Rapid gas-chromatographic method for the determination of diacetyl in milk, fermented milk and butter

In this work, a simple and fast method for the determination of diacetyl by gas-chromatographic technique coupled with flame ionisation detector (GLC-FID) was developed. Diacetyl is the typical butter flavour, but it is also commonly present in others fermented dairy products. Recently, diacetyl determination has also attracted interest because it is one of the parameters on which lactic acid bacteria (L.A.B.) are characterized and valued. Only acetone and 2,3-pentanedione were used as chemicals. After centrifugation of acetone–milk mixture, supernatant was filtered and directly injected into gas-chromatographic apparatus, without a further purification procedure step.

This method was accurate and precise; diacetyl recovery on milk was 97% and the detection limit was 1 mg L⁻¹. Finally, by using this method, diacetyl was easily determined in fresh and high-temperature treated milk, commercial butter, yoghurt and also in a series of L.A.B. performance tests.     

Impact of sodium sulfate on soil frost heaving in an open system

The existence of solutes and their redistribution during freezing have a deep influence on the process of soil freezing. We performed unidirectional freezing experiments in an open system with red clay collected at the Beiluhe test site along the Qinghai–Tibet Railway. The groundwater supply of the soil was simulated in the laboratory experiment by attaching a liquid replenishment system to the bottom of the sample container. In order to see the influence of the salt on the evolution of the sample during unidirectional freezing, two types of experiments were performed. (i) The soil samples were supplied with a sodium sulfate solute of 5% concentration, and (ii) only distilled water without any salty component was added. Based on the freezing temperature measurements of salty soil, migration of sodium sulfate solution towards a lower temperature zone during freezing 0 °C isotherm in the soil moved gently towards deeper layers, but frost depth of the soil ascended slightly with time when the sample was constantly cooled. Compared to the distilled water replenishment, the amount of frost-heaving was smaller in the soil column with sodium sulfate solution replenishment. Based on the frost depth curve, the solubility curve of the Na₂SO₄–H₂O system and the amount of frost heaving and salt expansion in the soil column we have calculated the amount of frost heaving and salt expansion. In an early stage of the experiment deformation of the soil column was mainly caused by frost heaving, while in a later phase crystallization of the sodium sulfate played a lager role. This conclusion is confirmed by the results of the dry density measurement after the experiments.     

西藏旁多水利枢纽坝基深厚覆盖层防渗分析论证

旁多工程坝基覆盖层深厚。防渗面积大,且处于4000m以上的高海拔地区。因此,坝基防渗形式的选择合理与否是个关键问题。为此。通过比较灌浆帷幕、混凝土防渗墙、上墙下幕以及悬挂式防渗墙等方案,从防渗可靠性、施工技术条件、电力资源损失、运行检修条件及工程投资等诸多方面进行了综合比较,优选出坝基防渗的最佳方案。     

黄山毛峰茶主要呈味物质浸出浓度与浸出率的研究

为了探索黄山毛峰茶主要呈味物质的浸出规律,按水温、冲泡时间双因子与水温、冲泡次数双因子正交对黄山毛峰茶做冲泡试验,并对茶汤中的氨基酸、茶多酚、咖啡碱、水浸出物的浓度进行动态分析,结果表明:1次冲泡过程中,茶汤中主要呈味物质的浓度随冲泡时间的延长与温度的提高而增加,但浸出速率在不同的时间段和不同的温度下有所差异;分次冲泡过程中,茶汤中各成分浸出浓度最大值的出现受冲泡温度与冲泡次数的影响,酚氨比随冲泡次数的增加而增大。     

Content of various elements in different parts of the tea plant and in infusions of black tea from Southern India

Contents of various elements in dyferent parts of the tea plant (shoot, mature leaf, small stem, thick wood and root), black tea manufactured by the crush-tear-curl and orthodox processes, and tea brew after 1 and 5 min of infusion were determined by inductively coupled plasma atomic emission spectrometry. From these, the amount of each element assimilated in the production of 1000 kg of marketable tea, as well as the quantity of each element brought into infusion and thus possib f y taken up through drinking tea, were calculated and discussed. Among the various elements assimilated by the tea plant, the shoot jraction (economically important for manufacturing commercial tea) contained high concentrations of N, P, K and Mg while the mature leaf accumulated Al, Bu, Ca, Cd, Mn, Pb and Sr. Of the dgerent elements brought into infusion while brewing black tea, the amount of K was found to be the largest (> 10000 μg g⁻¹ tea) followed by P (700–1200 μg g⁻¹), Mg (300–700 μg g⁻¹), Ca and A1 (each 150–300 μg⁻¹), Mn (60–150 μg g⁻¹), Cu, Na, Si and Z n (each 6–50 μg g⁻¹), B, Ba, Cr, Fe, Ni and Pb (each Id μg g⁻¹), and Sr, Co and Gd (each <1μg g⁻¹). The proportion of the totalamount of an element brought into infusion showed that the elements Ba, Ca, Fe and Sr were less soluble (<10 % of total amount), Al, B, Cd, Co, Cr, Cu, Mg, Mn, P, Pb, Si and Zn were moderately soluble (10–50 %), and K, Nu and Ni were highly soluble (>50%). The overall mean of the extent of solubility of all elements in 1 and 5 min showed that, out of the amount soluble in 5 min, about 68% was dissolved within 1 min.     

青藏直流投运后藏中电网稳定特性研究

藏中电网规模较小,网架结构相对较弱,青藏直流联网工程投运后给藏中电网的安全稳定运行带来诸多挑战,交直流系统稳定问题突出。从联网工程投运前藏中电网的电源特性、大机小网等固有特性出发,结合青藏直流联网以来青藏直流以及藏中电网运行中存在的各种稳定问题,深入分析了青藏直流投运后藏中电网的电源特性变化、稳定特性转化、虎曲线功率送出、直流换相失败、以及交直流影响等安全稳定问题。同时针对西藏电网的运行特性,分析并指出了青藏直流几个重要而特殊的安全稳定运行特性。     

Role of Tea1p, Tea3p and Pom1p in the determination of cell ends in Schizosaccharomyces pombe

Schizosaccharomyces pombe cells are rod-shaped and grow along a single axis from their two ends. Microtubules extend from the cell centre terminating at the cell ends. The ERM(ezrin/radixin/moesin)-like proteins Tea1p and Tea3p, and the Dyrk-like kinase Pom1p are cell end markers involved in the regulation of growth and microtubular dynamics at the cell ends. We have analysed the relative contribution of these three proteins to the determination of cell ends as sites both for cell growth and for microtubular termination. Pom1Delta, in combination with Tea1Delta or Tea3Delta, has the greatest difficulty in relocalizing actin to the cell ends following actin depolymerization and generates the most defective growth pattern. Tea1Delta, in combination with Pom1Delta or Tea3Delta, displays the highest number of microtubules bending round the cell ends. Tea1DeltaPom1Delta, which has the most defective growth pattern and microtubules, also displays the highest number of branched cells. We show that Tea1p, Tea3p and Pom1p all contribute, to different extents, to the determination of cell ends, as sites for both cell growth and microtubular termination. We also show that the fission yeast cell relies on both the positioning of landmarks and a properly organized microtubule cytoskeleton to direct cell growth.     

茶叶中多种农药残留测定方法研究

采用气相色谱-串联质谱法同时测定了茶叶中多种农药残留。样品加水后用乙腈提取,采用GCB/PSA固相萃取柱净化,淋出液浓缩至近干后用正己烷-丙酮（9：1,V/V）溶液定容,气相色谱-串联质谱测定。结果表明目标农药添加于样品中质量浓度在0.050～0.500mg/kg（r〉0.9700）范围内与峰面积呈线性关系,检出限（3S/N）位在0.1～37.5ng/g之间。加入0.100和0.400mg/kg两个浓度水平的农药标准溶液,目标农药的回收率在66.5%～114.7%之间,相对标准偏差（n=5）均小于20%。     

增效剂对油溶性茶多酚硒的抗氧化增效作用研究

在100℃恒温及黑暗条件下,采用空气自然氧化考察了维生素C、酒石酸、柠檬酸对LTP-Se在蓖麻油中抗氧化性能。结果表明m(增放剂)的添加量为0.01%、0.03%、0.05%时,对油溶性茶多酚硒抗氧化增效效果较好,m(VC)添加量为0.05%,LTP-Se添加浓度为100mg/kg的油样抗氧化生最佳。     

Rebranding Terroir: Ethnoecology and Tea Agro-Ecosystem Management in Response to Increased Market Integration in Southern Yunnan,China

Prompted by increased domestic and transnational demand for Pu’er tea, an emergence of agroecosystem intensification in Southern Yunnan, China has resulted in various agro-ecosystems including tea forests, mixed crop systems, and monocultural terrace tea gardens, in the tea production system. Plants of Camellia sinensis assamica often grow as trees in forests whilst C. sinensis sinensis grow as shrubs in terrace tea gardens. Inspired by the wine industry, the concept „Terroir” acts as a framework that analyzes both environmental and human factors yielding var ying botanic profiles, and hence quantifies values created by the cultivation process. The approach allows economic opportunities of place-based tea products to be driven by the origin in lieu of extrinsic qualities, which has resulted in to the fabricated reputation of terroir. In response to a common gap in terms of botanical and cultural values between tea cultivation and marketing trends, this artic le investigates an alternative scenario in which tea production and promotion model could minimize its environmental impacts and utilize its economic weight to advance land conservation efforts specific to cultural complexity at community scales.