Intramuscular fat and muscle aerobicity reduce colour stability

The brown discolouration of lamb meat reduces its appeal to consumers, costing the Australian Lamb industry considerably due to the discounting of product. Lamb meat browning is caused by the oxidisation of myoglobin pigments into the brown metmyoglobin form. The rate of this oxidisation is greater in more aerobic muscles (O'Keeffe and Hood 1982), with aerobicity quantified by the measurement of isocitrate dehydrogenase activity (ICDH). High intramuscular fat percentages (IMF) have been associated with high ICDH levels, so if industry moves to increase IMF we can hypothesise that there will be an ICDH linked increase in the brownness of lamb meat after 3 days of retail display.

Using vitamin E to improve colour stability is less effective in long aged lamb meat

Brown discolouration of lamb meat on retail display reduces consumer appeal, limiting the shelflife and value of the product. The rate of change in colour from red to brown, known as colour stability, is increased in short aged meat with high intramuscular fat (IMF) content (Calnan et al 2014). Therefore genotypic selection for IMF to improve sensory appeal may reduce lamb meat colour stability. Extended aging of lamb meat also reduces colour stability of lamb meat (Jose et al, 2008), a concern for chilled meat shipped for 35 - 70 days to distant markets. High intramuscular vitamin E (a-tocopherol) concentration, achieved by dietary supplementation, slows the loss of redness in lamb aged 5 - I 0 days (Jose et al, 2008). Given that colour stability worsens with aging, the impact of a-tocopherol may be greater in long-aged and high IMF meat. We hypothesised that high muscle a-tocopherol concentration in lambs will retain redness during display of the longissimus, particularly in long-aged and high IMF meat

Selection for intramuscular fat and lean meat yield will improve the bloomed colour of Australian lamb loin meat

The colour of bloomed m. longissimus was measured 24 h post slaughter for 8165 lamb carcasses produced over 5 years across 8 sites in Australia. Intramuscular fat across a 2 to 8% range and shortloin fat weight were positively associated with meat lightness (L*), redness (a*), yellowness (b*), hue and chroma (P < 0.01). Shortloin muscle weight was negatively associated with these meat colour parameters (P < 0.01), although this was largely accounted for by correlated changes in intramuscular fat (P < 0.01). The effect of sire breeding values for lamb weight, shortloin muscle depth and fat depth on loin L*, a*, b*, hue and chroma were small and varied between lambs of different sire type, dam breed and sex. Thus selection for lean meat yield will have neutral or positive effects on meat colour, while selection for increased intramuscular fat will make the bloomed colour of lamb meat lighter and redder

Reducing the pH of lamb carcasses will improve retail meat colour

Meat colour data was collected from 4,953 lambs produced at 5 sites across Australia over a 5 year period (2007-2011) as part of the Sheep Cooperative Research Centre’s information nucleus flock experiment. Longissimus muscle samples were collected 24 h post-mortem, vacuum packaged, aged for 5 days and then placed under simulated retail display conditions for 3 days. At the end of this period light reflectance of the meat surface was measured with a Hunterlab reflectometer and a ratio was calculated (630 nm/580 nm reflectance) to represent redness, with higher values redder and hence more desirable. These ratios were analysed using linear mixed effects models. The base model included fixed effects for site, year of birth, kill group, sire type and dam breed. In a second analysis pH measured 24 h post-mortem was included in the base model as a covariate. Of the dam breeds, Merino progeny had 0.19 units lower redness than those of Maternal dam breed. Similarly the Merino sire type produced lower redness values than Maternal or Terminal sired lambs, with 0.39 units difference seen between lambs of Merino and Terminal sire types. pH was negatively associated with meat redness, with a 0.92 unit decrease (P<0.01) in redness across the pH range of 5.4 to 6. With pH included in the model, the effect of sire type was not significant, suggesting that differences in post-mortem muscle pH between sire types may underpin the observed variation in retail meat colour. Our findings suggest that by reducing the pH of lamb loins we can improve the redness of the meat whilst on retail display

Sire selection for muscling improves the lightness and redness of lamb meat

Meat colour was measured in 7732 lambs produced at 8 sites across Australia over a 5 year period (2007-2011) and slaughtered in 125 groups as pari of the Sheep Cooperative Research Centre's information nucleus flock experiment. Lambs were the progeny of sites of different types (merino, maternal and terminal) selected for a diverse range in Australian Sheep Breeding Values for post weaning eye muscle depth (PEMD). 24 hours post slaughter them. longissimus was cut at the 12th rib, a probe was used to measure pH and the meat surface was allowed to bloom/oxygenate for 30 minutes before fresh colour measures of lightness (L*), redness (a*) and yellowness (b*) were captured using a Minolta colorimeter. These measures were analysed in a multivariate analysis before least square means were produced for L *,a* and b* using a linear mixed effects model in SAS. The base model included fixed effects for site, year of birth, slaughter group, sex and dam breed within sire type as well as random effects for sire and dam by year. In a second analysis sire PEMD estimates were included in the model as a covariate. Increasing sire PEMD across a range of -2 to 4 was associated with an increase (P<0.01) in the predicted means for L*, a* and b* by 1.15, 0.38 and 0.55 units respectively. When pH measured 24 hours post-m01iem was accounted for in the model, the impact of sire PEMD estimates on L *, a* and b* were halved. This suggests that selection for sires based on PEMD may impact meat colour via changes in muscle metabolism that affect the extent of glycolysis and pH decline post slaughter. Our findings suggest that using sires with high PEMD will improve the lightness and redness of the meat produced

Dietary vitamin E supplementation reduces lamb meat browning on display following up to 70 days of chilled storage

Rapid browning limits the retail display of lamb meat, particularly following extended chilled storage that is typical of international shipment. Lamb stored chilled for short periods browns more rapidly on retail display when the meat has high levels of marbling (intramuscular fat), a high pH or greater oxidative capacity. In contrast, high muscle vitamin E concentration reduces browning of short stored lamb meat on retail display. However, the capacity of dietary vitamin E supplementation to reduce retail browning in lamb meat following extended chilled storage is unknown. Additionally, the ability of vitamin E to mitigate the negative impacts of intramuscular fat, pH and oxidative capacity on meat browning following chilled storage is unknown. Sixty six industry sires of Terminal, Merino and Maternal breed types were bred with Merino and Merino-cross dams to produce 132 lambs. The two lambs from each sire were divided into two vitamin E treatment groups that were housed in 12 pens (6 pens per treatment) for 8 weeks leading up to slaughter. Control lambs (6 pens of 11 lambs) were fed a pelleted ration containing basal levels of vitamin E (30 mg/kg feed) while supplemented lambs (6 pens of 11 lambs) were fed the same ration with increased vitamin E content (275 mg/kg feed). After slaughter, the m. longissimus lumborum was sampled for measurement of vitamin E concentration, intramuscular fat, pH, oxidative enzyme isocitrate dehydrogenase activity, and retail meat colour. Colour samples were vacuum packaged for storage at −1°C for 5, 35 and 70d, before being re-sliced, wrapped and placed under stimulated retail display where meat redness (R630/R580) was measured 24 hourly for 72 h. Lamb pens supplemented with vitamin E produced redder loin meat at 24, 48 and 72 h of display compared to control pens of lambs (P < 0.05), regardless of storage time. Increasing muscle vitamin E concentration from 0.8 to 4 mg/g of loin muscle improved meat redness to a slightly greater extent in meat stored for 35 d than 5 or 70 d (P < 0.05). High intramuscular fat reduced redness in 5 day stored lamb (P < 0.05) and increasing muscle vitamin E had a greater effect improving the display colour in this highly marbled meat. These results demonstrate that dietary vitamin E supplementation will improve the display colour of highly marbled or long stored lamb meat

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