Formation of 2-alkyl-(2H)-thiapyrans and 2-alkylthiophenes in cooked beef and lamb

2-Alkyl-(2H)-thiapyrans and 2-alkylthiophenes have been identified in the volatiles of cooked beef and lamb. The quantities of both groups of compounds were higher in the meat of animals fed lipid supplements high in n-3 polyunsaturated fatty acids. 2-Alkyl-(2H)-thiapyrans were formed when (E,E)-2,4-dienals (C(6)-C(11)) and hydrogen sulfide were heated at 140 degrees C for 30 min. This confirmed their proposed route of formation in cooked meat from lipid-derived aldehydes and hydrogen sulfide; the latter was produced from the degradation of cysteine, via the Maillard reaction. The mass spectra and NMR spectra of these thiapyrans are reported for the first time. Although 2-alkyl-(2H)-thiapyrans were found to have only low odor potency, the reactions by which they are formed may have important implications for meat flavor. These reactions may remove potent aroma compounds and their intermediates from meat, thus modifying the overall aroma profile.     

土壤CO2与喀斯特洞穴CO2季节变化响应分析

为了揭示土壤CO_2对洞穴内环境的意义,对大风洞和响水洞2016年洞内环境指标和上覆土壤的相关数据进行统计与回归分析。结果表明,洞内CO_2浓度、土壤CO_2浓度具有显著的季节性特征,土壤2#对应的洞内空气CO_2在夏冬两季差值达793~884mg/kg。土壤水PCO_2和滴水PCO_2在夏冬两季的差值最高可分别达1.12和0.41,因此洞内滴水PCO_2、土壤水PCO_2也表现出明显的季节性特征。土壤CO_2、洞内空气CO_2、洞内滴水PCO_2和土壤水PCO_2间均表现出一定的滞后现象,如4#土壤水PCO_2与滴水PCO_2的相关系数,由非滞后条件下的0.123上升至滞后条件下的0.596。同时在滞后条件下,土壤CO_2对洞内CO_2的贡献率的总和最高可达84.6%,高于非滞后条件下的值。     

CaCl_2和SrCl_2提取土壤氮钾的比较

为了探讨0.01mol L-1 CaCl2和0.02mol L-1 SrCl2提取土壤氮、钾能力的差异,用0.01mol L-1 CaCl2和0.02mol L-1 SrCl2提取14个土壤样品,再分别用流动分析和火焰光度法测定提取液中的硝态氮和亚硝态氮之和和钾的含量,以1mol L-1 KCl和1mol L-1中性醋酸铵提取液作为无机氮和钾的对照提取剂,同时选择部分土壤样品用盆栽试验测定提取数量与土壤氮、钾有效性的关系。结果表明,两种方法和对照方法提取氮和钾数量的相关性均达到p<0.01水平,对照提取剂、0.01mol L-1 CaCl2和0.02mol L-1 SrCl2对于14个土壤的硝态氮和亚硝态氮之和提取含量平均值分别为13.36、15.33和26.62mgkg-1,14个土样的提取钾含量的平均值分别为120.4、33.58和54.24mgkg-1。盆栽试验结果表明,对照提取剂和0.01molL-1CaCl2和0.02molL-1SrCl2提取氮的数量与植物吸氮量的相关性达到p<0.05显著水平,钾的相关性达到p<0.01显著水平。与对照提取剂的氮、钾分别提取相比,SrCl2和CaCl2提取剂均可大大降低样品提取中试剂费用。以上结果表明,0.01mol L-1 CaCl2和0.02mol L-1 SrCl2提取对土壤氮和钾的提取能力均可反映土壤硝态氮和亚硝态氮、有效钾的含量和供应能力,而提取能力以0.02mol L-1 SrCl2为高。     

Lipase-assisted generation of 2-methyl-3-furanthiol and 2-furfurylthiol from thioacetates

Enzymatic hydrolysis of S-3-(2-methylfuryl) thioacetate and S-2-furfuryl thioacetate using lipase from Candida rugosa produced 2-methyl-3-furanthiol and 2-furfurylthiol, respectively. When reactions were carried out at room temperature and pH 5.8, 2-methyl-3-furanthiol was produced in a optimal yield of 88% after 15 min of reaction, whereas 2-furfurylthiol was obtained in a yield of 80% after 1 h of reaction time. Enzymatic hydrolysis was also performed in n-hexane, n-pentane, and water/propylene glycol mixture. The reaction rates in these media were slower as compared to those in aqueous medium; however, the reaction yields were quite similar. As expected, the stability of the generated 2-methyl-3-furanthiol and 2-furfurylthiol was better in n-hexane, n-pentane, and the water/propylene glycol mixture as compared to that in water or phosphate buffer.     

Anaerobic reoxidation of Mn2+, Fe2+, S0 and S2– in submerged paddy soils

Anaerobic reoxidation of reduced products in paddy soils was investigated. Ferrous iron (Fe²⁺) and monosulfide ion (S^2–) added to the soil chemically reduced MnO₂ to Mn²⁺, and MnO₂ and Fe(OH)₃ to Mn²⁺ and Fe²⁺, respectively, where Fe²⁺ and S^2– were considered to be oxidized to Fe³⁺ and S⁰. Elemental sulfur was oxidized to sulfate by anaerobic incubation with NO₃ ^– MnO₂ and Fe(OH)₃. A new conceptual model for the reduction processes in submerged paddy soil including the reoxidation processes of reduced products, in which soil heterogeneity in paddy fields was taken into consideration, was proposed based on the results. Received: 20 October 1996     

Effects of combined and sequential addition of dual oxidants (H2O2/S2O8(2-)) on the aqueous carbofuran photodegradation

Carbofuran (2,3-dihydro-2,2-dimethylbenzofuran-7-yl methylcarbamate) (CBF) is a widely used insecticide. Traditional methods like hydrolysis and direct photolysis cannot remove CBF effectively. In this study, the photodecay of 0.1 mM CBF in UV/H2O2, UV/S2O8(2-), and UV/H2O2/S2O8(2-) and sequential addition of a second oxidant were studied under UV light at 254 nm. The degradations of CBF follow pseudo-first-order decay kinetics. Direct photolysis was slow, but the corresponding degradation rate was increased with the addition of hydrogen peroxide (H2O2) or potassium peroxydisulfate (K2S2O8). In the UV/H2O2 reaction, the optimum reaction rate was 0.9841 min-1 at 10 mM H2O2 (pH 7); however, retardation is observed if H2O2 is overdosed. Such retardation is not observed in the UV/S2O8(2-) system, but a nonlinear increment of removal efficiency is identified. The UV/H2O2/S2O8(2-) process on the other hand shows the best performance in CBF degradation, but it has a less effective mineralization than that of the sole UV/S2O8(2-) reaction.     

GDA2基因的克隆、原核表达与融合蛋白的纯化

摘要：GDA2（G2 pea dark accumulated gene）是与G2豌豆（Pisum sativum L.）短日照条件下不衰老现象紧密相关的基因之一。实验用cDNA差示分析法（representational difference analysis, RDA）得到一个短日照下特异表达的G2豌豆cDNA，并命名为 GDA2。核酸序列分析表明，该cDNA全长1 120 bp，最大的开放阅读框为642 bp，编码一个由213个氨基酸构成的分子量约为24 kD的蛋白质，与GDA1的同源性为36%。在GDA2的cDNA两端分别引入Bgl Ⅱ与XhoⅠ的酶切位点，用PCR方法将其克隆到原核表达载体pGEX-4T-1中，经过酶切筛选和测序鉴定，得到所需的表达载体pGEX-GDA2。将pGEX-GDA2导入E.coli BL21菌株，经IPTG诱导，得到分子量约51 kD的 GST-GDA2融合蛋白，并利用Glutathione Sepharose 4B亲和柱对该融合蛋白加以纯化。GDA2-GST融合蛋白的表达和纯化工作，为深入研究GDA2蛋白的结构与功能以及该基因同衰老的关系打下良好的基础。     

2BLZ-2型垄上镇压式精密播种机的研制与试验

2BLZ-2型垄上镇压式精密播种机，设计安装了组合式仿形传动轮，集仿形传动作用为一体。采用了组合内窝孔式玉米排种器，实现精密播种。设置了两组弹簧，以保证播深一致及实现镇压力可调。通过田间作业试验和技术性能分析，证明该机具有良好的工作质量和可靠的技术性能。     

Synthesis and sensorial properties of 2-alkylalk-2-enals and 3-(acetylthio)-2-alkyl alkanals

Parallel synthesis was applied to prepare a series of 3-(acetylthio)-2-alkyl alkanals by Michael addition of thioacetic acid under alkaline conditions to alpha,beta-unsaturated 2-alkyl-substituted aldehydes, which were obtained by aldol condensation of the corresponding primary aldehydes as starting materials. The target compounds were characterized in terms of GC, MS, and NMR data. The sensory properties of the odorants, such as odor quality and odor detection threshold value, were determined with a trained panel. Structure-activity relationships are discussed, suggesting that the 1,3-oxygen-sulfur functionality, required for the "olfactophore" of tropical/vegetable notes, can further be extended to the acetylthio derivatives.     

Cacao polyphenols influence the regulation of apolipoprotein in HepG2 and Caco2 cells

Cocoa powder is rich in polyphenols, such as catechins and procyanidins, and has been shown to inhibit low-density lipoprotein (LDL) oxidation and atherogenesis in a variety of models. Human studies have also shown daily intake of cocoa increases plasma high-density lipoprotein (HDL) and decreases LDL levels. However, the mechanisms responsible for these effects of cocoa on cholesterol metabolism have yet to be fully elucidated. The present study investigated the effects of cacao polyphenols on the production of apolipoproteins A1 and B in human hepatoma HepG2 and intestinal Caco2 cell lines. The cultured HepG2 cells or Caco2 cells were incubated for 24 h in the presence of cacao polyphenols such as (-)-epicatechin, (+)-catechin, procyanidin B2, procyanidin C1, and cinnamtannin A2. The concentration of apolipoproteins in the cell culture media was quantified using an enzyme-linked immunoassay, and the mRNA expression was quantified by RT-PCR. Cacao polyphenols increased apolipoprotein A1 protein levels and mRNA expression, even though apolipoprotein B protein and the mRNA expression were slightly decreased in both HepG2 cells and Caco2 cells. In addition, cacao polyphenols increased sterol regulatory element binding proteins (SREBPs) and activated LDL receptors in HepG2 cells. These results suggest that cacao polyphenols may increase the production of mature form SREBPs and LDL receptor activity, thereby increasing ApoA1 and decreasing ApoB levels. These results elucidate a novel mechanism by which HDL cholesterol levels become elevated with daily cocoa intake.     

纳米TiO2对土壤Hg2+吸附解吸性能的影响

为了研究纳米TiO_2对土壤吸附解吸汞性能的影响,以三峡水库消落区土壤为代表,选择2种晶型(锐钛矿和金红石)的纳米TiO_2颗粒,设置3个浓度梯度(2,4,8g/kg),制成含有不同浓度纳米TiO_2颗粒的土样,配制不同浓度的Hg~(2+)溶液,进行吸附解吸试验。结果表明:纳米TiO_2颗粒可提高土壤对Hg~(2+)的吸附量,但受颗粒的晶型和浓度的影响;锐钛矿颗粒对土壤吸附解吸Hg~(2+)的影响更大,其吸附作用力更强,不易解吸,其中4g/kg处理组吸附作用最强,与对照相比,最大吸附量可提高32.65%,且其解吸率低于对照组;金红石颗粒处理组对Hg~(2+)的吸附量随颗粒浓度的升高而增大,但吸附作用力较弱,容易被解吸,8g/kg处理组影响最大,与对照相比,最大吸附量提高18.18%,但其解吸率也最大。因此,纳米TiO_2颗粒增强土壤对汞的吸附作用,从而可能影响汞在环境中的迁移转化过程,特别是锐钛矿型颗粒。     

Simultaneous analysis of T-2 toxin and HT-2 toxin by an indirect enzyme-linked immunosorbent assay

An indirect enzyme-linked immunosorbent assay (ELISA) for the detection of HT-2 toxin in the presence or absence of T-2 toxin is described. In the indirect ELISA, the relative cross-reactivities of antibodies against T-2 toxin (anti-T-2) with T-2 toxin and HT-2 toxin were 1 and 0.1, whereas anti-HT-2 cross-reactivities with T-2 toxin and HT-2 toxin were 0.33 and 1, respectively. Using such relationships, a formula was established that could be used to calculate the individual toxin concentration in a mixed sample after experimentally analyzing for T-2 and HT-2 toxins in the 2 indirect ELISAs. This method was tested by analyzing urine samples spiked with HT-2 toxin alone and samples spiked with both T-2 toxin and HT-2 toxin. A cleanup protocol for treatment of urine samples before ELISA was also established. The overall analytical recovery of HT-2 toxin when it was added at concentrations of 0.1-10 parts per billion (ppb) to the urine samples was ca 89%. When both T-2 and HT-2 toxins were added to the urine samples at equal concentrations of 0.5 to 5.0 ppb, their recoveries were 112 and 109%, respectively.     

Enrichment of N2 and Ar in the atmosphere of CO2-consuming soils

The phenomenon of unexplained N₂Ar-enrichment in soil air is quite frequently to be encountered in soil air studies on anthropogenically influenced sites. In the present study two anthropogenic deposits and a calcareous fluvisol were investigated for their soil air composition. While in the alkaline deposits extreme enrichments of N₂ and Ar (N₂ + Ar: up to 99%, v/v) were found as persistent site characteristics, the fluvisol showed only slight (about 1%, v/v) transient N₂/Ar-enrichments in summer. All sites, which did not show substantial vertical seepage percolation, exhibited enhanced CO₂-solubility-either due to strong calcite precipitation or dissolution. So, it was concluded that intensive continuous depletion of CO₂ was responsible for the subsequent convective influx of atmospheric air. From the results obtained it was concluded that an encasement of the concerned soil volume rather impermeable to gas transport as well as intense dissolution of CO₂ in the pore water are prerequisites for substantial N₂/Ar-enrichments in soil air.     

Effects of CO2 concentration in rhizosphere on nodulation and N2 fixation of soybean and cowpea

Soybean (Glycine max L. Merr.) cvs. Akisengoku and Peking, and cowpea (Vigna unguiculata Walp.) cv. Kegonnotaki were inoculated with Bradyrhizobium japonicum AlO17, Shinorhizobium fredii USDAI93, and B. sp. Vigna MAFF03-03063, respectively and were cultured hydroponically with supply of CO₂-free air, 3dm³ m^-3 CO₂ air, or 25 dm³ m^-3 CO₂ air to study the effects of the CO₂ concentration in the rhizosphere on plant growth, nodulation, and nitrogen fixation. Increase of the CO₂ concentration in the rhizosphere led to the increase of the plant dry weight in the symbiosis between Peking and USDAI93, and that between Kegonnotaki and MAFF03-03063. On the other hand, dry matter accumulation in the symbiosis between Akisengoku and AI017 decreased under the supply of 25 dm³ m^-3 CO₂ air aimed at increasing the CO₂ concentration in the rhizosphere beyond the optimum CO₂ concentration for growth. Nodule mass and nodule number per plant were highest in Akisengoku, followed by Kegonnotaki and lowest in Peking. Also the increase of the CO₂ concentration in the rhizosphere led to the increase of the nodule mass and number in Kegonnotaki, while no changes were observed in Akisengoku and Peking. Biological nitrogen fixation (BNF) was highest in Akisengoku, followed by Kegonnotaki, and lowest or near zero in Peking. BNF in Akisengoku and Kegonnotaki showed a similar tendency to that of dry matter accumulation. BNF of Peking was especially low under the supply of CO₂-free air, and it increased with the increase of the CO₂ concentration in the rhizosphere. For the symbiosis of Bradyrhizobium strains with soybean and cowpea, the most suitable CO₂ concentration for N₂ fixation and plant growth was estimated to be about 10 dm³ m^-3, while for the symbiosis of S. fredii with soybean, the value was estimated to be above 30 dm³ m^-3.     

N2O and N2 emissions from denitrification respond differently to temperature and nitrogen supply

Journal of Soils and Sediments - The reduction of nitrate (NO3ˉ) to nitrous oxide (N2O) and eventually to dinitrogen (N2) during denitrification in soil has rarely been studied at temperatures...     

CeO2/Al2O3催化剂的制备表征及在污水处理中的应用

为了提高臭氧催化氧化污水深度处理的效率,分别利用CeO_2和Al_2O_3作为活性组分和载体制备掺杂型CeO_2/Al_2O_3催化剂,通过X-射线衍射、透射电镜、N2吸附脱附曲线、X射线光电子能谱等方法对催化剂性能进行表征,考察CeO_2/Al_2O_3催化活性的变化,分析催化臭氧化去除有机物的作用机制。结果表明,制备的掺杂型CeO_2/Al_2O_3催化剂具有较大的比表面积、孔容和孔径,分别达到125 m2/g、0.242 2 cm3/g和7.777 8 nm。催化剂的活性组分主要为高度结晶化立方萤石结构的CeO_2,煅烧并未改变CeO_2的结构晶型。当进水化学需氧量(Chemical oxygen demand)为70~80 mg/L,催化剂用量为110 g/L,臭氧浓度为18 g/m3,p H值为7.8时,COD去除率最高42.8%。较高的催化效率归功于活性物质CeO_2中同时具有Ce3+和Ce4+,加速了臭氧生成更多的强氧化性?OH,催化剂的多孔结构为有机物的降解提供了充足的反应空间。催化剂使用寿命长,当催化剂重复使用5次后,COD去除率仍保持40%以上。     

硝态氮源及碳源有效性对土壤N_2O和CO_2排放的影响

以华北平原农田土壤为对象,通过室内静态培养系统研究NO_3~--N与不同碳源组合对土壤N_2O和CO_2排放的影响。结果表明,NO_3~--N作为氮源和不同碳源施入土壤,除NO_3~-+纤维素,其余土壤N_2O排放通量均高于对照组和只添加氮源土壤;NO_3~--N和不同碳源组合的CO_2累积排放量均高于对照和只添加氮源土壤。NO_3~-+果胶的N_2O排放量在第1 d达到最大值1 383.42μg N·kg~(-1)·d~(-1);NO_3~-+葡萄糖的CO_2排放量在第1 d达到最大值370.13 mg C·kg~(-1)·d~(-1),CO_2累积排放量顺序为:葡萄糖果胶秸秆纤维素淀粉木质素。土壤NO_3~--N含量与N_2O排放呈极显著正相关。总之,添加纤维素可以抑制N_2O的排放,促进CO_2排放,并增加土壤中NO_3~--N含量,添加其余碳源均会促进土壤N_2O和CO_2排放。     

农田土壤N2O排放和减排措施的研究进展

氧化亚氮(N2O)是一种受人类活动影响的重要温室气体。农业土壤是其主要的排放源之一,土壤中硝化和反硝化作用是N2O产生的主要过程。N2O的排放受多种因素的影响,农业活动尤其是施用化学氮肥是农田N2O排放量增加的主要因素。提高氮肥利用率,使用硝化抑制剂等措施将有助于减少N2O的排放量,更有效的减排措施还有待进一步的研究与应用。     

Mousy off-flavor of wine: precursors and biosynthesis of the causative N-heterocycles 2-ethyltetrahydropyridine, 2-acetyltetrahydropyridine,and 2-acetyl-1-pyrroline by Lactobacillus hilgardii DSM 20176

The N-heterocyclic bases, 2-ethyltetrahydropyridine (1), 2-acetyl-1-pyrroline (2), and 2-acetyltetrahydropyridine (3) are associated with the occurrence of mousy off-flavor in wine. The biosynthesis of these N-heterocycles by the wine lactic acid bacterium, Lactobacillus hilgardii DSM 20176, was studied by high-cell-density incubation in combination with a minimal chemically defined N-heterocycle assay medium. The key components of the defined N-heterocycle assay medium included D-fructose, ethanol, L-lysine, L-ornithine, and mineral salts. N-heterocycle formation was quantitatively determined by gas chromatography-mass spectrometry. The formation of 2 and 3 required the concomitant availability of a fermentable carbohydrate (D-fructose), ethanol, and iron (Fe(2+)). In addition, L-ornithine stimulated the formation of 2 and repressed 3 formation, whereas L-lysine stimulated the formation of 3 and repressed 2 formation. Incorporation of d(6)-ethanol into the acetyl side chain of 2 and 3, and of d(4)-acetaldehyde into the acetyl side chain of 3, confirmed that ethanol and acetaldehyde could serve as major side chain precursors. A pathway for the formation of 2 and 3 by heterofermentative lactic acid bacteria is proposed involving the interaction of accumulated C-2 intermediates from the heterolactic pathway and N-heterocyclic intermediates derived from the metabolism of L-ornithine and L-lysine.     

IPCC SRES A2和B2情景下我国玉米产量变化模拟

利用最新的温室气体和SO2 排放方案,即政府间气候变化委员会(IPCC)排放情景特别报告(SRES)的A2和B2方案,通过区域气候模式和区域作物模型模拟了未来2080s我国玉米产量的变化。主要结果如下:两种温室气体排放方案下,A2方案对我国玉米产量造成的负面影响大于 B2方案;气候变化对灌溉玉米造成的负面影响大于雨养玉米;气候变化造成玉米单产的变化表现为大多数玉米主产区减产,而非玉米主产区增产。