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1.
An emerging model to test antioxidants for application in seafoods is washed cod mince fortified with hemoglobin (Hb) as a catalyst. This system has been used to test the antioxidative activity of certain muscle extracts and some pure compounds such as BHA, BHT, TBHQ, and propyl gallate during ice storage. However, the washed cod mince model has occasionally been resistant to Hb-mediated oxidation. This has been in cases when the moisture of the model has been minimized by washes at the protein isoelectric point (pH approximately 5.5) to allow for large additions of potentially antioxidative solutions. In this paper, noncontrollable and controllable factors for this intriguing occasional oxidation resistance were studied. Compositional analyses (lipid content, alpha-tocopherol, and lipid hydroperoxides) and structural analysis of a "normal" oxidizing model and a stable model were done to identify any differences among them. Some controllable factors related to the model preparation that were studied included different washing pH values (5.5-6.6), Hb concentrations (7.2 and 13.5 microM), final model moisture contents (75, 81, and 90%), and light exposure during ice storage (0 h, 3-4 h, or 24 h of light/day). Results revealed a 2-fold higher alpha-tocopherol content in the stable model than in the oxidizing model. Electron microscopy images showed a more and less disrupted myofibrillar structure in the stable and the oxidizing cod model, respectively. This indicated that "cold setting" (i.e., pre-gelation) of the stable model may have occurred and prevented Hb from diffusing freely in the model. Controllable factors that reduced lipid oxidation in the models were less Hb and lower moisture.  相似文献   

2.
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   

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.
The effectiveness of a white grape dietary fiber concentrate (WGDF) against hemoglobin-mediated oxidation of washed cod mince, with and without 10% added herring oil, was evaluated during ice storage. WGDF was added at two different levels: 2 and 4% based on final weight. An ethanol extract with the ethanol extractable polyphenols (EPP) and the ethanol-extracted grape dietary fiber residue were also tested as antioxidants in the washed cod mince. The addition of WGDF to the model system completely and significantly (p 相似文献   

5.
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   

6.
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   

7.
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   

8.
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   

9.
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   

10.
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   

11.
Lipid pro-oxidative properties and deoxygenation/autoxidation patterns of hemoglobins from nonmigratory white-fleshed fish (winter flounder and Atlantic pollock) and migratory dark-fleshed fish (Atlantic mackerel and menhaden) were compared during ice storage at pH 7.2 and 6. A washed cod mince model system and a buffer model system were used for studying lipid changes and hemoglobin changes, respectively. TBARS and painty odor were followed as markers for lipid oxidation. At pH 6, all four hemoglobins were highly and equally active as pro-oxidants. At pH 7.2, pro-oxidation by all hemoglobins except that from pollock was slowed down, and activity ranked as pollock > mackerel > menhaden > flounder. The higher catalytic activities of the hemoglobins at pH 6 than at pH 7.2 corresponded with higher formation of deoxyhemoglobin and methemoglobin. Pollock had the most extensive formation of deoxy- and methemoglobin at both pH values, which could explain its high catalytic activity. The pro-oxidative differences among the other hemoglobins at pH 7.2 did not correlate with deoxygenation and autoxidation reactions. This indicates involvement of other structural differences between the hemoglobins such as differences in the heme-crevice volume. It is suggested that a biological reason for the species differences was their adaptations to different depths/water temperatures.  相似文献   

12.
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   

13.
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   

14.
The influence of galloyl residues on the antioxidant mechanism of polyphenols to prevent hemoglobin-promoted lipid oxidation was investigated by using polyphenolic fractions with different degrees of galloylation: nongalloylated structures from pine bark (IVP), medium-galloylated from grape pomace (IVG), and high-galloylated from witch hazel bark (IVH). Hemoglobin (Hb) from the pelagic fish horse mackerel (Trachurus trachurus) was employed as a Hb standard. In vitro experiments showed an important increase in the deoxygenation and autoxidation of horse mackerel Hb at acidic pH values. All polyphenolic fractions significantly reduced the redox stability of Hb in buffer solutions, showing a greater deoxygenation and methemoglobin (metHb) formation in the presence of IVH, followed in decreasing order by IVG and IVP. However, galloylated polyphenols (IVH and IVG) were efficient to inhibit the oxidation of the oxygenated Hb (OxyHb) and the formation of lipid oxidation products in chilled washed fish muscle. This antioxidant activity of galloylated proanthocyanidins showed a positive relationship with the phenolic concentration. Polyphenols devoid of galloyl groups (IVP) were less active to prevent either Hb oxidation or lipid oxidation in fish muscle. The results draw attention to the potential role of galloyl residues to lessen Hb-catalyzed lipid oxidation in muscle and to maintain Hb in reduced and oxygenated states, which exhibit lower pro-oxidant activity as compared to the metHb and deoxyHb species.  相似文献   

15.
It has previously been found that a process based on solubilization at pH 2.7 gives high yields of herring muscle proteins with good functionality. In this study, the development of lipid oxidation during acid processing of herring mince was studied. It was tested how modifications of the process conditions and/or additions of antioxidants could prevent lipid oxidation during the actual process and then during ice storage of the protein isolates. Processing parameters evaluated were prewash of the mince, exposure time to pH 2.7, inclusion or exclusion of a high-speed centrifugation, and addition of antioxidants. Antioxidants tested were erythorbate (0.2%, 9.3 mM), sodium tripolyphosphate (STPP; 0.2%, 5.4 mM), ethylenediaminetetraacetic acid (EDTA; 0.044%, 1.5 mM), and milk proteins (4%). The first three antioxidants were added in the prewash or during the homogenization step, whereas milk proteins were added to the final precipitate. At time 0, all isolates were analyzed for pH, moisture content, and thiobarbituric reactive substances (TBARS). Selected isolates were also analyzed for lipid and protein content. Stability during ice storage was followed in terms of odor, TBARS, and color (a/b values). Extensive lipid oxidation took place using the "control" process without high-speed centrifugation. This was not significantly (p < or = 0.05) affected by a prewash or varied exposure time to pH 2.7. Including high-speed centrifugation (20 min, 10,000g) significantly (p < or = 0.05) reduced TBARS values, total lipids, a values and b values. Erythorbate alone, or in combination with STPP/EDTA, significantly (p < or = 0.05) reduced lipid oxidation during processing if added in the prewash or homogenization step. During ice storage, better stability was gained when antioxidants were added in both of these steps and when EDTA was used instead of STPP.  相似文献   

16.
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   

17.
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   

18.
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   

19.
Seafood from Gilbert Bay, southern Labrador, was sampled for lipid classes, fatty acid, and sterol composition. Gilbert Bay is a proposed Marine Protected Area, and the composition of seafood from this region is interesting from both human health and ecological perspectives. Analyses included four species of bivalves and flesh and liver samples from four fish species. Lipids from a locally isolated population of northern cod (Gadus morhua) were also compared to lipids from other cod populations. Lipid classes were analyzed by Chromarod/Iatroscan TLC-FID, fatty acids by GC, and sterols by GC-MS. Three cod populations had similar levels of total lipid per wet weight (0.6%) with triacylglycerols (TAG), sterols, and phospholipids comprising on average 13, 11, and 51%, respectively, of their total lipids. Fatty fish such as capelin and herring contained on average 8.4% lipid with 86% present as TAG. Fish livers from cod and herring showed opposite trends, with cod having elevated lipid (27%) and TAG (63%) and herring containing only 3.8% lipid and 20% TAG. Shellfish averaged 0.6% lipid; however, significant lipid class differences existed among species. Fatty acid analysis showed few significant differences in cod populations with on average 57% polyunsaturated fatty acids (PUFA), 18% monounsaturated fatty acids (MUFA), and 24% saturated fatty acids (SFA). Cod livers had lower PUFA (34%) and elevated MUFA (44%) relative to flesh. Bivalves averaged 25% SFA, 18% MUFA, and 57% PUFA, whereas scallop adductor muscle had the highest PUFA levels (63%). Bivalves contained 20 different sterols with cholesterol present as the major sterol (19-39%). trans-22-Dehydrocholesterol, brassicasterol, 24-methylenecholesterol, and campesterol individually accounted for >10% in at least one species. High levels of PUFA and non-cholesterol sterols observed in Gilbert Bay seafood demonstrate their positive attributes for human nutrition.  相似文献   

20.
Nearly all the mercury (Hg) in whole muscle from whitefish (Coregonus clupeaformis) and walleye (Sander vitreus) was present as methyl mercury (MeHg). The Hg content in whole muscle from whitefish and walleye was 0.04-0.09 and 0.14-0.81 ppm, respectively. The myofibril fraction contained approximately three-fourths of the Hg in whitefish and walleye whole muscle. The sarcoplasmic protein fraction (e.g., press juice) was the next most abundant source of Hg. Isolated myosin, triacylglycerols, and cellular membranes contained the least Hg. Protein isolates prepared by pH shifting in the presence of citric acid did not decrease Hg levels. Addition of cysteine during washing decreased the Hg content in washed muscle probably through the interaction of the sulfhydryl group in cysteine with MeHg. Primary and secondary lipid oxidation products were lower during 2 °C storage in isolates prepared by pH shifting compared to those of washed or unwashed mince from whole muscle. This was attributed to removing some of the cellular membranes by pH shifting. Washing the mince accelerated lipid peroxide formation but decreased secondary lipid oxidation products compared to that of the unwashed mince. This suggested that there was a lipid hydroperoxide generating system that was active upon dilution of aqueous antioxidants and pro-oxidants.  相似文献   

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