Comparison of some components of pigs kept in natural (free-range) and large-scale conditions

A new pig genotype of Hungarian Large White (75%) × Mangalica (pig with curly bristles, 25%) was used in the experiments. The experimental group was kept in a farming system under strictly natural circumstances until a body weight of 120 kg was attained. Neither antibiotics nor yield-increasing hormones were given to this group. The control group was kept in the usual large-scale farming conditions until body weight of 120 kg was attained. In most cases, protein, zinc, and copper levels and, in some cases, iron levels were significantly higher in some major cuts (neck-end (Boston-butt), loin, ham) of the 'free-range' pigs (n = 12) in comparison with the control animals kept in large-scale farming conditions. There was, on average, 15% less cholesterol in the muscles and 30% less cholesterol in the liver and less linoleic acid in all tissues of 'free-range' pigs than in the control group. There was less fat, but the amount of thiamin and riboflavin in the liver of the naturally kept pigs was twice that in the controls. In respect of TBA-reactive compounds, there were no significant differences between the two groups, but superoxide dismutase (SOD) showed significantly higher activities in all cuts from pigs kept in a large-scale farming system. This may be the effect of a higher level of linoleic acid in the fat.     

Effectson carcass weight and meat quality of pigs dehaired by scalding or singering post-mortem

Two experiments were designed to compare the effects of two pig dehairing techniques. In the first experiment, 120 pigs were slaughtered in the same abattoir in five weekly sereis. One half of each series was dehaired by singeing (the usual technique in this abattoir), while the other half was dehaired in a scalding-dehairing combination. In the second experiment, 48 pigs were slaughtered in two series, one-half of each series in an abattoir practising singeing, the other half in an abattoir practising scalding. Temperature and pH were measured 30 min after slaughter in the longissimus lumborum. Meat quality was assessed the day after slaughter in various muscles. One ham was cured and cooked, while the other one was processed by dry-curing. In both experiments, carcass weights and yields were noticeably higher after singeing. Hams were heavier in singed carcasses, but their proportions in the carcasses were little or not at all affected by the dehairing technique. Proportions of loins, shoulders and bellies were similar with both dehairing techniques. The dehairing technique affected neither temperature nor rate of post-mortem pH fall. Meat quality as assessed on fresh meat was slightly better in singed carcasses. Weights of cooked ham and dry ham per side were higher in singed carcasses, due to the higher initial ham weight, but processing yields were not affected by the dehairing technique.     

Influence of temperature variation on the metabolism of pig muscle in situ and after excision

The experiment involved six halothane-positive (HP) and six halothane-negative (HN) pigs of about 100 kg liveweight. Under general anaesthesia the tibialis cranialis was exposed. The temperature of the muscle was maintained at either 35 or 40°C (in situ). The muscle was stimulated via the peroneal nerve at 0·1 Hz for 10 min then 1 Hz for 10 further min. Twitch contractions were recorded throughout the stimulation, after which the muscle was excised and split into two parts which were kept in paraffin oil at either 35 or 40°C (post-excision temperature) for 2 h. Samples were taken just before and after the 20 min stimulation period, and at 1 and 2 h after muscle excision for determination of pH and concentrations of PC, ATP, IMP, glycogen, G-6-P and lactate. As soon as one muscle was removed, the operation was repeated on the other leg. Both temperatures (35 and 40°C) were applied to each animal in a balanced design. However data were obtained from only 11 pigs at 40°C as one HP pig died accidentally at the beginning of the 40°C experiment. Halothane sensitivity influenced the pH value and the levels of PC, G-6-P and lactate of the muscle in situ (P < 0·01 in all cases). Temperature affected contrction time (P < 0·01). Both halothane sensitivity and Post-excision temperature affected the pH values and the levels of PC, ATP, IMP, G-6-P and lactate (P < 0·01 in all cases) in the excised muscle. By contrast, the in situ temperature treatments did not affect any of the muscle traits measured after excision. It was concluded that the effects of the various treatments on the rate of metabolism in the excised muscle were wholly explainable in terms of temperature from the time of excision, and that the in situ temperature treatments may not be responsible for the differences after excision.     

Structural and mechanical changes in raw and cooked single porcine muscle fibres extended to fracture

Tensile tests on single muscle fibres from raw and cooked porcine longissimus thoracis muscle were performed to explore the structural mechanisms responsible for their deformation and fracture properties. Measurements of load and deformation were made simultaneously with light microscopy observations of the structural changes which occur on extension. On extending the fibres to fracture, an r-shaped stress-strain curve was observed and the structural changes which occurred during this process could be divided into three phases. Phase one, was characterised by a rapid increase in stress with little change in strain and ended at the yield point. Sarcomere length was uniform along the fibre in this initial phase. Raw fibres yielded at strains of between 2 and 5% of their resting lengths and cooked fibres at strains of between 10 and 20%. In phase two, there was rapid increase in strain with minimal changes in stress. In most fibres this phase was characterised by multiple cracks on the fibre surface and unequal sarcomere stretching. Sarcomeres in the regions where the surface had ruptured extended faster than those in areas still covered by the surface membrane, where sarcomere length remained relatively unchanged. In some cooked fibres, there was little or no surface cracking and all the sarcomeres in these fibres extended almost uniformly. Phase three was characterised by a rise in stress as strain increased and then a final fall in stress at the breaking point. This was accompanied by myofibrillar failure and finally breakage of the whole fibre. The myofibrils did not always fail as one unit; a progressive snapping of small bundles of myofibrils was seen in some raw fibres. Muscle fibres could be stretched to 10·9 ± 1·45% of their resting length before breaking when raw, but to 130 ± 42% of their rest lengths after they were cooked for 1 h at 80°C. Where multiple surface cracking was observed in phase two, sarcomeres in some cracked areas lengthened faster than others and the cracked areas which extended fastest were usually the focus of the eventual failure of the fibre. In raw fibres, sarcomeres in the areas where the fibre surface had ruptured could be stretched up to 107·7% before failure, while those in areas of the fibre with an intact surface remained relatively unchanged. In cracked areas of cooked fibres the sarcomeres were more extensible and could be stretched to 169·7% before breaking. The order-of-magnitude increase in overall extension to failure of fibres resulting from cooking is only partially due to this increase in sarcomere extensibility in cracked areas. Mechanically demembranating raw fibres depressed the stress at which yielding occurred and doubled their breaking strain. However, this process had no effect on the stress at which the fibres fractured. The results show that deformation is not uniform along individual fibres, especially in the raw case and that the endomysium has an important contribution to this non-uniform deformation.     

Inter-animal variation in the biological characteristics of muscle tissue in male limousin cattle

The biochemical, metabolic and contractile characteristics of semitendinosus (ST) and longissimus thoracicus (LT) muscles were studied in 147 male Limousin cattle. The animals, which were slaughtered at 16 months, were the offspring of 15 different sires. Weight gain and carcass tissue composition (proportion of muscle and adipose tissue) were also measured. The biochemical characteristics of the two muscles studied had coefficients of variation between 13 and 30% markedly higher than for proximate characteristics of the carcass, in which coefficients were all lower than 18%. There were significant differences between the two muscles: ST had a higher protein/DNA ratio and greater lactate dehydrogenase (LDH) activity than LT, also a lower isocitrate dehydrogenase (ICDH) activity and lower slow myosin heavy chain (MHCI) content. The percentage of MHC 1 was positively correlated with ICDH activity and negatively with LDH activity and protein/DNA ratio. These muscle characteristics were also correlated with weight gain: animals with greater weight gain had a higher protein/DNA ratio and lower oxidative activity, with differences in the level of significance of the correlations according to muscles. Selection of animals on the basis of muscle growth may therefore be a means of improving the quality of meat.     

圣维森特坝加高工程设计施工

从圣维森特坝加高项目兴建的缘由、方案设计以及项目对环境的影响、采用碾压混凝土方案的益处等方面进行分析研究,最终确定该项目采用碾压混凝土方案。实践证明,圣维森特大坝的高度加高采用碾压混凝土方案高效且经济,能够满足该地区的紧急蓄水需要。     

Three－Dimensional Numerical Simulation of Natural Convection Heat Transfer in an Inclined Cylindrical Annulus

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电压预测技术提高HVDC混合实时仿真器接口稳定性

介绍使用电压预测技术提高HVDC混合实时仿真系统接口的稳定性。接口稳定性是建立混合实时仿真系统的关键问题。利用电压预测技术，结合“虚”阻尼并联支路，可以有效地减小接口电流噪声，提高RTDS数值计算稳定性，保证数模接口在稳态和暂态仿真中的稳定。各AC/DC接口的电压预测步长需独立精心选择，典型值在1个～3个步长，取决于直流平波电抗值的大小和直流输电线的长度。文中给出了接口的技术实现和性能校验结果。