Effect of glutathione on oxymyoglobin oxidation

The oxidation of oxymyoglobin (OxyMb) to metmyoglobin (MetMb) is responsible for fresh meat discoloration. Glutathione (GSH) is an important tripeptide reductant that can protect lipid and protein from oxidation. The objective of this research was to investigate the effect of GSH on MetMb formation in vitro and in bovine skeletal muscle cytosol. Equine MetMb formation was greater in the presence of GSH than controls at pH 5.6 or 7.2 and 25 or 37 degrees C (p < 0.05); GSH addition to purified bovine OxyMb solution also resulted in more MetMb formation at pH 7.2 and 25 or 37 degrees C (p < 0.05). This effect on MetMb formation was partly or completely inhibited by EDTA or catalase in the GSH-equine OxyMb system (p < 0.05). The addition of GSH to bovine muscle cytosol inhibited MetMb formation at pH 5.6 or 7.2 and 4 or 25 degrees C (p < 0.05); the effect was concentration-dependent. The inhibitory effect was observed in a high molecular weight (HMW) but not low molecular weight fraction of cytosol at pH 7.2 and 25 degrees C (p < 0.05); there was no effect when HMW was heated at 90 degrees C for 15 min. These results suggest the antioxidant effect of GSH on bovine OxyMb is dependent on heat-sensitive HMW cytosolic component(s).     

alpha,beta-unsaturated aldehydes accelerate oxymyoglobin oxidation.

This study investigates the potential basis for enhancement of oxymyoglobin (OxyMb) oxidation by lipid oxidation products. Aldehydes known to be formed as secondary lipid oxidation products were combined with OxyMb in aqueous solution at 37 degrees C and pH 7.4. Metmyoglobin (MetMb) formation was greater in the presence of alpha,beta-unsaturated aldehydes than their saturated counterparts of equivalent carbon chain length. Additionally, increasing chain length from hexenal through nonenal resulted in increased MetMb formation (P < 0.05). Electrospray ionization mass spectrometry (ESI-MS) revealed that OxyMb incubated with 4-hydroxynonenal (HNE) at pH 7.4 at 37 degrees C yielded myoglobin molecules adducted with one to three molecules of HNE from 0.5 to 2 h of incubation, respectively. A prooxidant effect of HNE was noted at pH 7.4 but was not apparent at pH 5.6 when compared to the control (P < 0.05). This appeared to be due to rapid OxyMb autoxidation at this pH compared to pH 7.4. ESI-MS demonstrated that adduction of HNE to OxyMb occurred at pH 5.6. This research demonstrates that alpha, beta-unsaturated aldehydes accelerate OxyMb oxidation and appear to do so via covalent attachment.     

Effect of aldehyde lipid oxidation products on myoglobin

The effects of aldehyde lipid oxidation products on myoglobin (Mb) were investigated at 37 degrees C and pH 7.2. Oxymyoglobin (OxyMb) oxidation increased in the presence of 4-hydroxynonenal (4-HNE) compared to controls (P < 0.05). Preincubation of metmyoglobin (MetMb) with aldehydes rendered the heme protein a poorer substrate for enzymatic MetMb reduction compared to controls, and the effect was inversely proportional to preincubation time; unsaturated aldehydes were more effective than saturated aldehydes (P < 0.05). The order of MetMb reduction as affected by preincubation was control > hexanal > heptanal > octanal > nonanal = decanal = hexenal > heptenal = octenal > nonenal = decenal = 4-HNE (P < 0.05). Preincubation of MetMb with 4-HNE enhanced the subsequent ability of the heme protein to act as a prooxidant in both liposomes and microsomes when compared to controls (P < 0.05); the effect was reduced in microsomes containing elevated concentrations of alpha-tocopherol (P < 0.05). MetMb preincubation with mono-unsaturated aldehydes enhanced the catalytic activity of MetMb to a greater degree than saturated aldehydes (P < 0.05). These results suggest that aldehyde lipid oxidation products can alter Mb stability by increasing OxyMb oxidation, decreasing the ability of MetMb to be enzymatically reduced and enhancing the prooxidant activity of MetMb.     

Effect of heating oxymyoglobin and metmyoglobin on the oxidation of muscle microsomes

Myoglobin (Mb) and its iron have been proposed to be major prooxidants in cooked meats. To understand the mechanisms and differentiate between the prooxidant and antioxidant potential of oxymyoglobin (OxyMb) and metmyoglobin (MetMb), their prooxidant activity, iron content, solubility, free radical scavenging activity, and iron binding capacity were determined as a function of thermal processing. The ability of native and heat denatured OxyMb and MetMb to promote the oxidation of muscle microsomes was different. MetMb promoted lipid oxidation in both its native and denatured states. Conversely, OxyMb became antioxidative when the protein was heated to temperatures >or=75 degrees C. The increased antioxidant activity of heat denatured OxyMb was likely due to a decrease in its prooxidative activity due to its loss of solubility. These data show that the impact on oxidative reactions of Mb is the result of the balance between its antioxidant and prooxidant activities.     

Postmortem oxygen consumption by mitochondria and its effects on myoglobin form and stability

The objective of this study was to assess the morphological integrity and functional potential of mitochondria from postmortem bovine cardiac muscle and evaluate mitochondrial interactions with myoglobin (Mb) in vitro. Electron microscopy revealed that mitochondria maintained structural integrity at 2 h postmortem; prolonged storage resulted in swelling and breakage. At 2 h, 96 h, and 60 days postmortem, the mitochondrial state III oxygen consumption rate (OCR) and respiratory control ratio decreased with time at pH 7.2 and 5.6 (p < 0.05). Mitochondria isolated at 60 days did not exhibit ADP-induced transitions from state IV to state III oxygen consumption. Tissue oxygen consumption also decreased with time postmortem (p < 0.05). Mitochondrial oxygen consumption was inhibited by decreased pH in vitro (p < 0.05). In a closed system, mitochondrial respiration resulted in decreased oxygen partial pressure (pO(2)) and enhanced conversion of oxymyoglobin (OxyMb) to deoxymyoglobin (DeoMb) or metmyoglobin (MetMb). Greater mitochondrial densities caused rapid decreases in pO(2) and favored DeoMb formation at pH 7.2 in closed systems (p < 0.05); there was no effect on MetMb formation (p > 0.05). MetMb formation was inversely proportional to mitochondrial density at pH 5.6 in closed systems. Mitochondrial respiration in open systems resulted in greater MetMb and DeoMb formation at pH 5.6 and pH 7.2, respectively, vs controls (p < 0.05). The greatest MetMb formation was observed with a mitochondrial density of 0.5 mg/mL at both pH values in open systems. Mitochondrial respiration facilitated a shift in Mb form from OxyMb to DeoMb or MetMb, and this was dependent on pH, oxygen availability, and mitochondrial density.     

Redox instability induced by 4-hydroxy-2-nonenal in porcine and bovine myoglobins at pH 5.6 and 4 degrees C

Myoglobin (Mb) redox stability affects meat color and is compromised by lipid oxidation products such as 4-hydroxy-2-nonenal (HNE). Pork lipids are generally more unsaturated and would be expected to oxidize readily and produce more oxidation products than beef. Supranutritional supplementation of vitamin E improves Mb redox stability of beef but not pork. The present study investigated HNE-induced redox instability in porcine and bovine myoglobins at 4 degrees C and pH 5.6. Oxymyoglobin (OxyMb) was incubated with HNE (0.075 mM porcine OxyMb + 0.5 mM HNE; 0.15 mM bovine OxyMb + 1.0 mM HNE). In porcine Mb, only monoadducts formed via Michael addition were detected after 72 h, whereas in bovine Mb both mono- and diadducts were identified. LC-MS-MS identified four histidine residues (His 36, 81, 88, and 152) of bovine Mb that were readily adducted by HNE, whereas in porcine Mb only two histidine residues (His 24 and 36) were adducted. These results suggested that the primary structure of bovine Mb predisposes it to greater nucleophilic attack by HNE and subsequent adduction than is suffered by porcine Mb.     

Mitochondrial reduction of metmyoglobin: dependence on the electron transport chain

Reduction of ferric myoglobin (metmyoglobin, MetMb) to its ferrous form is important for maintaining fresh meat color because only reduced myoglobin can bind oxygen to form the consumer-preferred cherry red color in fresh meat. The objective of this study was to characterize an apparent mitochondria electron transport chain (ETC)-linked pathway for MetMb reduction in vitro. MetMb was reduced in the presence of mitochondria and succinate (p < 0.05); mitochondria or succinate alone did not facilitate MetMb reduction relative to controls (p > 0.05). Flushing samples with oxygen greatly decreased MetMb reduction, while flushing with argon increased MetMb reduction when compared with controls (p < 0.05). ETC inhibitors were used to localize the site where electrons became available for MetMb reduction. MetMb reduction was increased by rotenone addition and decreased by malonic acid (p < 0.05); the reduction was completely abolished by additions of antimycin A or myxothiazol when compared with controls (p < 0.05). These results suggest that electrons become available for MetMb reduction at a site(s) between complex III and IV. Mitochondrial ETC-linked MetMb reduction increased with increased mitochondrial density and succinate concentration (p < 0.05); the greatest MetMb reduction was observed at pH 7.2 and 37 degrees C, and ETC-linked MetMb reducing activity decreased with time postmortem (p < 0.05). These results indicate that ETC-linked MetMb reduction exists but would be minimally active in postmortem muscles.     

Characterization of polyphenol oxidase from the Manzanilla cultivar (Olea europaea pomiformis) and prevention of browning reactions in bruised olive fruits

The crude extract of the polyphenol oxidase (PPO) enzyme from the Manzanilla cultivar (Olea europaea pomiformis) was obtained, and its properties were characterized. The browning reaction followed a zero-order kinetic model. Its maximum activity was at pH 6.0. This activity was completely inhibited at a pH below 3.0 regardless of temperature; however, in alkaline conditions, pH inhibition depended on temperature and was observed at values above 9.0 and 11.0 at 8 and 25 degrees C, respectively. The thermodynamic parameters of substrate oxidation depended on pH within the range in which activity was observed. The reaction occurred according to an isokinetic system because pH affected the enzymatic reaction rate but not the energy required to carry out the reaction. In the alkaline pH region, browning was due to a combination of enzymatic and nonenzymatic reactions that occurred in parallel. These results correlated well with the browning behavior observed in intentionally bruised fruits at different temperatures and in different storage solutions. The use of a low temperature ( approximately 8 degrees C) was very effective for preventing browning regardless of the cover solution used.     

Species-specific myoglobin oxidation

The effect of the lipid oxidation product, 4-hydroxy-2-nonenal (HNE), on oxidation of oxymyoglobin (OxyMb) from seven different meat-producing species was investigated. Relative to controls, HNE increased OxyMb oxidation within all species (p < 0.05) at both 25 and 4 °C, pH 5.6. The relative effect of HNE was greater for myoglobins (Mbs) that contained 12 ± 1 histidine (His) residues than for those that contained 9 His residues (p < 0.05); HNE efficacy in all species except chicken and turkey decreased with time. Mono-HNE adducts were detected in all species except chicken and turkey. In general, HNE alkylation increased the Mbs' ability to accelerate lipid oxidation in a microsome model. However, neither an HNE nor a Mb species dependent effect was observed. Results suggested that microsome model system associated lipid oxidation overshadowed HNE and species effects on OxyMb oxidation observed in lipid-free systems.     

基于高光谱技术的猪肉肌红蛋白含量无损检测

为充分利用猪肉光谱与图像信息,实现猪肉肌红蛋白含量的在线检测,该研究提出一种基于深度学习模型的猪肉肌红蛋白含量无损检测方法。采用高光谱设备采集冷藏过程中猪肉高光谱图像,通过ENVI5.3选择图像感兴趣区域（Region Of Interest,ROI）,分别提取ROI平均光谱信息与主成分图像信息。利用卷积自动编码器（Convolutional Auto Encoder,CAE）提取光谱与图像信息深度特征,分别建立光谱特征、图像特征及图-谱融合特征与肌红蛋白含量之间关系的卷积神经网络（Convolutional Neural Network,CNN）预测模型。其中基于融合深度特征CNN预测模型准确度较高,该模型对脱氧肌红蛋白（DeoMb）、氧合肌红蛋白（OxyMb）、高铁肌红蛋白（MetMb）含量预测集决定系数分别为：0.964 5、0.973 2、0.958 5,预测集均方根误差 RMSEP分别为：0.015 8、0.226 6、0.381 6。为进一步验证图-谱融合特征与猪肉肌红蛋白存在对应关系,分别建立偏最小二乘回归（Partial Least Squares Regression,PLSR）、支持向量机回归（Support Vector Regression,SVR）预测模型。结果表明：CAE能充分提取图像与光谱特征;基于融合特征建立回归模型能提高肌红蛋白含量预测精度,相比于光谱信息与图像信息,以MetMb为例其分别提高5.42%、16.12%。该检测方法为肉类质量在线检测提供参考,具有好的应用前景。     

Effects of pulsed electric fields on the quality of orange juice and comparison with heat pasteurization

Effects of pulsed electric fields (PEF) at 35 kV/cm for 59 micros on the quality of orange juice were investigated and compared with those of heat pasteurization at 94.6 degrees C for 30 s. The PEF treatment prevented the growth of microorganisms at 4, 22, and 37 degrees C for 112 days and inactivated 88% of pectin methyl esterase (PME) activity. The PEF-treated orange juice retained greater amounts of vitamin C and the five representative flavor compounds than the heat-pasteurized orange juice during storage at 4 degrees C (p < 0.05). The PEF-treated orange juice had lower browning index, higher whiteness (L), and higher hue angle (theta) values than the heat-pasteurized orange juice during storage at 4 degrees C (p < 0. 05). The PEF-treated orange juice had a smaller particle size than the heat-pasteurized orange juice (p < 0.05). degrees Brix and pH values were not significantly affected by processing methods (p > 0. 05).     

The effect of freezing and aldehydes on the interaction between fish myoglobin and myofibrillar proteins

The interaction between fish myoglobin (Mb) and natural actomyosin (NAM) extracted from fresh and frozen fish was studied. The quantity of soluble Mb in Mb-NAM extracted was less in frozen than in fresh fish (P < 0.05). However, no differences were observed in Mb that remained in solution following preparation of Mb-NAM from frozen whole fish vs frozen fillets (P > 0.05). MetMb formation in Mb-NAM was generally greater than that observed in control Mb (P < 0.05); the greatest MetMb content occurred in Mb-NAM extracted from frozen whole fish (P < 0.05). The effect of different aldehyde oxidation products on the interaction between fish Mb and NAM was also studied in vitro. The loss of soluble Mb from NAM:Mb preparations was greater in the presence of hexenal and hexanal (P < 0.05) relative to controls, and the degree of solubility loss varied with aldehyde type. Hexenal caused greater OxyMb oxidation than hexanal (P < 0.05). Whiteness of washed NAM and NAM-Mb mixtures decreased following aldehyde addition (P < 0.05). In the absence of Mb, the Ca2+ -ATPase activity of NAM was lower with added hexenal than with hexanal (P < 0.05). However, no differences in Ca2+ -ATPase activity between hexanal and hexenal-treated samples were observed when Mb was present (P > 0.05). Reducing and nonreducing sodium dodecyl sulfate-polyacrylamide gel electrophoresis analyses suggested that both disulfide and nondisulfide covalent linkages contributed to aldehyde-induced cross-linking between Mb and myofibrillar proteins.     

Effects of cationic species on visual color formation in model Maillard reactions of pentose sugars and amino acids

Effects of cationic species on Maillard browning were examined after heating (ca. 100 degrees C) aqueous pH 7.2 buffered solutions of amino acids and pentose sugars. Metallic ions of Group I metals (Li, Na, K, Rb and Cs) produced a small increase in browning (A420), but somewhat greater effects were observed with ions of Group II metals Ca and Mg. Browning was suppressed by triethylammonium ion, but unaffected by a salt of the stronger base, guanidine. The quaternary amine salt choline chloride produced enhanced browning and served as a model for phospholipid involvement in Maillard reactions. With alpha,omega-diamino acids increases in browning were observed which related to lowered pK2 values resulting from positively charged omega-substituents in these molecules.     

Heat-induced, metal-catalyzed oxidative degradation of quercetin and rutin (Quercetin 3-O-rhamnosylglucoside) in aqueous model systems

The oxidative degradation of quercetin and rutin in phosphate buffer solutions, pH 8.0, at 97 degrees C, was studied by means of UV-vis spectroscopy and reversed-phase high-performance liquid chromatography (HPLC). The effect of the transition metal ions Fe(2+) and Cu(2+) on degradation rate and browning development was also assessed. It was shown that both flavonols are very labile to thermally induced degradation under oxidative conditions. Fe(2+) and Cu(2+) caused an increase in the degradation rate, as well as an increase in browning (A(420)). Significant differences were observed in the degradation mechanisms, as implied by HPLC analyses. It is postulated that metal ions promote flavonol oxidation through reactive oxygen species formation, whereas increases in browning could be ascribed to oxidation and metal-polyphenol interactions.     

Maintaining quality of fresh-cut mangoes using antibrowning agents and modified atmosphere packaging

Treatments to inhibit browning and decay and prolong shelf life of fresh-cut mangoes were investigated. Combinations of antibrowning agents and modified atmosphere packaging (MAP) resulted in a reduction of browning and deterioration of fresh-cut mangoes stored at 10 degrees C. Combinations of several browning inhibitors were more effective than those applied individually. Among these treatments, solutions containing 4-hexylresorcinol (0.001 M) (HR) plus potassium sorbate (0.05 M) (KS) and HR plus KS plus D-isoascorbic acid (0.5 M) (ER) reduced changes in color (L, a, and b) and microbial growth and did not affect sensory characteristics of fresh-cut mangoes. In general, these treatments did not affect significantly the changes in organic acids and sugar content of slices during the 14 days of storage at 10 degrees C. High humidity created in the in-package atmosphere alleviated tissue dryness and was an important factor in the ability of the antibrowning solutions to prevent browning and decay. It appears that the maintenance of quality of fresh-cut mangoes is more related to particular combinations of the antibrowning agents used rather than the modified atmosphere created inside the package. HR + ER + KS treatment in combination with MAP could be used to inhibit browning, decay, and deterioration of fresh-cut mangoes.     

Characterization of polyphenol oxidase and peroxidase and influence on browning of cold stored strawberry fruit

Polyphenol oxidase and peroxidase were extracted from two different varieties of strawberry fruit (Fragaria x ananassa D, cv. 'Elsanta' and Fragaria vesca L, cv. 'Madame Moutot') and characterized using reliable spectrophotometric methods. In all cases, the enzymes followed Michaelis-Menten kinetics, showing different values of peroxidase kinetics parameters between the two cultivars: Km = 50.68 +/- 2.42 mM ('Elsanta') and 18.18 +/- 8.79 mM ('Madame Moutot') mM and Vmax = 0.14 +/- 0.03 U/g ('Elsanta') and 0.05 +/- 0.01 U/g ('Madame Moutot'). The physiological pH of fruit at the red ripe stage negatively affected the expression of both oxidases, except polyphenol oxidase from 'Madame Moutot' that showed the highest residual activity (68% of the maximum). Peroxidase from both cultivars was much more thermolable as compared with PPO, losing over 60% of relative activity already after 60 min of incubation at 40 degrees C. The POD activation energy was much lower than the PPO activation energy (DeltaE = 97.5 and 57.8 kJ mol-1 for 'Elsanta' and 'Madame Moutot', respectively). Results obtained from d-glucose and d-fructose inhibition tests evidenced a decreasing course of PPO and POD activities from both cultivars as the sugar concentration in the assay medium increased. Changes in CIE L*, a*, b*, chroma, and hue angle values were taken as a browning index of the samples during storage at 4 degrees C. A decrease in L* was evident in both cultivars but more marked in 'Elsanta'. PPO and POD activities from cv. 'Elsanta' were very well-correlated with the parameter L* (r2=0.86 and 0.89, respectively) and hue angle (r2=0.85 and 0.93, respectively). According to these results, the browning of the fruit seemed to be in relation to both oxidase activities.     

Heat-induced aggregation of whey proteins: comparison of cheese WPC with acid WPC and relevance of mineral composition

Heat-induced aggregation of whey proteins in solutions made from two commercial whey protein concentrates (WPCs), one derived from mineral acid whey (acid WPC) and the other from cheese whey (cheese WPC), was studied using polyacrylamide gel electrophoresis (PAGE), size exclusion chromatography (SEC), and transmission electron microscopy (TEM). Heat treatment (75 degrees C) of acid WPC solutions (12.0%, w/w, pH 6.9) resulted in formation of relatively small "soluble" aggregates that were predominantly disulfide-linked. By contrast, heat treatment of the cheese WPC solutions (under the same conditions) caused formation of relatively large aggregates, containing high proportions of aggregates linked by noncovalent associations. The rate of aggregation of both beta-lactoglobulin and alpha-lactalbumin at 75 degrees C, measured as the loss of native proteins by PAGE, was higher in the cheese WPC solution than in the acid WPC solution. Cross dialysis of the two WPC solutions resulted in alteration of the mineral composition of each WPC solution and reversing their heat-induced aggregation behavior. The results demonstrated that the mineral composition is very important in controlling the aggregation behavior of WPC products.     

Hydrolytic products and kinetics of triazophos in buffered and alkaline solutions with different values of pH

The hydrolysis of triazophos was studied in buffered solutions in the range of pH 4-10 and in sodium hydroxide solutions with pH values up to 12. The results showed that the degradation of triazophos in the above solutions followed simple pseudo-first-order kinetics. At 35 degrees C, the rate constants in buffered solutions ranged from 0.0222 d(-1) at pH 4 to 0.5357 d(-1) at pH 10, and increased to 0.6251 h(-1) in 0.01 mol/L sodium hydroxide solution. The results also indicated that the base-catalysis was more important than acid-catalysis in the hydrolysis of triazophos. On the basis of the Arrhenius plot, the calculated activation energy (E(a)) and the frequency factor (A) for the hydrolysis of triazophos in buffered solution of pH 10 were 78.6 kJ/mol and 1.13 x 10(13) d(-1), respectively. Hydrolytic products of triazophos in buffered solutions of pH 4 and 10, as well as in sodium hydroxide solution of pH 11, were identified as their corresponding trimethylsilyl derivatives with a gas chromatography-mass spectrometer (GC-MS). The possible hydrolytic pathways of triazophos were also proposed.     

Comparative study on pressure and temperature stability of 5-methyltetrahydrofolic acid in model systems and in food products

A comparative study on the pressure and temperature stability of 5-methyltetrahydrofolic acid (5-CH(3)-H(4)folate) was performed in model/buffer systems and food products (i.e., orange juice, kiwi puree, carrot juice, and asparagus). Effects of pH and ascorbic acid (0.5 mg/g) on 5-CH(3)-H(4)folate stability in buffer systems were studied on a kinetic basis at different temperatures (from 65 to 160 degrees C) and different pressure/temperature combinations (from 100 to 700 MPa/from 20 to 65 degrees C). These studies showed that (i) the degradation of 5-CH(3)-H(4)folate in all model systems could be described by first-order reaction kinetics, (ii) the thermostability of 5-CH(3)-H(4)folate was enhanced by increasing pH up to 7, (iii) 5-CH(3)-H(4)folate was relatively pressure stable at temperatures lower than 40 degrees C, and (iv) ascorbic acid enhanced both the thermo- and barostabilities of 5-CH(3)-H(4)folate. In food products, temperature and pressure stabilities of 5-CH(3)-H(4)folate were studied at different temperatures (70-120 degrees C) and different pressure/temperature combinations (from 50 to 200 MPa/25 degrees C and 500 MPa/60 degrees C). 5-CH(3)-H(4)folate in orange juice and kiwi puree was relatively temperature (up to 120 degrees C) and pressure (up to 500 MPa/60 degrees C) stable in contrast to carrot juice and asparagus. Addition of ascorbic acid (0.5 mg/g) in carrot juice resulted in a remarkable protective effect on pressure (500 MPa/60 degrees C/40 min) and temperature degradation (120 degrees C/40 min) of 5-CH(3)-H(4)folate.     

Interactions between mitochondrial lipid oxidation and oxymyoglobin oxidation and the effects of vitamin E

Off-flavor and discoloration of meat products result from lipid oxidation and myoglobin (Mb) oxidation, respectively, and these two processes appear to be interrelated. The objective of this study was to investigate their potential interaction in mitochondria and the effects of mitochondrial alpha-tocopherol concentrations on lipid oxidation and metmyoglobin (MetMb) formation in vitro. The addition of ascorbic acid and ferric chloride (AA-Fe(3+)) increased ovine and bovine mitochondrial lipid oxidation when compared with their controls (p < 0.05); MetMb formation also increased with increased lipid oxidation relative to controls (p < 0.05). Reactions containing Mb and mitochondria with greater alpha-tocopherol concentrations demonstrated less lipid oxidation and MetMb formation than mitochondria with lower alpha-tocopherol concentrations. Greater mitochondrial alpha-tocopherol concentration was also correlated with increased mitochondrial oxygen consumption in vitro and with a more pronounced effect at pH 7.2 than at pH 5.6. Relative to controls, succinate addition to bovine mitochondria resulted in increased concentrations of ubiquinol 10 and alpha-tocopherol and decreased lipid and Mb oxidation (p < 0.05). Mitochondrial lipid oxidation was closely related to MetMb formation; both processes were inhibited by alpha-tocopherol in a concentration-dependent manner.