Porcine oxymyoglobin and lipid oxidation in vitro

The color of fresh pork: Consumers expectations, underlying farm-to-fork factors, myoglobin chemistry and contribution of proteomics to decipher the biochemical mechanisms

The color of fresh pork is a crucial quality attribute that significantly influences consumer perception and purchase decisions. This review first explores consumer expectations and discrimination regarding pork color, as well as an overview of the underlying factors that, from farm-to-fork, contribute to its variation. Understanding the husbandry factors, peri- and post-mortem factors and consumer preferences is essential for the pork industry to meet market demands effectively. This review then delves into current knowledge of pork myoglobin chemistry, its modifications and pork discoloration. Pork myoglobin, which has certain peculiarities comparted to other meat species, plays a weak role in determining pork color, and a thorough understanding of the biochemical changes it undergoes is crucial to understand and improve color stability. Furthermore, the growing role of proteomics as a high-throughput approach and its application as a powerful research tool in meat research, mainly to decipher the biochemical mechanisms involved in pork color determination and identify protein biomarkers, are highlighted. Based on an integrative muscle biology approach, the available proteomics studies on pork color have enabled us to provide the first repertoire of pork color biomarkers, to shortlist and propose a list of proteins for evaluation, and to provide valuable insights into the interconnected biochemical processes implicated in pork color determination. By highlighting the contributions of proteomics in elucidating the biochemical mechanisms underlying pork color determination, the knowledge gained hold significant potential for the pork industry to effectively meet market demands, enhance product quality, and ensure consistent and appealing pork color.

Application of portable Vis-NIR spectroscopy for rapid detection of myoglobin in frozen pork

Myoglobin content is considered as a crucial index to evaluate the quality of frozen pork. In this study, a portable visible and near-infrared (Vis-NIR) spectrometer combined with chemometrics was used to detect myoglobin content in frozen pork. Metmyoglobin, deoxymyoglobin, oxymyoglobin, and total myoglobin were assessed spectrophotometrically. The raw Vis-NIR spectra of frozen pork samples were pre-processed using 1^st derivatives (FD). Afterward, Synergy Interval Partial Least Square (Si-PLS) coupled Competitive Adaptive Reweighted Sampling algorithm (Si-CARS-PLS) was applied to select characteristic variables. The Si-CARS-PLS models revealed the probability of estimating myoglobin content in frozen pork, with predictive correlation coefficients (R_p) for metmyoglobin, deoxymyoglobin, oxymyoglobin, and total myoglobin as 0.9095, 0.9004, 0.8578, and 0.9133, respectively. The findings of this study showed that Vis-NIR spectroscopy coupled with Si-CARS-PLS is a promising method and offered a way forward for determining the myoglobin content in frozen pork.

Myoglobin Post-Translational Modifications Influence Color Stability of Beef Longissimus Lumborum

Post-translational modifications (PTM) of proteins play critical roles in biological processes. PTM of muscle proteins influence meat quality. Nonetheless, myoglobin (Mb) PTM and their impact on fresh beef color stability have not been characterized yet. Therefore, our objectives were to identify Mb PTM in beef longissimus lumborum muscle during postmortem aging and to characterize their influence on color stability. The longissimus lumborum muscles from 9 (n = 9) beef carcasses (24 h postmortem) were subjected to wet aging for 0, 7, 14, and 21 d. At the end of each wet-aging period, steaks were fabricated. One steak for analyses of PTM was immediately frozen at −80°C, whereas other steaks were assigned to refrigerated storage in the darkness under aerobic packaging. Instrumental color and biochemical attributes were evaluated on day 0, 3, or 6 of storage. Mb PTM were analyzed using two-dimensional electrophoresis and tandem mass spectrometry. Surface redness (a* value), color stability, and Mb concentration decreased (P < 0.05) upon aging. Gel image analyses identified 6 Mb spots with similar molecular weight (17 kDa) but different isoelectric pH. Tandem mass spectrometry identified multiple PTM (phosphorylation, methylation, carboxymethylation, acetylation, and 4-hydroxynonenal alkylation) in these 6 isoforms. The amino acids susceptible to phosphorylation were serine (S), threonine (T), and tyrosine, whereas other PTM were detected in lysine (K), arginine (R), and histidine residues. Additionally, distal histidine (position 64), critical to heme stability, was found to be alkylated. Overall, Mb PTM increased with aging. The aging-induced PTM, especially those occurring close to hydrophobic heme pocket, could disrupt Mb tertiary structure, influence heme affinity, and compromise oxygen binding capacity, leading to decreased color stability of fresh beef. Furthermore, PTM at K45, K47, and K87 were unique to Mb from non-aged beef, whereas PTM at R31, T51, K96, K98, S121, R139, and K147 were unique to Mb from aged counterparts, indicating that these Mb PTM could be used as novel biomarkers for fresh beef color stability.

Principal component analysis of lipid and protein oxidation products and their impact on color stability in bison longissimus lumborum and psoas major muscles

The study aims were to compare lipid (malondialdehyde [MDA], 4-hydroxy-2-nonenal [HNE]) and protein (carbonyl content [CAR]) oxidation products between two bison muscles (longissimus lumborum [LL] and psoas major [PM]) at different aging and retail display time and determine their influence on muscle color stability. Regardless of the aging and retail display time, LL showed greater redness (a* value; P = 0.04) and lower surface discoloration (P < 0.01) than PM as well as LL exhibited lower MDA, HNE, and CAR content compared to PM (P < 0.05). In both muscles, MDA showed the highest correlation to a* (r = -0.78; P < 0.01) and discoloration (rs = 0.82; P < 0.01) scores, particularly in PM muscle compared to LL muscle. In conclusion, the principal component analysis revealed 4 distinct color deterioration clusters within steaks displayed at d 4 according to the muscle and aging time, and MDA critically influences color deterioration patterns in bison muscles.

Effects of Astragalus Membranaceus supplementation on oxidative stability of Cashmere goat

Astragalus membranaceus (AM) provides a rich source of polysaccharides that can act as powerful antioxidants, but their potential as feed ingredients in the lamb industry still rarely exploited. The objective of this study was to investigate the effect of dietary astragalus membranaceus supplementation on oxidative stability of goat muscles. Longissimus dorsi (LD) muscles from two groups of Cashmere goat (basal diet, C group; basal diet supplemented with 1% astragalus membranaceus root, AM group) were evaluated for lipid oxidation, myoglobin oxidation, activity of antioxidant enzymes, and antioxidant capacity. The results showed that color parameters in Cashmere goat of two feeding conditions were no significant difference (p > .05). In AM group, myoglobin (Mb) content was higher than C, while metmyoglobin (MMb) (p < .05) and malondialdehyde (MDA) (p < .01) were lower. Additionally astragalus membranaceus supplementation had a significant effect on superoxide dismutase (SOD) and catalase (CAT) (p < .001). In whole, the AM group goats presented a relatively higher antioxidant capacity than C. Especially, RSA and CUPRAC values of AM group goats had significantly higher than C (p < .05). Consequently, the AM group goats ingested abundant astragalus membranaceus, which enhanced the antioxidant capacity. Thus, it can eliminate free radicals and effectively inhibit oxidation.

Physicochemical and Biochemical Properties of Ground Pork Formulated with Addition of Prunus cerasus (cv Montmorency) Extract and Subjected to Freezing Storage

Broad research interest is observed over last decade, toward searching for a new natural antioxidants, which could be applied in food industry. Especially attractive seems to be those rich in polyphenols, such as cherry. Thus, presented study determine the effect of cherry extract (equivalent of 20 mg and 40 mg GAE kg−1) on physicochemical properties of ground pork frozen for 80 days. Samples were analyzed for color, color change, color attractiveness, myoglobin oxidation, fat oxidation, fatty acids profile, cooking loss, texture profile. The positive effect of cherry extract was observed for fat oxidation but cooking loss was higher in samples with extract addition. Color, color change, color attractiveness, myoglobin oxidation or fatty acids profile did not differ between groups.

The Effect of Long-Term Frozen Storage on the Quality of Meat (Longissimus thoracis et Lumborum) from Female Roe Deer (Capreolus capreolus L.)

The objective of this study was to determine the quality of meat (Longissimus thoracis et lumborum) from 10 female roe deer (Capreolus capreolus L.), which was vacuum-packaged, frozen-stored (−26°C) for 6, 10, and 12 months, and compared with fresh, nonfrozen meat. Roe deer (aged 3 to 5 years) were hunter-harvested in north-eastern Poland in December and January during the same hunting season. Frozen storage did not affect the proximate chemical composition of meat (except for ash content). An analysis of the physicochemical properties of meat revealed that frozen-stored meat was characterized by a darker color, a higher hue angle, lower ability to bind its own and added water, and lower cooking loss compared with nonfrozen meat. The values noted for meat samples that were stored in the freezer for 12 months (increase in pH, considerable decrease in water-holding capacity, and first symptoms of flavor deterioration) indicate that frozen roe deer meat should be stored for no more than 10 to 12 months to maintain its high quality.

The Effect of PUFA-Rich Plant Oils and Bioactive Compounds Supplementation in Pig Diet on Color Parameters and Myoglobin Status in Long-Frozen Pork Meat

The study evaluated the effect of pig diet supplementation with rapeseed or linseed oil, and vitamin E or selenium, or both vitamin E and selenium on color parameters and myoglobin content of pork Semimembranosus muscle after long-term freezing storage during nine months. The influence of the type of the bioactive compounds added to pig diet on the content of myoglobin or oxymyoglobin, metmyoglobin and deoksymyoglobin in Semimembranosus m. was also assessed. The results indicate that the presence of oils rich in polyunsaturated fatty acids (PUFA) in pig diet improves the color of pork meat. Supplementation of dietary plant oils or dietary oils with antioxidants tended to increase significantly the concentration of oxymyoglobin and decrease the concentration of metmyoglobin in meat compared to the control group. The highest content of oxymyoglobin was observed in meat obtained from pigs fed diets with linseed oil. The best color scores (highest a* parameter) was noted for rapeseed oil group (with no addition of antioxidants). In conclusion, the addition of antioxidants to pigs’ forage supplemented with PUFA-rich oils is not recommended in order to improve color of long-term frozen pork.

Evaluation of Physicochemical Deterioration and Lipid Oxidation of Beef Muscle Affected by Freeze-thaw Cycles

This study was performed to explore the deterioration of physicochemical quality of beef hind limb during frozen storage at -20℃, affected by repeated freeze-thaw cycles. The effects of three successive freeze-thaw cycles on beef hind limb were investigated comparing with unfrozen beef muscle for 80 d by keeping at -20±1℃. The freeze-thaw cycles were subjected to three thawing methods and carried out to select the best one on the basis of deterioration of physicochemical properties of beef. As the number of repeated freeze-thaw cycles increased, drip loss decreased and water holding capacity (WHC) increased (p<0.05) till two cycles and then decreased. Cooking loss increased in cycle one and three but decreased in cycle two. Moreover, drip loss, WHC and cooking loss affected (p<0.05) by thawing methods within the cycles. However, pH value decreased (p<0.05), but peroxide value (p<0.05), free fatty acids value (p<0.05) and TBARS value increased (p<0.05) significantly as the number of repeated freeze-thaw cycles increased. Moreover, significant (p<0.05) interactive effects were found among the thawing methods and repeated cycles. As a result, freeze-thaw cycles affected the physicochemical quality of beef muscle, causing the degradation of its quality.

Current research in meat color

This review surveyed recent literature focused on factors that affect myoglobin chemistry, meat color, pigment redox stability, and methodology used to evaluate these properties. The appearance of meat and meat products is a complex topic involving animal genetics, ante- and postmortem conditions, fundamental muscle chemistry, and many factors related to meat processing, packaging, distribution, storage, display, and final preparation for consumption. These factors vary globally, but the variables that affect basic pigment chemistry are reasonably consistent between countries. Essential for maximizing meat color life is an understanding of the combined effects of two fundamental muscle traits, oxygen consumption and metmyoglobin reduction. In the antemortem sector of research, meat color is being related to genomic quantitative loci, numerous pre-harvest nutritional regimens, and housing and harvest environment. Our knowledge of postmortem chilling and pH effects, atmospheres used for packaging, antimicrobial interventions, and quality and safety of cooked color are now more clearly defined. The etiology of bone discoloration is now available. New color measurement methodology, especially digital imaging techniques, and improved modifications to existing methodology are now available. Nevertheless, unanswered questions regarding meat color remain. Meat scientists should continue to develop novel ways of improving muscle color and color stability while also focusing on the basic principles of myoglobin chemistry.

Redox instability and hemin loss of mutant sperm whale myoglobins induced by 4-hydroxynonenal in vitro

The effects of 4-hydroxy-2-nonenal (HNE) on redox stability of Oxy- and Deoxy- wild-type (WT) and recombinant sperm whale myoglobins (P88H/Q152H, L29F, H97A, and H64F) and hemin loss from Met-myoglobin (Mb) were investigated. HNE induced greater redox instability in WT and mutant Mbs compared to controls (p < 0.05). The extent of HNE-induced OxyMb oxidation was lesser in L29F (p < 0.05) and greater in H97A and P88H/Q152H than in WT (p < 0.05). H64F DeoxyMb was more redox stable than WT DeoxyMb in the presence of HNE (p < 0.05). HNE alkylation occurred exclusively on histidine residues, and histidine 48 was alkylated in all sperm whale myoglobins. HNE alkylation accelerated the protoporphyrin moiety loss only in H97A. Met- forms of WT and L29F but not Deoxy- or Oxy- forms released hemin during storage. Primary structure strongly influenced Mb redox stability in the presence of reactive secondary lipid oxidation products.

Species-specific myoglobin oxidation

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

Characterization of bison (Bison bison) myoglobin

Bison is an alternate meat species gaining increased popularity in North America. Although previous investigations reported that bison meat discolors faster than beef, the molecular basis of this observation has not been investigated. Therefore, the objective of the present study was to determine the redox stability, thermostability, and primary structure of bison myoglobin (Mb), in comparison with beef Mb. Purified bison and beef myoglobins were analyzed for autoxidation, lipid oxidation-induced oxidation, and thermostability. Matrix Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometry was utilized for determining the exact molecular mass of bison Mb, whereas Edman degradation was employed to determine the amino acid sequence. Bison and beef myoglobins behaved similarly in autoxidation, lipid oxidation-induced oxidation, and thermostability. The observed molecular mass of bison and beef myoglobins was 16,949 Da, and the primary structure of bison Mb shared 100% similarity with beef and yak myoglobins. Noticeably, the amino acid sequence of bison Mb was different from other ruminant myoglobins, such as water-buffalo, sheep, goat, and red-deer. The present study is the first to report the primary structure of bison Mb. Same primary structure and similar biochemical attributes of bison and beef myoglobins suggested that the observed rapid discoloration in bison meat could not be attributed to biochemistry of bison Mb.

Differences in pig muscle proteome according to HAL genotype: implications for meat quality defects

Bidimensional electrophoresis was used to compare sarcoplasmic protein profiles of early post-mortem pig semimembranosus muscles, sampled from pigs of different HAL genotypes (RYR1 mutation 1841T/C): 6 NN, 6 Nn, 6 nn. ANOVA showed that 55 (18%) of the total of 300 matched protein spots were influenced by genotype, and hierarchical clustering analysis identified 31 (10% of the matched proteins) additional proteins coregulated with these proteins. Fold-changes of differentially expressed proteins were between 1.3 and 21.8. Peptide mass fingerprinting identification of 78 of these 86 proteins indicates that faster pH decline of nn pigs was not explained by higher abundance of glycolytic enzymes. Results indicate further that nn muscles contained fewer proteins of the oxidative metabolic pathway, fewer antioxidants, and more protein fragments. Lower abundance of small heat shock proteins and myofibrillar proteins in nn muscles may at least partly be explained by the effect of pH on their extractability. Possible consequences of lower levels of antioxidants and repair capacities, increased protein fragmentation, and lower extractability of certain proteins in nn muscles on meat quality are discussed.

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 degrees 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.

Fluorescent image analysis of lipid hydroperoxides in fish muscle with 3-perylene diphenylphosphine

A fluorescent image analysis method was developed to evaluate lipid hydroperoxide formation in fish muscle. The lipid hydroperoxides generated in white and dark fish muscles during storage at 5-6 degrees C oxidized 3-perylene diphenylphosphine located in the tissue to yield the fluorescent derivative, 3-perylene diphenylphosphine oxide (3-PeDPPO). 3-PeDPPO thus obtained was determined by digital fluorescent image analysis. The 3-PeDPPO fluorescence intensity of white and dark muscle increased during low-temperature storage (0-24 h) and was clearly correlated with total lipid hydroperoxide levels in muscle extracts, which were determined by using HPLC based on a triphenylphosphine oxidation method (R2 = 0.954). These results suggest that 3-PeDPPO fluorescence, coupled with fluorescent image analysis, is a novel tool for direct determination of lipid hydroperoxides in fish muscle without a need for extraction of lipid.