Phenotypic characterisation of colour stability of lamb meat

Molecular insights into quality and authentication of sheep meat from proteomics and metabolomics

Sheep meat (encompassing lamb, hogget and mutton) is an important source of animal protein in many countries, with a unique flavour and sensory profile compared to other red meats. Flavour, colour and texture are the key quality attributes contributing to consumer liking of sheep meat. Over the last decades, various factors from 'farm to fork', including production system (e.g., age, breed, feeding regimes, sex, pre-slaughter stress, and carcass suspension), post-mortem manipulation and processing (e.g., electrical stimulation, ageing, packaging types, and chilled and frozen storage) have been identified as influencing different aspects of sheep meat quality. However conventional meat-quality assessment tools are not able to elucidate the underlying mechanisms and pathways for quality variations. Advances in broad-based analytical techniques have offered opportunities to obtain deeper insights into the molecular changes of sheep meat which may become biomarkers for specific variations in quality traits and meat authenticity. This review provides an overview on how omics techniques, especially proteomics (including peptidomics) and metabolomics (including lipidomics and volatilomics) are applied to elucidate the variations in sheep meat quality, mainly in loin muscles, focusing on colour, texture and flavour, and as tools for authentication. SIGNIFICANCE: From this review, we observed that attempts have been made to utilise proteomics and metabolomics techniques on sheep meat products for elucidating pathways of quality variations due to various factors. For instance, the improvement of colour stability and tenderness could be associated with the changes to glycolysis, energy metabolism and endogenous antioxidant capacity. Several studies identify proteolysis as being important, but potentially conflicting for quality as the enhanced proteolysis improves tenderness and flavour, while reducing colour stability. The use of multiple analytical methods e.g., lipidomics, metabolomics, and volatilomics, detects a wider range of flavour precursors (including both water and lipid soluble compounds) that underlie the possible pathways for sheep meat flavour evolution. The technological advancement in omics (e.g., direct analysis-mass spectrometry) could make analysis of the proteins, lipids and metabolites in sheep meat routine, as well as enhance the confidence in quality determination and molecular-based assurance of meat authenticity.

Retail Packaging Affects Colour, Water Holding Capacity, Texture and Oxidation of Sheep Meat more than Breed and Finishing Feed

This study investigated the CIELab colour, water holding capacity, texture and oxidative stability of sheep meat from different breeds, finishing feeds, and retail packaging methods. Leg primal cuts from a subset of Composite wether lambs (n = 21) and Merino wether yearlings (n = 21) finished on a standard diet containing grain and cereal hay, a standard diet with camelina forage, or a standard diet with camelina meal, were used in this study. Semimembranosus and Vastus lateralis were packaged in vacuum skin packaging (VSP), or modified atmosphere packaging with 80% O₂ and 20% CO₂ (HioxMAP), or with 50% O₂, 30% N₂, and 20% CO₂ (TrigasMAP). Packaging had a greater effect (p < 0.001) on L*, a*, b*, hue, and chroma than the effects from breed and finishing feed. Purge loss was affected by packaging. Cooking loss was affected by breed for Semimembranosus and packaging for both muscle types. HioxMAP and TrigasMAP increased WBSF and Texture Profile Analysis hardness of the meat compared to VSP. Lipid oxidation, assessed by TBARS, were lower in camelina forage or camelina meal supplemented diets and TrigasMAP compared to standard diet and HioxMAP, respectively. Total carbonyl and free thiol content were lower in VSP. Thus, supplementing feed with camelina forage or meal and lowering oxygen content in retail packaging by TrigasMAP or VSP are recommended to ensure optimal sheep meat quality.

Proteomic Changes in Sarcoplasmic and Myofibrillar Proteins Associated with Color Stability of Ovine Muscle during Post-Mortem Storage

The objective of this study was to investigate the proteomic characteristics for the sarcoplasmic and myofibrillar proteomes of M. longissimus lumborum (LL) and M. psoasmajor (PM) from Small-tailed Han Sheep. During post-mortem storage periods (1, 3, and 5 days), proteome analysis was applied to elucidate sarcoplasmic and myofibrillar protein changes in skeletal muscles with different color stability. Proteomic results revealed that the identified differentially abundant proteins were glycolytic enzymes, energy metabolism enzymes, chaperone proteins, and structural proteins. Through Pearson’s correlation analysis, a few of those identified proteins (Pyruvate kinase, Adenylate kinase isoenzyme 1, Creatine kinase M-type, and Carbonic anhydrase 3) were closely correlated to representative meat color parameters. Besides, bioinformatics analysis of differentially abundant proteins revealed that the proteins mainly participated in glycolysis and energy metabolism pathways. Some of these proteins may have the potential probability to be predictors of meat discoloration during post-mortem storage. Within the insight of proteomics, these results accumulated some basic theoretical understanding of the molecular mechanisms of meat discoloration.

Insights on meat quality from combining traditional studies and proteomics

Following a century of major discoveries on the mechanisms determining meat colour and tenderness using traditional scientific methods, further research into complex and interactive factors contributing to variations in meat quality is increasingly being based on data-driven "omics" approaches such as proteomics. Using two recent meta-analyses of proteomics studies on beef colour and tenderness, this review examines how knowledge of the mechanisms and factors underlying variations in these meat qualities can be both confirmed and extended by data-driven approaches. While proteomics seems to overlook some sources of variations in beef toughness, it highlights the role of post-mortem energy metabolism in setting the conditions for development of meat colour and tenderness, and also points to the complex interplay of energy metabolism, calcium regulation and mitochondrial metabolism. In using proteomics as a future tool for explaining variations in meat quality, the need for confirmation by further hypothesis-driven experimental studies of post-hoc explanations of why certain proteins are biomarkers of beef quality in data-driven studies is emphasised.

Effect of Sex and Breed on HSPA1A, Blood Stress Indicators and Meat Quality of Lambs

The objective of this study was to examine sex and breed effects on heat shock protein 70 (HSPA1A), blood stress indicators and meat quality attributes of lambs. A hundred male and female lambs from the Dorper (n = 50) and Merino (n = 50) breeds were used in this study. Breed and sex had a significant (p < 0.05) effect on the levels of plasma HSPA1A and lactate; where the Merino lambs had higher levels than Dorper. The female lambs had higher levels of plasma HSPA1A than male lambs. Significant sex and breed interactions (p < 0.05) on the levels of plasma HSPA1A were seen. Females had higher (p < 0.05) pHu than males. Dorper lambs had higher (p < 0.05) pH₄₅, meat lightness, thawing loss and tougher meat the Merino breed. Significant correlations were found amongst plasma stress indicators and meat quality attributes. The results indicate that female lambs were more stressed by the pre-slaughter period than males, while the Merino had a higher physiological stress response compared to the Dorper. However, the Dorper breed produced tougher meat.

Effects of active edible coating based on thyme and garlic essential oils on lamb meat shelf life after long-term frozen storage

BACKGROUND

The frozen preservation of lamb meat could be crucial for successful international trade. The shelf life of thawed meat is shorter than that of fresh meat, so techniques or procedures are required to improve post-thawing meat quality attributes. This study investigated the effect of alginate-based edible coatings after the incorporation of essential oils of thyme (Thymus vulgaris L.) and garlic (Allium sativum L.) on thawed lamb meat (longissimus thoracis et lumborum muscle) quality after long-term frozen storage. Meat samples came from ten light lambs and the evolution of attributes related to shelf life, such as water-holding capacity, color stability, and lipid oxidation, was monitored during display (1, 4 and 7 days). Four meat treatments were evaluated: control (CON, uncoated meat), edible coat of alginate meat (ECA), and ECA with thyme or garlic essential oils (0.05%) (THY and GAR).

RESULTS

The alginate-based edible coatings decreased exudative losses (P < 0.001) and modified color characteristics, especially increasing yellowness (P < 0.001) and chrome (P < 0.001). GAR decreased redness (P < 0.001) and the oxy/met ratio [R (630/580) wavelength light reflectance] or discoloration [R (630-580)]. THY was the treatment that best retained color during display and also showed a significantly lower lipid oxidation (P < 0.05) than CON and ECA, whereas GAR presented intermediate values.

CONCLUSION

The addition of bioactive essential oils to alginate-based edible coatings improved preservation and shelf life of lamb meat after thawing. © 2019 Society of Chemical Industry.

Implications of the variation in bloom properties of red meat: A review

This review aimed to examine the literature about blooming to determine any practical implications for meat colour and colour stability. Blooming is critical to surface colour in addition to pigment and achromatic factors and causes meat to become lighter (higher L*) and redder (higher a*) due to the formation of oxymyoglobin (OMb). Bloom depth of red meat varies in the range of about 1-12 mm due to a range of extrinsic factors notably oxygen partial pressure, temperature and time post slicing. A range of intrinsic factors also affect bloom acting via the oxygen consumption rate of mitochondria and metmyoglobin (MMb) reductase activity post mortem, such as post mortem age, muscle type, rigor temperature, ultimate pH (pHu), genotype and vitamin E status. These sources of variation have implications for measurement protocols and commercial applications for colour and colour stability. Development of a rapid method to measure bloom depth would enable assessment of bloom independently of surface colour.

High Oxygen Modified Atmosphere Packaging Negatively Influences Consumer Acceptability Traits of Pork

Current trends in meat packaging have seen a shift from conventional overwrap to vacuum packing (VAC) and modified atmosphere packaging (MAP). The aim of this experiment was to investigate the effects of high oxygen MAP (HiOxMAP) of pork loins compared with vacuum packed (VAC) on eating quality and colour, after storage in simulated illuminated retail display conditions. Pork loins (n = 40) were cut and stored under two packaging methods (HiOxMAP, 80% O₂, 20% CO₂; VAC) for up to 14 days, with samples taken at various times for measurements. After 7 days of storage, HiOxMAP samples exhibited inferior consumer acceptability for tenderness, flavor, overall liking, quality and re-purchase intention as well as higher shear force and hardness, relative to VAC samples (p < 0.05 for all). Loins stored in HiOxMAP had higher lightness (L*), redness (a*) and yellowness (b*) values at 3 and 7 days, but lower ratio of oxymoglobin to metmyoglobin (oxy/met) values in the meat surface at 14 days of display, relative to VAC samples (p < 0.05 for all). The oxy/met ratio declined from 2.3 to 1.7 between days 3 and 14 of display in HiOxMAP samples (p < 0.05), whereas the ratio was similar and stayed relatively high for VAC samples. VAC samples produced consistently higher colour values (a*, b*, oxy/met) when left to bloom 30 min after removal from packaging (p < 0.05). Lipid oxidation values, measured using thiobarbituric acid reactive substances, in HiOxMAP pork loins, were higher at all time points compared to VAC during the 14 day storage period (p < 0.05). The use of vacuum packing for retail shelves, should be considered as the preferred option, over HiOxMAP.

Genetic variation in colour stability traits of lamb cuts under two packaging systems

Data from samples of longissmus lumborum (LL) and semimembranosus (SM) muscles from 391 lamb carcasses, which had been packaged in overwrap (OW) or high oxygen modified atmosphere packaging (MAP_O2) systems and then subjected to simulated retail display, were used to estimate genetic variation for colour stability traits of lamb meat as a step in identifying a trait for genetic evaluation. Traits included the ratio of the reflectance of light at wavelengths of 630 nm and 580 nm (oxy/met) measured at a single time point at the end of the display period (day 3 under OW; day 8 under MAP_O2) and the predicted time for oxy/met to reach a benchmark value. Under OW and MAP_O2, the measures of meat colour stability of the LL tended to be of moderate heritability (0.09-0.29), but for the SM were of low heritability (0-0.10). Improving retail colour stability of lamb loins through selection of genetically superior animals may be better based on measurement of oxy/met.

Initial Bloom Color is a Poor Predictor of Retail Color Stability in Lamb Loin Meat

The rapid browning of lamb meat on retail display reduces its appeal to consumers and thus the marketability of lamb meat. Predicting the rate of meat browning on retail display would allow retailers to effectively manage this issue. The ability of bloomed meat color at the start of retail display to predict meat browning over subsequent retail display was investigated in lamb loin meat. Mixed breed lambs (n = 4404) produced at 5 sites over 5 yr were slaughtered at ∼23kg carcass weight and measured for loin pH at 24 h, myoglobin, iron and zinc concentrations, isocitrate dehydrogenase activity and intramuscular fat. Loin meat was aged for 5 d before being re-sliced and overwrapped for color measurement over a 72 h simulated retail display. Meat redness (R630/R580) was measured after blooming and every 24 h across display using a Hunterlab spectrophotometer. Simple and partial correlation coefficients between initial and subsequent R630/R580 measures over the display were low (≤ 0.4). Accounting for key muscle traits influencing meat color such as pH24, myoglobin, iron or intramuscular fat concentration did not improve these correlations between bloomed meat color and subsequent meat color over retail display. Therefore bloomed meat color at the start of display is not a useful predictor of meat browning after 24 h of retail display. Alternatively, correlations between 24, 48, and 72 h R630/R580 were > 0.8, suggesting that meat color measured from 24 h of display can accurately predict subsequent retail meat browning.

Genetic correlations between wool traits and meat quality traits in Merino sheep

Genetic correlations between 29 wool production and quality traits and 25 meat quality and nutritional value traits were estimated for Merino sheep from an Information Nucleus (IN). Genetic correlations among the meat quality and nutritional value traits are also reported. The IN comprised 8 flocks linked genetically and managed across a range of sheep production environments in Australia. The wool traits included over 5,000 yearling and 3,700 adult records for fleece weight, fiber diameter, staple length, staple strength, fiber diameter variation, scoured wool color, and visual scores for breech and body wrinkle. The meat quality traits were measured on samples from the and included over 1,200 records from progeny of over 170 sires for intramuscular fat (IMF), shear force of meat aged for 5 d (SF5), 24 h postmortem pH (pHLL; also measured in the , pHST), fresh and retail meat color and meat nutritional value traits such as iron and zinc levels, and long-chain omega-3 and omega-6 polyunsaturated fatty acid levels. Estimated heritabilities for IMF, SF5, pHLL, pHST, retail meat color lightness (), myoglobin, iron, zinc and across the range of long-chain fatty acids were 0.58 ± 0.11, 0.10 ± 0.09, 0.15 ± 0.07, 0.20 ± 0.10, 0.59 ± 0.15, 0.31 ± 0.09, 0.20 ± 0.09, 0.11 ± 0.09, and range of 0.00 (eicosapentaenoic, docosapentaenoic, and arachidonic acids) to 0.14 ± 0.07 (linoleic acid), respectively. The genetic correlations between the wool production and meat quality traits were low to negligible and indicate that wool breeding programs will have little or no effect on meat quality. There were moderately favorable genetic correlations between important yearling wool production traits and the omega-3 fatty acids that were reduced for corresponding adult wool production traits, but these correlations are unlikely to be important in wool/meat breeding programs because they have high SE, and the omega-3 traits have little or no genetic variance. Significant genetic correlations among the meat quality traits included IMF with SF5 (-0.76 ± 0.24), fresh meat color * (0.50 ± 0.18), and zinc (0.41 ± 0.19). Selection to increase IMF will improve meat tenderness and color which may address some of the issues with Merino meat quality. These estimated parameters allow Merino breeders to combine wool and meat objectives without compromising meat quality.

Effect of vacuum ageing on quality changes of lamb steaks from early fattening lambs during aerobic display

The effects of vacuum ageing on the quality changes of lamb steaks during retail display were assessed. Biceps femoris and Quadriceps femoris muscles from thirty early fattening lambs fed barley straw and concentrate or alfalfa and concentrate were used. Half of the muscles were vacuum aged for three weeks (VA), and the other half were not aged (control). Control and VA muscles were sliced and aerobically displayed. Weight loss, pH, aldehyde contents, instrumental color characteristics and color acceptance were measured at display days 1, 3, 7 and 14. At day 1 redness was higher in VA lamb. However, redness of VA lamb decreases more rapidly during further storage. Redness and color acceptance decreased in VA lamb from day 3, whereas in not-aged lamb the decrease was observed from day 7 onwards. From days 7 to 14 a drop of color acceptance accompanied by an increase in pH and a decrease in lightness was observed in control and VA lamb.

Balancing consumer and societal requirements for sheep meat production: an Australasian perspective

Although there has been a decline in sheep numbers in Australia and New Zealand, both countries remain significant producers and exporters of sheep meat. The ongoing demand for more sustainable and ethical animal farming systems and practices requires sheep production industries to be both vigilant and responsive to consumer and the broader societal needs. Demonstration of continuous improvement in animal welfare is paramount and the welfare risks and challenges confronting Australasian sheep industries now and into the future are discussed.

Genetic parameters for meat quality traits of Australian lamb meat

Genetic parameters were estimated for a range of meat quality traits recorded on Australian lamb meat. Data were collected from Merino and crossbred progeny of Merino, terminal and maternal meat breed sires of the Information Nucleus programme. Lambs born between 2007 and 2010 (n=8968) were slaughtered, these being the progeny of 372 sires and 5309 dams. Meat quality traits were found generally to be of moderate heritability (estimates between 0.15 and 0.30 for measures of meat tenderness, meat colour, polyunsaturated fat content, mineral content and muscle oxidative capacity), with notable exceptions of intramuscular fat (0.48), ultimate pH (0.08) and fresh meat colour a* (0.08) and b* (0.10) values. Genetic correlations between hot carcass weight and the meat quality traits were low. The genetic correlation between intramuscular fat and shear force was high (-0.62). Several measures of meat quality (fresh meat redness, retail meat redness, retail oxy/met value and iron content) appear to have potential for inclusion in meat sheep breeding objectives.

Factors affecting the colour of lamb meat from the longissimus muscle during display: the influence of muscle weight and muscle oxidative capacity

Spectrophotometric measures were used to determine the redness:browness (R630/R580) of 4238 lamb longissimus muscle after 3 days under simulated display. The results were analysed using linear mixed effects models. Environmental factors represented by effects such as kill group and site of production produced the greatest variation of up to 2.76 units in R630/R580. Isocitrate dehydrogenase activity, reflecting muscle oxidative capacity, reduced R630/R580 by 0.5 units. Selection for high muscling sires increased R630/R580 by 0.27 units, likely due to changes in muscle oxidative capacity. Lamb carcass weight also increased R630/R580 by 0.5 units. Analysis of genotypic factors influencing lamb size and growth rate such as sire type and dam breed further supported that increased growth rate improves meat R630/R580. Our findings suggest that breeding for increased growth rate and increased muscle weight could result in Australian lamb meat retaining its red colour for extended periods whilst on display.