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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., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

The antioxidant effect of porcine pancreatic phospholipase A2 (PLA2) was previously demonstrated. Understanding how PLA2 inhibits lipid oxidation promoted by hemoglobin (Hb) is important for its applications in muscle foods. Effects of enzyme dose, pH, and calcium ion on the ability of PLA2 to inhibit trout hemoglobin-mediated lipid oxidation were investigated in washed cod muscle (WCM). Results indicated that PLA2 required calcium ion for both the hydrolyzing activity and the antioxidant effect. The abilities of PLA2 to inhibit lipid oxidation and suppress oxidation of Hb to form methemoglobin and ferryl hemoglobin were pH-dependent. The lag phase before lipid oxidation enters the exponential phase reciprocally shortened as more hemin was bound to the insoluble matrix of WCM. However, PLA2 was able to inhibit lipid oxidation without preventing the interaction between hemin and the insoluble matrix of the washed muscle., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Background: Hemoglobin (Hb) is a lipid oxidation promoter in fish muscle. Phospholipase A2 (PLA2; EC 3.1.1.4) is linked to an increased resistance to lipid oxidation of frozen-thawed cod fillets via an unknown mechanism. The present study aimed to investigate the mechanism of Hb-mediated lipid oxidation with a focus on ferryl Hb and methemoglobin (metHb), the pro-oxidative Hb species, and to examine how porcine pancreatic PLA2 inhibits Hb-mediated lipid oxidation in washed cod muscle (WCM). Lipid hydroperoxides (LOOHs) and thiobarbituric acid reactive substances (TBARS) were measured as primary and secondary lipid oxidation products, respectively. The formation of metHb and ferryl Hb was also monitored., Results: Ferryl Hb and metHb formed during the Hb-mediated lipid oxidation. PLA2 inhibited the formation of LOOHs and TBARS and suppressed the formation of metHb and ferryl Hb. WCM was pre-oxidized by hemin to increase the amount of LOOHs. PLA2 promoted the depletion of LOOHs in the pre-oxidized WCM with limited TBARS formation at the expense of the heme moiety of Hb., Conclusion: The results of the present study suggest that ferryl Hb may play a role in Hb-mediated lipid oxidation and that PLA2 from pig pancreas may work together with Hb as a novel antioxidant with an ability to remove pre-formed LOOHs from a lipid substrate. © 2017 Society of Chemical Industry., (© 2017 Society of Chemical Industry.)

Bovine hemolysate was purified by size exclusion chromatography, and one high molecular weight protein was detected relative to the hemoglobin (Hb) fraction. Purified Hb promoted lipid oxidation in washed muscle slightly but significantly better than hemolysate, which may have been due to the absence of catalase and peroxiredoxin in the purified Hb. Purified Hb auto-oxidized to metHb more rapidly than Hb in the hemolysate (P<0.05). OxyHb promoted lipid oxidation in washed muscle more effectively compared to oxyMb (P<0.05). This was ascribed to hemin, released from metHb, promoting lipid oxidation more readily than oxidative forms of Mb that retain their protoporphyrin moiety. A 3:1 ratio of Mb:Hb promoted lipid oxidation similarly compared to adding a 1:1 ratio of Mb:Hb to washed muscle. Lipid oxidation products due to Hb-mediated lipid oxidation were elevated 60-fold at pH 6.3 compared to pH 6.7., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Bovine myoglobin (Mb) auto-oxidized 11-fold faster at pH 5.7 compared to bovine hemoglobin (Hb). Replacement of Ser(F7) in bovine Mb with positively charged or large apolar residues decreased auto-oxidation rates (2- to 4-fold) in comparison with wild-type Mb (P < 0.05). However, the same substitutions increased hemin loss rate (15- to 28-fold), indicating that hydrogen bonding between Ser(F7) and the heme-7-propionate is critical for stabilizing protoporphyrin in the globin. The anchoring of Ser(F7) to the heme-7-propionate in the proximal pocket of Mb is suggested to expose the distal pocket to solvent molecules that accelerate auto-oxidation. The rate of hemin loss from metHb at pH 5.7 was 68-fold faster compared to metMb. The ability of Ser(F7) and His(FG3) in Mb to form stabilizing contacts with the heme-7-propionate maintains hemin within the globin whereas Leu(F7) and Leu(FG3) of Hb cannot form stabilizing contacts which results in low hemin affinity. MetHb promoted lipid oxidation more effectively in washed muscle at pH 5.7 compared to metMb (P < 0.05). The greater ability of bovine metHb to promote lipid oxidation is likely due to its enhanced rate of hemin dissociation compared to bovine metMb., (© 2015 Institute of Food Technologists®)

Electrostatic interactions between haemoglobin (Hb) and muscle components of fish may be an initial step of Hb-mediated lipid oxidation. This mechanism was investigated by examining the interaction of anionic HbIV and cationic HbI with insoluble components of washed cod mince under different pH and salt conditions. Lipid oxidation was monitored in parallel using the thiobarbituric acid reactive substances (TBARS) test. Higher binding of HbI to washed cod mince occurred compared to HbIV, yet HbIV better promoted lipid oxidation. An increase in pH from 5.7 to 6.3 and further to 7.0 lowered both Hb-binding and TBARS development. Addition of NaCl decreased Hb-binding but still did not influence Hb-mediated lipid oxidation. Thus, Hb binding had no consistent effect on lipid oxidation of washed cod mince. Rapid haemin release from the anionic Hb appeared to be a primary facilitator of lipid oxidation, overshadowing the greater binding ability of the cationic Hb., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

The recombinant streptococcal protein apoShp can be used as a probe for hemoglobin (Hb) reactivity in fish muscle due to its specific affinity for hemin that is released from Hb at post-mortem pH values. Hemin affinity measurements indicated that apoShp binds hemin released from Hb but not myoglobin (Mb). Hemin affinity of holoShp was higher at pH 5.7 compared to pH 8.0. This may be attributed to enhanced electrostatic interaction of His58 with the heme-7-propionate at lower pH. ApoShp readily acquired hemin that was released from trout IV metHb in the presence of washed cod muscle during 2 °C storage at pH 6.3. This was based on increases in redness in the washed cod matrix, which occurs when apoShp binds hemin that is released from metHb. ApoShp prevented Hb-mediated lipid oxidation in washed cod muscle during 2 °C storage. The prevention of Hb-mediated lipid oxidation by apoShp was likely due to bis-methionyl coordination of hemin that dissociated from metHb. This hexacoordination of hemin appears to prevent peroxide-mediated redox reactions, and there is no component in the matrix capable of dissociating hemin from Shp. ApoShp was also added to minced muscle from rainbow trout ( Oncorhynchus mykiss ) to examine the degree to which Hb contributes to lipid oxidation in trout muscle. Addition of apoShp inhibited approximately 90% of the lipid oxidation that occurred in minced trout muscle during 9 days of 2 °C storage on the basis of lipid peroxide, hexanal, and thiobarituric acid reactive substances (TBARS) values. These results strongly suggest that Hb is the primary promoter of lipid oxidation in trout muscle.

Antioxidative activities of phenolic compounds (caffeic acid, gallic acid and tannic acid; 200 ppm) in washed mince (pH 6), with added myoglobin (Mb) and haemoglobin (Hb), from bighead carp (Hypophthalmichthys nobilis), during 9 days of iced storage, were studied. Tannic acid exhibited the preventive effect on discolouration of washed mince containing Mb or Hb during storage (P<0.05). High peroxide value (PV) was found and large amount of, thiobarbituric acid-reactive substances (TBARS) and hexanal were formed in washed mince containing haem proteins, especially Hb. As determined by apo Streptococcal haem-associated protein, Hb had the lower haem affinity than Mb. Phenolic compounds, especially caffeic acid and gallic acid, could lower lipid oxidation induced by Mb or Hb throughout storage (P<0.05). Prevention of haem release, as well as inhibition of lipid oxidation induced by haem proteins with selected phenolic compounds, should be an alternative means in lowering discolouration and lipid oxidation in fish muscle., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

Fish hemoglobins (Hbs) frequently contain glycine at site E14 while mammalian Hbs contain larger residues (e.g., alanine and serine). These differences were examined by creating structural variants at E14 using recombinant bovine myoglobin (Mb) as a model heme protein that contains alanine at E14. The Ala(E14)Gly mutation increased k(ox) and hemin loss 3-fold and 45-fold, respectively. Glycine at E14 creates a channel for solvent to enter the heme crevice, which enhances autoxidation and hemin loss rates. Hydration of the proximal heme pocket facilitates hemin loss because protonation of the proximal histidine weakens the linkage of the imidazole group to the iron atom of the hemin moiety. Ala(E14)Gly promoted lipid oxidation in washed fish muscle more rapidly during iced storage compared to wild type Mb at pH 5.7. This suggested that the rapid hemin loss from Ala(E14)Gly accelerated lipid oxidation. Ala(E14)Ser and Ala(E14)Val had little effect on k(ox) but somewhat accelerated net hemin loss. These studies suggest that enhanced access of solvent to the heme crevice of many fish Hbs at site E14 facilitates rapid hemin loss and moderately accelerates autoxidation. This likely is part of the reason fish Hbs promote lipid oxidation much more effectively compared to mammalian Hbs.

The underlying stereochemical mechanisms for the dramatic differences in autooxidation and hemin loss rates of fish versus mammalian hemoglobins (Hb) have been examined by determining the crystal structures of perch, trout IV, and bovine Hb at high and low pH. The fish Hbs autooxidize and release hemin approximately 50- to 100-fold more rapidly than bovine Hb. Five specific amino acid replacements in the CD corner and along the E helix appear to cause the increased susceptibility of fish Hbs to oxidative degradation compared with mammalian Hbs. Ile is present at the E11 helical position in most fish Hb chains whereas a smaller Val residue is present in all mammalian alpha and beta chains. The larger IleE11 side chain sterically hinders bound O(2) and facilitates dissociation of the neutral superoxide radical, enhancing autooxidation. Lys(E10) is found in most mammalian Hb and forms favorable electrostatic and hydrogen bonding interactions with the heme-7-propionate. In contrast, Thr(E10) is present in most fish Hbs and is too short to stabilize bound heme, and causes increased rates of hemin dissociation. Especially high rates of hemin loss in perch Hb are also due to a lack of electrostatic interaction between His(CE3) and the heme-6 propionate in alpha subunits whereas this interaction does occur in trout IV and bovine Hb. There is also a larger gap for solvent entry into the heme crevice near beta CD3 in the perch Hb (approximately 8 A) compared with trout IV Hb (approximately 6 A) which in turn is significantly higher than that in bovine Hb (approximately 4 A) at low pH. The amino acids at CD4 and E14 differ between bovine and the fish Hbs and have the potential to modulate oxidative degradation by altering the orientation of the distal histidine and the stability of the E-helix. Generally rapid rates of lipid oxidation in fish muscle can be partly attributed to the fact that fish Hbs are highly susceptible to oxidative degradation., ((c) 2008 Wiley-Liss, Inc.)

Background: Hemoglobin and amino-terminal pro-brain natriuretic peptide (NT-proBNP) are both independent predictors of mortality in patients with chronic HF. Their combined predictive power for mortality in the setting of acute HF is uncertain., Methods: In an international prospective cohort design, we evaluated the relationships between hemoglobin, NT-proBNP, and 60-day mortality in 690 patients with acute HF., Results: The median hemoglobin for the entire cohort was 13.0 g/dL (interquartile range 11.6-14.3). The WHO criterion for anemia was met by 44% (n=305). The 60-day mortality rate for anemic patients was 16.4% vs. 8.8% in non-anemic patients (p<0.001). Anemia was an independent predictor of short-term mortality (OR=1.72, 95% CI=1.05-2.80, p=0.03), as was a NT-proBNP concentration >5180 pg/mL (OR=2.32, 95% CI=1.36-3.94 p=0.002). Consideration of four risk groups: not anemic/low NT-proBNP (reference group, n=220), anemic/low NT-proBNP (n=152), not anemic/high NT-proBNP (n=165), and anemic/high NT-proBNP (n=153) revealed respective 60-day mortality rates of 5.0% (referent), 9.2% (OR=1.93, 95% CI=0.85-4.36; p=0.12), 13.9% (OR=3.07, 95% CI=1.45-6.50, p=0.003), and 23.5% (OR=5.84, 95% CI=2.87-11.89, p<0.001)., Conclusions: Anemia was common in this cohort of subjects with acute HF and was related to adverse short-term outcome. Integrated use of hemoglobin and NT-proBNP measurements provides powerful additive information and is superior to the use of either in isolation.

Hemoglobin (Hb) promoted lipid oxidation more effectively in washed tilapia as compared to washed cod in spite of a 2.8-fold higher polyenoic index in the washed cod. This suggested that increasing the fatty acid unsaturation of the substrate did not accelerate the onset of lipid oxidation. Substantial phospholipid hydrolysis in the washed cod was observed, which has the potential to inhibit lipid oxidation. MetHb formation and lipid oxidation occurred more rapidly at pH 6.3 as compared to pH 7.4. Trout Hb autoxidized faster and was a better promoter of lipid oxidation as compared to tilapia Hb. The greater ability of trout Hb to promote lipid oxidation was attributed in part to its lower conformational and structural stability based on secondary and tertiary structure, acid-induced unfolding, and thermal aggregation measurements. It is suggested that the structural instability and lipid oxidation capacity of trout Hb were at least partly due to low hemin affinity. Trout and tilapia Hb were equivalent in their ability to cause lipid oxidation in washed cod muscle heated to 80 degrees C. Apparently, these high temperatures denature both trout and tilapia Hb to such an extent that any differences in conformational stability observed at lower temperatures were negated.

The hemoglobin variant rHb 0.1, which possesses a decreased ability to form subunits, stimulated lipid oxidation in washed fish muscle less effectively as compared to wild-type hemoglobin (rHb 0.0). This could be due to the lower hemin affinity and more rapid autoxidation rate of subunits as compared to tetramers. To differentiate between hemin affinity and autoxidation effects, ferrous V68T Mb was compared to ferrous wild-type myoglobin (WT Mb). WT Mb has a more rapid hemin loss rate (25-fold) than does V68T, while V68T autoxidized more rapidly than did WT Mb (60-fold). Ferrous WT Mb promoted TBARS and lipid peroxide formation more rapidly than did ferrous V68T (p < 0.01). This indicated hemin loss rate was more critical in determining onset of lipid oxidation as compared to autoxidation rate. Hemin alone was capable of stimulating lipid oxidation. Albumin enhanced the ability of hemin to promote lipid oxidation. MetMb promoted lipid oxidation more effectively than did ferrous Mb, which could be due to the lower hemin affinity of metMb as compared to that of ferrous Mb. EDTA, an iron chelator, had no effect on the rate or extent of lipid oxidation mediated by Mb in the cooked system. Variants with a 975-fold range of hemin affinities promoted lipid oxidation with equivalent efficacy in cooked washed cod contrary to results in uncooked washed cod. The cooking temperatures apparently denature the globin and release hemin reactant to such an extent that the impact of hemin affinity on lipid oxidation observed in the raw state is negated in the cooked state. These studies collectively suggest released hemin is of primary importance in promoting lipid oxidation in raw and cooked washed fish muscle.

The molecular mass of trout myoglobin was 16017 Da based on electrospray ionization mass spectrometry. A Root effect (low oxygen affinity at pH 6.3) was determined in trout hemoglobin but not myoglobin. At pH 6.3, myoglobin autoxidized more rapidly (3.5-fold) as compared to anodic hemoglobin. Anodic hemoglobin was a better catalyst of lipid oxidation in washed cod muscle as compared to myoglobin at pH 6.3. This suggested that some process other than met heme protein formation was the rate-limiting step in lipid oxidation processes. Heme loss rates were determined using the apomyoglobin mutant H64Y prepared from sperm whale. Anodic hemoglobin released its heme group much more rapidly than myoglobin. In comparisons of anodic and cathodic hemoglobins, heme loss rate better predicted the onset of lipid oxidation than autoxidation rate. These studies collectively suggest that heme dissociation has a primary role in the ability of different heme proteins to promote lipid oxidation processes.

Unheated press juice (PJ) obtained from chicken breast muscle was a potent inhibitor of hemoglobin-mediated lipid oxidation in washed cod muscle. The <1 kDa fraction had a negligible effect on the rate of lipid oxidation. The high-molecular-weight (HMW) fraction was mildly inhibitory when added alone and highly inhibitory in the presence of <1 kDa components. Proteins of the HMW fraction were further fractionated by ammonium sulfate precipitation. Proteins in the 80% fraction were most inhibitory compared with other precipitated fractions on an equal protein basis. Inhibition by PJ was substantially decreased due to treatment with ascorbate oxidase. Adding ascorbate to the HMW fraction did not increase its inhibition, which suggested the presence of a complex ascorbate-reducing system in PJ consisting of HMW and low-molecular-weight (LMW) components. The ability of added ceruloplasmin to inhibit lipid oxidation was remarkably enhanced by addition of ascorbate or the <1 kDa fraction. Heated and centrifuged PJ had 8 times more LMW iron compared to unheated PJ. Adding heated PJ to washed cod containing hemoglobin slightly increased the rate and extent of lipid oxidation.

Approximately 7% of the iron associated with hemoglobin was released from the heme protein during 2 degrees C storage in washed cod muscle. EDTA (2.2 mM) neither accelerated nor inhibited hemoglobin-mediated lipid oxidation based on the formation of lipid peroxides and TBARS. This suggested that low molecular weight iron was a minor contributor to hemoglobin-mediated lipid oxidation in washed cod muscle. Ascorbate (2.2 mM) was a modest to highly effective inhibitor of hemoglobin-mediated lipid oxidation depending on which washed cod preparation was assessed. Experimental evidence suggested that the ability of residual ascorbate to breakdown accumulating lipid hydroperoxides to reactive lipid radicals can explain the shift of ascorbate from an antioxidant to a pro-oxidant. Increasing the lipid peroxide content in washed cod muscle accelerated hemoglobin-mediated lipid oxidation and decreased the ability of ascorbate to inhibit lipid oxidation. Preformed lipid peroxide content in cod muscle was highly variable from fish to fish.

Beef hemoglobin (Hb) had lower levels of deoxyHb and autoxidized much slower as compared to trout Hb at pH 6.3. Chicken Hb autoxidized at a rate intermediate between beef and trout Hb. In the presence of hydrogen peroxide, metHb formed rapidly from trout Hb whereas beef Hb was essentially nonreactive with hydrogen peroxide. The autoxidation rate of perch Hb was more rapid than trout Hb despite the low deoxyHb content of perch Hb. Perch Hb was a better catalyst of lipid oxidation than trout Hb when added to washed cod muscle based on formation of lipid hydroperoxides and thiobarbituric acid reactive substances. These studies indicate that autoxidation rate does not always increase with increasing deoxyHb content. The role of heme crevice volume in heme protein autoxidation is discussed. Among other factors, these studies suggest that rates of lipid oxidation in various muscle foods may depend on the relative ability of hemoglobins from different animal species to promote lipid oxidation.

It was evaluated whether trout hemoglobin (Hb)-mediated oxidation of minced washed cod muscle lipids could be prevented by an aqueous isolate from cod and some other muscle sources. Lipid hydroperoxides and painty odor developed approximately 4 days faster in washed than unwashed cod mince. When adding back an aqueous fraction (press juice) isolated from unwashed mince to washed mince at 2-6-fold dilutions, development of hydroperoxides and painty odor was either delayed or completely prevented. The inhibitory substances were heat stable, and their effect was slightly reduced at reduced pH. The <1 kDa fractions of whole and heated press juices were as inhibitory as the unfractionated press juices. Inhibition by the unheated, heated, and ultrafiltered (30 kDa) press juices was lost after dialysis. These findings implied the presence of one or more highly effective aqueous low molecular weight antioxidants in cod muscle press juice. The same antioxidative properties were found in heated haddock, dab, and winter flounder muscle press juices but not in heated herring and chicken muscle press juices. Unheated chicken press juice was however highly inhibitory.

Hemoglobin-mediated lipid oxidation in washed, minced cod muscle was related to the triacylglycerol to membrane lipid ratio. The same rapid development of thiobarbituric acid reactive substances (TBARS) and painty odor occurred with and without the presence of up to 15% menhaden oil. Without hemoglobin, development of TBARS and painty odor was slow, despite a high amount of hydroperoxides in samples with oil added (1135 micromol/kg muscle). This suggested that hemoglobin reacted by cleaving preformed hydroperoxides into secondary oxidation products. Nearly doubling the hemoglobin concentration approximately doubled the extent of lipid oxidation with and without added oil. This indicated that hemoglobin was limiting for the oxidation reaction. The noneffect of added oil suggests that membrane lipids and/or preformed membrane lipid hydroperoxides provided sufficient substrate in hemoglobin-catalyzed oxidation of washed minced cod muscle. Fe(2+-)ADP did not induce any oxidation of washed minced cod with/without added oil. Results suggest that lipid oxidation in fatty fish may be more related to the quantity and type of the aqueous pro-oxidant and the membrane lipids than to variations in total fat contents.

Deoxyhemoglobin-mediated lipid oxidation was studied by comparing the pro-oxidative activity of anodic and cathodic hemoglobins from trout in a washed cod muscle model system. At pH 6.3, cathodic hemoglobins were nearly fully oxygenated while anodic hemoglobins were poorly oxygenated. Anodic hemoglobins initiated lipid oxidation in washed cod muscle much more rapidly than cathodic hemoglobins, as measured by thiobarbituric acid reactive substances (TBARS) formation. Moreover, anodic hemoglobins appeared to oxidize more rapidly as compared to cathodic hemoglobins in the washed cod muscle model system, as measured by a decrease in redness (a value). A more pronounced pro-oxidative activity of deoxyhemoglobin as compared to oxyhemoglobin was confirmed by accelerated lipid hydroperoxide and TBARS formation in the washed cod muscle model system upon combined addition of anodic hemoglobins and adenosine triphosphate, which is known to lower the oxygenation of anodic hemoglobins at pH 7.2, as compared to only addition of anodic hemoglobins to the washed cod muscle. These studies suggest that deoxyhemoglobin is more pro-oxidative than its oxygenated counterpart at pH values found in postmortem fish muscle.

There was a wide variation in the amounts of hemoglobin extracted from the muscle tissue of bled and unbled fish. Averaged values suggested that the residual blood level in the muscle of bled fish was substantial. Myoglobin content was minimal as compared to hemoglobin content in mackerel light muscle and trout whole muscle. Hemoglobin made up 65 and 56% of the total heme protein by weight in dark muscle from unbled and bled mackerel, respectively. Bleeding significantly reduced rancidity in minced trout whole muscle, minced mackerel light muscle, and intact mackerel dark muscle but not minced mackerel dark muscle stored at 2 degrees C. The reduction was in the number of fish that had a longer shelf life; muscle from certain bled fish had rancidity that was comparable to the rancidity in unbled controls. The soluble contents of erythrocytes accounted for all of the lipid oxidation capacity of whole blood added to washed cod muscle. Limiting lysis of erythrocytes delayed lipid oxidation, which was likely due to keeping hemoglobin inside the erythrocyte. Apparent breakdown of lipid hydroperoxides occurred only when a critical level of hemoglobin was present. Blood plasma was slightly inhibitory to oxidation of washed cod lipids. These studies suggest that blood-mediated lipid oxidation in fish muscle depends on various factors that include hemoglobin concentration, types of hemoglobin, plasma volume, and erythrocyte integrity.

The ability of Maillard reaction products (MRPs) to inhibit hemoglobin (Hb)‐mediated lipid oxidation is examined in washed cod muscle (WCM) and washed turkey breast muscle (WTM). Lipid peroxides and thiobarbituric acid reactive substances (TBARS) are used as markers of primary and secondary lipid oxidation products, respectively. MRPs inhibits Hb‐mediated lipid oxidation in WCM (p < 0.01) but are weakly inhibitory in WTM. α‐tocopherol concentration is 24‐fold greater in WCM compared to WTM. The elevated α‐tocopherol content of WCM may partly explain the enhanced antioxidant effectiveness of MRPs in WCM, noting that MRPs and α‐tocopherol act synergistically in the scavenging of free radicals. MRPs are more effective in inhibiting lipid oxidation in WCM at pH 6.6 compared to lower pH values. Antioxidant effectiveness of MRPs diminishes when stored refrigerated but not with frozen storage. MRPs obtained by 3 h heating contains more Maillard reaction intermediates than 2 h heating, which better inhibits LOOH formation (p < 0.01). These intermediates decrease faster during refrigerated compared to frozen storage. These studies suggest elevated pH and sufficient endogenous tocopherols are required for low concentrations of MRPs to protect highly unsaturated lipid in washed muscle from oxidation by hemoglobin. Practical Applications: This study shows that the maillard reaction products (MRPs) can be used to inhibit the oxidation of tocopherol‐rich meat products, and the MRPs stored in the frozen condition for a certain period also have antioxidant activity. [ABSTRACT FROM AUTHOR]

It is well documented that caffeic acid (3,4‐dihydroxycinnamic acid) (CA) interacts with and inhibits the oxidative reactions of myoglobin (Mb) and hemoglobin (Hb), and this interaction underlies its antioxidative action in meat. Sickle cell hemoglobin (HbS) is known for its tendency to oxidize more readily than normal HbA in the presence of hydrogen peroxide (H2O2), which leads to a more persistent and highly oxidizing ferryl Hb (HbFe4+). We have investigated the effects of CA on HbS oxidation intermediates, specifically on the ferric/ferryl forms. At a low concentration of H2O2 (0.5‐fold over heme), we observed a fivefold reduction in the amount of HbFe4+ accumulated in a mixture of ferric and H2O2 solution. Higher levels of H2O2 (onefold and twofold over heme) led to a lesser threefold and twofold reduction in the content of HbFe4+, respectively, possibly due to the saturation of the binding sites on the Hb molecule. The most intriguing finding was that when 5‐molar excess CA over heme was used, and a considerable increase in the delay time of HbS polymerization to approximately 200 s was observed. This delay in polymerization of HbS is theoretically sufficient to avoid microcapillary blockage and prevent vasoconstrictions in vivo. Mass spectrometry analysis indicated that CA was more extensively covalently bonded to βCys93 than to βCys112 and αCys104. The dual antioxidant and antisickling properties of CA may be explored further to maximize its therapeutic potential in SCD. [ABSTRACT FROM AUTHOR]

Abstract: The effect of a membrane permeable metal chelator, N′,N′,N′,N′-tetrakis(2-pyridylmethyl)-ethylenediamine (TPEN) on iron and hemoglobin-mediated lipid oxidation in washed cod muscle was evaluated. TPEN stimulated added iron-mediated lipid oxidation in washed cod muscle (pH 6.3) while ethylenediaminetetraacetic acid (EDTA) did not. TPEN delivered iron to cellular membranes of cod muscle more effectively compared to EDTA (p<0.05). Fe–TPEN remained intact in the presence of excess EDTA which indicated that TPEN had a relatively high affinity for iron. TPEN also promoted lipid hydroperoxide (LOOH) formation in washed cod alone, presumably by chelating and thereby activating endogenous metals. LOOH and hydrogen peroxide formation due to Fe–TPEN may partly explain the observation that TPEN accelerated trout hemoglobin-mediated lipid oxidation in cod muscle. Peroxides accelerate oxidation of hemoglobin (Hb). Oxidized trout Hb readily releases hemin that efficiently decomposes LOOH to free radicals that, in turn, incur oxidation of polyunsaturated fatty acids. These studies indicate that TPEN activates low molecular weight metals that are endogenously present in washed cod and facilitates transport of metals to cellular membranes which exacerbates the ability of hemoglobin to promote lipid oxidation. [Copyright &y& Elsevier]

Abstract: Hemopexin (Hx) was isolated from pig blood using hemin-agarose chromatography. The effect of addition of Hx on hemin and hemoglobin (Hb) mediated lipid oxidation in washed cod muscle was investigated during iced storage at pH 5.5. At a 1:1 ratio of Hx to hemin, lipid oxidation as measured by development of thiobarbituric acid reactive substances (TBARS) was not significantly inhibited (p = 0.12). This may be attributed to a lack of hemin binding by Hx due to influence of pH and hemin precipitation. At a 1:2 ratio of Hx to Hb on a heme basis, TBARS development was significantly inhibited (p < 0.01) but not prevented. Equimolar addition of bovine serum albumin (BSA) in place of Hx did not inhibit TBARS development (p = 0.43). Hemin release from porphyrin-containing Hx, i.e. holoHx, and ferric sperm whale myoglobin (Mb) was measured at 37 °C, pH 5.7. Hemin release rates of 0.27 h−1 and 0.05 h−1, were calculated for holoHx and Mb, respectively. While the hemin affinity of Hx was greater than published values for trout Hb, the relatively low value measured for Hx compared to Mb may be caused by a combination of low pH and the absence of NaCl in the assays. [Copyright &y& Elsevier]

pH can be manipulated to alter the oxidative stability of fish-based foods during storage. X-ray diffraction was used to investigate the ability of reduced pH to cause structural changes in fish hemoglobins that lead to enhanced oxidative degradation. Decreasing pH from 8.0 to 6.3 and 5.7 created a large channel for solvent entry into the heme crevice of perch hemoglobin beta chains. The proton-induced opening of this channel occurred between site CD3 and the heme-6-propionate. Solvent entry into the heme crevice can enhance metHb formation and hemin loss, processes that accelerate lipid oxidation. Reduced pH also decreased the distance between Ile at E11 in one of the alpha chains and the ligand above the heme iron atom. This sterically displaces O2 and protonated O2 which increases metHb formation. These studies demonstrate that pH reduction causes structural changes in perch hemoglobin which increase oxidative degradation of the heme pigment. [ABSTRACT FROM AUTHOR]

Deoxyhemoglobin content was measured in hemoglobins from trout, chicken and bovine sources between pH 5.5 and 7.5. With decreasing pH, deoxyhemoglobin content of trout was highest, low to intermediate in chicken, and lowest in beef hemoglobin. Each type of hemoglobin was added to washed cod muscle and lipid oxidation assessed during 2 °C storage. The lipid oxidation rate was trout >> chicken > beef based on thiobarbituric reactive substances (TBARS) and lipid hydroperoxide formation. There was no significant difference in pro-oxidative activity of chicken compared to turkey hemoglobin. Hemoglobins from trout appeared to oxidize more rapidly compared to chicken hemoglobin in the washed cod muscle model system, as measured by a decrease in redness (a-value) during storage. Loss of red color was slowest in beef samples. These studies suggest that deoxyhemoglobin may be a major catalyst of lipid oxidation at post mortem pH values found in muscle foods, especially in fish and poultry compared to beef. [Copyright &y& Elsevier]

Reduced trout haemoglobin (Hb) is a mixture of oxy- and deoxy-Hb at pH 6.3. Addition of oxy/deoxyHb to washed muscle resulted in detectable ferryl Hb while adding bovine oxyHb, trout metHb, or bovine metHb did not. Trout metHb promoted lipid oxidation more rapidly than bovine metHb, attributable to lower haemin affinity in fish Hbs. Protoporphyrin IX degradation was prevalent during trout and bovine Hb-mediated lipid oxidation. Caffeic acid prevented porphyrin degradation and lipid oxidation. Crosslinked myoglobin (Mb) promoted lipid oxidation more effectively than metMb. Fish metMb released haemin more readily than mammalian metMb at pH 5.5. These studies suggest haemin dissociation from metHb causes formation of free radicals that degrade protoporphyrin and cause lipid oxidation, and appreciable quantities of deoxyHb are needed to generate ferryl Hb oxidant. Crosslinking appears to facilitate Mb-mediated lipid oxidation in washed muscle yet haemin release can occur from fish metMb at low pH. [ABSTRACT FROM AUTHOR]

Abstract: Caffeic acid (CA) accelerated methemoglobin (Hb) formation at pH5.8 and 25°C. This was attributed to electron donation from CA to liganded O2 in Hb. CA inhibited hemin dissociation from metHb. Pig Hb remained mostly as oxyHb and did not promote lipid oxidation in washed cod muscle (WCM) nor washed turkey muscle (WTM) during iced storage at pH5.8. Conversely, perch Hb rapidly was converted to metHb and readily promoted lipid oxidation based on lipid peroxide and hexanal formation. CA strongly inhibited perch Hb-mediated lipid oxidation during storage. Once metHb formation occurred in WCM, CA appeared to maintain the heme protein as metHb during the remainder of iced storage. CA may have become bound to perch Hb based on filtration analysis. CA facilitated the transfer of perch Hb (but not pig Hb) from the aqueous phase to the insoluble components of WCM. Collectively, these results suggest that CA inhibited Hb-mediated lipid oxidation by various mechanisms not related to inhibition of metHb formation. [Copyright &y& Elsevier]