熟肉真空冷却过程中水分迁移理论分析和实验（简报）

真空冷却过程是复杂的相变传热传质过程。该文在能量和质量守恒理论的基础上,经过适当的简化,建立熟肉真空冷却过程中水分迁移的数学模型来分析水分迁移机理。利用圆柱形熟肉块的真空冷却实验来验证真空冷却过程中水分迁移的数学模型以获得真空冷却过程中熟肉的温度和压力的变化。结果分析发现：温度的模拟结果与实验数据基本一致,最大误差在5％以内,这表明此模型能够很好地预测真空冷却过程中熟肉内部的温度和压力分布。而且,通过模拟结果和实验数据可以得知：真空冷却过程中水分从熟肉内部向外部迁移的主要驱动力是熟肉内部之间的压差以及熟肉与真空室内之间的压差。因此,在实际应用过程中,为了提高真空冷却速率,应尽可能降低真空室内的压力以增加水分迁移的驱动力。     

熟肉真空冷却过程中水分迁移理论分析和实验

真空冷却过程是复杂的相变传热传质过程.该文在能量和质量守恒理论的基础上,经过适当的简化,建立熟肉真空冷却过程中水分迁移的数学模型来分析水分迁移机理.利用圆柱形熟肉块的真空冷却实验来验证真空冷却过程中水分迁移的数学模型以获得真空冷却过程中熟肉的温度和压力的变化.结果分析发现:温度的模拟结果与实验数据基本一致,最大误差在5%以内,这表明此模型能够很好地预测真空冷却过程中熟肉内部的温度和压力分布.而且,通过模拟结果和实验数据可以得知:真空冷却过程中水分从熟肉内部向外部迁移的主要驱动力是熟肉内部之间的压差以及熟肉与真空室内之间的压差.因此,在实际应用过程中,为了提高真空冷却速率,应尽可能降低真空室内的压力以增加水分迁移的驱动力.     

熟肉真空冷却过程的水分迁移对其肌肉组织的影响

该文以熟肉为试验材料,对真空冷却过程中熟肉内部温度场、水分蒸发速率以及含水率变化进行了试验研究。同时通过透射电子显微镜研究水分迁移对熟肉组织内部结构的影响。结果发现：熟肉的表面温度在4～5 min内从63℃降低到10℃,熟肉的平均含水率从71％降低到60.69％。真空冷却过程中水分的蒸发速率分为两个阶段：蒸发速率加速阶段和蒸发速率减速阶段。试验结果和理论分析显示,真空冷却过程中的水分迁移由两部分组成,一部分为由于产品内部温度不同造成不同的化学势引起食品内部的水分转移;另一部分为由于压力降低引起的水分蒸发或者沸腾后所产生的水蒸气的迁移。透射电子显微镜成像结果显示了经过真空冷却处理的熟肉中心和表面的肌肉组织形态没有发生大的变化。与真空冷却前相比,不管在熟肉中心还是表面,只是真空冷却后的肌肉纤维之间形成了更大的孔隙。     

球形食品真空冷却过程中参数分析

建立了描述球形食品在真空冷却中传热、传质的数学模型。通过数值求解得到真空压力、产品质量、产品温度(表面温度、中心温度、质量平均温度)随时间的变化曲线。实验装置中高精度的数据采集系统能够在线测定和记录真空室压力、产品质量、产品不同位置的温度随时间的变化。在春收甘蓝的真空冷却实验中，模拟的压力和实测的压力在10000～600 Pa的降压过程中最大相差100 Pa；模拟值和实测值间温度的最大差值小于1℃；真空冷却中，模拟的甘蓝的水分损失率是3.32%，实测的甘蓝水分损失率是2.97%，相差0.35%。研究结果对     

压力波动对卷心菜真空冷却效果的影响

为了提高结构紧密型果蔬的预冷效果,通过设定不同的压力波动区间,进行卷心菜真空冷却试验。分析了此过程中菜体温度变化规律,比较了不同的压力波动区间对冷却效果的影响。试验发现,压力波动区间分别为[560,660]Pa、[610,710]Pa和[660,760]Pa时,当卷心菜表面温度达到预定的2.50℃时,耗时分别为17.95、24.63和29.55 min,中心温度分别为8.50、2.99和3.26℃。结果表明：[610,710]Pa的压力波动区间,对卷心菜进行真空冷却的效果较好;真空冷却过程中,卷心菜中心至表面的温度变化的速度呈非线性分布;真空室的压力波动能够提高食品冷却过程中温度分布的均匀性。     

菜心真空预冷效果的试验研究

为进一步探讨叶菜真空预冷效果，采用实际生产使用的真空预冷设备对菜心进行小批量的真空预冷试验，考察了预冷过程中菜心的质量损失、温度随时间的变化情况及相互关系，以及真空预冷对菜心品质的影响。结果表明：小批量（120 kg/次）菜心真空预冷过程只需15 min，平均质量损失率为2.3%；冷却阶段的质量损失随预冷时间延长、物料温度降低而增大；菜心茎、叶冷却速度有明显差异，冷却均匀性稍差；经真空预冷处理后贮藏的菜心呼吸强度明显减弱，外观品质下降缓慢，贮藏寿命延长，维生素C含量有所减少。菜心对真空预冷有良好的适应性。     

果蔬气调贮藏冷却阶段温度变化的数值模拟及验证

该文主要针对果蔬的气调贮藏的冷却阶段进行了研究,建立了果蔬气调冷却阶段传热过程数学模型。采用有限差分法,编制了计算程序,对气调库中果蔬的降温进行了数值计算。对果蔬冷却降温过程进行了试验研究,试验结果与编程计算结果吻合较好,模拟温度与试验温度的差值在2℃以内。结果表明,文中的数学模型可以用于预测果蔬在气调冷却过程中的温度变化,这有助于科学地运行制冷设备,同时为气调贮藏果蔬系统的优化设计提供了理论基础。     

真空冷冻干燥在中药材加工中的应用及质量控制

中草药传统干燥加工过程中所造成的生物活性物质,特别是药用有效成分损失等问题,已引起国内外的普遍关注和担忧,真空冷冻干燥技术以其独有的特点和优势正逐渐成为贵重中草药干燥的首选。文中介绍了中草药真空冷冻干燥的原理和干燥过程中各阶段的工艺流程,并采用高效液相色谱法,以药材地黄的有效成分梓醇为检测指标,考察其在干燥过程中的化学动力学质量降解过程。通过试验确定了反应阶数、速度常数及模型参数,得出了控制其质量降解的预测模型,并对预测模型进行了验证。分析结果表明,所建立的质量降解模型能较好地反映地黄干燥质量随干燥时间、含水率及温度的变化过程,可用来进行中草药真空冷冻干燥质量降解的模拟。真空冷冻技术应用于中草药干燥能有效地保持中草药药用有效成分,避免传统干燥方法所造成的有效成分降低等缺陷     

基于数值模拟的红枣片不同干燥方式热质传递仿真与试验

为揭示并对比红枣片热风干燥、红外热风干燥及红外真空脉动干燥中的传热传质及干燥动力学特性,并填补关于果蔬红外真空脉动干燥数值模型的研究空白。该研究使用菲克扩散定律、安托因方程及比尔朗伯定律等控制方程分别建立了针对3种干燥方式的红枣片三维热质传递耦合数值模型,并利用试验数据对模型的可靠性进行验证。该研究基于枣片的实际几何尺寸进行建模并利用COMSOL求解。结果表明：1）与热风干燥相比,红外热风与红外真空脉动干燥分别缩短了46.43%和41.07%的干燥时间,且仿真结果与实测值吻合较好;2）温度场模拟图显示红外辐射可有效对红枣片内部进行加热,干燥20 min时红外热风和红外真空干燥的物料中心温度较热风干燥分别提高了11.33%和5.59%;3）模拟数据显示红外真空脉动干燥中的压力变化对干燥动力学产生了明显影响,其中含水率和干燥速率随压力脉动分别呈现阶梯状和峰状分布,并且干燥速率对压力变化的敏感性随着物料含水率的下降而下降;4）将测得的红枣片品质及质构特性与仿真数据进行综合对比,给出了关于分段组合干燥研究方向的见解,并对果蔬干燥数值模型的发展方向进行展望。该研究建立并验证了红枣片3种干燥方式下...     

青花椒真空脉动干燥特性及干燥品质工艺优化

为提升青花椒的干燥品质,减少其色泽褐变和风味物质流失等问题,该研究采用真空脉动干燥技术加工青花椒,并以热风干燥试验为对照组,研究了不同干燥温度、真空保持时间和常压保持时间对青花椒干燥特性及其品质的影响。在单因素试验基础上进行Box-Behnken中心组合试验设计,以青花椒的平均干燥速率、挥发油、酰胺含量、色差、开口率5个指标进行响应面优化分析。试验结果表明,Weibull模型可精确拟合青花椒真空脉动干燥曲线（R2>0.99）。干燥温度升高可在一定程度上提高青花椒的干燥效率和开口率,减少褐变和挥发油损失,同时酰胺类含量随干燥温度上升而有所下降。根据响应面试验结果,各因素对青花椒干燥综合评分的影响效果由大到小顺序为：干燥温度、真空保持时间、常压保持时间。优化的工艺参数为真空脉动干燥温度61.4 ℃、真空保持时间5 min、常压保持时间5 min,综合评分值达8.06,验证试验结果偏差仅为2.6%。研究结果为青花椒真空脉动干燥应用提供参考。     

低氮和干旱胁迫对富士和秦冠生长及氮素利用的影响

【目的】以富士（Fuji）、 秦冠（Qinguan）嫁接在平邑甜茶（Malus hupehensis Rehd.）上的当年生盆栽苗为试验材料,采用砂培方法,研究了缺氮胁迫和干旱对富士和秦冠生长情况、 光合参数、 植株各部位氮磷钾含量及氮素利用效率的影响,分析比较了低氮干旱条件下富士和秦冠生长及氮素利用的差异,以期为果树生产高效肥水利用提供理论指导。【方法】试验共设四个处理: 正常氮正常水（ZZ）、 低氮正常水（DZ）、 正常氮干旱（ZG）、 低氮干旱（DG）。氮素和水分均设置两个水平,分别为正常氮（6 mmol/L NO-3-N）、 低氮（0.3 mmol/LNO-3-N）、 正常供水（保持盆中砂子相对含水量为饱和含水量的80%~85%）、 干旱处理（保持盆中砂子相对含水量为饱和含水量的60%~65%）。【结果】富士和秦冠的生物量（茎和叶）、 株高茎粗等生长指标以及光合速率、 气孔导度、 蒸腾速率均为正常氮正常水（ZZ）＞低氮正常水（DZ）＞正常氮干旱（ZG）＞低氮干旱（DG）,并且相对应处理下秦冠的以上指标均高于富士;正常供水下,缺氮处理使富士、 秦冠的根冠比比正常氮处理均有所增加,富士提高了2.05%,秦冠提高了22.40%。富士和秦冠的氮、 磷、 钾含量均表现出正常氮正常水（ZZ）＞低氮正常水（DZ）＞正常氮干旱（ZG）＞低氮干旱（DG）; 氮、 钾元素含量在植株各部位的分布顺序依次是叶＞根＞茎,磷元素则是根＞叶＞茎;光合氮素利用效率（PNUE）和氮素利用效率表现为秦冠处理之间差异极显著,富士处理之间差异不显著;秦冠的PNUE和NUE明显高于富士,在低氮正常水（DZ）处理下,秦冠氮肥利用率比富士高42.07%,在低氮干旱（DG）处理下高64.14%;低氮胁迫下富士和秦冠的NUE显著提高,并且秦冠提高的幅度高于富士。【结论】施用氮肥能够显著提高富士与秦冠的干物质量,同等水肥条件下,秦冠生长优于富士;水分亏缺会减少叶片对氮的吸收,干旱条件下适度增施氮肥,可提高果树的抗旱能力;低氮干旱胁迫下秦冠的生长指标、 光合指标及氮素利用效率指标均优于富士,表现出较强的抗低氮干旱胁迫的能力。     

Pasture Vegetation Elemental Analysis by Laser-Induced Breakdown Spectroscopy

Laser-induced breakdown spectroscopy (LIBS) is a new technique for the analysis of plant material. This study investigates the application of LIBS to pasture-based plant samples. The LIBS measurements were obtained from pelletized pasture samples (100 samples) that had been also analyzed by inductively coupled plasma–optical emission spectroscopy (ICP-OES) following microwave digestion for calibration and comparison purposes. Comparisons for elements sodium (Na), potassium (K), magnesium (Mg), calcium (Ca), manganese (Mn), iron (Fe), copper (Cu), zinc (Zn), boron (B), phosphorus (P), and sulfur (S) showed that LIBS could be used for almost all the standard profile total elements with concentrations down to low mg/kg levels (observed error of Na: 0.024 percent, K: 0.18 percent, Mg: 0.016 percent, Ca: 0.073 percent, P: 0.017 percent, Mn: 31 mg/kg, Fe: 150 mg/kg, Zn: 6.6 mg/kg, and B: 1.1 mg/kg). Elemental analysis at less than mg/kg levels was not possible using LIBS. The elements S and Cu were particularly difficult to analyze with reliability using LIBS at the concentration levels found in the plant samples. Replacing microwave digestion and subsequent ICP analysis with a direct analysis of dried plant samples using LIBS has the potential to improve the productivity and reduce the cost of testing.     

Faculty positions:Center for Agricultural Resources Research,Chinese Academy of Sciences

正The Center for Agricultural Resources Research(CARR),the Institute of Genetics and Developmental Biology(IGDB),Chinese Academy of Sciences,invites applicants for several research group leader positions.CARR is one of the research organizations in Chinese Academy of Sciences(CAS).We seek nominations and applications from individuals who have expertise and a record of accomplishment in research areas related to ecology,agro-hydrology,     

Macroinvertebrates in North American tallgrass prairie soils: effects of fire, mowing, and fertilization on density and biomass

The responses of tallgrass prairie plant communities and ecosystem processes to fire and grazing are well characterized. However, responses of invertebrate consumer groups, and particularly soil-dwelling organisms, to these disturbances are not well known. At Konza Prairie Biological Station, we sampled soil macroinvertebrates in 1994 and 1999 as part of a long-term experiment designed to examine the effects and interactions of annual fire, mowing, and fertilization (N and P) on prairie soil communities and processes. For nearly all taxa, in both years, responses were characterized by significant treatment interactions, but some general patterns were evident. Introduced European earthworms (Aporrectodea spp. and Octolasion spp.) were most abundant in plots where fire was excluded, and the proportion of the total earthworm community consisting of introduced earthworms was greater in unburned, unmowed, and fertilized plots. Nymphs of two Cicada genera were collected (Cicadetta spp. and Tibicen spp.). Cicadetta nymphs were more abundant in burned plots, but mowing reduced their abundance. Tibicen nymphs were collected almost exclusively from unburned plots. Treatment effects on herbivorous beetle larvae (Scarabaeidae, Elateridae, and Curculionidae) were variable, but nutrient additions (N or P) usually resulted in greater densities, whereas mowing usually resulted in lower densities. Our results suggest that departures from historical disturbance regimes (i.e. frequent fire and grazing) may render soils more susceptible to increased numbers of European earthworms, and that interactions between fire, aboveground biomass removal, and vegetation responses affect the structure and composition of invertebrate communities in tallgrass prairie soils.     

Variation in quality parameters between and within 14 Nordic tree fruit and berry species

Abstract

A 3-year study was carried out to investigate quality parameters in 14 tree fruit and berry species grown in southern Norway. The species were blueberry, apple, aronia, sour cherry, sweet cherry, red raspberry, strawberry, blackcurrant, gooseberry, red currant and elderberry, harvested along with wild bilberry, cloudberry and lingonberry. Significant differences between species were identified for all quality parameters. The coefficient of variation between species was lowest for pH (12.5%), dry matter (18.9%) and soluble solids (25.3%), followed by titratable acids (59.3%), total phenolics (83.8%), antioxidant capacity FRAP (85.7%) and antiradical power by the DPPH-assay (97.8%), total monomeric anthocyanins (132%) and ascorbic acid (137%). Average coefficient of variation within species were lower and ranged from 4 (pH) to 62% (ascorbic acid). Only the FRAP values were significantly affected by harvesting year with lower levels in 2004 than in 2005 and 2006. There were significant interactions between species and harvesting year for dry matter, soluble solids, pH, ascorbic acid and FRAP. The results indicate generic ranges in composition within species independent upon growing location and climate, and the composition of the tree fruits and berries is not likely to deviate from these ranges. It is concluded that desirable composition of tree fruits and berries and their products should primarily be achieved by selection among species rather than searching fors broadened variation within individual species.     

Potassium Fixation and Release Characteristics in Rhizosphere and Nonrhizosphere Soils for a Rapeseed–Rice Cropping Sequence

Potassium (K) fixation and release in soil are important factors in the long-term sustainability of a cropping system. Changes in K concentration and characteristics of K fixation and release in rhizosphere and nonrhizosphere soils in the rapeseed (Brassica napus L.)–rice (Oryza sativa L.) rotation were investigated using a rhizobox system. The concentrations of different forms of K in both rhizosphere and nonrhizosphere soils decreased with plants compared to without plants, regardless of K fertilizer application. Potassium uptake by crops mainly came from the rhizosphere soil. In the treatment without K fertilizer (–K), the main form of K supplied by the soil to the crops was 1.0 mol L^?1 nitric acid (HNO₃) nonextractable K, followed by nonexchangeable K, and then exchangeable K. In the treatment with K fertilizer (+K), the main K forms supplied by the soil to the crops were exchangeable K and nonexchangeable K. The amount and rate of K fixation after one cycle of the rapeseed–rice rotation was greater in rhizosphere soil than in nonrhizosphere soil. The amount and rate of K fixation of soil in the +K treatment were significantly less than in the –K treatment. The cumulative amounts of K released with 1.0 mol L^?1 ammonium acetate (NH₄OAc) and 1.0 mol L^?1 HNO₃ extraction increased with the increasing numbers of extractions, but the K-releasing power of soil by successive extraction decreased gradually and finally became almost constant. The release of K was less in rhizosphere soil than in nonrhizosphere soil. The release of K in the +K treatment was similar to that in the –K treatment in rhizosphere soil, but the K release in nonrhizosphere soil was greater with the +K than the –K treatment. Overall, the information obtained in this study will be helpful in formulating more precise K fertilizer recommendations for certain soils.     

Electron donor and pH relationships for biologically enhanced dissolution of chlorinated solvent DNAPL in groundwater

Biologically enhanced dissolution offers a method to speed removal of chlorinated solvent dense non-aqueous-phase liquid (DNAPL) sources such as tetrachloroethene (PCE) and trichoroethene (TCE) from aquifers. Bioremediation is accomplished by adding an electron donor to the source zone where fermentation to intermediates leading to acetic acid and hydrogen results. The hydrogen and possibly acetic acid are used by dehalogenating bacteria to convert PCE and TCE to ethene and hydrochloric acid. Reductive dehalogenation is thus an acid forming process, and sufficient alkalinity must be present to maintain a near neutral pH. The bicarbonate alkalinity required to maintain pH above 6.5 is a function of the electron donor: 800 mg/L of bicarbonate alkalinity is sufficient to achieve about 1.2 mM TCE dechlorination with glucose, 1.7 mM with lactate, and a much higher 3.3 mM with formate. Laboratory studies indicate that in mixed culture, formate can be used as an electron donor for complete conversion to ethene, contrary to pure cultures studies indicating it cannot. Various strategies can be used to add electron donor to an aquifer for DNAPL dehalogenation while minimizing pH problems and excessive electron donor usage, including use of injection-extraction wells, dual recirculation wells, and nested injection-extraction wells.     

Biodiversity and ecogeography of wild Lactuca spp. in some European countries

Staff members of the Department of Botany of Palacký University in Olomouc and Gene Bank Department – Workplace Olomouc, Research Institute of Crop Production in Prague, Czech Republic, conducted an expedition in seven European countries (Austria, Czech Republic, France, Germany, Italy, the Netherlands, Switzerland) in August/September 1999 to collect wild Lactuca spp. germplasm and study its geographic distribution, ecology and biodiversity. During the mission, more than 600 locations were visited resulting in the collection of 602 seed samples (accessions) of wild Lactuca species and 13 seed samples of related genera (Chondrilla and Mycelis). Lactuca serriola f. serriola, L. serriola f. integrifolia, L. saligna and L. viminea subsp. chondrilliflora were prevalent in southern Europe (Italy, France), however, only L. serriola was common in central and western Europe (Austria, Czech Republic, Germany, Netherlands, Switzerland). The greatest diversity of Lactuca species was found in France, where also the most seed samples (165) were collected. The most characteristic habitats with a high density of Lactuca spp. populations were observed along roads and highways, grassy ditches, ruderal communities, and dust-heaps. Natural infections by powdery mildew (Erysiphe cichoracearum) and downy mildew (Bremia lactucae) on some wild Lactuca spp. were observed. Recent observations concerning the geographic distribution, population structure, habitats, and natural occurrence of diseases of Lactuca spp. are discussed. This assemblage of genetic resources of Lactuca spp. can serve as the basis of future studies of species diversification, spatial population structure, plant microevolution, domestication processes, and genetic variability of host-parasite interactions.     

Increase in auxiliary photoprotective photosynthetic pigments in wheat seedlings induced by Azospirillum brasilense

Inoculation of wheat seedlings with the plant growth-promoting bacterium Azospirillum brasilense Cd was immobilized in alginate microbeads and, without applying any stress, significantly increased the quantity of several photosynthetic pigments, such as chlorophyll a, chlorophyll b, and the auxiliary photoprotective pigments violaxanthin, zeaxanthin, antheroxanthin, lutein, neoxanthin, and β-carotene. This resulted in greener plants with no apparent visible stress. After monitoring the quantity of photosynthetic pigments for 4 weeks, we observed that inoculated plants had higher quantities of pigments in shoot and stem. The greatest difference in the quantity of all pigments between inoculated and noninoculated plants occurred in the first week of growth. Regardless of treatment, the quantity of pigments in stems was three to four times less than the quantity of these pigments in shoots. Application of Azospirillum, either as liquid inoculant or as alginate microbeads, did not alter the positive effect of the bacteria on pigment production or the positive response of the plants towards A. brasilense Cd inoculation.     

In-situ enrichment and analysis of atrazine-degrading microbial communities using atrazine-containing porous beads

We examined the community composition of microbes that colonized atrazine-containing beads buried in agricultural soils that differed in atrazine treatment history. Bacterial abundance was 5-40-fold greater in atrazine-fortified beads. In beads containing 20 mg atrazine kg⁻¹ buried in soil with a history of atrazine application (conditioned soil), the abundance of Actinobacteria increased approximately 80-fold whereas in control soil, Actinobacteria were enriched only 10-fold and the gamma-Proteobacteria and Planctomycetes increased by 60- and 25-fold, respectively. The gamma-Proteobacteria were enriched by 120- and 230-fold in beads containing 200 mg atrazine kg⁻¹ in conditioned and control soil, respectively. The results demonstrate that BioSep^® beads are a suitable matrix for recruiting a diverse subset of the bacterial community involved in atrazine degradation.