C. Faustman

Myoglobin and lipid oxidation interactions: mechanistic bases and control.

Lipid oxidation and myoglobin oxidation in meat lead to off-flavor development and discoloration, respectively. These processes often appear to be linked and the oxidation of one of these leads to the formation of chemical species that can exacerbate oxidation of the other. Several investigators have reported preservation of fresh meat color following the inclusion of antioxidant ingredients. An understanding of the complementary oxidation interaction provides a basis for explaining quality deterioration in meat and also for developing strategies to maintain optimal sensory qualities.

Proteomics of lipid oxidation-induced oxidation of porcine and bovine oxymyoglobins.

Myoglobin (Mb) redox state affects meat color and is destabilized by lipid oxidation products such as 4‐hydroxy‐2‐nonenal (HNE). Our objective was to investigate lipid oxidation‐induced oxymyoglobin (OxyMb) oxidation in Mb from two major meat‐producing livestock species utilizing MS and proteomics tools. Porcine OxyMb was incubated with HNE and analyzed for metmyoglobin (MetMb) formation. MetMb formation was greater in the presence of HNE than controls at pH 7.4 and 37°C (p <0.05). MALDI‐TOF MS was used to identify adduct formation; only mono‐adducts of HNE (via Michael addition) with porcine Mb were detected. LC‐ESI‐MS/MS identified three histidine (HIS) residues in porcine Mb that were readily adducted by HNE (HIS 24, 36 and 119), whereas in bovine Mb seven histidine residues (HIS 24, 36, 81, 88, 93, 119 and 152) were adducted. Quantitation of HNE‐adducted peptides using isotope‐labeled phenyl isocyanate indicated that, initially, HIS 36 was preferentially adducted in porcine Mb whereas HIS 81, 88 and 93 were the predominant sites of early HNE adduction in bovine Mb. Preferential HNE adduction at the proximal histidine (HIS 93) was observed exclusively in bovine OxyMb and may explain why lipid oxidation‐induced OxyMb oxidation appears more extensive in beef, than in pork.

Lipid oxidation induced by oxymyoglobin and metmyoglobin with involvement of H2O2 and superoxide anion

The role of oxymyoglobin oxidation in lipid oxidation was studied in a myoglobin-liposome system. The pro-oxidant effect of oxymyoglobin towards lipid oxidation was concentration-dependent. At equimolar concentrations, oxymyoglobin showed higher pro-oxidative activity towards lipid than metmyoglobin (p < 0.05). These results suggested that the process of oxymyoglobin oxidation is involved in catalyzing lipid oxidation. The addition of catalase into the oxymyoglobin-liposome system resulted in significantly decreased oxidation of oxymyoglobin and lipid (p < 0.05) suggesting a role for H(2)O(2) in the interaction between oxymyoglobin and lipid. The addition of Superoxide dismutase was without effect (p > 0.05) suggesting that Superoxide anion was not directly involved in mediating oxidation of oxymyoglobin and lipid. Albumin was added as a control for a non-specific protein antioxidant; it did not affect oxymyoglobin or lipid oxidation (p > 0.05). Our in vitro results support the hypothesis that the actual process of oxymyoglobin oxidation is a catalyst of lipid oxidation with H(2)O(2) a major factor.

The effects of antioxidant combinations on color and lipid oxidation in n - 3 oil fortified ground beef patties

This study was carried out to determine an effective combination of chelators, reductants and free radical scavengers for enhancing color stability and minimizing lipid oxidation in muscle foods fortified with n-3 fatty acids. Chelators (sodium tripolyphosphate, STPP; sodium citrate, CIT), reductants (sodium erythorbate, ERY) and radical scavengers (butylhydroxyanisole, BHA; mixed tocopherols from two different sources, 30 or 95TOC; rosemary extract, ROSE) were incorporated in various combinations into ground beef (15% fat) with or without n-3 oil fortification (n=8). Individually, STPP and CIT had no significant effect on a* values except day 4, but showed higher a* values when combined with ERY (STPP+ERY and CIT+ERY) (P<0.05). CIT had lower hue angle values than STPP on days 4 and 6, but CIT+ERY showed more discoloration than STPP+ERY (P<0.05). CIT+ERY showed less lipid oxidation than CIT alone (P<0.05), whereas there was no difference between STPP and STPP+ERY. CIT+ERY+ROSE demonstrated higher a* values than CIT+ERY+95TOC on days 4 and 6 (P<0.05); there was no difference between ROSE and 95TOC groups when n-3 oil was incorporated into ground beef patties (P>0.05). The combination of ROSE and ERY appeared to be effective in slowing the decline of a* values. All antioxidant combinations were effective at delaying lipid oxidation when compared to CON or n-3. A combination of CIT, ERY and ROSE was most effective for stabilizing color and delaying lipid oxidation.

Effect of antioxidants on stabilization of meat products fortified with n − 3 fatty acids

The effects of an n-3 oil emulsion, with and without added antioxidants, on lipid oxidation in n-3 polyunsaturated fatty acid (PUFA)-fortified meat products were studied. An emulsion of n-3 PUFAs was prepared (25% algal oil, 2.5% whey protein isolates, 10mM sodium citrate, 0.2% potassium sorbate, 500ppm of 70% mixed tocopherols, 100μM EDTA, pH 3, pasteurized at 75°C for 30min) and incorporated into fresh ground turkey, and fresh pork sausage (20% fat) to achieve a concentration of 500mg n-3 PUFA/110g meat. An antioxidant combination containing rosemary (0.2% w/w; radical quencher), citrate (0.5% w/w; sequestrant) and erythorbate (1g/kg product; reductant) was prepared and incorporated into ground turkey patties (5cm dia, 1.5cm thick) or fresh pork sausages (5cm dia, 1.5cm thick). Meat products were stored at 4°C or -18°C and analyzed for color (L*, a*, b* values), lipid oxidation (TBARS and lipid hydroperoxides) and n-3 PUFA profile. a* Values of refrigerated ground turkey patties decreased with storage, and an antioxidant combination effect was observed after 4 days (P<0.05). For fresh pork sausages at 4°C, control+antioxidant (CON+ANTI), and n-3+antioxidant (n-3+ANTI) groups showed greater a* values than controls (CON) indicating that the antioxidant combination stabilized meat color. TBARS and lipid hydroperoxides of both n-3 PUFA-enhanced meat products increased with storage (P<0.05); there were no significant changes in TBARS or lipid hydroperoxides for treatments containing the antioxidant combination (P<0.05). The actual level of n-3 PUFA incorporation in both meat products was greater than 87%; n-3 PUFA concentrations did not change within any treatment during storage (P>0.05). These results provide support for including antioxidant protection in n-3 PUFA fortified meat products.

Effect of dietary α-tocopherol supplementation on color and lipid stability in pork

Myoglobin and lipid oxidation are major causes of quality deterioration in fresh pork. A process to enhance color and lipid stability would prove valuable to the pork industry given the current trend of centralized packaging and distribution to retail markets. Our objective was to determine the effects of dietary α-tocopherol (α-Toc) supplementation on color and lipid stability in ground pork, and loin chops stored in modified atmosphere packaging (MAP). Yorkshire crossbred pigs (n=20) were randomized into two groups and fed diets containing 48 (CON) or 170 mg α-Toc acetate/kg feed (VIT-E) for 6 weeks before slaughter. Plasma α-Toc concentration was measured weekly. Post-slaughter, Boston butt shoulders were ground, formed into patties with or without 1.5% salt, and stored fresh at 4°C for 0, 2, 4, or 6 days, and frozen at -20°C for 45 or 90 days. Pork loin chops were packaged aerobically and stored at 4°C for 0, 2, 4 or 6 days, or in MAP at 4°C for 7, 10 or 13 days prior to Hunter L*,a*,b* and TBARS analyses. α-Toc concentration of longissimus dorsi, psoas major, biceps femoris, semimembranosus and semitendinosus muscles was determined. Plasma α-Toc was greater (P<0.05) in VIT-E animals compared with CON and α-Toc concentrations were greater (P<0.05) in all VIT-E muscles compared with CON. TBARS values of both fresh and salted patties were less in VIT-E than in CON meat following 6 days at 4°C; VIT-E TBARS of salted patties were less (P<0.05) after 45 days at -20°C compared with CON. α-Toc supplementation did not influence (P>0.05) color of aerobically packaged or MAP chops, or of fresh or salted pork patties. α-Toc supplementation reduced TBARS formation in fresh and salted pork but had no significant impact on color.

Effect of dietary vitamin E supplementation on the colour and lipid stability of fresh, frozen and vacuum-packaged beef.

The effects of dietary vitamin E supplementation on tissue α-tocopherol (α-Toc) levels and on the susceptibility of fresh, frozen and vacuum-packaged beef to lipid oxidation and colour deterioration were investigated. Friesian cattle were fed diets containing 20 (basal, n=5) or 2000 (supplemented, n=5) IU (α-tocopheryl acetate/kg feed/day for approximately 50 days prior to slaughter. α-Toc levels were higher (p<0.05) in muscles from supplemented animals than from those on a basal diet. Significant differences in α-Toc levels were also observed between muscles from different treatment groups, the order of the supplemented group was: M. psoas major (PM)>M. longissimus dorsi (LD)>M. gluteus medius (GM) (p<0.05), and in the basal group the order was: PM>GM>LD (p<0.05). Supplemented fresh, frozen and vacuum packed beef showed greater colour and lipid oxidative stability than meat from the basal group after 7 days retail display at 4°C (p<0.05). Thus, dietary (α-Toc supplementation appeared to retard metmyoglobin and TBARS formation in LD, GM and PM and increased the colour shelf life of these muscles.

Supranutritional Administration of Vitamins E and C Improves Oxidative Stability of Beef

Vitamins E and C are important antioxidants in animals. Their antemortem activity continues to function in postmortem muscle (meat), where they have a critical role in maintaining quality in the food product. Dietary supplementation of vitamin E, and intravenous infusion of vitamin C immediately before harvest, are efficacious techniques for increasing the concentration of these vitamins in beef skeletal muscle. Meat with elevated levels of either and probably both of these antioxidant vitamins possesses greater stability of oxymyoglobin and lipid, which results in less discoloration and rancidity, respectively. A model is proposed for the redox relationships between myoglobin and phospholipid in beef with emphasis on vitamins E and C. Antemortem nutritional intervention appears to be a promising approach for improving the quality of fresh meat products subsequently obtained from livestock.

Influence of carbon monoxide in package atmospheres containing oxygen on colour, reducing activity, and oxygen consumption of five bovine muscles

Steaks from five bovine muscles [psoas major (PM), longissimus lumborum (LL), deep semimembranosus (DSM), superficial semimembranosus (SSM), and semitendinosus (ST)] were packaged in atmospheres containing 20% or 80% oxygen, with and without 0.4% carbon monoxide. Steaks were evaluated on d 0, 4, and 7 of retail display for instrumental (CIE L(∗), a(∗), and b(∗)) and visual colour, total- and metmyoglobin-reducing activity, and oxygen consumption rate. Combining carbon monoxide with either oxygen level had no effect (P>0.05) on any measured attribute. Using higher oxygen levels increased colour stability and reduced variability (P<0.05) among muscles for all measured attributes. In general, colour stability and reducing activity for the muscles were LL>ST>SSM>PM>DSM. Including 0.4% carbon monoxide with 20% or 80% oxygen may not have impacted colour, due to preferential formation of oxymyoglobin, rather than carboxymyoglobin, at these oxygen levels.

Aldehyde reactivity with 2-thiobarbituric acid and TBARS in freeze-dried beef during accelerated storage.

When lipid oxidation is evaluated in freeze-dried beef, a yellow 450-nm-absorbing pigment develops during the 2-thiobarbituric acid (TBA) assay. TBA analysis and high performance liquid chromatography (HPLC) were applied to measure oxidative changes in salted freeze-dried beef patties (15% fat) initially during storage at 49°C. The TBA pink pigment (λ(max)=532 nm) was most pronounced in unstored salted freeze-dried beef, and yellow pigment (λ(max)=450 nm) predominated in stored samples. An in vitro study of TBA reactivity of different aldehydes, known to be secondary lipid oxidation products, showed that alkanals and alk-2-enals favored TBARS(450) formation, while alka-2,4-dienals favored TBARS(532). Values of TBARS(450) from 95°C TBA incubation were lower than those from 25°C incubation (P<0.05), indicating that the yellow chromophore from the aldehyde-TBA complex was less thermally stable than the pink pigment. 5-Hydroxymethyl-2-furfural, an aldehyde produced from Maillard reaction, also produced strong TBARS(450). Propional, butanal and 5-hydroxymethyl-2-furfural (HMF), were tentatively identified in freeze-dried beef during accelerated storage at 49°C, and have the potential to yield TBARS @450.