Thawed drip and its membrane-separated components: Role in retarding myofibrillar protein gel deterioration during freezing-thawing cycles.

Myofibrillar proteins are crucial for gel formation in processed meat products such as sausages and meat patties. Freeze-thaw cycles can alter protein properties, impacting gel stability and product quality. This study aims to investigate the potential of thawed drip and its membrane-separated components as potential antifreeze agents to retard denaturation, oxidation and gel deterioration of myofibrillar proteins during freezing-thawing cycles of pork patties. The thawed drip and its membrane-separated components of > 10 kDa and < 10 kDa, along with deionized water, were added to minced pork at 10 % mass fraction and subjected to increasing freeze-thaw cycles. Results showed that the addition of thawed drip and its membrane separation components inhibited denaturation and structural changes of myofibrillar proteins, evidenced by reduced surface hydrophobicity and carbonyl content, increased free sulfhydryl groups, protein solubility and α-helix, as compared to the deionized water group. Correspondingly, improved gel properties including water-holding capacity, textural parameters and denser network structure were observed with the addition of thawed drip and its membrane separation components. Denaturation and oxidation of myofibrillar proteins were positively correlated with gel deterioration during freezing-thawing cycles. We here propose a role of thawed drip and its membrane separation components as cryoprotectants against myofibrillar protein gel deterioration during freeze-thawing cycles.

Effects of multi-frequency ultrasound-assisted immersion freezing processing on myofibrillar protein structure and lipid oxidation of large yellow croaker (Larimichthys crocea) during long-time frozen storage.

In this study, large yellow croaker (Larimichthys crocea) was frozen using multi-frequency ultrasound-assisted freezing (MUIF) with different powers (160 W, 175 W, and 190 W, respectively) and stored at -18 °C for ten months. The effect of different ultrasound powers on the myofibrillar protein (MP) structures and lipid oxidation of large yellow croaker was investigated. The results showed that MUIF significantly slowed down the oxidation of MP by inhibiting carbonyl formation and maintaining high sulfhydryl contents. These treatments also held a high activity of Ca2+-ATPase in the MP. MUIF maintained a higher ratio of α-helix to ß-sheet during frozen storage, thereby protecting the secondary structure of the tissue and stabilizing the tertiary structure. In addition, MUIF inhibited the production of thiobarbituric acid reactive substances value and the loss of unsaturated fatty acid content, indicating that MUIF could better inhibit lipid oxidation of large yellow croaker during long-time frozen storage.

Potential mechanisms and effects of ultrasound treatment combined with pre- and post-addition of κ-carrageenan on the gelling properties and rheological behavior of myofibrillar proteins under low-salt condition.

This study investigated the effect of ultrasound (US) combined with pre- and post-addition of κ-carrageenan (KC) on the gelling properties, structural characteristics and rheological behavior of myofibrillar proteins (MP) under low-salt conditions. The results showed that US combined with either pre- or post-addition of KC rendered higher gel strength and water holding capacity (WHC) of MP gels than those treated with US alone and added with KC alone (P < 0.05). US combined with pre-addition of KC facilitated the binding between MP and KC, which enhanced the gel strength and WHC of the mixed MP gels and significantly improved the rheological behavior of MP. This was also confirmed by the highest surface hydrophobicity, disulfide bonds and ß-sheet content of the MP gels with US combined with pre-addition of KC. Moreover, microstructural results reflected a denser structure for the pre-addition of KC in combination with US. However, US combined with post-addition of KC resulted in limited MP unfolding and relatively weak hydrophobic interactions in the composite gels, which were less effective in improving the gel properties of the MP gels. This study provides potential strategies for enhancing the gelling properties of low-salt meat products via application of US and KC.

Effects of high-intensity ultrasound on physicochemical and gel properties of myofibrillar proteins from the bay scallop (Argopecten irradians).

Myofibrillar proteins (MPs) have a notable impact on the firmness and flexibility of gel-based products. Therefore, enhancing the gelation and emulsification properties of scallop MPs is of paramount significance for producing high-quality scallop surimi products. In this study, we investigated the effects of high-intensity ultrasound on the physicochemical and gelation properties of MPs from bay scallops (Argopecten irradians). The carbonyl content of MPs significantly increased with an increase in ultrasound power (150, 350, and 550 W), indicating ultrasound-induced MP oxidation. Meanwhile, high-intensity ultrasound treatment (550 W) enhanced the emulsifying capacity and the short-term stability of MPs (up to 72.05 m2/g and 153.05 min, respectively). As the ultrasound power increased, the disulfide bond content and surface hydrophobicity of MPs exhibited a notable increase, indicating conformational changes in MPs. Moreover, in the secondary structure of MPs, the α-helix content significantly decreased, whereas the ß-sheet content increased, thereby suggesting the ultrasound-induced stretching and flexibility of MP molecules. Sodium-dodecyl sulfate-polyacrylamide gel electrophoresis and scanning electron microscopy analysis further elucidated that high-intensity ultrasound induced MP oxidation, leading to modification of amino acid side chains, intra- and intermolecular cross-linking, and MP aggregation. Consequently, high-intensity ultrasound treatment was found to augment the viscoelasticity, gel strength, and water-holding capacity of MP gels, because ultrasound treatment facilitated the formation of a stable network structure in protein gels. Thus, this study offers theoretical insights into the functional modification of bay scallop MPs and the processing of its surimi products.

Thermal aggregation behavior of silver carp myofibrillar protein at low salt content: Effect of oat ß-glucan combined with ultrasound-assisted heating.

The effects of oat ß-glucan (OG) combined with ultrasound-assisted treatment on thermal aggregation behavior of silver carp myofibrillar protein (MP) under low salt concentration were investigated. The particle size and turbidity of MP were increased to higher levels by OG participation or ultrasound treatment during the two-stage heating. Both OG and ultrasonic treatment promoted the unfolding of MP structure, evidenced by the gradual decrease of α-helix content and fluorescence intensity, as well as the increase of ß-sheet content, surface hydrophobicity and sulfhydryl content. Compared to solely OG or ultrasonic treatment, the combination of OG and ultrasound further promoted the unfolding of MP and more sulfhydryl groups were exposed in the pre-heating stage, which was conducive to strengthen the chemical forces between MP molecules. Additionally, AFM analysis revealed that the apparent morphology of the OG combined with ultrasonic treated group exhibited a smoother surface and a more uniform distribution of aggregates.

The interplay of muscle and pea proteins in low-salt gels: An insight into in situ structure formation in hybrid meat alternatives.

The present study investigated thermal gelation of mixed sarcoplasmic (Sarc), myofibrillar (Myof), and pea proteins corresponding to partial meat replacements (0, 25, and 50%) by pea protein isolate (PPI) at reducing salt levels (0.6 â†’ 0.1 M NaCl) to understand in situ (simulated) structure-forming properties of hybrid meat analogues. The amount of soluble proteins in hybrids generally increased with salt concentrations and PPI substitution. While muscle proteins (mixed Sarc and Myof) had the strongest gelling capacity, hybrid proteins also exhibited moderate aggregation and gelling activity based on the sol→gel rheological transition and gel hardness testing. Sarc and pea 7S/11S globulins collectively compensated for the attenuated gelling capacity of mixed proteins due to diminishing Myof in the hybrids. Immobilized water within hybrid protein gels was tightly bonded (T2 from nuclear magnetic resonance), consistent with the dense and uniform microstructure observed. These findings offer a new knowledge base for developing reduced-salt hybrid meat analogues.

Molecular structural modification of myofibrillar protein from oyster (Crassostrea gigas) with oligosaccharides for improving its gel properties.

Glycation is a promising approach to enhance protein gel characteristics in the food industry. The impact of oyster myofibrillar protein (MP) being glycosylated with six oligosaccharides (dextran [Dex]-1 kDa, 5 kDa, 6 kDa, and 10 kDa, xylan [Xyla], and xyloglucan [Xyg]) on structural properties, aggregation behavior and gel properties was investigated in this study. The findings demonstrated that oligosaccharides significantly increased the glycation degree of MP by forming a stable tertiary conformation, increasing the contents of the disulfide bond and hydrogen bonds. Additionally, particle sizes decreased and solubility increased after glycation, improving the gel's strength, water-holding capacity, thermal stability, elastic modulus, and ordered network layout. It was determined that MP-Dex 5 had the best gel properties. The gel strength and water holding capacity of MP-Dex 5 increased by 70.59% and 32.27%, respectively. Molecular dynamics simulations results showed van der Waals energy and electrostatic interactions favor myosin binding to Dex or Xyla units. This study will provide insights into the relationship between molecular structure, aggregation behavior and gel property of oyster MP-oligosaccharide couples, and expand the application of oyster MP in food gels.

Structural determinants of ivabradine block of the open pore of HCN4.

HCN1-4 channels are the molecular determinants of the If/Ih current that crucially regulates cardiac and neuronal cell excitability. HCN dysfunctions lead to sinoatrial block (HCN4), epilepsy (HCN1), and chronic pain (HCN2), widespread medical conditions awaiting subtype-specific treatments. Here, we address the problem by solving the cryo-EM structure of HCN4 in complex with ivabradine, to date the only HCN-specific drug on the market. Our data show ivabradine bound inside the open pore at 3 Å resolution. The structure unambiguously proves that Y507 and I511 on S6 are the molecular determinants of ivabradine binding to the inner cavity, while F510, pointing outside the pore, indirectly contributes to the block by controlling Y507. Cysteine 479, unique to the HCN selectivity filter (SF), accelerates the kinetics of block. Molecular dynamics simulations further reveal that ivabradine blocks the permeating ion inside the SF by electrostatic repulsion, a mechanism previously proposed for quaternary ammonium ions.

Inhibitive effect of trehalose and sodium pyrophosphate on oxidation and structural changes of myofibrillar proteins in silver carp surimi during frozen storage.

This work investigated the cryoprotective effect of trehalose (TH) and sodium pyrophosphate (SPP) alone and in combination on myofibrillar protein (MP) oxidation and structural changes in silver carp surimi during 90 days of frozen storage (-20 °C). TH combined with SPP was significantly more effective than single TH or SPP in preventing MP oxidation (P < 0.05), showing a higher SH content (6.05 nmol/mg protein), and a lower carbonyl (4.24 nmol/mg protein) and dityrosine content (1280 A.U.). SDS-PAGE results indicated that TH combined with SPP did not differ significantly from TH and SPP in inhibiting protein degradation but was more effective in inhibiting protein crosslinking. Moreover, all cryoprotectants could stabilise the secondary and tertiary structures and inhibit unfolded and aggregation of MP, with the combination of TH and SPP being the best. It's worth noting that TH combined with SPP had a synergistic effect on inhibiting the decrease in α-helix content and gel-forming ability, and the increase in surface hydrophobicity. Overall, TH combined with SPP could significantly inhibited MP oxidation and structural changes in surimi during frozen storage and improve the gel-forming ability, which was significantly better than single TH or SPP.

Salt reduction in myofibrillar protein gel via inhomogeneous distribution of sodium-containing encapsulated fish oil coacervate: Mucopenetration ability of sodium carboxymethyl cellulose.

The potential application of fish oil microcapsules as salt reduction strategies in low-salt myofibrillar protein (MP) gel was investigated by employing soy protein isolates/carboxymethyl cellulose sodium (SPI-CMC) coacervates enriched with 25 mM sodium chloride and exploring their rheological characteristics, taste perception, and microstructure. The results revealed that the SPI-CMC coacervate phase exhibited the highest sodium content under 25 mM sodium level, albeit with uneven distribution. Notably, the hydrophilic and adhesive properties of CMC to sodium facilitated the in vitro release of sodium during oral digestion, as evidenced by the excellent wettability and mucopenetration ability of CMC. Remarkably, the fish oil microcapsules incorporating SPI-CMC as the wall material, prepared at pH 3.5 with a core-to-wall ratio of 1:1, demonstrated the highest encapsulation efficiency, which was supported by the strong hydrogen bonding. Interestingly, the presence of SPI-CMC coacervates and fish oil microcapsules enhanced the interaction between MPs and strengthened the low-salt MP gel network. Coupled with electronic tongue analysis, the incorporation of fish oil microcapsules slightly exacerbated the non-uniformity of sodium distribution. This ultimately contributed to an enhanced perception of saltiness, richness, and aftertaste in low-salt protein gels. Overall, the incorporation of fish oil microcapsules emerged as an effective salt reduction strategy in low-salt MP gel.

Correlation analysis of phosphorylation of myofibrillar protein and muscle quality of tilapia during storage in ice.

In this study, the correlation between protein phosphorylation and deterioration in the quality of tilapia during storage in ice was examined by assessing changes in texture, water-holding capacity (WHC), and biochemical characteristics of myofibrillar protein throughout 7 days of storage. The hardness significantly decreased from 471.50 to 252.17 g, whereas cooking and drip losses significantly increased from 26.5% to 32.6% and 2.9% to 9.1%, respectively (P < 0.05). Myofibril fragmentation increased, while myofibrillar protein sulfhydryl content and Ca2+-ATPase activity decreased from 119.33 to 89.29 µmol/g prot and 0.85 to 0.46 µmolPi/mg prot/h, respectively (P < 0.05). Correlation analysis revealed that the myofibrillar protein phosphorylation level was positively correlated with hardness and Ca2+-ATPase activity but negatively correlated with WHC. Myofibrillar protein phosphorylation affects muscle contraction by influencing the dissociation of actomyosin, thereby regulating hardness and WHC. This study provides novel insights for the establishment of quality control strategies for tilapia storage based on protein phosphorylation.

Structural domain in the Titin N2B-us region binds to FHL2 in a force-activation dependent manner.

Titin N2B unique sequence (N2B-us) is a 572 amino acid sequence that acts as an elastic spring to regulate muscle passive elasticity. It is thought to lack stable tertiary structures and is a force-bearing region that is regulated by mechanical stretching. In this study, the conformation of N2B-us and its interaction with four-and-a-half LIM domain protein 2 (FHL2) are investigated using AlphaFold2 predictions and single-molecule experimental validation. Surprisingly, a stable alpha/beta structural domain is predicted and confirmed in N2B-us that can be mechanically unfolded at forces of a few piconewtons. Additionally, more than twenty FHL2 LIM domain binding sites are predicted to spread throughout N2B-us. Single-molecule manipulation experiments reveals the force-dependent binding of FHL2 to the N2B-us structural domain. These findings provide insights into the mechano-sensing functions of N2B-us and its interactions with FHL2.

Modification of myofibrillar protein structural characteristics: Effect of ultrasound-assisted first-stage thermal treatment on unwashed Silver Carp surimi gel.

The hardness properties of unwashed surimi gel are considered as the qualities of gelation defect. This research investigated the effect of ultrasound-assisted first-stage thermal treatment (UATT) on the physicochemical properties of unwashed Silver Carp surimi gel, and the enhancement mechanism. UATT could reduce protein particle size, which significantly reduced from 142.22 µm to 106.70 µm after 30 min of UATT compared with the nature protein. This phenomenon can promote the protein crosslinking, resulting in the hardness of surimi gel increased by 15.08 %. Partially unfolded structure of myofibrillar protein and exposures of tryptophan to water, lead to the increase in the zeta potential absolute value, driven by UATT. The reduced SH group level and the conformational conversion of proteins from random coiling to α-helix and ß-sheet, which was in support of intermolecular interaction and gel network construction. The results are valuable for processing protein gels and other food products.

Myofibrillar protein hydrolysis under hydroxyl radical oxidative stress: Structural changes and their impacts on binding to selected aldehydes.

In this study, a hydroxyl radical oxidation system was established to simulate the oxidation process in fermented meat products. This system was employed to examine the structural changes in myofibrillar proteins (MPs) resulting from tryptic hydrolysis after a hydroxyl radical oxidative regime. The effect of these changes on the ability of MPs to bind selected aldehydes (3-methyl butanal, pentanal, hexanal, and heptanal) was also investigated. Moderate oxidation (H2O2 ≤ 1.0 mM) unfolded the structure of MPs, facilitating trypsin-mediated hydrolysis and increasing their binding capacity for the four selected aldehydes. However, excessive oxidation (H2O2 ≥ 2.5 mM) led to cross-linking and aggregation of MPs, inhibiting trypsin-mediated hydrolysis. The oxidised MPs had the best binding capacity for heptanal. The interaction of the oxidised trypsin-hydrolysed MPs with heptanal was driven by hydrophobic interactions. The binding of heptanal affected the structure of the oxidised trypsin-hydrolysed MPs and reduced their α-helix content.

Effect of constant-current pulsed electric field thawing on proteins and water-holding capacity of frozen porcine longissimus muscle.

This study explored the effect of constant-current pulsed electric field thawing (CC-T) on the proteins and water-holding capacity of pork. Fresh meat (FM), and frozen meat after constant-voltage thawing (CV-T), air thawing (AT) and water immersion thawing (WT) were considered as controls. The results indicated that CC-T had a higher thawing rate than conventional thawing during ice-crystal melting stage (-5 to -1 °C). It also showed a lower water migration and thawing loss, maintaining pH and shear force closer to FM. Meanwhile, CC-T decreased myoglobin oxidation, resulting in a favorable surface color. The results of protein solubility, differential scanning calorimetry, total sulfhydryl, carbonyl and surface hydrophobicity demonstrated that CC-T reduced myofibrillar protein oxidative denaturation by suppressing the formation of disulfide and carbonyl bonds, thus enhancing solubility and thermal stability. Additionally, microstructural observation found that CC-T maintained a relatively intact muscle fiber structure by reducing muscle damage and myosin filament denaturation.

Effects of Eleutherine bulbosa extract on the myofibrillar protein oxidation and moisture migration of yak meat under oxidation stress.

The influence of Eleutherine bulbosa (EB) extract at various levels (1, 4, 7, 10 or 13 g/kg) on the myofibrillar protein oxidation and moisture migration of yak meat in Fenton oxidation system was investigated. The results showed that inclusion of EB extract in yak meat efficiently inhibited carbonyl formation triggered by hydroxyl radicals. Supplementation of EB extract at 1-10 g/kg manifested more contents of the active sulfhydryl, ε-NH2 groups and α-helix structure, and higher solubility of myofibrillar proteins (MPs), but alleviated the turbidity of MPs. However, adding high level of EB extract (13 g/kg) induced the loss of free amine and α-helix content and resulted in more aggregation of MPs. The SDS-PAGE demonstrated that adding 1-7 g/kg EB extract had an obvious protective effect for myosin heavy chain and actin, whereas 10 or 13 g/kg EB extract led to weakened intensities of protein bands. DSC and LF-NMR analysis revealed that 7 g/kg EB extract had appreciable effects on thermal stabilities of MPs, and improved the hydration of yak meat induced by oxidation, while 13 g/kg EB extract accelerated MP structure destabilization and lowered water retention. Our results suggested that incorporation of low levels of EB extract (1-7 g/kg) effectively retarded the oxidative damage to MPs and EB extract could be a promising natural antioxidant in meat processing.

Effect of ultrasound-assisted L-lysine treatment on pork meat quality and myofibrillar protein properties during postmortem aging.

This paper aimed to investigate the effects of ultrasound-assisted L-lysine treatment on meat quality and myofibrillar proteins (MPs) properties of pork longissimus dorsi during postmortem aging. The results revealed that the L-lysine (Lys) and/or ultrasound treatment significantly increased (p < 0.05) the water-holding capacity and tenderness of the pork during postmortem aging, while the ultrasound-assisted Lys treatment had the lowest cooking loss, pressurization loss, Warner-Bratzler shear force, and hardness. In addition, L-lysine and/or ultrasound treatment increased (p < 0.05) pH value, T21, and myofibrillar fragmentation index, while the ultrasound-assisted Lys treatment had the highest value. Meanwhile, the protein solubility was increased with Lys and/or ultrasound treatment during postmortem aging, and ultrasound-assisted Lys treatment had the highest solubility, reaching 88.19%, 92.98%, and 91.73% at 0, 1, and 3 days, respectively. The result of protein conformational characteristics showed that Lys and/or ultrasound treatment caused the unfolding of the α-helix structure, resulting in the exposure of more hydrophobic amino acids and buried sulfhydryl groups, ultimately enhancing MPs solubility. In summary, ultrasound-assisted Lys treatment altered the structure of MPs, resulting in the enhancement of the water-holding capacity and tenderness of the pork. PRACTICAL APPLICATION: This study showed that ultrasound-assisted L-lysine (Lys) treatment could enhance the water-holding capacity and tenderness of pork during postmortem aging. The results might provide a reference for the application of ultrasound-assisted Lys treatment on the improvement of pork meat quality. To facilitate practical applications in production, the development of medium and large-sized ultrasound equipment for conducting small-scale and pilot experiments is crucial for future research.

Modulation of the conformation, water distribution, and rheological properties of low-salt porcine myofibrillar protein gel influenced by modified quinoa protein.

High-pressure homogenization modified quinoa protein (HQP) was added to porcine myofibrillar proteins (MP) to study its the influence on protein conformation, water distribution and dynamical rheological characteristics of low-salt porcine MP (0.3 M NaCl). Based on these results, the WHC, gel strength, and G' value of the low-salt MP gel were significantly improved with an increase in the added amount of HQP. A moderate amount of HQP (6%) increased the surface hydrophobicity and active sulfhydryl content of MP (P < 0.05). Moreover, the addition of HQP decreased particle size and endogenous fluorescence intensity. FT-IR results indicated that the conformation of α-helix gradually converted to ß-sheet by HQP addition. The incorporation of HQP also shortened the T2 relaxation time and enhanced the proportion of immobile water, contributing to the formation of a compact and homogeneous gel structure. In conclusion, the moderate addition of HQP can effectively enhance the structural stability and functionality of low-salt MP.

Effect of starch and peanut oil on physicochemical and gel properties of myofibrillar protein: Amylose content and addition form.

Starch and peanut oil (PO) were widely used to improve the gel properties of surimi, however, the impact mechanism of addition forms on the denaturation and aggregation behavior of myofibrillar protein (MP) is not clear. Therefore, the effect of starch, PO, starch/PO mixture, and starch-based emulsion on the physicochemical and gel properties of MP was investigated. The results showed that amylose could accelerate the aggregation of MP, while amylopectin was conducive to the improvement of gel properties. The addition of PO, starch/PO mixture, or starch-based emulsion increased the turbidity, solubility, sulfhydryl content of MP, and improved the gel strength, whiteness, and texture of MP gel. However, compared with starch/PO mixture group, the gel strength of MP with waxy, normal and high amylose corn starch-based emulsion increased by 22.68 %, 10.27 %, and 32.89 %, respectively. The MP containing emulsion had higher storage modulus than MP with starch/PO mixture under the same amylose content. CLSM results indicated that the oil droplets aggregated in PO or starch/PO mixture group, while emulsified oil droplets filled the protein gel network more homogeneously. Therefore, the addition of starch and PO in the form of emulsion could effectively play the filling role to improve the gel properties of MP.

Impact of Flammulina velutipes polysaccharide on properties and structural changes of pork myofibrillar protein during the gel process in the absence or presence of oxidation.

The present study aimed to investigate the impact of Flammulina velutipes polysaccharide (FVSP) on the rheological properties and structural alterations of myofibrillar protein (MP) and oxidized MP (OMP), utilizing techniques such as rhehometer, fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). In the unoxidized system, the addition of 5.00% FVSP significantly improved (p < 0.05) the storage and loss moduli of the composite gel and promoted the α-helix to ß-sheet transformation. These effects enhanced the protein's gel strength and water-holding capacity (WHC). In the oxidation system, 5.00% FVSP had significant effects (p < 0.05) on repair and improvement of the oxidized MP. These effects inhibited the cross-linking aggregation and degradation of the protein. In addition, the addition of FVSP significantly improved the gel properties of MPs after oxidation (p < 0.05), hindered fracture of the protein gel network structure. In summary, polysaccharides have a substantial effect on the functional characteristics of MP, and FVSP could potentially be applied in meat products.