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.

Divergent Reactivity of Hemoglobin Isoforms α2Aß2 and α2Dß2 from Meleagris gallopavo in Native and Fatty Acid-Modified States.

Meleagris gallopavo (turkey) coexpresses distinct hemoglobin (Hb) isoforms, Hb α2Aß2 (HbA) and α2Dß2 (HbD), at a ratio of ∼3:1 (HbA:HbD). Herein, the reactivities of HbA and HbD were investigated in their native and free fatty acid (FFA)-modified states. Results indicated that HbD displays elevated autoxidation (kox) and an increased propensity to oxidize lipids in its reduced (oxy) and oxidized (met) forms. Interestingly, metHbD displayed less heme-globin cross-linking compared to HbA. Regarding FFA-modified Hb, we found that an FFA mixture and linoleic acid (LA) produced a bis-histidyl ferric (Bis-His) Hb species, decreasing the ability of Hb to oxidize lipids. Using molecular docking, we found LA to hydrogen bond with ß Arg C6, found at the α1ß2 interface, but the extent of Bis-His formation differs between HbA and HbD. Our findings suggest HbA displays elevated oxidative stability compared to HbD and that FFA may act as allosteric effectors of metHb.

Exploring the potential effect of phospholipase A2 antibody to extend beef shelf-life in a beef liposome model system.

The objective of this study was to elucidate the effect of phospholipase A2 (PLA2) and a PLA2 antibody (aPLA2) on phospholipid (PL) hydrolysis in beef and to understand how the altered PL composition may affect lipid oxidation and antioxidant capacity of beef in an in vitro system. Various combinations of PLA2 and aPLA2 were introduced to a beef liposome model system and exposed to a retail display. The PL and free fatty acid (FFA) profiles, antioxidant capacity and lipid oxidation were measured for the liposome system. Key PL classes were reduced and the release of polyunsaturated FFAs was increased with the inclusion of PLA2 in the treatments (P < 0.05). There was no inhibition of PL hydrolysis with the addition of aPLA2. PLA2 showed strong antioxidant capacity in the liposome system (P < 0.01), but lipid oxidation still increased in samples treated with PLA2 throughout the retail display (P < 0.01). Finally, aPLA2 treatments demonstrated potential to decrease lipid oxidation (P < 0.01).

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

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.

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.

Paradoxical effects of lipolysis on the lipid oxidation in meat and meat products.

Lipolysis in meat and meat products is a phenomenon involving hydrolysis of lipids, notably via enzymatic catalysis that takes place even postmortem. During refrigerated and frozen storage of meat, in particular fish, endogenous lipolytic enzymes actively degrade triacylglycerols and phospholipids resulting in accumulation of free fatty acids and other hydrolytic products. A classical conjecture suggests that lipolysis enhances lipid oxidation which is involved in quality deterioration of fresh meat and, to some degrees, flavor development of certain meat products. Recent studies (<5 years) have shown that under some circumstances, lipolysis of certain lipolytic enzymes can inhibit lipid oxidation in muscle models, which provides more insight in lipid oxidation mechanisms in muscle matrices as well as implies potential strategies for improving meat quality. This review will discuss such paradoxical effects and potential mechanisms of lipolysis on lipid oxidation in meat and meat products.

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 ß-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.

Lipid oxidation and antioxidant delivery systems in muscle food.

Lipid oxidation accelerates quality deterioration in muscle-based foods (fish, red meat, and poultry), resulting in off-odors/flavors, color problems, texture defects, and safety concerns. Adding antioxidants is one approach to control lipid oxidation, and several delivery strategies have been applied, such as supplementing antioxidants to the feed, direct mixing into minces, or, for whole muscle pieces; spraying, glazing, and injection. However, some issues linked to these technologies hinder their wide utilization, such as low effectiveness, noncompatibility with clean label, and off-flavor. These shortcomings have promoted the development of new antioxidant delivery technologies. In this review, the main focus is on the principles, characteristics, and implementation of five novel antioxidant delivery methods in different types of muscle food products. Their advantages and drawbacks are also summarized, plus comments about future trends in this area. Among novel routes to deliver antioxidants to muscle foods are, for whole tissues, recyclable dipping solutions; for minces, encapsulation; and, for both minces and whole tissues, cross-processing with nonmuscle antioxidant-containing raw materials as well as applications of edible films/coatings and active packaging. Advantages of these technologies comprise, for example, low price, the possibility to control the antioxidant release rate, overcoming strong aromas from natural antioxidants, and allowing antioxidant-containing raw materials from the food industry to be valorized, providing an opportunity for more circular food production.

Caffeic acid: an antioxidant with novel antisickling properties.

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 (H2 O2 ), 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 H2 O2 (0.5-fold over heme), we observed a fivefold reduction in the amount of HbFe4+ accumulated in a mixture of ferric and H2 O2 solution. Higher levels of H2 O2 (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 ßCys93 than to ßCys112 and αCys104 . The dual antioxidant and antisickling properties of CA may be explored further to maximize its therapeutic potential in SCD.

Hexanal as a Predictor of Development of Oxidation Flavor in Cured and Uncured Deli Meat Products as Affected by Natural Antioxidants.

Effectiveness of commercial natural antioxidants from rosemary and green tea were investigated in deli-style meat products via headspace hexanal by solid-phase microextraction gas chromatography and sensory oxidation flavor by a trained panel at weeks 1, 7, and 13 of refrigerated storage. A water/oil-soluble rosemary extract at 400 mg/kg proved the most effective antioxidant in cured deli turkey (CDT). In chicken fillet (CF), a water-soluble rosemary extract at 400 mg/kg was most efficient, especially in combination with phosphate. In pulled pork (PP), none of the antioxidants were as efficient as phosphate, though all three tested antioxidants were moderately effective in PP without phosphate. Nitrite was such an efficient antioxidant on its own in CDT that hexanal levels were so low that it was not possible to build correlation models between headspace hexanal and sensory oxidation flavor throughout the storage period. Phosphate also proved very efficient on its own in both CF and PP. It was possible to build good correlation models throughout storage for both CF and PP. Hence, hexanal was found to satisfactorily predict development of oxidation flavor in different types of uncured deli meat products both with and without added phosphate.

Vascular infusion with concurrent vascular rinsing on color, tenderness, and lipid oxidation of hog meat.

Market hogs were conventionally chilled (CN, n = 12) or Rinse & Chill® processed (RC, n = 13, MPSC Inc.). Muscles (Longissimus lumborum, LL; picnic shoulder, PS) were processed (chops, ground), packaged, and displayed or stored in the dark. Color, pH, moisture fat free (MFF), expressible moisture (EM), oxygen consumption, Warner-Bratzler shear (WBS), total pigment, TBARS, and hexanal content were determined. RC generally resulted in a lower pH during the first 4 h compared to CN. RC compared to CN had lower fat, but were not different in moisture fat free, expressible moisture, and total pigments. RC did not affect cooler shrink, cook loss and WBS force. RC PS was redder than RC LM. RC had greater deoxymyoglobin than CN on 7 d display. RC chops (LL) were lighter and had less deoxymyoglobin compared to CN. RC ground pork had greater oxygen consumption, lower TBARS and hexanal values compared to CN. RC has the potential to improve color and reduce lipid oxidation.

Impact of lipid composition and muscle microstructure on myoglobin-mediated lipid oxidation in washed cod and pig muscle.

The roles of lipid oxidation substrates and muscle microstructure in lipid oxidation were investigated in two muscle models (cod and pig). Added myoglobin (Mb) promoted lipid oxidation in washed cod muscle (WCM) but not in washed pig muscle (WPM). The differing microstructure of WCM e.g. more exposed fat cells or membrane of muscle cells compared to the "denseness" or "wrapped" structure of WPM, may have contributed to the better ability of Mb to facilitate lipid oxidation in the WCM. Added phospholipids with polyenoic indexes of 282 and 24 activated Mb as an oxidant similarly in WPM while added neutral lipids and added free fatty acids had little effect. It is suggested that muscle microstructure and accessibility of Mb to phospholipids play critical roles in relation to Mb-mediated lipid oxidation while the degree of unsaturation in the phospholipids was less important.

Mechanisms involved in the inhibitory effects of free fatty acids on lipid peroxidation in turkey muscle.

The pro-oxidant and anti-oxidant effects of free fatty acids (FFA) in meat remain ambiguous. To clarify the role of FFA in lipid oxidation of muscle food, the FFA was added into two systems (turkey mince and washed turkey muscle (WTM)) and lipid oxidation was investigated. A mixture of FFA inhibited lipid oxidation in both systems. The absorbance spectrum of oxyHb and metHb was determined in the presence of C18:1 and C18:2. Conversion to hemichrome spectra was observed and was particularly rapid when metHb was mixed with C18:2. C18:2 was also reacted with metHb followed by a chromatography step to remove unbound C18:2, and termed 'modified Hb'. Electron spin resonance (ESR) spectra of the modified Hb was indicative of hemichrome formation. The modified Hb did not promote lipid oxidation in washed turkey muscle during storage. This suggested that hemichrome formation due to added FFA diminished the lipid oxidation capacity of Hb.

Factors influencing the antioxidant effect of phospholipase A2 against lipid oxidation promoted by trout hemoglobin and hemin in washed muscle.

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.

Presence of lipid oxidation products in swine diet lowers pork quality and stability during storage.

Studies examining the effects of feeding lipid oxidation products (LOPs) to pigs on pork quality and storage stability have mostly focused on refrigerated storage and produced mixed results. We investigated the effects of adding yellow grease, containing commercially relevant levels of LOPs, to swine diets on quality and storage stability of ground salted pork. Twenty-four domestic pigs were divided into three study groups and fed the following diet regimens for five months: (1) Standard Diet (STD), (2) STD + yellow grease (YG, high LOPs), or (3) STD + corn oil (CO, negligible LOPs). Post-harvest carcass characteristics and the effects of frozen and refrigerated storage on color and lipid oxidation of salted pork patties were studied. While feeding of yellow grease had no impact on color, it increased the susceptibility of pork patties to lipid oxidation during storage (186% and 73% higher accumulation of LOPs in patties from pigs fed STD + YG when compared to those fed STD and STD + CO, respectively).

Exogenous phospholipase A2 affects inflammatory gene expression in primary bovine mammary epithelial cells.

This Research Communication addresses the hypothesis that exogenously administered phospholipase A2 (PLA2) affects the inflammatory responses of bovine mammary epithelial cells (bMEC) in vitro with the aim of providing preliminary justification of investigation into the uses of exogenously administered PLA2 to manage or treat bovine mastitis. Primary bMEC lines from 11 lactating Holstein dairy cows were established and the expression of 14 pro-inflammatory genes compared under unchallenged and lipopolysaccharide (LPS)-challenged conditions, with and without concurrent treatment with bovine pancreatic PLA2G1B, a secreted form of PLA2. No differences in the expression of these genes were noted between PLA2-treated and untreated bMEC under unchallenged conditions. Following LPS challenge, untreated bMEC exhibited significant downregulation of CXCL8, IL1B, CCL20, and CXCL1. In contrast, PLA2-treated bMEC exhibited significant downregulation of IL1B and CCL20 only. These findings indicate that exogenous PLA2 affects the expression of some pro-inflammatory factors in immune-stimulated bMEC, but does not influence the constitutive expression of these factors. Further investigation of the influence of exogenous PLA2 in the bovine mammary gland is justified.

Hemolysis, tocopherol, and lipid oxidation in erythrocytes and muscle tissue in chickens, ducks, and turkeys.

Muscle from turkeys is more sensitive to lipid oxidation during post mortem storage compared with that of chicken and duck which may involve increased lysis of turkey erythrocytes that releases hemoglobin oxidant. Three separate experiments were conducted to study characteristics of chicken, duck, and turkey erythrocytes in which dietary tocopherols were standardized. In Experiment I, tocopherol, fatty acid composition, and lipid oxidation capacity were measured in erythrocytes from chickens, ducks, and turkeys. Tocopherol content was greater in chicken erythrocytes compared with that of duck and turkey (P < 0.05). Oleic and linoleic acid content was higher in chicken erythrocytes compared with that of turkey (P < 0.05). Lipid oxidation capacity of erythrocytes in washed turkey muscle (WTM) at pH 5.8 ranked chicken > duck > turkey (P < 0.05). In Experiment II, hemolysis was measured in erythrocytes from turkeys and chickens. Detergent-induced hemolysis (pH 7.4) was on average 12-fold greater for turkey erythrocytes compared with that of chicken (P < 0.05). In Experiment III, the ability of lysed and non-lysed erythrocytes to promote lipid oxidation was examined. Lysed erythrocytes promoted lipid oxidation in WTM more effectively than intact erythrocytes (P < 0.05). Reasons that turkey erythrocytes were more labile to detergent-induced hemolysis whereas chicken erythrocytes more effectively promoted lipid oxidation in the WTM model system are discussed. These studies describe variation in chemical and physical properties of erythrocytes from chickens, ducks, and turkeys that can influence progression of lipid oxidation in poultry muscle.

Mechanisms involved in hemoglobin-mediated oxidation of lipids in washed fish muscle and inhibitory effects of phospholipase A2.

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.

Factors Affecting Lipid Oxidation Due to Pig and Turkey Hemolysate.

Turkey hemolysate promoted lipid oxidation in washed muscle more effectively than pig hemolysate, which was partly attributed to the greater ability of H2O2 that formed during auto-oxidation to oxidize the avian hemoglobin (Hb). Turkey and pig hemolysate (2.5 µM Hb) exposed to 10 µM H2O2 oxidized to 48% and 4% metHb, respectively. Catalase activity, which converts H2O2 to water, was elevated in the pig hemolysate. The larger difference in Hb oxidation when comparing turkey and pig hemolysate in washed muscle (relative to their auto-oxidation rates) suggested that lipid oxidation products facilitated formation of metHb. Turkey metHb released hemin more readily than pig metHb, which coincided with turkey metHb promoting lipid oxidation more effectively than pig metHb. Ferryl Hb was not detected during storage of turkey or pig hemolysate in washed muscle, which suggested a minor role for hypervalent forms of Hb in the oxidation of the lipids.

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

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.