Cellular model for induction of drip loss in meat

Drip loss from porcine muscle (M. longissimus dorsi) contained high concentrations of K(+) ( approximately 135 mM) and organic osmolytes, for example, taurine ( approximately 15 mM), as well as significant amounts of protein ( approximately 125 mg.mL(-1)). Thus, the drip reflects release of intramuscular components. To simulate events taking place at the time of slaughter and leading to release of osmolytes and subsequent formation of drip loss, C2C12 myotubes were exposed to anoxia and reduction in pH (from 7.4 to 6.0). Anoxia and acidification increased the cellular Ca(2+) concentration ([Ca(2+)](i)) at a rate of 22-32 nM.min(-)(1). The anoxia-induced increase in [Ca(2+)](i) was mainly due to influx via sarcolemmal Na(+) channels. As mammalian cells swell and release lysophospholipids during anoxia, C2C12 cells and primary porcine muscle cells were exposed to either hypotonic shock or lysophosphatidylcholine (LPC) and the release of taurine was followed. The swelling-induced taurine efflux was blocked in the presence of the anion channel blocker (DIDS), the 5-lipooxygenase inhibitors (ETH 615-139 and NDGA) but unaffected by the presence of vitamin E. In contrast, the LPC-induced taurine release was unaffected by DIDS but abolished by antioxidants (butylated hydroxytoluene and vitamin E). Thus, stress-induced taurine release from muscles may precede by two different mechanisms, one being 5-lipooxygenase dependent and the other involving generation of reactive oxygen species. A model for the cellular events, preceding formation of drip in meat, is presented.     

无定形锰氧化物在氮素损失中的作用

Studies have been made,by ^15N-tracer technique on nitrogen loss resulting from adding amorphous manganese oxide to NH4^ -N medium under anaerobic conditions.The fact that the total nitrogen recovery was decreased and that ^15NO2,^15N2O,^15N^14NO,^15NO,^15N2 and ^15N^14N were emitted has proved that,like amorphous iron oxide,amorphous manganese oxide can also act as an electron acceptor in the oxidation of NH4^ -N under anaerobic conditions and give rise to nitrogen loss.This once again illustrates another mechanism by which the loss of ammonium nitrogen in paddy soils is brought about by amorphous iron and manganese oxides.The quantity of nitrogen loss by amorphous manganese oxide increased with an increase in the amount of amorphous manganese oxide added and lessened with time of its aging.The nitrogen loss resulting from amorphous manganese oxide was less than that from amorphous iron oxide.And the nitrogen loss resulting from amorphous manganese oxide was less than that from amorphous iron oxide.And the nitrogen loss by cooperation of amorphous manganese oxide and microorganisms (soil suspension) was larger than that by amorphous manganese oxide alone.In the system,nitrogen loss was associated with the specific surface ares and oxidation-reduction of amorphous manganese oxide.However,their quantitative relationship and the exact reaction processes of nitrogen loss induced by amorphous manganese oxide remain to be further studied.     

滴灌施肥对农田土壤氮素利用和流失的影响

通过2年在果园和蔬菜田的生产试验及田问氮素流失监测,对比研究常规施肥管理和精确滴灌施肥技术在作物产量、肥料消耗量和农田氮素流失负荷等方面的差异,分析不同施肥方式对农田土壤氮素利用和流失的影响.结果表明:滴灌施肥技术把定量的溶解态肥料直接输送到作物根部,提高了肥料利用效率,农作物产量与常规产量基本持平甚至略有提高,而氮肥消耗量和氮素流失负荷则显著降低.与常规施肥管理方式相比,2006年梨、大豆和玉米的单位产量氮肥消耗量分别降低10.8、11.8和8.9 g/kg,削减率分别为22.8%、26.6%和30.8%;单位产量总氮流失量也分别削减45.2%、14.5%和26.3%.2007年梨、西瓜和玉米的单位产量氮肥消耗量分别降低11.1、8.1和5.0 g/kg,削减率分别达到29.7%、65.8%和21.5%;单位产量总氮流失量分别削减56.4%、49.7%和51.8%.     

Postmortem proteome changes of porcine muscle related to tenderness

Proteome analysis was used to investigate the relation between changes in postmortem proteome of porcine muscle and tenderness development. Muscle samples were taken at slaughter and 72 h postmortem, and the registered changes in the proteome were related to Warner-Bratzler shear force. One hundred and three protein spots were found to change significantly (P < 0.01) over time, and of these the 27 most pronounced changes were identified. Eleven out of the 27 changes were fragments of actin. Other identified myofibril proteins or fragments included myosin heavy chain, titin, myosin light chain I, myosin light II, CapZ, and cofilin. Correlation analysis revealed significant correlations between three of the identified actin fragments and the myosin heavy chain fragment to shear force. Moreover, myosin light chain II and triose phosphate isomerase I were also found to correlate significantly to shear force. The results clearly demonstrate that postmortem degradation of actin and myosin heavy chain is related to meat tenderness.     

Role of the waxy skin layer in moisture loss during dehydration of prunes

Permeability studies of water through the skin and flesh of d'Agen plums have been carried out by radiotracer and PGSE NMR techniques as a function of moisture content. The results have shown that the diffusion coefficient of water through the skin layer increases as the fruit is dried at 70 degrees C or above. By contrast, the water diffusion through the fruit becomes more hindered as moisture is lost and structural collapse of the cell layers takes place. Values for diffusion coefficients of water at 21 degrees C through the fruit of 1 x 10(-)(9) m(2) s(-)(1) for fresh plums and 2.0 x 10(-)(10) m(2) s(-)(1) for fruit dried to 50% moisture content (wet basis) were found. Structural studies using scanning electron microscopy techniques were also performed. These showed that drying induces marked changes to the waxy skin layer of the fruit as well as the fruit flesh. These results are discussed in terms of the important role that the plum skin has in modulating the moisture loss process during dehydration, particularly at early stages of drying.     

Impact of a treatment with phospholipase A2 on the physicochemical properties of hen egg yolk

Changes in physicochemical properties of egg yolk were investigated after a treatment with phospholipase A 2 (PLA 2), where phospholipids are converted in lyso-phospholipids. Protein solubility and protein denaturation before and after modification by PLA 2 was monitored as well as the functionality of egg yolk by means of interfacial tension. Enzymatic treatment showed a significant impact on the properties of egg yolk with regard to protein solubility and denaturation behavior. To gain a closer insight, egg yolk was separated in its water-soluble fraction called plasma and the insoluble granules. Both fractions were separately modified by PLA 2. The granule fraction shows a higher protein solubility, and the plasma proteins show very high heat stability after modification by PLA 2. Hypotheses regarding related changes in the low-density lipoprotein (LDL) particles are discussed. Results suggest that significant differences in the functional properties of untreated and PLA 2-modified egg yolk do not primarily result from the existence of lyso-phospholipids but from structural changes in egg yolk granules and LDL particles.     

Purification and biochemical properties of dipeptidyl peptidase I from porcine skeletal muscle

Dipeptidyl peptidase I (DPP I; EC 3.4.14.1) was purified from porcine skeletal muscle after several steps such as heat treatment, ammonium sulfate fractionation, gel filtration chromatography, and HPLC anion exchange chromatography. The purified enzyme showed a native molecular mass of approximately 200 kDa on Sephacryl S-200 column chromatography. Two protein bands of 65 and 42 kDa were obtained by SDS-PAGE, indicating its oligomeric nature. Maximum activity was reached at pH 5.5 and 55 degrees C. DPP I shared some common substrate specificities, both on synthetic derivatives and on real peptides, with porcine muscle DPP III. The enzyme required reducing agents for full activation, although the halide requirement was not proved. DPP I was inhibited by the assayed cysteine peptidase inhibitors except p-CMB. The serine peptidase inhibitor 3, 4-DCI also inhibited the enzyme as did the divalent cations Co(2+), Mn(2+), and Zn(2+). On the basis of its properties, DPP I may contribute to the generation of dipeptides during the processing of meat and/or meat products, including cooked ham.     

Proteome analysis applied to meat science: characterizing postmortem changes in porcine muscle

The aim of this work was to test the application of two-dimensional electrophoresis (2DE)-based proteome analysis in studying muscle tissues and meat of pork, and to use this technology to characterize as many of the changes that occur in pig muscle proteins during post mortem storage of the carcass as possible. For this purpose, 2DE proved to be a powerful tool, as it is far more sensitive and shows a higher resolving power than conventional SDS-PAGE, allowing for the precise and semiquantitative recognition of approximately 1000 individual muscle proteins in every 2DE display. In this study, we have chosen to analyze the subset of muscle proteins that have molecular masses of 5-200 kDa, and can be reproducibly separated in the pH span of 4-9. By comparing 2DE patterns of muscle samples taken immediately after slaughter (time 0), as well as those taken 4, 8, 24, and 48 h post mortem, we have estimated the relative changes of individual muscle proteins during the post mortem storage of the carcass. In this paper, of these changes we report the 15 most notable.     

猪MYL4基因的克隆及其在猪胚胎骨骼肌中的差异表达分析

克隆了猪MYL4基因的cDNA序列,并利用生物信息学方法进行验证。所得cDNA序列全长1105bp,包含一个完整的开放阅读框,编码197个氨基酸。序列分析表明,该基因与已报道的狗、人、黑猩猩和恒河猴等物种的MYL4基因高度同源,氨基酸序列同源性分别为98.4%、95.9%、95.4%和95.4%。该基因编码的蛋白具有EFH和FRQ1保守功能域。荧光定量分析该基因在猪胚胎骨骼肌（妊娠33 、65 和90 天）中的表达规律,发现MYL4基因在通城猪和长白猪中呈波浪式表达模式,在妊娠第33 天时中外猪品种间无显著差异,但在65 和90 天时长白猪中显著高于通城猪。     

Role of anthranilic acid in background levels of sulfonamide in porcine livers when determined by the Tishler method

Anthranilic acid occurs in excised swine livers as a result of temperature abuse before and/or after freezing. The tryptophan metabolite is the major source of the variable non-sulfonamide background level frequently encountered in the Tishler method for determining sulfonamide residues in swine livers. Diazotized anthranilic acid reacts slowly with N-1-(naphthyl)ethylenediamine [k(s-1) = 5.79 (+/- 0.07) X 10(-5)] and the final background level depends on the time elapsed between addition of the coupling agent and spectrophotometric determination. Kynurenine was tentatively identified as a minor source of the non-sulfonamide background level.     

Mechanism of production of troponin T fragments during postmortem aging of porcine muscle

Troponin T (TnT) is one of the myofibrillar proteins that is easily degraded during postmortem aging of pork. In this study, we determined the N-terminal amino acid sequences of TnT degradation fragments produced during postmortem aging and by m-calpain hydrolysis. The N-terminal amino acid sequences of TnT fragments produced during postmortem aging were EVHEPEEKPRPKLTAP, EKPRPKLTAPKIPEG, and APKIPEGEKVDF. On the other hand, the N-terminal amino acid sequences of TnT fragments produced by the action of m-calpain were APPPPAEV, EVHEPEEK, and APK. These sequences of degradation fragments could be mapped on fast type TnT isoform 2. The peptide bonds of His37-Glu38 and Thr51-Ala52 in fTnT2 were cleaved during postmortem aging as well as by the calpain hydrolysis; therefore, calpain was concluded to have an important role in TnT degradation during postmortem aging. It was also found that the sourness-suppressing peptide APPPPAEVHEVHEEVH (Okumura et al. Biosci. Biotechnol. Biochem. 2004, 68, 1657-1662) derived from TnT degradation could be produced by the action of calpains on Glu21-Ala22 and His37-Glu38 sites.     

膜下滴灌条件下灌水水质和流量对土壤盐分分布影响的田间试验研究

膜下滴灌是一种既节水,又能抑制土壤盐分上移的灌水技术。该文着重研究在田间条件下,滴头流量、灌水量和灌水水质对微咸水点源入渗水盐运移的影响。研究结果表明,在充分供水条件下,水平湿润锋和积水锋面随时间的推进符合幂函数关系;滴头流量越小,沿土壤深度方向上的盐分含量越小;滴头流量越大,水平方向含盐量随距离增加的趋势越不明显;灌水量是微咸水灌溉条件下控制盐分累积的一个重要因素,灌水量不足,没有足够的入渗水量以确保盐分的淋洗;灌水矿化度的升高会显著增加土壤表层的含盐量。     

滴施磷酸二氢钾后土壤中磷的移动和分布

在室内采用土柱模拟滴灌施P肥,研究了P在土壤中的移动和分布。试验结果表明:①滴施含P量200mg/L的KH2PO4后P在砂壤土、轻壤土、重壤土中分别纵向移动了22、16、14cm。横向和纵向移动的距离基本相同。②随着滴施P浓度的增加,P的移动距离增大,P的主要累积层加深。赤红壤中滴施P浓度200、400、800、1000mg/L时,P分别移动了12、16、20、22cm,而且有效P和全P含量增加显著的土层深度分别为0～8、0～12、0～18、0～20cm。在相同质地情况下,滴施高浓度P肥溶液可以明显增加P的移动距离。     

地下滴灌灌水器堵塞研究

地下滴灌(SDI)是一种高效的节水灌溉技术，但系统易于堵塞，堵塞问题成为影响地下滴灌成败的关键。通过对运行8年的地下滴灌系统堵塞的实地调查，迷宫式、微管式和孔口式等3类型的灌水器均有不同程度的堵塞，堵塞率分别达到16.67%、25%和63.89%。分析3类型灌水器的堵塞状况，引起地下滴灌堵塞的主要原因是进入系统的微粒在流道壁的附着和发育。为此，提出加强过滤、定时冲洗和改变滴头流道设计等解决地下滴灌堵塞的建议。     

地下滴灌毛管水力要素试验

地下滴灌毛管滴头的压力和流量分布是其主要的水力要素,研究这一问题对地下滴灌工程的设计和运行管理具有重要的意义。该文提出了地下滴灌毛管水力要素的试验方案,可用较短毛管获得其压力流量测试数据和分布规律。针对提出的试验方案,结合地下滴灌单滴头的水力特性研究成果,建立了描述地下滴灌毛管压力、滴头流量和局部水头损失系数之间关系的非线性方程组。将这一非线性方程组计算转化为一个函数优化问题,建立其求解的优化数学模型,采用遗传算法求解。用试验数据验证了计算结果,表明用此非线性方程组可反映地下滴灌毛管压力流量分布规律,求解方法具有较高的计算精度。该方法为进一步研究地下滴灌毛管的水力要素奠定了基础。     

地下滴灌技术节水潜力及机理研究进展

地下滴灌是一种用水效率极高的节水灌溉技术,具有少量多次、节水增产的特点,能有效减少土壤蒸发和深层渗漏,提高灌溉水利用效率,同时其自动化程度高,可降低劳动力和运行管理成本,已成为国内外水资源匮乏地区的重要灌溉技术之一。本文通过回顾地下滴灌技术的发展研究历程,概述了早期发展存在的问题以及现今研究的热点。系统对比了多种灌溉方式对作物产量、灌溉量与蒸散量的影响,指出地下滴灌技术具有极高的节水增产减蒸潜力;通过总结室内控制试验与已建立的数学模型,阐明了地下滴灌点源条件下多因素影响的土壤水分及养分运动过程,揭示了其节水增产的内在机理。进一步指出地下滴灌系统的多种关键技术参数,讨论了地下滴灌灌水设备、灌水均匀度、灌溉定额、灌水频率、滴灌带埋深与间距对作物产量与水分利用效率的影响。最后提出现阶段地下滴灌技术的应用难点和需进一步研究的问题。本文旨在阐述地下滴灌技术在水资源节约方面中的潜力及产生机理,为推动地下滴灌技术广泛应用提供科学依据。     

缓冲带在减少集约经营雷竹林养分渗漏流失中的作用

<正>雷竹(Phyllostachys praecox f.prevelnalis)是优良的笋用竹种。近二十年来,通过冬季覆盖和重施肥技术,使雷竹笋实现了反季节生产,并使产量上升,从而使竹农获得可观的经济效益。因此,雷竹在浙江的栽培面积不断扩大,已达20000hm2,而且被江苏、安徽等11个省市大量引种栽培。     

Overlap PCR克隆黄牛脂肪特异性磷脂酶A2基因(AdPLA)及其原核表达

脂肪特异性磷脂酶A2基因(adipose-specific phospholipase A2,A dPLA)在脂肪组织甘油三酯水解过程中发挥着重要的调节作用,为了构建黄牛AdPLA基因原核表达系统,本研究通过Overlap PCR方法从黄牛(Bos taurus)基因组DNA中得到了AdPLA基因编码区全长,将其克隆到pGM-T载体上,阳性克隆经测序表明,与NCBI公布的序列(GenBank No.NM_001075280)完全一致.阳性质粒经BamH Ⅰ和HindⅢ双酶切后,将其定向重组到pET28a(+)原核表达载体上,转化感受态大肠杆菌(Escherichia coli) BL21 (DE3)中,用IPTG诱导融合蛋白表达.SDS-PAGE电泳表明,融合蛋白His-AdPLA在大肠杆菌中表达,证明成功构建了AdPLA基因原核表达系统,为进一步研究黄牛AdPLA基因的功能和AdPLA蛋白产品开发提供了依据.     

Role of beta-adrenoceptor signaling and AMP-activated protein kinase in glycolysis of postmortem skeletal muscle

Postmortem glycolysis is directly linked to the incidences of PSE (pale, soft, and exudative) and DFD (dark, firm, and dry) meats, which cause significant economic loss to the meat industry. However, mechanisms controlling postmortem glycolysis are unclear. The objective of this study was to determine the role of beta-adrenoceptor signaling and AMP-activated protein kinase (AMPK) in postmortem glycolysis. Eighteen 2 month old C57BL/6J female mice were randomly separated into three groups. Group I received an intraperitoneal injection of saline solution only and served as the control; group II received a saline injection and then were forced to swim for 1 min; and group III received an injection of propranolol (1 mg/kg) in saline. In addition, six C57BL/6J female AMPK knockout mice were assigned to group IV, which received a saline injection and were forced to swim for 1 min. The longissimus dorsi muscle was sampled at 0, 1, and 24 h postmortem for pH and enzyme activity measurements. The objective is to elucidate the roles of beta-adrenoceptor signaling and AMPK in the glycolysis of postmortem muscle. Results showed that AMPK activity had a major role in determining the ultimate muscle pH, with an ultimate pH for control mice of 6.16 and AMPK knockout mice of 6.48. The beta-adrenoceptor signaling is essential for initial rapid glycolysis. Blocking beta-adrenoceptor signaling prevented the initial pH decline induced by stress. Activation of beta-adrenoceptor signaling due to preslaughter stress activates glycogen phosphorylase, resulting in a rapid glycolysis shortly after slaughter. On the other hand, the activation of AMPK is important for maintaining the activity of glycogen phosphorylase and pyruvate kinase, leading to a sustained glycolysis and a low ultimate pH.