Nutrition and Health
The Colour Stability of Aged Lamb benefits from VitE supplementation.
CG. Jose¹, DW. Pethick¹ , GE. Gardner¹ and RH. Jacob²
1Divison of Vet and Biomedical Science, Murdoch University, Murdoch, Western Australia 6150
²Department of Agriculture and Food, South Perth, Western Australia 6151
Australian Sheep Industry CRC
c.jose@murdoch.edu.au
Abstract
This study investigated the effect of Vitamin E (VitE) supplementation on the retail display color of lamb m. semimembranosus (SM) and m. longissimus thoracis et lumborum (LL) and its interaction with pre-display aging. Treatments were designed in a 2x4 factorial, with 2 VitE treatments (175.7 mg VitE/kg of DM grain feed, or no supplementation for 31 days) and 4 aging periods (5 days in air and 10, 20 and 30 days in CO2 packs pre display). Retail colour was measured using a ratio of the percent reflectance of light at 630 nm to 580 nm (oxy/met ratio). Muscle VitE concentration ranged from 0.5 up to 3.5 mg/g in both muscles. Across this range, the oxy/met ratio after 60h display increased (P<0.05) by about 1.5 units, for all aging treatments in the SM, and by a similar amount in the LL but only for samples aged in CO2 for 30days. For the SM, VitE concentrations of above 3.0mg/kg are required to improve the oxy/met ratio to an acceptable level (above 3.5). With sufficient muscle VitE concentrations it may be possible to increase the shelf life of lamb cuts to 60 hours. The stabilizing effect of VitE becomes particularly important when meat is aged longer than 10 days before display.
Introduction
Consumers choose to purchase a cut of lamb primarily based on its visual appearance. A cut which appears red is most desirable, while cuts which appear brown often cannot be sold at the full retail price, resulting in an economic loss to the meat industry. This browning of meat is caused by the oxidation of the muscle pigment myoglobin, from the red oxymyoglobin form, to the brown metmyoglobin from. This oxidation process often causes the development of the brown surface colour within 48 hours of retail display.
The formation of metmyoglobin is effected by many factors including storage conditions, aging, nutrition, and packaging (Faustman & Cassens, 1990; Renerre, 1990; Faustman et al., 1998). The colour stability of lamb can be improved by addition of the antioxidant VitE, via nutritional supplementation (Wulf et al., 1995). VitE (?-tocopherol) is a lipid soluble antioxidant, responsible for protecting the cellular membranes from damage by lipid peroxidation. It seems likely that there is a relationship between lipid peroxidation and the formation of metmyoglobin, but the mechanism is yet to be proved (Faustman et al., 1998). Thus the mechanism that VitE protects myoglobin against oxidation is not fully understood.
Many Primal cuts are exported to overseas markets resulting in extended aging of the product. During aging proteases cause the breakdown of cell membranes which often results in premium, more tender cuts of meat. However aging cuts can often lead to a decline in retail colour stability (Wulf et al., 1995) as the surface of meat prematurely turns brown due to the build up of oxidized lipids, free radicals and other oxidation products.
This study investigated the hypothesis that the colour stability of aged cuts of lamb will be stabilized by the addition of VitE through nutritional supplementation. When sufficient VitE is present, cuts of lamb will have an improved retail shelf life of 60 hours.
Methods
Eighty (forty-if I take out ES) 6-8 month old crossbred whether lambs with a live weight of 42.44±0.54 kg (mean±sem) were used for this experiment. Prior to slaughter the lambs were fed for 31 days on a pelleted ration (11 MJ/kg ME 18% crude protein) at a rate of 1.6kg/hd/day. For half of the lambs the diet was supplemented with synthetic ? tocopherol (175.7mg/kg VitE), the other half (control) received no supplementation (5.85mg/kg VitE).
After slaughter at a commercial abattoir, carcases were halved and primal cuts were either packed fresh in air for 5 days, or in 99% CO2 (2:1 gas to muscle headspace) for 10, 20 or 30 days at a temperature of 2oC (n=10). At the end of each period the m.longissimus thoracis et lumborum (LL) and m.semimembranosus (SM) were dissected from the primals, cut into equal portions 3 cm in thickness, over wrapped with polyvinyl chloride wrap, and displayed under fluorescent lights at 4oC for 96 hours. At the same time samples were taken for analysis of VitE concentration.
Colour measurements were made using a Hunter Lab Mini Scan XE Plus every 12 hours during the display period. Myoglobin oxidation was predicted from the oxy/met ratio calculated as the ratio of light reflectance at 580 and 630 nm (Hunt, 1980). A ratio score of 3.5 was used as a consumer discrimination point, below which the browning of meat becomes evident. Linear mixed effects models (SAS®) were used to test the fixed effects of muscle, aging periods and VitE concentration as a covariate on the oxy/met ratio at 60h display, with animal as a random term.
Results and Discussion
Muscle VitE concentration increased with supplementation (P<0.05). The muscle VitE concentrations ranged from 0.5 up to 3.5 mg/g in both muscles (figure 1a; SM data only). Among the supplemented animals there was a large variation in the VitE accumulated in the muscle compared to the controls (figure 1a); this variation is not yet understood. VitE had a much greater effect on colour stability in the SM muscle across the range of VitE concentration, the oxy/met ratio at 60h increased (P<0.05) by one unit (on average) for all aging treatments (Figure 1a only 30day data only). In the LL the only effect of VitE was in the 30 days aged treatment (figure 1b). Furthermore at 60 hours retail display most LL samples still had a satisfactory retail display colour, even for the control aged samples, contrasting with the SM, where VitE concentrations of above 3.0mg/kg were required to maintain the oxy/met ratio at an acceptable level (above 3.5; figure 1a).
Aging worsened the oxy/met ratio across both muscles in the control (non-supplemented) samples (P<0.05). An effect of aging was evident from 10 days in the SM (data not shown), while in the LL this effect was not evident until 30 days. However these effects were stabilized by the antioxidant activity of VitE, thus underpinning the importance of a VitE supplementation regime when aging lamb meat. This result is supported by Lanari et al. (2002), who showed that aged beef had a better colour stability when supplemented with VitE.
Wulf et al. (1995) showed that malonaldehyde (an indicator of lipid peroxidation) in the muscle increased linearly with aging periods, however lambs supplemented with VitE significantly reduced levels of this product. Although, the link between lipid peroxidation and colour stability has not yet been proved (Faustman et al., 1998), this suggests a possible mechanism as to the poor colour stability in the aged control samples compared to those supplemented with VitE.
Figure 1; the oxy/met ratio at 60 hours retail display in relation to the muscle vitamin E concentration of the a) SM , 30 day aged samples and b) the LL across all aging periods. Means ±sem.
Conclusion
VitE will improve the colour of aged lamb meat over retail display periods particularly in the more oxidative muscles like the SM. With muscle VitE concentrations greater than 3.0mg/kg tissue it may be possible to increase the shelf life of lamb cuts to 60 hours. The stabilizing effect of VitE becomes particularly important when meat is aged. Without VitE supplementation, SM cuts should not be aged for more than 10 days before display, while LL cuts can be aged for up to 20 days without any detrimental effect on the retail colour stability.
References
Faustman C & Cassens RG (1990) The Biochemical Basis for Discoloration in Fresh Meat: A Review. Journal of muscle Foods, 217-243.
Faustman C, Chan WKM, Schaefer DM & Havens A (1998) Beef Color Update: The Role for Vitamin E. Journal of Animal Science 76, 1019-1026.
Hunt M (1980) Meat colour measurements. Reciprocal Meat Conference 33, 41-46.
Lanari MC, Brewer MS, Yang A & Tume RK (2002) Pasture and grain finishing affect the colour stability of beef. Journal of food science 67, 2467-2473.
Renerre M (1990) Review: Factors involved in the discoloration of beef meat. International Journal of Food Science and Technology 25, 613.
Wulf DM, Morgan JB, Sanders SK, Tatum JD, Smith GC & Williams S (1995) Effect of dietary supplementation of vitamin E on storage and caselife properties of lamb retail cuts. Journal of Animal Science 73, 399-405.