Nix Pro Color Sensor provides comparable color measurements to HunterLab colorimeter for fresh beef.

The HunterLab MiniScan (HunterLab) colorimeter is used in meat quality research worldwide for measuring meat color; however, the Nix Pro Color Sensor (Nix) could be a less expensive alternative that is easier to operate. Therefore, the objective of this study was to compare the two colorimeters to objectively evaluate fresh beef color. Longissimus thoracis muscle from one side of A maturity beef carcasses (n = 200) was evaluated using both the HunterLab (3 technical replicate scans) and Nix (3, 5, 7, and 9 technical replicate scans) colorimeters. The correlation between the HunterLab and Nix for L* (lightness), a* (redness), and b* (yellowness) values ranged between r = 0.80 to 0.85 and the Bland Altman Limits of Agreement analysis indicated good agreement between the Nix and HunterLab colorimeters for all the color parameters. These results indicated that the Nix colorimeter could be a viable alternative for HunterLab colorimeters.

Investigation of muscle-specific beef color stability at different ultimate pHs.

OBJECTIVE: This study was aimed to investigate the muscle-specific beef color stability at normal and high ultimate pHs. METHODS: The impact of muscle (Longissimus lumborum [LL] vs psoas major [PM]) and pH (normal ultimate pH [Np] vs high pH dark cutting beef [Hp]) on color stability, indicated by basic color traits, metmyoglobin reducing activity (MRA) and oxygen consumption (OC), as well as the lipid oxidation, were determined over 7 days of display at 4°C. RESULTS: Hp-LL had the highest pH (6.92), followed by Hp-PM (6.01), Np-PM (5.76), and Np-LL (5.52). Hp-LL had increased (p<0.05) a*, chroma and % oxymyoglobin during display. Hp-LL also had the highest metmyoglobin (MMb) reducing activity and OC among all the samples, thus, the greatest color stability, although very dark throughout storage, with lowest values for lightness (L*) and yellowness (b*). Np-LL also exhibited relatively high color stability, as a result of its lower % MMb and OC and higher MRA than psoas muscle samples. The 0.2 unit difference of the pH between Hp and Np psoas muscle, resulted in the difference of the color intensity, not the color stability. Interestingly, high pH psoas muscle (Hp-PM) did not have better color stability than Np-PM, and in fact had lower color stability than even Np-LL. The similar level of OC and lipid oxidation cannot explain the difference in color stability between Hp-PM and Np-LL. CONCLUSION: The Hp does not always show better color stability compared with Np beef, which depends on the muscle type. The balance of MRA and OC is important to keep the color in great intensity and stability in the meantime.

The effect of succinate on color stability of Bos indicus bull meat: pH-dependent effects during the 14-day aging period.

Bos taurus indicus bulls are very susceptible to pre-slaughter stress, which directly impacts the decline in muscle pH, leading to darker meat. The aim was to investigate the effect of succinate and atmosphere on the color stability of Nellore (Bos taurus indicus) Longissimus lumborum steaks classified by ultimate pH (pHu): normal pHu (5.40 ≤ pHu ≤ 5.79) and high pHu (pHu ≥ 5.80). The experimental treatment systems were: (i) vacuum packaging without succinate injection, (ii) HiOx-MAP (80 % O2 + 20 % CO2), and (iii) HiOx-MAP (80 % O2 + 20 % CO2) enhanced with sodium succinate injection (pH 5.4). Steaks from all treatment systems were stored at 4 °C for 14 days and tested for instrumental color, myoglobin content, oxygen consumption (OC), metmyoglobin-reducing activity (MRA), lipid oxidation, and microbiological analysis. High and normal pHu vacuum-packaged steaks exhibited greater color stability due to higher MRA. High and normal pHu steaks packaged with HiOx-MAP or HiOx-MAP enhanced with succinate showed improved color due to lower deoxymyoglobin content (%DMb) and OC up to the eighth day of storage. Still, succinate injection promoted increased (P < 0.05) lipid oxidation in normal pHu steaks and reduced MRA after 14 days. These findings emphasize the intricate interplay between pHu and packaging systems on Bos taurus indicus meat quality. Further research in this area could contribute to a better understanding of meat color abnormalities and provide insights into potential meat preservation and enhancement strategies.

Investigation of oxygen packaging to maintain beef color stability and microbiology safety after periods of long-term superchilled storage.

This study aimed to develop an appropriate modified atmosphere packaging (MAP) system for displayed beef steaks following long-term superchilled (-1 °C) storage. After superchilled storage for 0, 2, 8, or 16 weeks, beef loins were fabricated into steaks and displayed with 20%, 50%, or 80% O2-MAP under chilled conditions. At each storage point, after display for 0, 3, 7, or 10 days, instrumental color, myoglobin redox forms percentage, lipid oxidation, total viable count (TVC), and total volatile basic nitrogen (TVB-N) were evaluated. Meat color stability decreased, with prolonged storage period and display time. When the storage period was within 8 weeks, under all the above MAP conditions, the display time for the beef steaks was up to 10 days. Considering 80% O2-MAP promoted lipid oxidation, 50% and 80% O2-MAP were not recommended for displaying steaks for more than 10 and 7 days respectively after 16 weeks of storage. However, 20%, 50%, or 80% O2-MAP could maintain 3 days of microbial shelf-life according to TVC and TVB-N results. Additionally, after long-term superchilled storage for 16 weeks, the various O2 concentrations had minimal impact on microbiota succession during the MAP display period. Furthermore, beef steaks packaged under various MAP systems exhibited similar microbial compositions, with the dominant bacteria alternating between Lactobacillus and Carnobacterium. This study provided practical guidance for improving beef color stability after long-term superchilled storage.

Analysis of beef quality according to color changes using computer vision and white-box machine learning techniques.

The quality of beef products relies on the presence of a cherry red color, as any deviation toward brownish tones indicates a loss in quality. Existing studies typically analyze individual color channels separately, establishing acceptable ranges. In contrast, our proposed approach involves conducting a multivariate analysis of beef color changes using white-box machine learning techniques. Our proposal encompasses three phases. (1) We employed a Computer Vision System (CVS) to capture the color of beef pieces, implementing a color correction pre-processing step within a specially designed cabin. (2) We examined the differences among three color spaces (RGB, HSV, and CIELab*) (3) We evaluated the performance of three white-box classifiers (decision tree, logistic regression, and multivariate normal distributions) for predicting color in both fresh and non-fresh beef. These models demonstrated high accuracy and enabled a comprehensive understanding of the prediction process. Our results affirm that conducting a multivariate analysis yields superior beef color prediction outcomes compared to the conventional practice of analyzing each channel independently.

Proteomic approaches to characterize biochemistry of fresh beef color.

Color of retail fresh beef is the most important quality influencing the consumers' purchase decisions at the point of sale. Discolored fresh beef cuts are either discarded or converted to low-value products, before the microbial quality is compromised, resulting in huge economic loss to meat industry. The interinfluential interactions between myoglobin, small biomolecules, proteome, and cellular components in postmortem skeletal muscles govern the color stability of fresh beef. This review examines the novel applications of high-throughput tools in mass spectrometry and proteomics to elucidate the fundamental basis of these interactions and to explain the underpinning mechanisms of fresh beef color. Advanced proteomic research indicates that a multitude of factors endogenous to skeletal muscles critically influence the biochemistry of myoglobin and color stability in fresh beef. Additionally, this review highlights the potential of muscle proteome components and myoglobin modifications as novel biomarkers for fresh beef color. SIGNIFICANCE: This review highlights the important role of muscle proteome in fresh beef color, which is the major trait impacting consumers' purchase decisions. In recent years, innovative approaches in proteomics have been exploited for an in-depth understanding of the biochemical mechanisms influencing color development and color stability in fresh beef. The review suggests that a wide range of factors, including endogenous skeletal muscle components, can affect myoglobin biochemistry and color stability in beef. Furthermore, the potential use of muscle proteome components and myoglobin post-translational modifications as biomarkers for fresh beef color is discussed. The currently available body of evidence presented in this review can have important implications in meat industry as it provides novel insights into the factors influencing fresh beef color and an up-to-date list of biomarkers that can be used to predict beef color quality.

Effect of different feeding systems on color of longissimus muscle from Bos cattle: A systematic review and meta-analysis.

Considering the relevance of meat discoloration for meat production chain and the conflicting results regarding the influence of feeding regimes on color of fresh beef and the lack of meta-analytic studies on this subject we investigated the effect of grain-fed and pasture-fed regimes on color of beef longissimus from Bos cattle through a systematic review with meta-analysis. A systematic search from 2001 to 2021 was performed in two databases and 126 papers were eligible for meta-analysis. Pasture-fed longissimus beef exhibited higher a* (8.21%) and C* (8.61%) values, and lower h* values (17.18%) than grain-fed counterparts, indicating a greater color for longissimus beef from pasture-fed animals. Among the pasture-fed regimes, those containing alfalfa, bermudagrass, cowpea and pearl millet were the most effective for color improvements. Our findings indicate potential feeding regimes to mitigate global economic losses from meat discoloration and suggest the necessity to develop suitable processing strategies to improve the color of beef from grain-fed Bos cattle.

Dark-cutting beef mitochondrial proteomic signatures reveal increased biogenesis proteins and bioenergetics capabilities.

Mitochondria remain active in postmortem muscles and can influence meat color via oxygen consumption. Previous studies have shown that dark-cutting compared with normal-pH beef has greater mitochondrial protein and DNA content per gram of muscle tissue. However, the mechanism regulating mitochondrial content in dark-cutting vs. normal-pH beef is still unknown. Therefore, the objective was to compare mitochondrial proteomes of dark-cutting vs. normal-pH beef using LC-MS/MS-based proteomics and mitochondrial respiratory capacity using a Clark oxygen electrode. Dark-cutting compared with normal-pH beef has up-regulation of proteins involved in mitochondrial biogenesis, oxidative phosphorylation, intracellular protein transport, and cellular calcium ion homeostasis. Mitochondria isolated from dark-cutting phenotypes showed greater mitochondrial complex II respiration and uncoupled oxidative phosphorylation. However, mitochondrial membrane integrity and respiration at complexes I and IV were not different between normal-pH and dark-cutting beef. These results indicate that dark-cutting beef has greater mitochondrial biogenesis proteins than normal-pH beef, increasing mitochondrial content and contributing to dark-cutting beef. SIGNIFICANCE: Defective glycogen metabolism resulting from chronic stress before slaughter coupled with the greater mitochondrial protein and DNA content per gram of muscle tissue promotes muscle darkening in dark-cutting phenotypes in beef. However, the mechanistic basis for this occurrence in dark-cutting phenotypes is still unknown. In this work, we show that dark-cutting beef phenotype is caused, in part, as a consequence of over-proliferation of mitochondria. This is supported by the up-regulation of proteins involved in mitochondrial biogenesis, mitochondrial electron transport, calcium homeostasis, and fatty acid metabolism. Hence, the study of mitochondrial proteome changes provides a set of mitochondrial biogenesis proteins that could be used as potential candidate markers for detecting changes in pre-slaughter developmental events contributing to dark-cutting phenotypes in beef.

Pulmonary arterial pressure in fattened Angus steers at moderate altitude influences early postmortem mitochondria functionality and meat color during retail display.

Pulmonary hypertension is a noninfectious disease of cattle at altitudes > 1524 m (5,000 ft). Mean pulmonary arterial pressures (PAP) are used as an indicator for pulmonary hypertension in cattle. High PAP cattle (≥50 mmHg) entering the feedlot at moderate elevations have lower feed efficiency as compared to low PAP cattle (< 50 mmHg). The impact of pulmonary arterial pressure on mitochondrial function, oxidative phosphorylation (OXPHOS) protein abundance, and meat color was examined using longissimus lumborum (LL) from high (98 ± 13 mmHg; n = 5) and low (41 ± 3 mmHg; n = 6) PAP fattened Angus steers (live weight of 588 ± 38 kg) during early postmortem period (2 and 48 h) and retail display (days 1 to 9), respectively. High PAP muscle had greater (P = 0.013) OXPHOS-linked respiration and proton leak-associated respiration than low PAP muscles at 2 h postmortem but rapidly declined to be similar (P = 0.145) to low PAP muscle by 48 h postmortem. OXPHOS protein expression was higher (P = 0.045) in low PAP than high PAP muscle. During retail display, redness, chroma, hue, ratio of reflectance at 630 and 580 nm, and metmyoglobin reducing activity decreased faster (P < 0.05) in high PAP steaks than low PAP. Lipid oxidation significantly increased (P < 0.05) in high PAP steaks but not (P > 0.05) in low PAP. The results indicated that high PAP caused a lower OXPHOS efficiency and greater fuel oxidation rates under conditions of low ATP demand in premortem beef LL muscle; this could explain the lower feed efficiency in high PAP feedlot cattle compared to low PAP counterparts. Mitochondrial integral function (membrane integrity or/and protein function) declined faster in high PAP than low PAP muscle at early postmortem. LL steaks from high PAP animals had lower color stability than those from the low PAP animals during simulated retail display, which could be partially attributed to the loss of muscle mitochondrial function at early postmortem by ROS damage in high PAP muscle.

The impact of pulmonary arterial pressure (PAP) on mitochondrial function, oxidative phosphorylation protein abundance, and meat color was examined using longissimus lumborum (LL) from high (98 ± 13 mmHg) and low (41 ± 3 mmHg) PAP fattened Angus steers (live weight of 588 ± 38 kg) during early postmortem period (2 and 48 h) and retail display (days 1 to 9), respectively. The results indicated that high PAP caused a lower oxidative phosphorylation efficiency and greater fuel oxidation rates under conditions of positive energy balance in beef LL muscle. This could explain the lower feed efficiency in high PAP feedlot cattle compared to low PAP counterparts. Mitochondrial integral function declined faster in high PAP than low PAP muscle at early postmortem. LL steaks from high PAP animals had lower color stability than those from the low PAP animals during simulated retail display, which could be partially attributed to the loss of muscle mitochondrial function at early postmortem in high PAP muscle.

Spectro 1-A Potential Spectrophotometer for Measuring Color and Myoglobin Forms in Beef.

The objective of this study was to compare the Color Muse Spectro 1 sensor to the HunterLab MiniScan XE Plus spectrophotometer for evaluating beef color. Color coordinates (lightness (L*), redness (a*), yellowness (b*), chroma (C*), and hue (h*)), myoglobin redox forms (metmyoglobin (MMb), deoxymyoglobin (DMb), and oxymyoglobin (OMb)), and metmyoglobin reducing ability (MRA) were measured on beef steaks over a 5-days storage period. The results indicated that L*, b*, C*, MMb%, OMb%, and MRA% values obtained with Spectro 1 were comparable to those of MiniScan. However, Spectro 1 values for a* were overestimated compared to MiniScan (p < 0.05), whereas those for h* and DMb% were underestimated (p < 0.05). Regardless, Spectro 1 had the capability to detect changes in color coordinates, myoglobin forms, and MRA throughout the storage period. Bland−Altman plots demonstrated that L*, b*, and C* are interchangeable between the two instruments, but it was not the case for a*, h*, myoglobin forms, and MRA. Color coordinates measured by Spectro 1 exhibited excellent stability over time, evidenced by the low total color difference (ΔE*ab) values. Collectively, these findings indicate that Spectro 1 is a potential alternative spectrophotometer for studying meat color and myoglobin redox forms.

The effect of black rice water extract on surface color, lipid oxidation, microbial growth, and antioxidant activity of beef patties during chilled storage.

Black rice is rich in phenolic acids and anthocyanin; however, limited studies have determined its effect on ground beef quality. The objective was to determine the effects of 0, 0.4, 0.8, and 1.2% black rice water extract (BRWE) on ground beef patties quality when packaged in polyvinyl chloride (PVC). pH, surface color, lipid oxidation, total plate count, and antioxidant capacity were determined on 0, 3, and 6 days of storage under fluorescent light at 2 °C. Addition of BRWE had no effect (P = .98) on pH. Incorporating BRWE in ground beef improved (P < .0001) redness compared with control. The addition of BRWE decreased (P < .0001) lipid oxidation compared with control during storage; while antioxidant capacity increased with the addition of extract. BRWE at 1.2% reduced (P = .007) aerobic microbial counts after 6 days of storage. These results suggested that BRWE could be used as a natural antioxidant in ground beef to limit lipid oxidation and discoloration.

Impact of Up- and Downregulation of Metabolites and Mitochondrial Content on pH and Color of the Longissimus Muscle from Normal-pH and Dark-Cutting Beef.

Limited knowledge is currently available on the biochemical basis for the development of dark-cutting beef. The objective of this research was to determine the metabolite profile and mitochondrial content differences between normal-pH and dark-cutting beef. A gas chromatography-mass spectrometer-based nontargeted metabolomic approach indicated downregulation of glycolytic metabolites, including glucose-1- and 6-phosphate and upregulation of tricarboxylic substrates such as malic and fumaric acids occurred in dark-cutting beef when compared to normal-pH beef. Neurotransmitters such as 4-aminobutyric acid and succinate semialdehyde were upregulated in dark-cutting beef than normal-pH beef. Immunohistochemistry indicated a more oxidative fiber type in dark-cutting beef than normal-pH beef. In support, the mitochondrial protein and DNA content were greater in dark-cutting beef. This increased mitochondrial content, in part, could influence oxygen consumption and myoglobin oxygenation/appearance of dark-cutting beef. The current results demonstrate that the more tricarboxylic metabolites and mitochondrial content in dark-cutting beef impact muscle pH and color.

Mitochondrial Degeneration, Depletion of NADH, and Oxidative Stress Decrease Color Stability of Wet-Aged Beef Longissimus Steaks.

Interrelationship between mitochondria and myoglobin function influence beef color. NADH level in postmortem muscle is an important determinant of mitochondrial activity and metmyoglobin reduction. Increased aging time promotes discoloration of steaks; however, the mechanism of this effect is not clear. The objective was to characterize the role of wet-aging in beef longissimus lumborum muscle mitochondrial function and to characterize the global metabolome to determine the mechanism of that can regenerate NADH. Beef longissimus lumborum muscles were randomly assigned to 3, 7, 14, 21, and 28 days aging periods. Surface color, biochemical, mitochondrial, and metabolite profiles were determined at each aging period and at the end of 6-day display. During 6-day display, sections aged for 28 days had 30.4% decrease in redness than sections aged for 3 days. Aging time decreased (P <0.05) muscle oxygen consumption, mitochondrial protein content, and antioxidant capacity. Metabolites such as fumaric acid, creatinine, and fructose, that can take part in glycolytic/TCA cycle and regenerate NADH decreased (P <0.05) with aging and display time. In support, NADH levels also decreased (P <0.05) with aging time, but aging time had no effect (P = 0.44) on NADH-dependent reductase activity. The results suggest that decreased color stability in aged beef can be attributed to increased mitochondrial damage, depletion of metabolites that can regenerate NADH, and increased oxidative stress. PRACTICAL APPLICATION: Beef aging time results in increased discoloration of steaks under retail display. The current research determines the fundamental basis of lower color stability in aged beef. The results indicate that mitochondrial degeneration, depletion of metabolites that produce NADH, and increased oxidative stress can limit shelf-life of aged steaks. Hence, application of post-harvest strategies to minimize mitochondrial damage and oxidative changes may have the potential to increase shelf-life of aged beef.

Carbon Chain Length of Lipid Oxidation Products Influence Lactate Dehydrogenase and NADH-Dependent Metmyoglobin Reductase Activity.

The biochemical basis of lower metmyoglobin reducing activity (MRA) in high-oxygen modified atmospheric packaged (HiOx-MAP) beef than those in vacuum and polyvinyl chloride (PVC) packaging is not clear. To explore this, the effects of lipid oxidation products with varying carbon chain length on lactate dehydrogenase (LDH) and NADH-dependent metmyoglobin reductase activity were evaluated. Surface color, MRA, and lipid oxidation of beef longissimus lumborum steaks (n = 10) were measured during 6-day display. Further, two enzymes, LDH and NADH-dependent metmyoglobin reductase (n = 5), critical for MRA were incubated with or without (control) lipid oxidation products of varying carbon chain length: malondialdehyde (3-carbon), hexenal (6-carbon), and 4-hydroxynonenal (9-carbon). Steaks in HiOx-MAP had greater (P < 0.05) redness than vacuum and PVC, but had lower (P < 0.05) MRA and greater (P < 0.05) lipid oxidation on day 6. LDH and NADH-dependent metmyoglobin reductase activities were differentially influenced by lipid oxidation products (P < 0.05). The results indicate that the difference in reactivity of various lipid oxidation products on LDH (HNE > MDA = hexenal) and NADH-dependent metmyoglobin reductase (HNE = MDA > hexenal) activity could be responsible for lower MRA in HiOx-MAP.

Stability of vacuum-packed meat from finishing steers fed different inclusion levels of brewer's spent grain.

Brewer's spent grain (BSG) as a partial substitute for corn silage (CS) was evaluated in finishing feedlot steers on the lipid, protein, color, and microbiological stability of vacuum-packed meat for 75 days under refrigerated storage. Twenty steers were distributed in four treatments in a completely randomized design with five replicates each: 50% concentrate + 50% CS; + 35% CS + 15% BSG; + 25% CS + 25% BSG; and 15% CS + 35% BSG for 90 days. After the animals were slaughtered and the carcasses cooled, the Longissimus thoracis muscle was collected for analyzes. The lipid and protein oxidation, color parameters and microbiological stability of the beef although not affected by the diets (P > .05) oscillated throughout the storage time (P < .05). BSG can be included in the finishing diets of beef cattle by up to 35% (dry basis) and as a forage source without adverse effects on beef shelf life.

Novel nitrite-embedded packaging improves surface redness of dark-cutting longissimus steaks.

The objective of this research was to determine the effects of nitrite-embedded/FreshCase packaging on lean color of dark-cutting beef. Eight dark-cutting (pH > 6.0) and eight USDA Low Choice (normal-pH; mean pH = 5.6) beef strip loins (longissimus lumborum) were selected 3 day after harvest. Each dark-cutting loin was sliced into five 2.5-cm thick steaks and randomly assigned to 1) dark-cutting steak packaged in polyvinyl chloride film (PVC) overwrap, 2) dark-cutting steak packaged in nitrite-embedded film, 3) dark-cutting steaks dipped in 0.2% rosemary solution and packaged in nitrite-embedded film, and 4) dark-cutting steak dipped in deionized water and packaged in nitrite-embedded film. The fifth dark-cutting steak was used to determine pH and proximate composition. Normal-pH choice loins were used as a control and each loin was randomly assigned to either PVC overwrap for retail display or to determine pH and proximate composition. Packages were placed in coffin-style retail display cases under continuous fluorescent lighting for 3 days. A HunterLab MiniScan XE Plus spectrophotometer was utilized to characterize steak color every 24 h. There was a significant treatment × storage time interaction (P < 0.05) for a* values and nitric oxide myoglobin formation. On days 1, 2, and 3 of the display, nitrite-embedded treatment improved (P < 0.05) redness compared to other dark-cutting steaks in PVC. A 45% increase in redness (P < 0.05) was observed for nitrite-embedded rosemary treatment over dark-cutting steak in PVC on day 3 of display. Nitric oxide myoglobin formation on day 0 was less for all dark-cutting steaks in nitrite-embedded packaging. Metmyoglobin content was greater (P < 0.05) on day 0 for dark-cutting steaks packaged in nitrite-embedded treatments than dark-cutting steaks in PVC. However, metmyoglobin level in dark-cutting steaks packaged in nitrite-embedded treatments decreased (P < 0.05) on day 1 compared with day 0. Dark-cutting steaks packaged in PVC had greater (P < 0.05) L* values on day 0 than other dark-cutting steaks in nitrite-embedded packaging. Conversely, on days 1, 2, and 3, there were no differences (P > 0.05) in L* values between dark-cutting treatments. Dark-cutting steaks in nitrite-embedded packaging had lower total plate count (P < 0.05) than dark-cutting steak packaged in PVC. The current research indicated that nitrite-embedded packaging has the potential to improve surface color of dark-cutting beef.

Associations among animal, carcass, muscle characteristics, and fresh meat color traits in Charolais cattle.

This study investigated the effects of animal, carcass and muscle characteristics on initial color traits of steaks from 887 Charolais cattle. First, the fixed factors of year of birth, experiment and sex had strong impacts on color traits. From the covariates, increased age lead to intense color (low h*, -1.55 units) and darker and vivid meat (high a*, b* and C*: +4.56, +3.41 and +5.61, respectively). Increases in fatness score and carcass fat weight were associated with increases in a*, b* and C* (redness; +2.90 to +4.06 for a*; yellowness; +2.60 to +3.76 for b*; and vividness, +3.87 to +5.49 for C*) and a darker colored lean (L*; -1.56 to -3.23). As pH24h increased, a* (less red) and C* (less vivid) decreased (-3.06), whereas hue angle increased (+2.69) leading to poorer color. The selection of animals for high degree of muscularity or slaughter weight resulted in lighter and darker meat, respectively. The studied covariates could be used as indicators of Charolais beef color traits.

Effect of freezing prior to aging on myoglobin redox forms and CIE color of beef from Nellore and Aberdeen Angus cattle.

The objective of this study was to evaluate the effect of freezing prior to wet aging on the color of Nellore and Aberdeen Angus cattle meat. Samples of the Longissimus thoracis muscle were subjected to two treatments: conventional aging (0, 7, 14 and 21days); and freezing (-20°C for 40days) followed by thawing and aging. Freezing promoted (P<0.05) formation of metmyoglobin during aging, especially in Nellore beef. Frozen meats showed (P<0.05) lower lightness (L*) values and higher redness (a*), chroma (C*) and hue angle (h*) values at the first day of storage, deteriorating quickly with aging time. The color of the Nellore meat was less (P<0.05) stable to freezing, being lighter, yellower and less red than Angus meat. The results suggest that color stability in vacuum-packed beef is reduced by freezing prior to aging and that reduction depends on the animal breed.

Effects of Metmyoglobin Reducing Activity and Thermal Stability of NADH-Dependent Reductase and Lactate Dehydrogenase on Premature Browning in Ground Beef.

Premature browning is a condition wherein ground beef exhibits a well-done appearance before reaching the USDA recommended internal cooked meat temperature of 71.1 °C; however, the mechanism is unclear. The objectives of this study were: (1) to determine the effects of packaging and temperature on metmyoglobin reducing activity (MRA) of cooked ground beef patties and (2) to assess the effects of temperature and pH on thermal stability of NADH-dependent reductase, lactate dehydrogenase (LDH), and oxymyoglobin (OxyMb) in-vitro. Beef patties (lean: fat = 85:15) were packaged in high-oxygen modified atmosphere (HiOX-MAP) or vacuum (VP) and cooked to either 65 or 71 °C. Internal meat color and MRA of both raw and cooked patties were determined. Purified NADH-dependent reductase and LDH were used to determine the effects of pH and temperature on enzyme activity. MRA of cooked patties was temperature and packaging dependent (P < 0.05). Vacuum packaged patties cooked to 71 °C had greater (P < 0.05) MRA than HiOX-MAP counterparts. Thermal stability of OxyMb, NADH-dependent reductase, and LDH were different and pH-dependent. LDH was able to generate NADH at 84 °C; whereas NADH-dependent reductase was least stable to heat. The results suggest that patties have MRA at cooking temperatures, which can influence cooked meat color.

Effects of Muscle-Specific Oxidative Stress on Cytochrome c Release and Oxidation-Reduction Potential Properties.

Mitochondria play a significant role in beef color. However, the role of oxidative stress in cytochrome c release and mitochondrial degradation is not clear. The objective was to determine the effects of display time on cytochrome c content and oxidation-reduction potential (ORP) of beef longissimus lumborum (LL) and psoas major (PM) muscles. PM discolored by day 3 compared with LL. On day 0, mitochondrial content and mitochondrial oxygen consumption were greater in PM than LL. However, mitochondrial content and oxygen consumption were lower (P < 0.05) in PM than LL by day 7. Conversely, cytochrome c content in sarcoplasm was greater on days 3 and 7 for PM than LL. There were no significant differences in ORP for LL during display, but ORP increased for PM on day 3 when compared with day 0. The results suggest that muscle-specific oxidative stress can affect cytochrome c release and ORP changes.