牛宰后肌肉生物电阻抗值、pH值、失水率的变化及相互关系的研究

本实验对牛宰后骨骼肌肉的生物电阻抗值、pH值、失水率进行了测试,且作出了相应得变化曲线图.结果表明宰后10d牛肉样三项指标均有明显的变化.电阻抗与pH值、电阻抗与失水率、pH值与失水率之问均呈现相关性,相关性在α=0.05水平下显著.     

牛宰后肌肉生物电阻抗值与失水率的变化及相互关系的研究

本试验对牛宰后骨骼肌肉的生物电阻抗值、失水率进行了测试,结果表明宰后十天牛肉样二项指标均有明显的变化,且做出了相应的变化曲线图。电阻抗与失水率之间呈现相关性,相关系数r=0.12698,在a=0.05水平下显著。     

牛宰后肌肉生物员阻抗值与失水率的变化及相互关系的研究

本试验对牛宰后骨骼肌肉的生物电阻抗值、失水率进行了测试,结果表明宰后十天牛肉样二项指标均有明显的变化,且做出了相应的变化曲线图.电阻抗与失水率之间呈现相关性,相关系数r=0.12698,在a=0.05水平下显著.     

牛宰后肌肉生物电阻抗与pH值相关性研究

试验在多频(5～200kHz)条件下采用四电极法对30头肉牛宰后背最长肌肉(Longissimusdorsi,LD)的生物电阻抗和pH值进行了为期10d的连续检测。发现肉牛肌肉生物电阻抗同pH值有显著相关性(γ=-1.000～-0.999)。宰后第3天(48h),驱动电流频率为40～200kHz时,肌肉组织生物电阻抗达到最大值,pH值降到最小值。在不同频率下肌肉生物电阻抗表现的离散度不同,尤其是在5～100kHz范围内,肌纤维的生物电阻抗受频率影响较明显,并且和宰后肌肉的贮藏时间有关。在相同的环境条件下,肌肉的横向电阻抗(平行于肌纤维横截面方向)均大于纵向电阻抗(平行于肌纤维方向)。     

牛宰后肌肉生物电阻抗值变化及其影响因素的研究

本试验用四电极法在多频(5-200KHz)条件下对宰后牛骨骼肌肉的电阻抗特性进行了初步的研究。发现牛骨骼肌生物电阻抗与肌肉纤维方向,电流信号频率和宰后肌肉所经历的阶段有关。横向电阻(沿垂直于骨骼肌纤维方向)大于纵向电阻(沿骨骼肌纤维方向),而且受电流信号频率的影响较明显,尤其是在5KHz～100KHz范围内。牛宰后生物电阻抗的变化与pH值的变化有一定的相关性。     

近冰点下牛骨骼肌糖原、pH值、失水率变化及相关性研究

试验以30头牛为研究对象,对宰后经电刺激并在近冰点温度(1～-1℃)下贮藏的牛骨骼肌肉(Longissimusdorsi,LD)的糖原含量、pH值、失水率进行了测试,结果表明,宰后10d内糖原含量、pH值、失水率在第1～3天变化幅度明显,之后几天变化趋于平缓,10d中上述指标的变化均在α=0.01的检验水平下差异极显著。糖原含量与pH值呈负相关,相关系数(r=-0.24351)在α=0.05水平下显著、pH值与失水率呈负相关,相关系数(r=-0.67314)在α=0.01水平下极显著;糖原含量与失水率相关系数在α=0.05水平下不显著。     

The effect of post-mortem ageing and heating on water retention in bovine muscles

The muscles semitendinosus (ST) and psoas major (PM) were removed from chilled young bull carcasses 24 h after slaughter and stored at 4 °C. At the 1st, 6th and 12th day of post-mortem ageing the chemical composition (moisture, fat, protein, collagen) and contents of free, immobilized and unfreezable water in the muscles were estimated. The muscle steaks were boiled at 100 °C, roasted at 170 °C or fried at 160 °C to an internal temperature of 75 °C, and the amounts of total, free, immobilized, and unfreezable water in heated muscles were evaluated. The unfreezable water was estimated by DSC. In the raw muscles immobilized water constituted 74–75%, free water 16.6–17.6% and unfreezable water 7–8% of the total water. Independent of time of ageing, PM muscle contained significantly more free water than ST muscle. During post-mortem ageing, changes in free, immobilized and unfreezable water in muscles were not significant. The level of free water was highest in boiled and least in fried meat, however the amount of immobilized water was highest in fried and lowest in boiled meat. The amount of unfreezable water in muscles heated after 12 days of post-mortem ageing decreased.     

Effect of post-mortem storage temperatures on isometric tension, pH, ATP, glycogen and glucose-6-phosphate for selected bovine muscles

Relationships between isometric tension development and pH, ATP, glucose-6-phosphate and glycogen levels as a function of post-mortem storage temperature were examined for three bovine muscles. Tension responses in the range of 5-37°C were similar for B. femoris, Vastus lateralis and outer M. semitendinosis. At 0°C, the three muscles developed considerably higher tension than at 5°C. Cold shortening developed only in the outer M. semitendinosis strips at 0°C. At low temperatures the drop in pH lagged compared to the decline in ATP and glycogen and maximum tension was attained several hours after ultimate pH and minimum levels of ATP and glycogen were reached. Glucose-6-phosphate was found to accumulate rapidly at 0°C in both outer M. semitendinosis and B. femoris, being more pronounced in the latter muscle. The responses of glucose-6-phosphate levels suggest that the relative activities of glycolytic enzymes in muscle stored at 0°C are altered compared to those in muscle stored at higher temperatures.     

Influence of temperature on the rate of post-mortem metabolism and water-holding capacity of bovine neck muscles

Strips of forty bovine neck muscles were placed at temperatures in the range -1° to +30°C within 45 min of slaughter and stored for up to 24 h. Strips were taken at various times during storage and assayed for pH, 'R' value (degree of transformation of ATP to IMP) and ATP concentration. The water-holding capacity (WHC) of the intact muscle was compared with the WHC of a salted muscle homogenate prepared at each sampling time. The rate of pH fall post mortem was relatively low around +5°C and increased at lower or higher temperatures. ATP concentration showed a delay phase dependent on storage temperature and a subsequent rate of depletion which was also temperature dependent. The patterns of change in WHC of the muscle samples and the salted homogenates differed, the former showing a rapid fall to a fairly steady level shortly after initiation of storage, the latter showing no appreciable change until the onset of rigor. It is suggested that salting meat at any time prior to the onset of rigor will confer improved WHC and that the temperature of storage post mortem should be chosen to induce low rates of ATP turnover so as to prolong the feasible delay between slaughter and salting.     

Calpains and calpastatin distribution in bovine, porcine and ovine skeletal muscles

The concentration of calpain II and calpastatin was determined in various beef, lamb and pork muscles showing very different metabolic and contractile types as assessed by measurement of lactic dehydrogenase (LDH), citrate synthetase (CS) and ATPase activities. The calpain II: calpastatin ratio, which is a good index of the efficiency of this proteolytic system, was also determined.

A species comparison revealed that while calpastatin level was lowest in pork, the ratio of calpain II to calpastatin was highest in this species. For both determinations, lamb was intermediate followed by beef. Conversely, the amount of calpain II was very similar in the three species.

In beef and pork, calpain II content decreased as muscle ATPase and LDH activities rose; and conversely increased with CS activity; whereas in lamb, the amount of this enzyme was highest in red muscles regardless of their speed of contraction. Except for masseter muscle, a comparable distribution was observed for calpastatin in beef and pork muscles. In lamb, the calplastatin concentration was highest in slow-twitch red muscles, intermediate in fast-twitch red muscles and lowest in fast-twitch white muscles. Variability of the calpain II: calpastatin ratio with muscle ATPase, LDH and CS activities appeared to be both muscle and species dependent. As results for masseter muscle are rather unexpected, especially in beef and lamb, this muscle was considered separately.

The present findings are discussed with regard to the conditioning rate of meat from different species and, within one species, from different muscles. It was concluded that the conditioning rate may be correlated positively to calpain II: calpastatin ratio and negatively to calpastatin content. In contrast, no relationship seems to exist between meat ageing rate and calpain concentrations.     

Metmyoglobin reductase activity in bovine muscles

Cow muscles (Longissimus dorsi, Tensor fasciae latae, Psoas major, Diaphragma medialis), with different colour stabilities, were used to measure 'Metmyoglobin reductase activity' in different conditions. The effects of pH and temperature on in vitro metmyoglobin reduction were analysed. The highest metmyoglobin reductase activity was localized in microsomes and in more or less intact mitochondria by means of differential centrifugations. The most unstable muscles, from the colour point of view, presented the highest reducing activities and no differences were noted between activities measured in aerobic or anaerobic conditions.     

The relationship between early post-mortem pH and the tenderisation of beef muscles

The rate of early post-mortem pH fall in bovine muscle was studied to determine its influence on the rate and extent of the tenderisation process. The pH of M. longissimus dorsi (LD) and M. semimembranosus (SM) muscles of Hereford cross Friesian heifers (n = 127) was taken up to 24 h post mortem. Twenty-four LD and 24 SM muscles were selected according to their rate of pH fall; slow (n = 8), intermediate (n = 8) and fast (n = 8) and were sampled at 2, 7 and 14 days post mortem for sensory, mechanical, physicochemical and biochemical analysis. Fast glycolysing LD muscles were rated more tender in sensory analysis and texture assessment whereas slow glycolysing muscles were considered significantly tougher (p < 0.001). Fast glycolysing LD had a significantly lower shear force (p < 0.001) at each stage of ageing. Slow glycolysing LD and SM had the highest shear force values. No significant difference was found in intramuscular fat or moisture content between the groups. Slow glycolysing LD muscles had shorter sarcomere lengths at 2 days post mortem. SDS-PAGE electrophoresis patterns showed increased proteolysis, such as the earlier appearance of the 30 kDa fragment, which is believed to be a good indicator of tenderness, in fast glycolysing muscle. These results suggest that the rate of post-mortem pH fall plays an important role in proteolysis and tenderisation.     

The association of bovine SH-kappa-casein at pH 7.0.

The self-association of SH-kappa-casein at pH 7.0 in 0.01 M-EDTA, 0.001 M-dithiothreitol buffer, containing 0.1, 0.2, 0.5 or 1.0 M-NaCl is of a monomer-polymer type. The polymer is a spherical particle, diam. 23 nm and mol. wt 570000 (30 monomers). These parameters are not greatly influenced by variations in ionic strength above 0.1. The critical micelle concentration, which is a property of a monomer--polymer equilibrium, decreases with increasing ionic strength. The standard free energy of association is about -36 kJ/mol. monomer at 20 degrees C.     

Vitamin K2 in different bovine muscles and breeds

Meat is a natural source of vitamin K, a vitamin associated with reduced bone loss and prevention of osteoporosis. Whether vitamin K content varies between breeds and muscles in cattle is not known. In the present study, contents of vitamin K1 (phylloquinone) and K2 (menaquinone, MK) were analysed in three different muscles from steers of two different breeds, Norwegian Red and Jersey, respectively. Results showed that MK4 was the most dominant of the vitamin K2 analogues, while only traces were found of MK6 and MK7. Both breeds had higher levels of MK4 in M. biceps femoris (BF) and M. longissimus dorsi (LD) compared to M. psoas major (PM). The results also showed significantly higher MK4 levels in muscles from Jersey compared to Norwegian Red. Furthermore, MK4 was not associated with intramuscular fat, suggesting a physiological role for MK4 in skeletal muscle cells. There were no association between vitamin K content and tenderness.     

Observations on muscle press juice from bovine, ovine and porcine muscles

Differences in the amounts and protein concentrations of muscle press juices from fresh and frozen psoas and l. dorsi muscles of bovine, ovine and porcine origin suggest the value of species and anatomical selection for functional applications in meat products.