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1.
The antioxidative effect of herring (Clupea harengus) light muscle press juice (PJ) against hemoglobin-(Hb-) mediated oxidation of washed cod mince during ice storage was tested. The PJ was fractionated into low-molecular-weight (LMW; <1 [corrected] kDa) and high-molecular-weight (HMW; >1, >3.5, and > 50 kDa) fractions; it was preheated (10 min, 100 degrees C) and tested with or without removing heat coagulated proteins. Its antioxidative effect was compared with that given by endogenous levels of two tentative antioxidant candidates: ascorbic acid and uric acid. Oxidation was followed by determining rancid odor, peroxide value, and redness. Whole herring PJ and the LMW-PJ fraction significantly (p < 0.001) extended the oxidation lag phase of controls, from 2 up to 8 and 7 days, respectively. The HWM-PJ fractions were significantly (p < 0.05) less efficient than the whole and LMW-PJ samples, giving only 3.5-4.5 days of lag phase. Heat-treated PJ, with and without the heat-coagulated proteins, gave 7 and 5 days of oxidation lag phase, respectively. Heating different batches of the LMW-PJ fraction grouped the results into two categories: one where heating almost fully destroyed the antioxidative activity (fractions prepared from spring-caught herring) and another where heating had no or a minor effect (fractions prepared from fall-caught herring). The spring LMW-PJ had low ascorbic acid levels (18-42.6 microM), and 50-100% were destroyed by the heating. In fall LMW-PJ, the levels were 76.2-137.6 microM, and only 43-51% were destroyed. Ascorbic acid fortification of heated spring LMW-PJ to reach the levels found in the corresponding unheated spring LMW-PJ sample and the heated fall LMW-PJ gave back most of the antioxidative activity, which proved an important role of ascorbic acid for the antioxidative activity of LMW-herring PJ. This conclusion is drawn despite the fact that pure solutions with endogenous levels of ascorbic acid (giving 8.4-19.6 microM in final model) only very slightly delayed Hb-mediated oxidation of the washed cod mince.  相似文献   

2.
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.  相似文献   

3.
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.  相似文献   

4.
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.  相似文献   

5.
The effect of a low molecular weight (<5kDa, LMW) and a high molecular weight (>5kDa, HMW) humic fractions on surface redox activities of oat roots was studied. Oxidation of the electron donor NADH and reduction of the artificial electron acceptor ferricyanide [K3Fe(CN)6] exogenously supplied to the roots both alone or in combination, was measured in the presence or absence of soil humic substances. HMW humic fraction inhibited NADH oxidation either in the presence or absence of ferricyanide, while LMW humic fraction inhibited NADH: ferricyanide oxidoreductase activity due to the contemporary addition of the two redox compounds to the solution bathing the roots. NADH: ferricyanide oxido‐reduction was partially due to the release of substances from the roots. However, the presence of soil humic fractions (LMW or HMW) did not significantly modify this behaviour. Rather, the inhibitory effect of soil humic substances was even more evident when the oxidoreduction solely due to the root activity was considered. The results confirm the presence of multiple types of oxidoreductase activities at the surface of oat roots and show that the two humic fractions HMW and LMW may differently affect these activities. Partial inhibition of NADH oxidase activity is interpreted as a possible way of interference of humic substances with metabolic processes involved in cell wall formation. The effects on surface redox activities are discussed in terms of the role of soil humic substances in promotion of plant growth.  相似文献   

6.
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.  相似文献   

7.
The effect of pH and hemoglobin on oxidation of the microsomal lipids of cod was determined in isolated microsomes and in washed cod muscle. An increase of hemoglobin concentration from 0.5 to 15 microM accelerated lipid oxidation in both systems. In cod microsomes the rate of lipid oxidation increased in the order pH 6.8 > pH 7.6 > pH 8.4 > pH 6.0 > pH 3.5. However, in washed cod muscle a decrease of pH from 7.8 to 6.8 greatly increased the lag phase and decreased the rate of lipid oxidation. A further decrease in pH to 3.5 decreased the lag phase and increased the rate of lipid oxidation further. A decrease of pH from 7.6 to 6.4 greatly reduced the affinity of hemoglobin for oxygen. Formation of methemoglobin due to autoxidation occurred more rapidly at pH 6.0 than at pH 7.5. Structural changes of the isolated microsomal membranes could be the reason for the unexpected slow lipid oxidation in microsomes at pH 6.0 and below.  相似文献   

8.
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.  相似文献   

9.
The use of washed cod light muscle minces in mechanistic studies of hemoglobin (Hb)-mediated fish lipid oxidation has largely increased in the past 5 years. Although cod light muscle has a low level of intrinsic lipid oxidation catalysts, a prerequisite for a good oxidation model system, we believe it cannot fully mimic the oxidation kinetics taking place in other fish species being more susceptible to lipid oxidation. The aim of this study was to systematically investigate whether washed mince model systems useful in Hb-mediated oxidation studies could be prepared also from herring (Clupea harengus) and salmon (Salmo salar) light muscles. The kinetics of oxidation in the washed models was measured during ice storage (+/-Hb), and the results were related to compositional differences. Minces from cod, herring, and salmon light muscles were washed 3 times with 3 volumes of water and buffer. A 20 microM portion of Hb and 200 ppm streptomycin was then added, followed by adjustment of pH and moisture to 6.3 and 86%, respectively. Samples with or without Hb were then stored on ice, and oxidation was followed as peroxide value (PV), rancid odor, redness (a*) loss and yellowness (b*). Prior to storage, all minces and models were also analyzed for total lipids, fatty acids, alpha-tocopherol, proteins, Hb, Fe, Cu, and Zn. Hb-mediated lipid oxidation appeared within 2 days on ice in all models. Small differences in the oxidation rates ranked the models as herring > cod > salmon. These differences were ascribed to more preformed peroxides and trace elements in the herring model, and more antioxidants in the salmon model. Controls, without Hb, stayed stable in all cases except herring, where a very slight oxidation appeared, especially if the herring raw material had been prefrozen. In conclusion, fattier fish like dark muscle species and salmonoids are useful for making washed mince model systems and would be a better choice than cod if there is an interest in the oxidation kinetics of such species.  相似文献   

10.
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.  相似文献   

11.
Deoxyhemoglobin-mediated lipid oxidation in washed fish muscle   总被引：1，自引：0，他引：1  
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.  相似文献   

12.
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.  相似文献   

13.
Effect of glutathione on oxymyoglobin oxidation   总被引：4，自引：0，他引：4  
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).  相似文献   

14.
The aqueous fraction (press juice, PJ) from herring muscle was recently shown to inhibit hemoglobin-mediated oxidation of washed fish mince lipids during ice storage. As a first step to evaluate potential in vivo antioxidative effects from herring PJ, the aim of this study was to investigate whether herring PJ retains its antioxidative capacity during a simulated gastrointestinal (GI) digestion. Press juice from whole muscle (WMPJ) and light muscle (LMPJ) was mixed with pepsin solution followed by stepwise pH adjustments and additions of pancreatin and bile solutions. Digestive enzymes were removed from samples by ultrafiltration (10 kDa). Before, during, and after digestion, samples were analyzed for their peptide content and for antioxidative properties with the oxygen radical absorbance capacity (ORAC) and the low-density lipoprotein (LDL) oxidation assays. From 0 to 165 min of digestion, the content of <10 kDa peptides in WMPJ and LMPJ samples increased 12- and 7-fold, respectively. Further, both samples got approximately 12.5 times higher ORAC values and gave rise to approximately 1.3-fold increased lag phase in Cu2+-induced LDL oxidation. The largest changes in peptide content, ORAC values, and LDL oxidation inhibition occurred between 30 and 75 min of digestion, indicating that these parameters might be interrelated. When comparing analytical data obtained after 165 min of digestion with data obtained from analyses of native nondigested PJs, it was found that the data on peptide content, ORAC, and LDL oxidation from digested PJs were 64-69%, 121-161%, and 112-115%, respectively, of those of nondigested PJs. The study thus showed that enzymatic breakdown of PJ proteins under GI-like conditions increases the peroxyl radical scavenging activity and the potential to inhibit LDL oxidation of herring PJs. These data provide a solid basis for further studies of uptake and in vivo activities of herring-derived aqueous antioxidants.  相似文献   

15.
Variants of sperm whale myoglobin (Mb) were used to assess the mechanism of heme protein-mediated lipid oxidation in washed cod muscle. A myoglobin variant with high hemin affinity (V68T) was an exceptionally poor promoter of lipid oxidation, while a Mb variant with low hemin affinity (H97A) was a potent promoter of lipid oxidation. V68T releases hemin slowly due to the ability of threonine to hydrogen bond with coordinated water and the distal histidine within the heme crevice. H97A rapidly releases hemin because the relatively small alanine residue creates a channel for water to easily enter the heme crevice which weakens the covalent linkage of hemin to the proximal histidine. A variant sensitive to heme degradation (L29F/H64Q) was a weaker promoter of lipid oxidation compared to wild-type Mb. This suggests that degrading the heme ring and releasing iron decreased the ability of Mb to promote lipid oxidation. Free radicals resulting from hemin-mediated decomposition of lipid hydroperoxides have the capacity to propagate lipid oxidation and degrade hemin catalyst. This may explain why heme proteins behave as reactants rather than "catalysts" of lipid oxidation in washed cod. Collectively these studies strongly suggest that released hemin is the critical entity that drives heme protein-mediated lipid oxidation in washed fish muscle.  相似文献   

16.
Reactive oxygen species (ROS) can cause oxidative stress, which has been linked to various diseases. It has been suggested that antioxidant-rich foods can reduce such oxidative stress. However, the lack of suitable model systems to screen for in vivo effects of food-derived antioxidants has prevented a clear consensus in this area. In this study, the aim was to use a single-cell model system (human monocyte) to evaluate whether certain pure antioxidants and complex muscle extracts (herring light muscle press juice, PJ) could prevent ROS formation under in vivo like conditions. ROS were excreted from the monocytes upon stimulation with phorbol myristate acetate and were then detected as isoluminol-enhanced chemiluminescence (CL). Adding 2000 units of catalase and 50 units of superoxide dismutase to the monocytes model lowered the CL response by 35 and 86%, respectively. Ascorbate (14.1 mM) lowered the response by 99%, alpha-tocoperhol (188 microM) by 37%, and Trolox (50 microM) by almost 100%. Crude herring PJ gave a dose-dependent reduction in the CL response. At 10, 100, and 1000 times dilution, the PJ reduced the CL signal by 93, 60.5, and 10.6%. PJ fractionated into low molecular weight (LMW) (<1000 Da) and high molecular weight (>3500 Da) fractions decreased the CL response by 52.9 and 71.4%, respectively, at a 100-fold dilution. Evaluation of the PJ samples in the oxygen radical absorbance capacity test indicated that proteins may be the primary radical scavenging compounds of PJ, whereas the ROS-preventing effect obtained from the LMW fraction may also be attributed to other mechanisms. Thus, this study proved that the monocyte assay can be a useful tool for studying whether food-derived antioxidants can limit ROS production under physiologically relevant conditions. It also showed that herring contains numerous aqueous compounds demonstrating antioxidative effects in the monocyte model system.  相似文献   

17.
High molecular weight (HMW) or low molecular weight (LMW) subunits of different chemical state (reduced, reoxidized with KBrO3, or KIO3) or gliadins were added in 1% amounts to a base flour of the wheat cultivar Rektor and mixed with water. The corresponding doughs were then characterized by microscale extension tests and by microbaking tests and were compared to doughs from the base flour without additives. The maximum resistance of dough was strongly increased by HMW subunits in a reduced state and by HMW subunits reoxidized with KBrO3. A moderate increase of resistance was caused by HMW subunits reoxidized with KIO3 and by LMW subunits reoxidized with KBrO3 or KIO3. This resistance was strongly lowered by LMW subunits in a reduced state and by gliadins. The extensibility of dough was significantly increased only by gliadins and reduced HMW subunits; HMW subunits reoxidized with KBrO3 had no effect, and all other fractions had a decreasing effect. In particular, glutenin subunits reoxidized with KIO3 induced marked decrease of extensibility, resulting in bell‐shaped curve extensigrams, which are typical for plastic properties. The effect of reoxidized mixtures (2:1) of HMW and LMW subunits on maximum resistance depended on the oxidizing agent and on the conditions (reoxidation separated or together); extensibility was generally decreased. Bread volume was increased by addition of HMW subunits (reduced or reoxidized with KBrO3) and decreased by LMW subunits (reoxidized with KBrO3 or KIO3) and by a HMW‐LMW subunit mixture (reoxidized with KBrO3). The volume was strongly decreased by addition of reduced LMW subunits. A high bread volume was related to higher values for both resistance and extensibility.  相似文献   

18.
Water‐soluble β‐glucan (BG) extracted from a high‐BG oat line was treated with different amounts of lichenase (1→3)(1→4)‐β‐d ‐glucanase) enzyme to yield three different molecular weight (MW) BG extracts. Low (LMW‐BG, 157,000), medium (MMW‐BG, 277,000), and high (HMW‐BG, 560,000) MW BG extracts were added to plain muffin formulations at a level of 0.52% (0.42% in the batter, 0.52% in the resultant muffins) to investigate the effect of MW of BG on textural and bile acid (BA) binding properties of the muffins. In addition, treatments were prepared containing LMW‐BG, MMW‐BG, and HMW‐BG extracts in amounts providing equivalent batter firmness as determined on a texture analyzer. Resultant BG concentrations (and per serving amounts) of these muffins were 1.36% (0.81 g/60 g muffin), 1.05% (0.63 g/60 g muffin), and 0.52% (0.31 g/60 g muffin), respectively; thus, the LMW treatment complied with a U.S. Food and Drug Administration health claim requiring 0.75 g of BG per serving. The firmness, springiness, and BA‐binding capacity of the muffins were unaffected by the MW of BG. However, when added at the maximum limit for equivalent batter firmness, the LMW treatment was more firm and less springy than the HMW treatment. Furthermore, BA‐binding capacities of LMW and MMW fractions tended to be greater than that of the HMW fraction when added at the maximum limit. These results add further evidence to the importance of fine‐tuning BG structure to provide maximum health benefits while maintaining high product quality.  相似文献   

19.
Protein oxidation in fish meat is considered to affect negatively the muscle texture. An important source of free radicals taking part in this process is Fenton's reaction dependent on ferrous ions present in the tissue. The aim of this study was to investigate the susceptibility of cod muscle proteins in sarcoplasmic and myofibril fractions to in vitro metal-catalyzed oxidation and to point out protein candidates that might play a major role in the deterioration of fish quality. Extracted control proteins and proteins subjected to free radicals generated by Fe(II)/ascorbate mixture were labeled with fluorescein-5-thiosemicarbazide (FTSC) to tag carbonyl groups and separated by two-dimensional gel electrophoresis. Consecutive visualization of protein carbonyl levels by capturing the FTSC signal and total protein levels by capturing the SyproRuby staining signal allowed us to quantify the relative change in protein carbonyl levels corrected for changes in protein content. Proteins were identified using MALDI-TOF/TOF mass spectrometry and homology-based searches. The results show that freshly extracted cod muscle proteins exhibit a detectable carbonylation background and that the incubation with Fe(II)/ascorbate triggers a further oxidation of both sarcoplasmic and myofibril proteins. Different proteins exhibited various degrees of sensitivity to oxidation processes. Glyceraldehyde 3-phosphate dehydrogenase (GAPDH), nucleoside diphosphate kinase B (NDK), triosephosphate isomerase, phosphoglycerate mutase, lactate dehydrogenase, creatine kinase, and enolase were the sarcoplasmic proteins most vulnerable to ferrous-catalyzed oxidation. Moreover, NDK, phosphoglycerate mutase, and GAPDH were identified in several spots differing by their pI, and those forms showed different susceptibilities to metal-catalyzed oxidation, indicating that post-translational modifications may change the resistance of proteins to oxidative damage. The Fe(II)/ascorbate treatment significantly increased carbonylation of important structural proteins in fish muscle, mainly actin and myosin, and degradation products of those proteins were observed, some of them exhibiting increased carbonylation levels.  相似文献   

20.
Instrumental measurement of redness loss (decrease in a* value) was evaluated as a tool to follow hemoglobin (Hb)-mediated lipid oxidation in fish muscle. Two washed cod mince model systems were used (prepared at pH 6.5 and 5.5), both fortified with 15 micromol/kg of trout Hb and adjusted to pH 6.5 and 81% moisture. The rate of oxidation was varied through pH alterations (pH 6.1 and 6.9) and addition of an antioxidative cod muscle press juice. During ice storage, TBARS, painty odor, and a* values were followed. In all "oxidizing" samples, a* values correlated well with TBARS and painty odor development; r = -0.95 and -0.77, respectively. In press juice containing samples, the correlation was lower (0.55 for a vs TBARS) because there was a slight a* value decrease even in the absence of measurable lipid oxidation. a* values distinguished between "oxidizing" and stable samples within 1 day, before any lipid oxidation products could be chemically detected. It was confirmed in an aqueous phosphate buffer model system that the redness loss corresponded to a buildup of brownish met-Hb at the expense of oxy- and deoxy-Hb. The a* value data were best used as a lipid oxidation index by calculating the rate of decrease (k value) in the "initial phase" of the redness loss (before accumulation of lipid oxidation products) or in the "differentiation phase" (during the exponential raise in TBARS/painty odor). Calibration to lipid oxidation products must, however, be made for each specific sample type. Washing method, pH, Hb-type, etc., all affected both k values and absolute a* readings. Small yellowness (b*) increases also occurred along with a value losses, possibly the result of polymerized Schiff bases.  相似文献   

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