Effect of glycogen concentration and form on the response to electrical stimulation and rate of post-mortem glycolysis in ovine muscle.
ABSTRACT The associations between the muscle glycogen concentration and form and the rate of post-mortem glycolysis in ovine muscle were investigated. Twenty-two merino wethers (18-24 months) were allocated to either roughage or concentrate pelleted diets for 34 days prior to slaughter. An exercise depletion/repletion model was applied four days prior to slaughter to generate differences in muscle glycogen levels at slaughter. Muscle biopsies were taken from the m. semimembranosus (SM) and m. semitendinosus (ST) prior to and immediately after exercise for muscle glycogen determination. At slaughter, one side was electrically stimulated and both sides were conventionally chilled for 24h. The pH response to electrical stimulation (ΔpH) and the rate of pH decline adjusted to a constant temperature of 38°C over the initial 6h post-mortem period was determined in three muscles (m. longissimus thoracis et lumborum LTL, SM and ST). In addition, the concentrations of glycogen, proglycogen (PG), macroglycogen (MG) and lactate in the three muscles immediately after slaughter were determined. The glycogen loss due to exercise was influenced by diet (P<0.01; concentrate 63% and roughage 73%) but did not differ between muscles. The rates of repletion significantly varied between muscles (SM>ST) and diet (concentrate>roughage). The available glycogen (glycogen(A)) and MG concentrations at slaughter varied significantly depending on the diet (P<0.01) and muscle (P<0.001). The percentage of MG relative to MG+PG varied between muscles (46%, 50% and 57% for the ST, LTL and SM). The concentration and form of available glycogen at slaughter did not influence the response to electrical stimulation after adjusting for pre-stimulation pH (P<0.01). The ΔpH varied significantly between muscles (0.39±0.03, 0.26±0.02 and 0.20±0.03 for the ST, LTL and SM) after adjusting for pre-stimulation pH. Differences in the temperature adjusted rate of pH decline were observed between the muscles (LTL>SM>ST). Importantly, a positive linear association (P=0.05) was found between muscle glycogen(A) concentration at slaughter and the rate of pH decline (temperature adjusted).
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ABSTRACT: The aim of this study was to assess the effect of location within bovine longissimus dorsi (thoracis et lumborum) muscle (LTL) when determining glycogen concentration. Six locations in Angus heifers were sampled post mortem (EXP-1) and eight locations in live Charolais crossbred steers were biopsied (EXP-2). In EXP-1, there was more glycogen in the animals' left LTL (64.1±1.6 mmol/kg) versus the right LTL (57.0±1.6 mmol/kg) (P<0.05). Locations along the cranial-caudal axis within LTL did not differ in glycogen concentration. Results for EXP-2 did not confirm the sidedness effect. Instead, it showed that glycogen concentration was lower at the cranial sampling locations near the 10th rib (89±2.5 mmol/kg) than at the middle (97±2.0 mmol/kg) or caudal locations (96±1.9 mmol/kg) (P<0.005). Taking lactate accumulation into account (glycolytic potential) rendered those differences insignificant. Nevertheless, the tendency remained clear. The potential for dilution of glycogen by intramuscular fat deposits is discussed. The results indicate that one needs to be cautious in performing repeated sampling on bovine LTL.Meat Science 02/2000; 54(2):163-7. · 2.75 Impact Factor
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ABSTRACT: Forty-one autumn-born Friesian bull calves were allocated to two production systems (Extensive='E' and Intensive='I'). In the E-system, animals were loose-housed and fed a roughage-based diet from October to May, followed by a grazing period from May to October. Ten animals were slaughtered directly from pasture (360 kg BW) and 11 after a 10-week finishing feeding in tie-stalls (460 kg). E-bulls were compared with intensively fed tie-stall housed young bulls (I) slaughtered at comparable weights (360 kg, n=11 and 460 kg, n=9). Semitendinosus (ST), longissimus dorsi (LD), and supraspinatus (SU) muscles were analysed histochemically, and the meat analysed for colour and pigmentation. In LD and SU, Type I % was higher in E- compared with I-bulls (P<0.05-0.006). In ST and LD, Type IIA % was higher in E- compared with I-bulls (P<0.01-0.009). As a result, Type IIB % was lower in all three muscles in E- compared with I-bulls (P<0.05-0.001). In E- compared with I-bulls, Type IIA and IIB fibre areas were larger in ST (P<0.05-0.03) and capillarization was higher in both ST and LD (P<0.001). In all three muscles, the activity of citrate synthase was higher (P<0.07-0.001) and that of lactate dehydrogenase lower (P<0.003-0.001) in E- compared with I-bulls. E-bulls had lower glycogen content than I-bulls in ST and LD at 360 kg, but higher at 460 kg following finishing feeding (P<0.008-0.001). Meat colour (lightness) was darker (P<0.001) and pigmentation was higher (P<0.001) in ST and LD of E- compared with I-bulls, with no effects in SU. In conclusion, histochemically different muscles respond differently to changes in the production system, and differences between the extensive and the intensive production system were narrowed after the finishing feeding.Meat Science 02/2000; 54(2):177-85. · 2.75 Impact Factor
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ABSTRACT: Electrical parameters previously employed to hasten the onset of rigor mortis in carcasses were derived empirically. Various parameters have been studied to determine their relationship to the two-stage fall of muscle pH resulting from stimulation. At any given stimulation period pulse frequency had a considerable effect on the magnitude of the pH fall that occurs during stimulation, the greatest falls, ∼ 0·7 pH units in a 120 sec period, being achieved with 5 to 16·6 pulses. sec(-1). The same total number of pulses delivered at differing frequencies did not produce pH falls of equal magnitude. Variation in pulse shape and polarity caused minor changes. Increased energy levels per pulse increases the magnitude of the pH fall during stimulation. All stimulation parameters tested resulted in the rate of pH fall after stimulation being one and a half times to twice that of non-stimulated muscle. The tension-time curves obtained with lower frequencies (< 10 pulses . sec(-1)) show incomplete summation of pulses with sustained tension. At higher frequencies a complete tetanus develops, while tension falls rapidly soon after achieving the peak tension. The relationship between the mechanical and biochemical responses and the implications for stimulation as a practical processing method are discussed.Meat Science 01/1978; 2(1):49-58. · 2.75 Impact Factor