelation of myofibrillar proteins (MP) from Ctenopharyngodon idellus by analyzing rheology, texture and microstructure of heat-induced MP/starch blends. Milling induced starch granules damage to micron and nano scale, causing a fall in starch swelling power and a jump in water solubility. Among raw and milled starches, nano-starch had the best reinforcement effect on MP gel, i.e., MP/nano-starch showed the lowest critical gel concentration, highest G', strongest resistance to deformation and highest texture performance. Correlation analysis revealed that starch water solubility was responsible for the reinforced MP gel rather than starch swelling power. A schematic model was proposed for illustrating the interaction of starches and MP. All the blends had the ordered filamentous network as the basic skeleton, with some starches (granules and their fragments) in the voids or on the edge or surface of MP filaments as inert fillers, and some (chain segments) embedded in the filaments as active fillers. Almost all nano-starch were actively filled into the MP filaments to enhance the strength of filaments, thus achieving the best reinforcement effect on MP gel.

Insight into the mechanism on texture change of Wuchang bream muscle during live transportation using a UPLC-QTOF-MS based metabolomics method.

Mechanism on texture change of Wuchang bream (Megalobrama amblycephala) muscle during live transportation was explored by UPLC-QTOF-MS. The shear force (hardness) of fish muscle decreased gradually as the transportation time was extended from 3 to 24 h, with a maximum decrease of 43.49 %. With the extension of the time, the cellular and ultrastructure of fish muscle fiber were gradually disrupted. There was a significant difference between metabolites of the samples after transporting for 6, 12, 24 h versus 3 h, with organic acids and their derivatives upregulated while nucleotide metabolites downregulated. The texture deterioration might be related to metabolism of amino acids, purine, histidine, and choline. The results showed that the deterioration of Wuchang bream texture during live transportation might be mainly related to the changes of the above metabolic pathways caused by oxidative stress, which resulting in the destruction of the muscle cells and fibers.

Myosin head as the main off-odors binding region: Key binding residues and conformational changes in the binding process.

This study aims to elucidate the dynamic binding characteristics between off-odors (hexanal, 1-octen-3-ol, nonanal) and myosin at cold storage (277 K) and oral temperatures (310 K) through spatial-temporal molecular dynamics (MD) simulation. Conformational analysis indicated that binding with off-odors could not significantly change the myosin secondary structure, and the myosin/(off-odors) structure became a stable and compact state in the later binding stages. Myosin head was the primary binding region with hydrophobic interactions as the dominant force rather than hydrogen bonds (average bond number 202.62 vs 55.20). Furthermore, the myosin/(off-odors) had larger binding energy at 310 than 277 K, and the myosin-nonanal showed the highest binding strength of 4050.93 kJ/mol at 310 K. The binding sites were observed to be concentrated in the 180-249, 350-410, 800-950 amino acid regions of myosin head, especially, Lys185, Tyr347, Leu901. These results provide accurate linkages between off-odors and myosin, laying a theoretical foundation for deodorization of fish products.

Gelation properties of tofu induced by different coagulants: Effects of molecular interactions between nano-sized okara dietary fiber and soybean proteins.

Gelation of soybean proteins with different coagulates as affected by okara nano-sized dietary fiber (NDF) were investigated. As compared with the MgCl2 tofu, the tofu induced by glocono-δ-lactone was softer with higher moisture and denser microstructure. As the volumetric ratio of NDF increased, pH, viscosity, particle size, and zeta potential of the NDF soymilk steadily increased. Regardless of coagulate type, tofu proteins' prevalence of α-helix + ß-turn increased with the NDF ratio up to 40 % while ß-sheet + random coil decreased. At the same time, intermolecular interactions (predominate hydrophobic interaction) significantly decreased, leading to form more porous structures in the two types of tofu. Accordingly, yield and moisture of tofu increased gradually with the NDF ratio, water holding capacity increased and then decreased, hardness decreased continuously. Results suggested that NDF affected the secondary structure and intermolecular interactions of soymilk proteins, which was independent of coagulate.

Evaluation of the Effect of Different Cooking Methods on the Heavy Metal Levels in Crayfish Muscle.

The current study investigated the effects of various cooking styles (boiling, frying, and steaming) and seasoning methods (home cooking and ready-to-eat commodity) on levels of nine heavy metals in the crayfish (Procambarus clarkii) muscle. The estimated daily intake (EDI), target hazard quotients (THQ), and target cancer risk (TCR) were used to assess the health risk in the crayfish muscle. The results showed that cooking processes significantly increased the concentration of Cu, which raises a potential risk for children (the THQ values > 1). The levels of toxic heavy metals in the ready-to-eat crayfish muscle were significantly higher than those in household cooking. Especially for As, the THQ values rose to 7.1 and 13.2 for adults and children respectively. Therefore, home cooking is safer than ready-to-eat crayfish, and children should consume crayfish within a limited range. The recommended consumption of the cooked abdominal muscle of crayfish should be 257 and 58 g/day, for children (16 kg) and adults (70 kg), respectively.

Simultaneous effect of high intensity ultrasound power, time, and salt contents on gelling properties of silver carp surimi.

Recently, the demand for salt-reduced products is rising. The objective of this study was to investigate the simultaneous effect of high intensity ultrasound (HIU) power (120-240 W), time (0-30 min), and salt (0-3.0 %) on the gelling properties of surimi gels through quadratic rotation orthogonal design. Results showed that the contribution to puncture properties was: salt > HIU time > HIU power. Moreover, low salt and HIU had a synergistic effect on the puncture properties of surimi gels by the formation of more non-disulfide covalent bonds. Furthermore, HIU induced formation of denser microstructures which decreased the mobility of free water of salt-reduced surimi gels. As a result, the water holding capacity significantly increased (P < 0.05). Likewise, the cooking loss of salt-reduced surimi gels (1 %) subjected to HIU decreased by 44.85 %, as compared to the control. In conclusion, HIU might be useful for the production of salt-reduced surimi gels.

The influence of pH and monovalent/divalent cations on the structural and physicochemical properties of myofibrillar protein from silver carp.

The present study aimed to investigate effects of pH and monovalent (Na+ and K+)/divalent (Ca2+ and Mg2+) cations on the structural and physicochemical properties of myofibrillar protein (MP) from silver carp. MP treated with divalent cation had lesser change for the structure than that treated with monovalent cation. Ca2+-ATPase activity of MP treated with monovalent cation was increased firstly and then decreased, while that treated with divalent cation was decreased with increasing ionic strength. Surface hydrophobicity and Z-average of MP treated with divalent cations was lower than that with monovalent cations, while they decreased and then increased with the pH shifting from 3.0 to 9.0. Zeta potential of MP was increased and then decreased with increasing the pH but decreased and then increased with increasing ionic strength. In general, the pH and monovalent/divalent cations could cause various hydrophobic and electrostatic interactions, resulting in changes of the physicochemical properties of MP.

Effect of Pretreatment Methods on the Formation of Advanced Glycation End Products in Fried Shrimp.

Fried shrimp are popular for their attractive organoleptic and nutritional qualities. However, consumers are more concerned about the safety of fried foods. To investigate the formation of advanced glycation end products (AGEs) in fried shrimp and provide pretreatment guidance for producing low-AGEs fried pacific white shrimp were treated with seven pretreatment methods before frying. The AGEs contents, physicochemical indicators, and their correlations in the fried shrimps' interior, surface, and batter layer were analyzed. Results indicated that pretreatment methods influenced both Maillard and oxidation reactions by altering the basic compositions, which controlled the formation of AGEs. The highest and lowest AGEs contents were obtained in shelled shrimp with exscinded back and whole shrimp, respectively. The batter-coated treatment reduced the AGEs contents in samples but increased the oil content. Correlation analysis showed that lipid oxidation was the decisive chemical reaction to the formation of AGEs by promoting the generation of dicarbonyl compounds and their combination with free amino acids. Conclusively, the whole shrimp was suitable for producing fried shrimp with low AGEs, oil content, and desirable color.