Comparison of oxidation extent, structural characteristics, and oxidation sites of myofibrillar protein affected by hydroxyl radicals and lipid-oxidizing system

Effect of air-conditioned packaging combined with temperature fluctuations on the preservation of mandarin fish (Siniperca chuatsi)

The objective of this study was to evaluate the impact of diverse packaging techniques on the moisture content, quality, microbiological profile and volatile compounds of mandarin fish (Siniperca chuatsi) fillets. Mandarin fish fillets were packaged in accordance with three distinct conditions: AP (Air packaging), MAP 1 (40 % CO2/45 % N2/15 % O2) and MAP 2 (50 % CO2/35 % N2/15 % O2) and stored at TC (Constant temperature at 4 °C) and TF (Temperature fluctuation at 4 °C and 8 °C), respectively. Results demonstrated that MAP effectively inhibited microbial growth, retarded pH increase, and reduced accumulation of TVB-N, TMA, and MDA. On the 18th day, the constant-temperature MAP 2 group exhibited optimal preservation, with TVB-N (14.70 mg/kg), TMA (2.74 mg/kg), and MDA (38.36 mmol/mg) lower than those in the fluctuating-temperature AP group (TVB-N: 115.07 mg/kg; TMA: 2.81 mg/kg; MDA: 84.39 mmol/mg). It proved that temperature fluctuations accelerated the spoilage process of mandarin fish.

Oxidation of aquatic products from the inside out accelerates their deterioration: A case study of sea bass (Lateolabrax japonicus) during storage

Sea bass (Lateolabrax japonicus) is favored by consumers, but the oxidation of visceral lipids during refrigeration has not been studied. This research investigates the effect of visceral lipid oxidation on storage quality. The results show that visceral lipids oxidize first, leading to a 1.72, 2.36, and 2.04-fold increase in malondialdehyde, 4-hydroxy-2-nonenal, and 4-hydroxy-2-hexenal levels, respectively. The total free radicals, alkoxy radicals, and hydrogen radicals increased by 18.13 %, 18.17 %, and 9.87 %, respectively. Visceral lipid oxidation damages myofibrillar proteins, reducing sulfhydryl content by 18.11 %. The viscera also promote protein oxidation, particularly of actin. Volatile component and electronic nose analyses revealed significant odor deterioration due to lipid oxidation and protein degradation. Molecular docking confirms that 4-hydroxy-2-nonenal binds to 15 amino acids in β-actin. Therefore, spoilage occurs from the inside out, and viscera should be removed before freezing.

Effects of freeze-thaw cycles on texture and protein digestive properties of scallop adductor muscles: Role of protein oxidative changes

This study investigated the effects of freeze-thaw cycles (F-T cycles) on texture and protein digestive properties of scallop adductor muscles and the underlying mechanisms involved. Results showed that F-T cycles significantly increased free radical intensity of scallop adductor muscles and oxidation level of scallop protein. Simultaneously, the protein oxidative degradation occurred, as evidenced by increased levels of TCA-soluble peptides and water-soluble Hyp, which led to myofiber breakage and decreased textural properties. Nile Red staining showed that F-T cycles-induced oxidation promoted protein aggregation, which in turn reduced protein digestibility. Peptidomics analysis further showed that F-T cycles-induced oxidation altered the enzymatic cleavage sites in scallop protein, resulting in an increased abundance of macromolecular peptides (>2500 Da) and decreased release of bioactive peptides. These results highlight the role of protein oxidation in the deterioration of texture and protein digestibility of scallops during frozen storage, providing a basis for improving quality preservation strategies.

Magnetic field-mediated oxidative modification of myoglobin: One effective method for improving the gel properties of myofibrillar protein

This study employed a magnetic field to investigate the impact of myoglobin (Mb) oxidation (0-20 mmol/L H2O2) on the gel properties of myofibrillar protein (MP). The results indicated that magnetic field could further facilitate the rearrangement of the Mb structure, resulting in the transfer of its internal reactive groups to the external environment. This contributed to hydration and cross-linking between MP. The Raman spectroscopy results demonstrated that the oxidised Mb altered the secondary structure of MP (increased α-helix content and reduced random coil), making its environment more hydrophobic. This significantly diminished gel water mobility (confirmed by low-field Nuclear Magnetic Resonance). While under the magnetic field treatment, the MP gel network was more relatively porous and uniformly flat, and the gel strength was significantly enhanced (P < 0.05). Ultimately, the water holding capacity increased from 62.47 % to 76.42 %. In conclusion, the magnetic field combined with moderately oxidised Mb had a ripple effect, resulting in an improvement in the gel quality of MP.

Investigation of heat-induced pork batter quality detection and change mechanisms using Raman spectroscopy coupled with deep learning algorithms

Pork batter quality significantly affects its product. Herein, this study explored the use of Raman spectroscopy combined with deep learning algorithms for rapidly detecting pork batter quality and revealing the mechanisms of quality changes during heating. Results showed that heating increased β-sheet content (from 26.38 to 41.42%) and exposed hidden hydrophobic groups, which formed aggregates through chemical bonds. Dominant hydrophobic interactions further cross-linked these aggregates, establishing a more homogeneous and denser network at 80 °C. Subsequently, convolutional neural networks (CNN), long short-term memory neural networks (LSTM), and CNN-LSTM were comparatively used to predict gel strength and whiteness in batters based on the Raman spectrum. Thereinto, CNN-LSTM provided the optimal results for gel strength (Rp = 0.9515, RPD = 3.1513) and whiteness (Rp = 0.9383, RPD = 3.0152). Therefore, this study demonstrated the potential of Raman spectroscopy combined with deep learning algorithms as non-destructive tools for predicting pork batter quality and elucidating quality change mechanisms.

The mechanism of peanut shell flavonoids inhibiting the oxidation of myofibrillar protein: An elucidation of the antioxidative preservation action of peanut shell flavonoids on chilled pork

Flavonoids, a significant subclass of polyphenols, possess antioxidant properties and contribute to the preservation of chilled meat. In this paper, a phosphate buffer solution (pH = 6.25, simulated chilled pork) and a Fenton oxidation system (simulated myofibrillar protein oxidation process during storage) were established to explain the antioxidative preservation of chilled pork using peanut shell flavonoids (PSFs). The results indicated that PSFs changed the secondary structure of myofibrillar protein (MP), significantly inhibiting the oxidation of amino acids and the formation of carbonyl groups in MP (P < 0.05). Because PSFs and amino acids in chilled pork were combined to form complex through non-covalent bond in a pH 6.25 environment and covalent bond in a Fenton oxidation system. The antioxidant capacity of the complex was significantly enhanced (P < 0.05). The molecular docking technique predicted the antioxidant binding sites were Cys176, Ala182 and Val 124. This study provides a theoretical foundation for the preservation of chilled pork using PSFs.

Amelioration of myofibrillar protein emulsion gel properties by mildly oxidized sunflower oil

Different oxidation states of oil affect the emulsion stablility and gel properties of emulsified meat products. Emulsified chicken gels were prepared using sunflower oil (SFO) with different oxidation levels (0, 20, 40, and 60 min, 120 °C). The pre-oxidation treatment of oils was investigated for emulsification and gelation of myofibrillar protein (MP). The results showed that MP emulsion gels with mildly oxidized (20 min) SFO had higher elastic modulus (G') and more homogeneous water distribution, which were due to increased hydrophobic interactions between MP and lipids, and improved emulsification stability. However, the addition of highly oxidized (60 min) SFO resulted in aggregation of proteins, increased emulsion particle size, significantly reduced hardness and chewiness (P > 0.05), and exhibited large pores in the network microstructure. The results suggested that mildly oxidized SFO has an ameliorating effect on MP emulsion gelation, which facilitates better comprehension of the protein oxidation process in oil-loaded meat systems.

Effect of Different Addition Amounts of Capsaicin on the Structure, Oxidation Sites, and Gel Properties of Myofibrillar Proteins under Oxidative Conditions

This study aimed to explore the mechanism influencing different addition amounts of capsaicin on the gel characteristics and microstructure of myofibrillar protein (MP) gels under conditions induced by hydroxyl free radicals (•OH). Results indicate that adding capsaicin can improve the gelling characteristics of the MPs. With an increased amount of capsaicin added, the oxidation of MPs by •OH decreased, and the number of oxidation sites decreased. Peptides located around residues 651-851 in the head domain SH1 and S2 subunits of the myosin heavy chain were susceptible to oxidation. Capsaicin primarily interacted with amino acids in SH1 (residues 1-151 and 601-651), reducing the effect of •OH on MPs and consequently decreasing the occurrence of MP aggregation. Capsaicin protected the structure and oxidation sites of MPs under oxidative conditions, ensuring the formation of an MP gel with uniformly dense pores during heating, thereby improving the texture characteristics and water-holding capacity of the gel.

Revealing the deterioration mechanism in gelling properties of pork myofibrillar protein gel induced by high-temperature treatments: Perspective on the protein aggregation and conformation

The purpose of the present study was to investigate the mechanism of gel deterioration of myofibrillar proteins (MP) gels induced by high-temperature treatments based on the protein aggregation and conformation. The results showed that the gel strength and water holding capacity of MP obviously increased and then decreased as the temperature increased, reaching the maximum value at 80 °C (P < 0.05). The microstructure analysis revealed that appropriate temperature (80 °C) contributed to the formation of a more homogeneous, denser, and smoother three-dimensional mesh structure when compared other treatment temperatures, whereas excessive temperature (95 °C) resulted in the formation of heterogeneous and large protein aggregates of MP, decreasing the continuity of gel networks. This was verified by the rheological properties of MP gels. The particle size (D4,3 and D3,2) of MP obviously increased with larger clusters at excessive temperature, and the surface hydrophobicity of MP decreased (P < 0.05), which has been linked to the formation of soluble or insoluble protein aggregates. Tertiary structure and secondary structure results revealed that the proteins had a tendency to be more stretched under higher temperature treatments, which resulted in a decrease in covalent interactions and non-covalent interactions, fostering the over-aggregation of MP. Therefore, our present study indicated that the degradation of MP gels treated at high temperatures was explained by protein aggregation and conformational changes in MP.

Effects of moderately oxidized lard on myofibrillar protein emulsion gels: Gel-forming properties, water distribution, and digestibility

Emulsion gels were prepared by adding lard with different degrees of oxidation (0, 1, 2, 3, 4, and 5 h, 110 °C) to porcine myofibrillar proteins (MP). The findings demonstrated that changes in sulfhydryl content and carbonyl content reflected that oxidized lard induced the oxidation of MP. Compared with the control (CON), moderately oxidized lard (2 h) led to the unfolding of the protein structure, increased β-sheet content, and exposed hydrophobic groups. These modifications facilitated interactions between the protein and lard at the interface, enhancing the emulsifying properties of MPs. Furthermore, the moderate oxidation of lard (2 h) enhanced the organization of the gel structure and improved the gel performance of MPs, resulting in uniform water distribution. In contrast, the hardness and springiness of MP gel treated with excessively oxidized lard (5 h) were significantly reduced (p < 0.05). The microstructure of MP gel also exhibited irregular aggregation, resulting in a decline in protein digestibility. In addition, lard oxidation (2 h) had a positive effect on maintaining gel stability during storage.

Mitigation of malondialdehyde-induced protein lipoxidation by epicatechin in whey protein isolate

Malondialdehyde (MDA) can induce lipoxidation in whey protein isolate (WPI). The physicochemical changes in this reaction with or without the presence of a phenolic compound epicatechin (EC) were characterized in this study. Results suggested the content of MDA was significantly reduced during co-incubation of MDA and EC. The addition of EC dose-dependently alleviated MDA-induced protein carbonylation, Schiff base formation and loss of tryptophan fluorescence. The interruption of MDA-binding to WPI was directly visualized by immunoblotting analysis. Observation of the surface microstructure of WPI showed that MDA-induced protein aggregation was partially restored by EC. Meanwhile, EC was found to promote loss of both protein sulfhydryls and surface hydrophobicity due to possible phenol-protein interactions. These observations suggested the potential of EC in the relief of MDA-mediated protein lipoxidation.

Hydroxyl radical-induced oxidation boosts the gelation of ginkgo seed protein in the presence of hyaluronic acid

Hydroxyl radical-induced oxidation can modify gelling properties of food proteins. In this study, a hydroxyl radical generating system (HRGS), consisting of 0.1 mM Fe3+, 0.1 mM ascorbic acid, and 1, 10, or 20 mM H2O2, was used to oxidize ginkgo seed protein isolate (GSPI) for 4 h at ambient temperature in the presence of 0.3 % (w/v) hyaluronic acid (HA) to enhance its gelation properties. HRGS treatment led to increased protein hydrophobicity, reduced sulfhydryl content, and disulfide bond-mediated protein crosslinking. Moreover, the secondary structure of GSPI varied with H2O2 concentrations. Moderate oxidation (approximately 10 mM H2O2) promoted GSPI aggregation and improved mechanical strength, rheological properties, water holding capacity, and whiteness of GSPI gels. However, excessive oxidation disrupted hydrogen bonding, generated excessive disulfide bonds, hindered active group interaction, inhibited gel network formation, and reduced gel strength. Hence, hydroxyl radical-induced oxidation holds potential for enhancing GSPI gelation within specific concentration ranges. This study suggests that controlled oxidation could be a novel approach for developing protein-based gel products.

Research Progress on the Mechanism of the Impact of Myofibrillar Protein Oxidation on the Flavor of Meat Products

Myofibrillar proteins primarily consist of myosin, actin, myogenin, and actomyosin. These proteins form complex networks within muscle fibers and are crucial to the physical and chemical properties of meat. Additionally, myofibrillar proteins serve as significant substrates for the adsorption of volatile flavor compounds, including aldehydes, alcohols, ketones, and sulfur and nitrogen compounds, which contribute to the overall flavor profile of meat products. A series of chemical reactions occur during the processing, storage, and transportation of meat products. Oxidation is one of the most significant reactions. Oxidative modification can alter the physical and chemical properties of proteins, ultimately impacting the sensory quality of meat products, including flavor, taste, and color. In recent years, considerable attention has been focused on the effects of protein oxidation on meat quality and its regulation. This study investigates the impact of myofibrillar protein oxidation on the sensory attributes of meat products by analyzing the oxidation processes and the factors that initiate myofibrillar protein oxidation. Additionally, it explores the control of myofibrillar protein oxidation and its implications on the sensory properties of meat products, providing theoretical insights relevant to meat processing methods and quality control procedures.

Metabolomic profile of muscles from tilapia cultured in recirculating aquaculture systems and traditional aquaculture in ponds and protein stability during freeze-thaw cycles

Muscle protein stability during freeze-thaw (F-T) cycles was investigated with tilapia cultured in recirculating aquaculture systems (RAS) and traditional aquaculture in ponds (TAP). This study found that fatty acids (eg., palmitic acid) were enriched in TAP, while antioxidants (eg., glutathione) were enriched in RAS. Generally, proteins in the RAS group exhibited greater stability against denaturation during the F-T cycle, suggested by a less decrease in haem protein content (77% in RAS and 86% in TAP) and a less increase in surface hydrophobicity of sarcoplasmic protein (63% in RAS and 101% in TAP). There was no significant difference in oxidative stability of myofibrillar protein between the two groups. This study provides a theoretical guide for the quality control of tilapia cultured in RAS during frozen storage.

Effect of three unsaturated fatty acids on the protein oxidation and structure of myofibrillar proteins from rainbow trout (Oncorhynchus mykiss)

In this study, the impact of three unsaturated fatty acids (Oleic acid: OA, Eicosapentaenoic acid: EPA, Docosahexaenoic acid: DHA) on the oxidation and structure of rainbow trout myofibrillar protein (MP) was explored. The findings revealed a notable increase in carbonyl content (P < 0.05) and a significant decrease in total sulfhydryl content (P < 0.05) of MP with the concentration increase of the three unsaturated fatty acids. Endogenous fluorescence spectroscopy and surface hydrophobicity analyses showed that unsaturated fatty acids can cause unfolding and exposure of hydrophobic groups in MP. In addition, SDS-PAGE showed that disulfide bonds were associated with MP cross-linking and aggregate size induced by unsaturated fatty acids. Overall, three unsaturated fatty acid treatments facilitated the oxidation of myofibrillar proteins, and the extent of protein oxidation was closely associated with the concentration of unsaturated fatty acids.

Impact of thermal ultrasound on enzyme inactivation and flavor improvement of sea cucumber hydrolysates

In this study, the effects of the thermal ultrasonic enzyme inactivation process on flavor enhancement in sea cucumber hydrolysates (SCHs) and its impact on the inactivation of neutral proteases (NPs) were investigated. The body wall of the sea cucumber was enzymatically hydrolyzed with NPs. On the one hand, the structure of NPs subjected to different enzyme inactivation methods was analyzed using ζ-potential, particle size, and Fourier transform infrared (FT-IR) spectroscopy. On the other hand, the microstructure and flavor changes of SCHs were examined through scanning electron microscopy, E-nose, and gas chromatography-ion mobility spectrometry (GC-IMS). The results indicated that thermal ultrasound treatment at 60 °C could greatly affect the structure of NPs, thereby achieving enzyme inactivation. Furthermore, this treatment generated more pleasant flavor compounds, such as pentanal and (E)-2-nonenal. Hence, thermal ultrasound treatment could serve as an alternative process to traditional heat inactivation of enzymes for improving the flavor of SCHs.

Ultrasonic treatment treated sea bass myofibrillar proteins in low-salt solution: Emphasizing the changes on conformation structure, oxidation sites, and emulsifying properties

The physiochemical properties, structure characteristics, oxidation, and emulsifying properties of myofibrillar proteins (MPs) in low salt solution after treated by the ultrasound were investigated. The solubility, mean diameters, sulfhydryl content, and carbonyl contents of MPs after ultrasonic treatment increased, while the turbidity decreased. The surface hydrophobicity of MPs with 200 W-600 W treatment increased, but decreased at 800 W treatment. The circular dichroism analysis revealed that α-helix content increased, while β-sheet and random coil content decreased after ultrasonic treatment. Fluorescence spectroscopy indicated the fluorescence intensities of MPs were increased after ultrasonic treatment. SDS-PAGE results showed more protein polymers due to myosin heavy chain (MHC) aggregation via disulfide bonds. Based on LC-MS/MS result, the myosin heavy chain was susceptible to oxidation, with monooxidation being the main oxidative modification. Finally, the emulsions stabilized by ultrasonically treated MPs, especially those treated at 800 W, exhibited decreased particle size, improved uniformity, and enhanced stability.

Biosynthesis of the phycocyanin β-subunit in Escherichia coli BL21 and its antioxidant activity and application in the preservation of fresh-cut apples

In this study, the biosynthesis of phycocyanin β-subunit (CpcB) in Escherichia coli BL21 was investigated, and its antioxidant activity and application in anti-browning of fresh-cut apples was explored. Four genes (cpcB, cpeS, hox1 and pcyA) involved in the biosynthesis of CpcB were cloned and transformed into E. coli BL21 by constructing recombinant plasmid pETDuet-5. The positive transformant was screened by ampicillin resistance. The analysis of SDS-PAGE and zinc fluorescence spectrum showed that CpcB was successfully expressed in E. coli BL21 with a molecular weight of 21 kDa. The purified CpcB had a maximum absorption peak at 615 nm, and its maximum florescence emission wavelength was 640 nm. It exhibited a stronger ability to scavenge four free radicals than Vc. The color change in fresh-cut apples was obviously delayed by the CpcB treatment. These results suggest that CpcB may be used as a potential anti-browning agent for food preservation.

Lipid oxidation in foods and its implications on proteins

Lipids in foods are sensitive to various environmental conditions. Under light or high temperatures, free radicals could be formed due to lipid oxidation, leading to the formation of unstable food system. Proteins are sensitive to free radicals, which could cause protein oxidation and aggregation. Protein aggregation significantly affects protein physicochemical characteristics and biological functions, such as digestibility, foaming characteristics, and bioavailability, further reducing the edible and storage quality of food. This review provided an overview of lipid oxidation in foods; its implications on protein oxidation; and the assessment methods of lipid oxidation, protein oxidation, and protein aggregation. Protein functions before and after aggregation in foods were compared, and a discussion for future research on lipid or protein oxidation in foods was presented.