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.

Modification of low-salt myofibrillar protein using combined ultrasound pre-treatment and konjac glucomannan for improving gelling properties: Intermolecular interaction and filling effect.

The quality deterioration of low-salt meat products has been gained ongoing focus of researchers. In this study, konjac glucomannan (KGM) was used to alleviate the finiteness of ultrasound treatment on the quality improvement of low-salt myofibrillar protein (MP), and the modification sequence was also investigated. The results revealed that the single and double sequential modification by utilizing KGM and ultrasound significantly influenced the gelation behavior of low-salt MPs. The uniform MP-KGM mixture formed by a single ultrasound treatment had limited protein unfolding, resulting in relatively weak intermolecular forces in the composite gel. Importantly, ultrasound pre-treatment combined with KGM modification promoted the unfolding and moderate thermal aggregation of proteins and remarkably improved the rheological behaviors and gel strength of the composite gel. This result could also be corroborated by the highest percentage of trans-gauche-trans conformation of SS bridges and maximum ß-sheet proportion. Furthermore, molecular dynamic simulation and molecular docking elucidated that the hydrogen bond length between protein and KGM was shortened after ultrasound pre-treatment, which was the molecular basis for the enhanced intermolecular interactions. Therefore, ultrasound pre-treatment combined with KGM can effectively improve the gelling properties of low-salt MPs, providing a practical method for the processing of low-salt meat products.

Regulation of yak longissimus lumborum energy metabolism and tenderness by the AMPK/SIRT1 signaling pathways during postmortem storage.

AMPK can activate nicotinamide phosphoribosyltransferase (NAMPT), increasing the ratio of oxidized nicotinamide adenine dinucleotide (NAD+)/reduced nicotinamide adenine dinucleotide (NADH) ratio, leading to the activation of the energy receptor SIRT1. This pathway is known as the AMPK/SIRT1 signaling pathway. SIRT1 deacetylates and activate LKB1, which is activated by phosphorylation of AMPK (Thr172) and inhibited by phosphorylase-mediated dephosphorylation of AMPK. At the same time, increased AMP/ATP and NAD+/NADH ratios lead to the activation of AMPK and SIRT1. SIRT1 and AMPK can activate each other forming a positive feedback loop, which can strengthen catabolism and weaken anabolism thus maintaining energy homeostasis of energy metabolism. At present, there has been no systematic study on AMPK-associated signaling cascades in stored yak meat and details of the AMPK/SIRT1 signaling under these conditions are not known. In this study, NAD+, NADH were added to yak longissimus thoracic muscles to study AMPK pathway regulation by AMPK/SIRT1 signaling. NAD+ significantly increased the activity of AMPK and glycolysis during postmortem maturation, increased the rate of energy metabolism, and increased the expression of AMPK protein, indicating that NAD+ increased energy metabolism in the stored muscle by promoting AMPK activity. NADH treatment inhibited both AMPK activation and glycolysis, together with increasing the pH in the muscle. The results showed that SIRT1 activation elevated the activity of AMPK, leading to its phosphorylation and the activation of glycolysis. Thus, AMPK activity was found to increase in yak meat as an adaptation to hypoxic conditions. This allows more effective regulation of energy production and improves the tenderness of the meat.

Konjac glucomannan improves the gel properties of low salt myofibrillar protein through modifying protein conformation.

Improving the characteristics of low salt proteins is the key to the gel properties of low-salt meat products which are demanded by people nowadays. The present study focused on the effects of KGM concentrations on the changes in structure and gelling properties of low-salt myofibrillar protein (MP). KGM addition (≤0.75 %) irrespective of salt concentration modified secondary and tertiary structures of MPs, enhanced the binding capacity of Troponin-T and Tropomyosin, augmented the gelling behavior of proteins, and remarkably improved the storage modulus (G') and gel strength of heat-induced MP gels. Interestingly, KGM addition in low salt condition showed the transformation of the all-gauche SS conformation into gauche-gauche-trans and trans-gauche-trans, and the partial transformation of α-helices into ß-sheets. overall, KGM modified the structure of low salt MPs and thus improved the gel properties of low salt MPs. Therefore, KGM is recommended for low-salt meat processing to enhance the MP gelling potential.

Ultrasonication promotes extraction of antioxidant peptides from oxhide gelatin by modifying collagen molecule structure.

This study primarily explored the internal mechanism underlying the ultrasonication-induced release of antioxidant peptides. An oxhide gelatin solution was treated ultrasonically (power = 200, 300, and 400 W), followed by enzymatic hydrolysis and structural and morphological analysis. The results showed that ultrasonication increased not only the degree of hydrolysis (DH) and protein recovery rate of the oxhide gelatin but also the ABTS radical scavenging, DPPH radical scavenging, ferrous chelating, and ferric reducing activities of its hydrolysate. The oxhide gelatin hydrolysate treated with 300-W ultrasonication had the maximum antioxidant activities. Ultrasonication inhibited hydrogen bond formation, reduced the crosslinking between collagen molecules, transformed part of the folded structure into a helical structure, and lowered the thermal stability of collagen molecules. The micromorphological analysis revealed that ultrasonication caused the gelatin surface to become loose and develop cracks, and as the power of the ultrasonication increased, the repetition interval distance (dÅ) also increased. Moreover, ultrasonication improved the solubilization, surface hydrophobicity, and interface characteristics and increased the content of basic and aromatic amino acids in the hydrolysate. In conclusion, ultrasonication modifies the protein structure, which increases the enzyme's accessibility to the peptide bonds and further enhances antioxidant peptide release. These findings provide new insights into the application of ultrasonication in the release of antioxidant peptides.

Enhanced gelling performance of oxhide gelatin prepared from cowhide scrap by high pressure-assisted extraction.

In this study, the feasibility of preparing oxhide gelatin from cowhide scrap by high pressure assisted-liquid extraction was verified. Different processing conditions, including high pressure time (15 to 25 min), pressure (250 to 350 MPa), and liquid-to-solid ratio (1:3 to 1:5), were optimized through response surface methodology. Under the optimum manufacturing conditions, when the high-pressure processing (HPP) time was 22 min, the pressure was 289 MPa, and the liquid-to-solid ratio was 1:4, the highest extraction yield (36%) and gel strength (224 g) were achieved. Based on DSC, XRD, FTIR, SEM, gelling and melting temperatures, HPP led to the structural modification of the gelatinized collagen, which enhanced the rearrangement of the gel structure during the gelation process and made it have better gelling properties. In addition, compared with the commercial sample, they do not differ significantly in the relaxation time and peak area of prepared oxhide gelatin. These findings provide new insights into the practicability of HPP during the preparation of oxhide gelatin, which can noticeably reduce the processing time and be applied to industrial production. PRACTICAL APPLICATION: Compared with traditional processing, a high pressure-assisted extraction process can noticeably reduce the processing time while producing cowhide gelation with similar physicochemical and functional properties. Meanwhile, high pressure processing (HPP) led to the structural destruction of the cowhide and gelatinized collagen, which enhanced the rearrangement of the gelatin structure during the gelation process and made it have better gelling properties. Importantly, high pressure-assisted extraction can facilitate the use of a low-cost raw material and improve the preparation efficiency of oxhide gelatin, which shows great potential in large-scale and efficient industrial production and the quality control of oxhide gelatin.

Effects of ultrasound and thermal treatment on the ultrastructure of collagen fibers from bovine tendon using atomic force microscopy.

As the most important tenderness related protein in mammal, there are few studies on how the nanoscale morphology of collagen I in tissues is related to traditional meat processing. The ultrastructure and mechanical characteristics of collagen fibers in tendon with different treatments have been explored in this study. Collagen fibers in homogenate group and acetic acid group were treated with ultrasound and thermal treatment. The nanoscale morphology of collagen fiber in homogenate group became granular at 60 °C and gelatin was formed at 70 °C. The collagen fibers extracted from acetic acid are unstable and easier to break under the same processing parameters, when compared with homogenated collagen fibers in both ultrasound and thermal treatment. The results suggested that acetic acid can disassemble the salt bond and Schiff-base in collagen, and the collagen fibers became loose but the triple helix structure remained integrity.

Study of the AMP-Activated Protein Kinase Role in Energy Metabolism Changes during the Postmortem Aging of Yak Longissimus dorsal.

To explore the postmortem physiological mechanism of muscle, activity of adenosine monophosphate activated protein kinase (AMPK) as well as its role in energy metabolism of postmortem yaks were studied. In this experiment, we injected 5-amino-1-beta-d-furanonyl imidazole-4-formamide (AICAR), a specific activator of AMPK, and STO-609 to observe the changes in glycolysis, energy metabolism, AMPK activity, and AMPK gene expression (PRKA1 and PRKA2) in postmortem yaks during maturation. The results showed that AICAR could increase the expression of the PRKKA1 and PRKAA2 genes, activate AMPK and increase its activity. The effects of AICAR include a lower concentration of ATP, an increase in AMP production, an acceleration of glycolysis, an increase in the lactic acid concentration, and a decrease in the pH value. In contrast, STO-609 had the opposite effect. Under hypoxic adaptation, the activity of the meat AMPK increased, which accelerated glycolysis and metabolism and more effectively regulated energy metabolism. Therefore, this study lays the foundation for establishing a theoretical system of energy metabolism in postmortem yak meat.

Phosphoproteomic analysis of longissimus lumborum of different altitude yaks.

Yaks in high altitude regions display good adaptability to hypoxic environment. However, the mechanism involved in regulating muscle protein expression in hypoxic environment is not completely clear yet. To explore the mechanisms modulating postmortem alterations, quantitative phosphoproteomic analysis was performed on muscles of yaks raised at two different altitudes. The results indicated that 475 differentially expressed proteins (DEPS) were identified in high-altitude yaks, among which, 439 DEPs were up-regulated and 36 DEPs were down-regulated. Of these, 26 phosphoproteins clustered into energy metabolism and hypoxic adaption were selected after bioinformatics analysis. In addition, some glycolytic enzymes were detected to be differentially phosphorylated. The difference in protein phosphorylation levels between the two groups may be the key factor involved in the regulation of muscle hypoxic adaption. The present results could provide proteomic insights into changes occurring in yak muscles at different altitudes and may be a valuable resource for future investigations.

Study on the effect of CaMKKß-mediated AMPK activation on the glycolysis and the quality of different altitude postmortem bovines longissimus muscle.

This study investigated the activity of adenosine monophosphate-activated protein kinase (AMPK), glycolysis, and meat quality index in three altitude bovines during postmortem aging process. Local cattle (altitude:1,500 m), Gannan yak (3,000 m), and Yushu yak (4,500 m) postmortem Longissimus Dorsi (LD) muscle were used. Results indicated that CaCl2 significantly increased the AMPK activity by increasing the calcium-regulated protein kinase kinase (CaMKKß) activity. Besides, AMPK activation enhanced the activity of lactate dehydrogenase (LDH) and Ca2+ -ATPase and accelerated the rate of muscle maturation during postmortem aging. Moreover, the expression of HIF-1, PRKAA2, and GLUT4 genes in high-altitude Yushu yak was higher than that of low-altitude bovines. CaCl2 activates AMPK by activating CaMKKß cascade and accelerates postmortem glycolysis affecting the intramuscular environment, color, and muscle protein degradation to accelerate postmortem muscle maturation, suggesting that AMPK has essential effects on postmortem muscle glycolysis and quality, and can regulate muscle quality by regulating postmortem muscle AMPK activity. PRACTICAL APPLICATIONS: Insufficient postmortem glycolysis usually leads to DFD (dark, firm, and dry) meat. Beef have relatively high incidences of DFD meat, which has an unattractive dark color and causes significant loss to the meat industry. Therefore, AMPK, which can regulate postmortem glycolysis to affect meat quality, is a valid research target.