The Solubility and Structures of Porcine Myofibrillar Proteins under Low-Salt Processing Conditions as Affected by the Presence of L-Lysine

Synergistic Effects of High-Intensity Ultrasound Combined with L-Lysine for the Treatment of Porcine Myofibrillar Protein Regarding Solubility and Flavour Adsorption Capacity

This study aimed to investigate the synergistic effects of high-intensity ultrasound (0, 5, 10, 15, and 20 min) in combination with L-lysine (15 mM) on improving the solubility and flavour adsorption capacity of myofibrillar proteins (MPs) in low-ion-strength media. The results revealed that the ultrasound treatment for 20 min or the addition of L-lysine (15 mM) significantly improved protein solubility (p < 0.05), with L-lysine (15 mM) showing a more pronounced effect (p < 0.05). The combination of ultrasound treatment and L-lysine further increased solubility, and the MPs treated with ultrasound at 20 min exhibited the best dispersion stability in water, which corresponded to the lowest turbidity, highest absolute zeta potential value, and thermal stability (p < 0.05). Based on the reactive and total sulfhydryl contents, Fourier transform infrared spectroscopy, and fluorescence spectroscopy analysis, the ultrasound treatment combined with L-lysine (15 mM) promoted the unfolding and depolymerization of MPs, resulting in a larger exposure of SH groups on the surface, aromatic amino acids in a polar environment, and a transition of protein conformation from α-helix to β-turn. Moreover, the combined treatment also increased the hydrophobic bonding sites, hydrogen-bonding sites, and electrostatic effects, thereby enhancing the adsorption capacity of MPs to bind kenone compounds. The findings from this study provide a theoretical basis for the production and flavour improvement of low-salt MP beverages and the utilisation of meat protein.

Use of basic amino acids to improve gel properties of PSE-like chicken meat proteins isolated via ultrasound-assisted alkaline extraction

To improve the gel quality of pale, soft, and exudative (PSE)-like chicken protein isolate (PPI) obtained via ultrasound-assisted alkaline extraction (UAE), l-lysine (l-Lys), l-arginine (l-Arg), or l-histidine (l-His) were used and the effects on the thermal gelling characteristics of PPI were studied. Compared with the nonbasic amino acid addition group, the addition of l-His/l-Arg/l-Lys significantly increased the solubility and absolute zeta potential of PPI, whereas reduced the particle size and turbidity (p < 0.05). They enhanced the gel strength and textural properties of PPI (p < 0.05) and reduced the cooking loss of PPI in the following order: l-Lys > l-Arg > l-His. The solubility, gel strength, and hardness of PPI with l-Lys were increased by 18.6%, 44.6%, and 57.6%, respectively, and cooking loss was decreased by 18.1%. Low-field nuclear magnetic resonance and magnetic resonance imaging revealed that basic amino acids addition decreased the water mobility in PPI gels with increasing immobile water content. Scanning electron microscopy revealed that the addition of basic amino acids promoted the formation of a more uniform and tight network microstructure in PPI gels. The α-helix content was decreased, whereas the β-sheet content was increased in PPI gels after basic amino acid addition. Therefore, addition of basic amino acids, especially l-Lys, enhances the gel properties of PPI. PRACTICAL APPLICATION: This study revealed that adding basic amino acids effectively improved the gel properties of PPI obtained via UAE method, with l-Lys exerting the best improvement effect. Our findings highlight the application value of PSE-like meat by the improvement of gel characteristics of PPI, providing a theoretical reference for the processing and utilization of PPI.

Protein carbonylation and structural changes in porcine myofibrillar protein exposed to metal ion-H2O2-ascorbate and linoleic acid-lipoxidase oxidizing systems

The present study aimed to compare two oxidizing systems commonly present in meat for their influence on protein oxidation patterns, with emphasis on the specific lysine-derived markers for protein carbonylation (α-aminoadipic semialdehyde, AAS; lysinonorlucine, LNL) and their relationships with the common markers for protein oxidation. For this purpose, pork myofibrillar proteins (MFP, 5 mg/mL) were suspended in 0.6 M NaCl (pH 7.5) and incubated at 4 ℃ for 24 h with two oxidizing systems: (1) a metal-catalyzed oxidizing system (MOS: 10 µM FeCl3, 100 µM ascorbic acid, and 0-10 mmol/L H2O2), (2) a linoleic acid - lipoxidase oxidizing system (LOS: 7500 units of lipoxidase/mL, and 0-10 mM linoleic acid). Results showed that the amounts of AAS and LNL in both MOS- and LOS-oxidized MFP was proportional to the oxidant concentrations (H2O2 or linoleic acid), while the formation of total carbonyl and total thiol also exhibited similar oxidant-dose-dependent patterns. Meanwhile, the α-helix contents of MFP declined with oxidant concentrations irrespective of the oxidizing systems. The reducing SDS-PAGE revealed that the myosin heavy chain band started to diminish at high H2O2 concentration (5 and 10 mM) in MOS whereas at low level of linoleic acid (0.5 mM) in LOS. Overall, these results demonstrated both oxidizing systems could be involved in the formation of AAS and LNL, and that the generation of AAS and LNL can be used as reliable markers for protein oxidation, but also might be directly involved in protein structural changes and then contribute to the alternations of protein functionality.

Ionic strength-mediated protein and flavor studies on thermally processed hairtail pieces

This study aimed to investigate the impact of different ionic strengths on the texture, protein, and flavor of thermally processed hairtail pieces. Incorporating salt ions into the heat treatment process had a positive impact on the quality of the cooked hairtail pieces. The pieces treated with 2 M NaCl showed superior texture and sensory scores. The ionic strength had a significant positive correlation with the chewiness and cohesion of cooked hairtail (p < 0.01). Furthermore, the myofibrillar protein content and total sulfhydryl content increased significantly. Circular dichroism spectra analysis revealed a transition in the protein structure from a β-sheet structure to an α-helical structure as the ionic strength decreased. The ionic strength had a significant impact on the interaction between protein and flavor compounds. Specifically, it impacted the expression of certain volatile components (p < 0.05). Our study suggests that selecting the appropriate cooking method is crucial for both healthiness and sensory quality of processed hairtail products, and ionic strength mediation is superior in both aspects.