Effects of electrical stimulation and delayed chilling on carcass and meat quality of indigenous and Boer goats in South Africa

Abstract

This study investigated the effects of electrical stimulation and delayed chilling on carcass and meat quality of indigenous and Boer goats in South Africa. Ten goats per breed were randomly selected from typical indigenous and Boer goats. The goats were slaughtered and dressed according to standard abattoir procedures. The goat carcasses were split into left and right sides along the vertebral column. Electrical stimulation (400 V for 30 seconds then chilling at 0 - 4 °C) or delayed chilling (10 - 15 °C for 6 hours, 0 - 4 °C until 24 hours) were applied to the carcass sides. Muscle fibre characteristics, the concentration of glycolytic metabolites, pH/temperature profiles, water holding capacity (WHC), thawing losses, evaporative losses, drip losses, cooking losses, surface myoglobin pigments, instrumental colour, sarcomere lengths and Warner Bratzler shear force (WBSF) values were evaluated on samples of both the m. longissimus dorsi (LD) and m. semimembranosus (SM). Carcasses of Boer goats were on average 2.9 kg heavier (P <0.001) than carcasses of indigenous goats. Dressing percentage was not different between the two goat breeds (47.5 ± 0.55%). Chilling losses were higher (P <0.01) in carcasses of Boer goats (4.81 ± 0.19%) than in carcasses of indigenous goats (4.03 ± 0.12%). The goat muscles were predominantly oxidative, with an average composition of 47 - 51%, 22 - 27% and 22 - 29% for red, intermediate and white fibres, respectively. The LD samples of indigenous goats had smaller (P <0.05) intermediate fibre cross sectional areas (2670 μm2 vs. 3510 μm2) and a higher (P <0.05) percentage of oxidative fibres (50.9% vs. 40.7%) than corresponding Boer goat samples. The composition of SM fibres of the two goat breeds were similar. Electrical stimulation hastened the rate of pH decline and muscle energy metabolism whilst delayed chilling showed slow but steady changes in pH and metabolic concentrations. Both slaughter procedures allowed carcasses to enter into rigor mortis without the risk of cold shortening (pH ~6 at temperatures above 10 °C). The measured sarcomeres (1.98 - 2.12 μm) confirmed that cold shortening did not occur under slaughter conditions set for this study. The average muscle ultimate pH values were ~5.8, with no significant differences between the two goat breeds or carcass treatments. The LD samples of delayed chilling treatment recorded higher instrumental colour values than corresponding samples of electrical stimulation treatment. The LD samples of electrical stimulation had higher evaporative losses (20.5 ± 0.93% vs. 17.9 ± 0.65%) and total cooking losses (20.9 ± 0.97% vs. 18.2 ± 0.65%) than corresponding samples of delayed chilling treatment. The WBSF values of the LD samples (4.03 - 4.53 kg) were not different (P >0.05) between the two goat breeds or carcass treatments. There were no significant differences between the two treatments in instrumental colour, surface myoglobin pigments or moisture parameters of the SM samples. Electrical stimulation was effective in improving the tenderness of the SM samples, particularly in Boer goats. This study showed that both indigenous and Boer goats can yield meat with acceptable objective properties, if appropriate slaughter conditions are practised.