The colour stability of aged lamb benefits from Vitamin E supplementation

Abstract

This study investigated the effect of Vitamin E (Vitamin E) 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 Vitamin E treatments (175.7 mg Vitamin E/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 Vitamin E 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, Vitamin E concentrations of above 3.0mg/kg are required to improve the oxy/met ratio to an acceptable level (above 3.5). With sufficient muscle Vitamin E concentrations it may be possible to increase the shelf life of lamb cuts to 60 hours. The stabilizing effect of Vitamin E 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 Vitamin E, via nutritional supplementation (Wulf et al., 1995). Vitamin E (α-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 Vitamin E 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 Vitamin E through nutritional supplementation. When sufficient Vitamin E is present, cuts of lamb will have an improved retail shelf life of 60 hours. Materials and 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 α tocopherol (175.7mg/kg Vitamin E), the other half (control) received no supplementation (5.85mg/kg Vitamin E). 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 2C (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 4C for 96 hours. At the same time samples were taken for analysis of Vitamin E concentration.