Attributes of lipid oxidation due to bovine myoglobin, hemoglobin and hemolysate

Use of plasma induced modification of biomolecules (PLIMB) to evaluate hemin dissociation from fish and bovine methemoglobins

Hemin dissociation occurs much faster from fish methemoglobin (metHb) compared to mammalian metHb yet the mechanism remains poorly understood. This may involve enhanced solvent access to His(E7) of fish metHbs by a protonation mechanism. Plasma induced modification of biomolecules (PLIMB) produces free radicals that covalently modify solvent accessible residues of proteins, and so can provide insight regarding accessibility of hydronium ions to protonate His(E7). PLIMB-induced modifications to heme crevice sites of trout IV and bovine metHb were determined using tandem mass spectrometry after generating peptides with Trypsin/Lys-C. αHis(CE3) was more modified in trout attributable to the more dynamic nature of bovine αHis(CE3) from available crystal structures. Although His(E7) was not found to be more modified in trout, aspects of trout peptides containing His(E7) hampered modification determinations. An existing computational structure-based approach was also used to estimate protonation tendencies, suggesting His(E7) of metHbs with low hemin affinity are more protonatable.

Effect of heme proteins on the lipid molecule profile and aroma formation during hot air drying of non-smoked bacon

Heme proteins and their derivatives play important roles in inducing lipid oxidation to produce volatile compounds during bacon drying. This study investigated the effects of heme proteins and their derivatives (hemoglobin, myoglobin, nitrosylmyoglobin, hemin, Fe2+, and Fe3+) on lipid and volatiles profiles in the washed pig muscle (WPM) model. The results of the study indicated that the inducers primarily caused the oxidation of glycerophospholipids. Furthermore, hemoglobin and myoglobin had the most significant impact, and their potential substrates may include PE (O-18:2/20:4), PE (O-18:1/20:4), PC (16:0/18:1), and PE (O-18:2/18:2). Nitrosomyoglobin has limited ability to promote lipid oxidation and may protect ether phospholipids from oxidation. The analysis of the volatiles in the model revealed that heme proteins and their derivatives have the ability to induce the production of key aroma compounds. The descending order of effectiveness in inducing the production of aroma compounds is as follows: hemoglobin, myoglobin, hemin, and nitrosylmyoglobin. The effectiveness of Fe2+ and Fe3+ is similar to that of nitrosylmyoglobin.

(-)-Epigallocatechin gallate as an inhibitor of hemoglobin-catalyzed lipid oxidation: molecular mechanism of action and nutritional application

Hemoglobin (Hb) is effective inducer for lipid oxidation and protein-polyphenol interaction is a well-known phenomenon. The effects of the interaction of (-)-epigallocatechin gallate (EGCG) with Hb on lipid oxidation were rarely elucidated. The detailed interaction between bovine Hb and EGCG was systematically explored by experimental and theoretical approaches, to illustrate the molecular mechanisms by which EGCG influenced the redox states and stability of Hb. EGCG would bind to the central pocket of protein with one binding site to form Hb-EGCG complex. The binding constant for Hb-EGCG complex was 0.34 × 104 M-1 at 277 K, and thermodynamic parameters (ΔH > 0, ΔS > 0 and ΔG < 0) revealed the participation of hydrophobic forces in the binding process. The binding of EGCG would increase the compactness of protein molecule and diminish the crevice near the heme cavity, which was responsible for the reduction of met-Hb to oxy-Hb and inhibition of hemin release from met-Hb. Moreover, EGCG efficiently suppressed Hb-caused lipid oxidation in liposomes and cod muscles, which was possibly attributed to the reduction to oxy-Hb state and declined hemin dissociation from met-Hb. Altogether, our results provide significant insights into the binding of EGCG to redox-active Hb, which represents a novel mechanism for the anti-oxidant capacity of EGCG in human health and is favorable to the applications of natural EGCG in the good quality of Hb-containing products.

Effects of sodium chloride and sodium tripolyphosphate on the prooxidant properties of hemoglobin in washed turkey muscle system

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MetHb in WTM acted as the most effective pro-oxidant, followed by hemin and oxyHb.

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The addition of NaCl significantly increased the oxyHb-mediated lipid oxidation.

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STPP inhibited oxyHb-mediated lipid oxidation.

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Formation of metHb and pH paly critical roles in oxyHb-mediated lipid oxidation.

This study examined the effects of sodium chloride (NaCl) and sodium tripolyphosphate (STPP) on lipid oxidation induced by oxyhemoglobin (oxyHb) in washed turkey muscle (WTM) model. To explore the reasons for observed effects, the pro-oxidant abilities of Hb derivatives (e.g., metHb, oxyHb, hemin, Fe²⁺, and Fe³⁺), pH change, and antioxidation of Hb in the presence of NaCl or STPP were also analyzed. The observed lipid oxidation capacity in WTM followed the order metHb > hemin > oxyHb > Fe²⁺ > Fe³⁺. Added Fe²⁺ accelerated auto-oxidation of oxyHb and oxyHb-mediated lipid oxidation. Hb auto-oxidation to metHb increased as the pH decreased from 6.6 to 5.0. NaCl promoted oxyHb-mediated lipid oxidation due to NaCl causing decreased pH value and increased formation of metHb. STPP inhibited oxyHb-mediated lipid oxidation and weakened the pro-oxidative effect of NaCl. This could be attributed to STPP increasing the pH, inactivating free iron, and inhibiting formation of metHb.

Binding of Quercetin to Hemoglobin Reduced Hemin Release and Lipid Oxidation

The interactions between quercetin and bovine (or human) hemoglobin (Hb) were systematically investigated by fluorescence, UV-vis absorption spectroscopy, and molecular docking to demonstrate the structural mechanism by which quercetin affected the Hb redox state and stability. Quercetin could interact with the central cavity of the Hb molecule with one binding site to generate an Hb-quercetin complex, and the hydrophobic interaction played an important role in the formation of the complex. The binding constant for the Hb-quercetin complex at 298 K was observed to be 1.25 × 10⁴ M^-1. In addition, quercetin effectively inhibited Hb-induced lipid oxidation in liposomes or washed muscles, which was ascribed to the conversion to oxy-Hb and decreased hemin dissociation from met-Hb. Consistent with its lower abilities to bind Hb and scavenge free radicals, rutin (i.e., quercetin-3-rhamnosylglucsoside) did not significantly influence the redox state of Hb nor reduce hemin release from Hb, and subsequently, it less effectively inhibited Hb-induced lipid oxidation than quercetin. Altogether, the results herein provide novel insights into the antioxidant mechanism for quercetin and are beneficial to the application of natural quercetin in Hb-containing foods.

Model systems for studying lipid oxidation associated with muscle foods: Methods, challenges, and prospects

Lipid oxidation is a complex process in muscle-based foods (red meat, poultry and fish) causing severe quality deterioration, e.g., off-odors, discoloration, texture defects and nutritional loss. The complexity of muscle tissue -both composition and structure- poses as a formidable challenge in directly clarifying the mechanisms of lipid oxidation in muscle-based foods. Therefore, different in vitro model systems simulating different aspects of muscle have been used to study the pathways of lipid oxidation. In this review, we discuss the principle, preparation, implementation as well as advantages and disadvantages of seven commonly-studied model systems that mimic either compositional or structural aspects of actual meat: emulsions, fatty acid micelles, liposomes, microsomes, erythrocytes, washed muscle mince, and muscle homogenates. Furthermore, we evaluate the prospects of stem cells, tissue cultures and three-dimensional printing for future model system development. Based on this reviewing of oxidation models, tailoring correct model to different study aims could be facilitated, and readers are becoming acquainted with advantages and shortcomings. In addition, insight into recent technology developments, e.g., stem cell- and tissue-cultures as well as three-dimensional printing could provide new opportunities to overcome the current bottlenecks of lipid oxidation studies in muscle.

Quercetin as an inhibitor of hemoglobin-mediated lipid oxidation: Mechanisms of action and use of molecular docking

The antioxidant effect of quercetin on hemoglobin(Hb)-mediated lipid oxidation and the mechanisms involved were investigated. Quercetin strongly inhibited Hb-mediated lipid oxidation in washed muscle. Quercetin showed effective hydroxyl radical scavenging ability similar to butylated hydroxytoluene (BHT). Quercetin reduced metHb resulting in formation of oxyHb. Bound quercetin decreased heme dissociation from metHb. Conversion to oxyHb and decreased heme dissociation represent routes to limit Hb-mediated lipid oxidation. Electrospray ionization mass spectrometry (ESI-MS) indicated one molecule of quercetin was covalently bound to Hb α-chain. Quercetin quinone docked 3.3 Å from the thiol of αCys(H15) but not near any other Cys residues of turkey Hb. At the docking site, hydrogen bonding between quercetin quinone and amino acids of α- and β-chain was demonstrated. This represents a path by which quercetin became covalently bound to α-chain. Molecular docking of heme proteins to polyphenols provides a template to better understand antioxidant interactions in muscle foods.

Interaction between secondary lipid oxidation products and hemoglobin with multi-spectroscopic techniques and docking studies

This study aimed to explore the effect of secondary lipid oxidation products (SLOPs) on hemoglobin (Hb) in chicken model. The fluorescence quenching technique and molecular docking were employed, and the apparent binding constants K_sv and the binding site numbers of SLOPs with Hb were calculated. The results revealed that three SLOPs (hexanal, benzaldehyde, and 2-pentanone) obviously promoted the oxidation of Hb, which is consistent with the change of Hb hydrophobicity, particle size, polydispersity index and zeta potential. The SLOPs strongly quenched the intrinsic fluorescence of Hb and triggered the alterations in the Hb structure. Hydrophobic interaction was the main force between SLOPs and Hb. Among the three SLOPs, hexanal demonstrated more stronger oxidation on Hb, which is closely related to its hydrophobic ability and structure characteristic, especially 10 μM hexanal is more prone to form an obvious unfolded structure and caused molecular aggregation than lower concentrations.

Effect of pH on lipid oxidation mediated by hemoglobin in washed chicken muscle

To investigate the effect of pH on lipid oxidation of chicken muscle, chicken hemolysates were added to washed chicken muscles to analyze lipid oxidation at pH 5.7, 6.3, and 7.2. The results showed that with a blue shift of the Soret peak, oxyhemoglobin gradually transformed to methemoglobin during storage, the shape of porphyrin rings of heme in fluorescence electron microscopy changed from round to trail-like structure. These changes were more significant at low pH. Comparing hemoglobin (Hb) structure, the distance ofamino acids between the E10 of lysine and metHb-7-propionate groups is longer at pH 5.7 than other pHs, which makes solvent easily enter the heme cavity, leading tothe severe destruction of Hb. The linear correlation between color and lipid oxidation also further confirmed that the increased oxidation of chicken Hb causes more rapid lipid oxidation in pH 5.7 than the other 2 pHs (p < 0.05).

The significant influences of pH, temperature and fatty acids on meat myoglobin oxidation: a model study

Colour is one of the important quality traits affecting the meat purchasing decision by consumers, and myoglobin is the principal heme protein responsible for the meat colour. This study aimed to investigate the effects of pH (5.3, 5.8, 6.4 and 7.4) and temperature (4 and 25 °C) on oxymyoglobin (OxyMb) oxidation in model reaction mixtures containing OxyMb, fatty acids (C18:2n-6 and C18:3n-3) and vitamin E. A decrease of the OxyMb concentration with increased acidity was observed for all the reaction mixtures with/without fatty acids and vitamin E. After 48 h of storage at 4 °C, the OxyMb concentration decreased by approximately 60-70%, 61-69%, 53.7-53.9% and 40.93-41.84% in the reaction mixtures containing [OxyMb + C18:2n-6 or C18:3n-3] at pH 5.3, 5.8, 6.4 and 7.4, respectively. While, after 48 h at 25 °C, the OxyMb concentration decreased by 95-98% in all the reaction mixtures containing [OxyMb + C18:2n-6 or C18:3n-3] under all the pH conditions. The presence of vitamin E significantly inhibited the OxyMb oxidation in the reaction mixtures containing fatty acids under acidic conditions, but a higher level of vitamin E may be required for meat(s) containing high n-3 fatty acids content that are stored at high temperature.

Changes in color, myoglobin, and lipid oxidation in beef patties treated by dielectric barrier discharge cold plasma during storage

The objective of this work was to investigate the changes in color, metmyoglobin reducing activity (MRA), and lipid oxidation (TBARS) and their relationships in beef patties treated by dielectric barrier discharge cold plasma (DBD-CP) at different voltages and frequencies during storage at 4 °C. DBD-CP treatment, including treatment voltages and frequencies, caused the decrease of a^⁎ value and MRA (P < 0.05), promoted the accumulation of metmyoglobin (P < 0.05), and significantly increased TBARS values (P < 0.05). It was the first time revealed that the effect of treatment voltage on the quality of beef patty was greater than that of frequency. In addition, there were significant and strong positive correlations between a^⁎ value and MRA and negative correlations between a^⁎ value, metmyoglobin (MMb)% and TBARS. Taken together, Data demonstrated that DBD-CP treatment can significantly affect meat redness, Mb contents, MRA, and lipid oxidation in ground beef during storage, and accelerate discoloration and lipid oxidation of meat.

Characterization of the Cofactors Involved in Non-enzymatic Metmyoglobin/Methemoglobin Reduction In Vitro

Previous research reported the role of nonenzymatic metmyoglobin (MetMb) and methemoglobin (MetHb) reduction in meat color; however, limited studies have characterized the cofactors involved in nonenzymatic reduction. The objective of this study was to characterize electron donors and carriers in nonenzymatic MetMb and MetHb reduction at various temperatures and postmortem muscle pHs in vitro. Methylene blue and cytochrome c (cyt-c) were evaluated as electron carriers and nicotinamide adenine dinucleotide, reduced form (NADH) and ascorbate were considered as electron donors. All combinations of electron donors and carriers were evaluated in the following order: NADH plus methylene blue, ascorbate plus methylene blue, NADH plus cyt-c, and ascorbate plus cyt-c. Spectrophotometry was utilized to monitor the rates of reduction. The results indicated that methylene blue was an effective electron carrier than cyt-c in the presence of NADH. Temperature and pH had cofactor-specific effects on nonenzymatic MetMb and MetHb reduction. Lower temperature resulted in an increased nonenzymatic MetMb reduction for methylene blue regardless of electron donor (ascorbate, P = 0.03, NADH, P = 0.04). As pH increased, MetHb reduction was enhanced in the presence of ascorbate plus cyt-c. Nonenzymatic MetHb reduction was numerically lower than nonenzymatic MetMb reduction in the presence of NADH plus methylene blue. In summary, in addition to NADH, the current in vitro research demonstrated that ascorbate plus cyt-c could contribute to nonenzymatic MetMb and MetHb reduction at meat-pH and storage temperature.

Lipid oxidation and its implications to meat quality and human health

Lipid oxidation not only negatively influences the sensory characteristics but also the functional characteristics of meat. During the process, various primary and secondary by-products are formed depending upon the types of fatty acids, oxygen availability, and the presence of pro- and antioxidants. Some of the lipid oxidation products only influence the quality of meat but others are implicated to various diseases and human health. Therefore, prevention of lipid oxidation in meat is important for meat quality and for human health as well. The imbalance of oxidants and antioxidants that favors oxidants in the biological system is called oxidative stress in the body. Although the body is equipped with defense enzymes and antioxidant compounds, there are many sources of oxidants or free radicals that can destroy the oxidants/antioxidants balance. Therefore, supply of extra antioxidants through food can help maintaining the balance in favor of antioxidants and help preventing various diseases and malfunctions of our body.

A novel non-enzymatic sensing platform for determination of 5'-guanosine monophosphate in meat

Graphitic carbon nitride (g-C₃N₄) doped carboxylated MWCNTs nanocomposite was synthesized using a simple method. The composite films containing 45 wt%, 50 wt%, 56 wt%, 67 wt% fraction of the carboxylated MWCNTs doped into g-C₃N₄ were fabricated and characterized. An electrochemical non-enzymatic sensor for determination of 5'-guanosine monophosphate (GMP) based on the nanocomposite was developed. The results indicate that the g-C₃N₄-carboxylated MWCNTs nanocomposite has highly electrocatalytic activity, good conductivity and biocompatibility, which plays an essential role in the determination of GMP. Under the optimum conditions, the linear fitting equation was I (µA) = -0.0022c (μg·mL^-1) + 0.3560 (R² = 0.9982). The linear range was from 0.5 to 100 μg·mL^-1 and the detection limit (LOD, S/N = 3) was 0.109 μg·mL^-1. This non-enzymatic sensor can offer a better alternative to other methods for the analysis of GMP because of cheap cost, low detection limit and good anti-jamming capability in meat quality evaluation.