鲜猪肉冷藏过程中沙门氏菌生长预测模型的选择

本文选择修正的Gompertz模型和BaranyiRoberts模型两种初级模型,分别通过Origin8.0软件和DMFit软件,将沙门氏菌在4、7、10、12和15℃鲜猪肉上的生长曲线进行拟合。以平方根方程为基础建立二级模型,描述猪肉冷藏温度对沙门氏菌最大生长速率的影响,通过偏差因子(Af)、准确因子(Bf)及均方根误差(RMSE)分析进行检验,选取最适生长模型。结果显示,在4℃条件下,沙门氏菌在鲜猪肉上未见生长,无法进行生长曲线拟合。其余温度条件下的生长情况,均能通过修正的Gompertz模型和BaranyiRoberts模型进行很好地描述。通过对二级模型的验证,结果显示,基于BaranyiRoberts模型所建立起的二级模型的偏差因子(Af)1.03、准确因子(Bf)0.97及均方根误差(RMSE)0.0035均优于修正的Gompertz模型所建立的二级模型的偏差因子(Af)1.12、准确因子(Bf)0.90及均方根误差(RMSE)0.0483。因此可以得出,BaranyiRoberts模型比修正的Gompertz模型能更好地预测7~15℃冷藏温度下鲜猪肉中沙门氏菌的生长情况。     

冷却猪肉不同贮藏温度的货架期预测模型

为了建立冷却猪肉货架期的预测模型,把特定腐败菌接种到无污染的冷却猪肉表面,托盘包装分别置于0℃,4℃,7℃,10℃,14℃和20℃的温度下贮藏,分别测定不同贮藏时间的细菌总数,同时对4℃贮藏的不同企业冷却猪肉进行品质分析,确定腐败限控量.结果表明,冷却猪肉腐败限控量为7.23 lg(cfu/g).应用修正的Gompertz函数能很好的描述特定腐败菌在不同温度下的生长动态,建立了6种温度下其在猪肉中的生长模型.温度对最大比生长速率和延滞时间等动力学参数的影响,采用平方根模型呈现良好的线性关系,模型残差值的绝对值均小于0.1,上下浮动于零左右,表明该模型描述的温度与比生长速率和延滞时间是可信的,由此建立了0～20℃范围内冷却猪肉贮藏过程中货架期的预测模型.     

冷却肉中假单胞菌温度预测模型的建立与验证

为了快速预测和监控引起冷却肉腐败变质的主要微生物--假单胞菌的生长,以从冷却猪肉中分离得到的假单胞菌P-1菌株作为受试菌,建立和验证0～10℃低温条件下假单胞菌的生长动力学模型.利用SAS程序拟合不同温度条件下的生长情况,经过比较发现,Gompcrtz模型比线性模型能更好地拟合假单胞菌的生长,从而得到假单胞菌生长的Gompcrtz模型参数;利用平方根模型对假单胞菌的最大比生长速率平方根一温度进行拟合,得到假单胞菌生长的二级模型:利用培养基数据、冷却肉产品数据和温度波动条件下的数据对所得到的二级模型进行验证,计算得到总的偏差因子和准确因子分别为0.944和1.256,结果表明建立的二级模型能真实快速有效地预测0～10℃下冷却肉中假单胞菌的生长.     

红烧卤牛肉货架期预测模型的建立

为了探究红烧卤牛肉在不同温度下的货架期,本试验将加工好的红烧卤牛肉真空包装,进行二次沸水煮制杀菌(中间相隔48 h)。以菌落总数为指标建立货架期预测模型,将二次杀菌后的红烧卤牛肉产品分别贮藏在4、10、15、20、25℃的恒温培养箱中,测定贮藏期间菌落总数的变化。结果表明,随着贮藏温度的升高,微生物的最大生长比率增大,迟滞期和货架期缩短;建立一级模型(修正Gompertz模型)与二级模型(Belehradek模型),修正Gompertz模型除4℃下微生物生长曲线无法拟合之外,其余4个温度拟合效果良好(相关系数R²>0.9),并通过了模型验证(准确因子Af与偏差因子Bf的范围分别在1.1～1.9与0.75～1.25之间);结合一、二级模型建立红烧卤牛肉货架期预测模型,模型通过了验证(预测值与实测值相对误差在10%以内),预测得到的10、15、20、25℃贮藏的红烧卤牛肉货架期分别为185.76、64.05、31.00、15.08 d。本研究获得了红烧卤牛肉在10～25℃的货架期预测模型,为红烧卤牛肉在不同温度下的贮藏时间选择提供了理论依据。     

瓢儿菜采后微生物生长动力学模型研究

以采后瓢儿菜为试验对象,研究了不同贮藏温度下瓢儿菜的微生物生长趋势,建立了瓢儿菜微生物生长动力学模型和微生物货架期预测模型。结果表明:修正的Gompertz方程能够较好地拟合不同温度下瓢儿菜微生物生长的初级模型,其R~2均大于0.90;瓢儿菜的最大菌数Nmax随温度的变化波动不大,平均值为(6.85±0.1265)cfu/g;最大比生长速率μmax随温度的上升而增加,生长延滞时间λ随温度的上升而减小;二级模型为=0.040×[T-(-0.198)]及=0.260×[T-(-3.379)],其R2均大于0.90。通过初级模型和二级模型确立了瓢儿菜的微生物货架期预测模型。     

电子鼻结合SAWR判定甜橙储存时间方法研究

本文采用电子鼻结合433MHz声表面波谐振器(SAWR)对不同储存时间的甜橙进行了检测,试验记录电子鼻和SAWR对甜橙样品的响应数据,同时测量了甜橙样品的质量变化百分数,分别拟合构建了电子鼻预测模型、SAWR频率预测模型和电子鼻结合SAWR混合预测模型。结果表明,随着储存时间的增加,甜橙样品失重百分比不断上升。电子鼻结合SAWR混合预测模型相比较其它两种模型可以更准确的预测甜橙储存时间。该方法具有响应迅速、准确性高、成本低廉等优势,为判定甜橙储存时间提供了一种新的思路。     

基于改进惯性矩算法的冷鲜猪肉新鲜度激光散斑图像检测

为了探究激光散斑技术检测冷鲜猪肉新鲜度的可行性,用660和465 nm 2种波长的激光对宰后24 h的猪肉样本在7 d内的激光散斑图像进行采集。以时间序列散斑(time history of speckle pattern,THSP)图像的惯性矩(inertia moment,IM)作为散斑活性,研究冷鲜猪肉散斑活性随货架期的变化规律。通过分析2种波长不同行的选取对IM值的影响,发现不同波长其奇偶行IM的规律不同,并针对传统IM算法容易出现异常值、稳定性差等缺点提出3点改进:设计排序算法动态选择散斑活性最高峰及周围2个相邻行,依此计算样本IM值;改进共生矩阵的修正矩阵计算方法;改进非零元素偏离对角线距离的计算方法。结果显示,改进方法可以有效地抑制异常值干扰,冷鲜猪肉散斑活性随货架期呈现先上升后下降的变化趋势。根据测得的挥发性盐基氮值(total volatile basic nitrogen,TVB-N)和散斑活性IM值建立猪肉新鲜度等级预测模型,结果显示465 nm波长的激光判别效果要好于660 nm激光,其训练集和预测集的识别率能达到87.5%和89.29%。试验结果表明利用激光散斑技术检测冷鲜猪肉新鲜度的具有可行性。     

豆腐中库特氏菌生长动力学模型和货架期预测

以引起豆腐腐败的特定腐败菌库特氏菌为研究对象,研究不同温度对其生长的影响,定量评价温度对豆腐货架期的影响,为货架期快速有效的估测提供有效的手段。将库特氏菌接种到豆腐表面,在4、12、20、30℃条件下贮藏,由此建立一级和二级生长动力学模型以及剩余货架期预测模型。结果表明,Gompertz函数能够很好的描述豆腐中的微生物生长动态,建立了4种温度下豆腐的微生物生长动力学模型。采用平方根模型(Belehradek)描述温度对最大比生长速率(μmax)和延滞时间(Lag)的影响,结果表明呈现良好的线性关系。用豆腐在8℃和25℃的库特氏菌实测值进行验证,偏差度(Bf)和准确度(Af)分别为1.04、1.02和1.20、1.18。获得的剩余货架期的预测模型为:SL=Lag-[(8.6-N0)/(μmax·2.718)]·{ln[-ln(7.14-N0)/(8.6–N0)]-1},用豆腐贮藏在8℃和25℃的货架期实测值验证建立的模型,预测值和实测值的相对误差分别为-3.47%和4.89%,说明建立的模型能够快速可靠的预测豆腐的微生物学品质和剩余货架期。     

基于多参数耦合的蓄冷温控箱冷板对流换热参数优化

蓄冷温控箱利用低温相变材料储存冷量,通过缓慢释放调节并保持箱内温度,目前仍存在冷量释放速率无法控制、剩余冷量预测难等问题,而蓄冷板表面对流换热系数直接影响冷量的释放速率。针对以上问题,搭建了蓄冷板表面对流换热系数测量试验平台,研究不同环境及蓄冷板参数对表面对流换热系数的影响。采用二次回归正交试验设计方案,探究了蓄冷区进口空气流速、进口空气温度、蓄冷板传热面积以及蓄冷板间距对表面对流换热系数的影响,并对结果进行分析,建立了表面对流换热系数二阶预测模型,获得影响表面对流换热系数大小较显著的因素及较优的参数组合。试验结果表明：各因素间存在明显交互作用,进口空气温度和蓄冷板传热面积的交互效应最大;通过响应曲面法建立的表面对流换热系数预测模型,得到最优参数组合为：进口空气流速4 m/s,进口空气温度25 ℃,蓄冷板传热面积0.455 m2,蓄冷板间距0.04 m,R2值为0.927 4,变异系数CV为5.78%。回归模型计算结果与试验结果吻合,最大误差为3.58%,平均相对误差为2.69%,表明该模型可以快速、准确地预测不同条件下的蓄冷板表面对流换热系数。试验结果为蓄冷温控箱冷量释放速率精准调控及剩余冷量预测提供参考。     

转lux基因簇大肠杆菌在小鼠肠道内定植模型的建立

发光细菌携带的lux基因簇能够利用体内脂肪酸分子和氧化还原反应产生自发荧光。本研究将携带lux基因簇的质粒转化到大肠杆菌(Escherichia coli)DH5α感受态细胞中,测定发光大肠杆菌的生长曲线和荧光光谱等生物学特性;同时,利用活体成像系统(IVIS)检测其生物发光活性,并收集对数生长期的发光大肠杆菌,注射到ICR小鼠(Mus musculus)盲肠内,24 h后检测小鼠肠道内微生物的荧光反应。结果显示,转lux基因簇的大肠杆菌能够产生较强的蓝绿荧光,持续发光16 h以上,且在完成肠道注射后能够观测到发光菌的荧光,表明发光大肠杆菌可在不影响小鼠正常生理活动的条件下完成在肠道内的定植。本研究初步建立了大肠杆菌在小鼠肠道内生存变化的实验模型,为进一步监测致病性大肠杆菌在动物肠道内的活动和致病机制的研究提供了新的实验方法。     

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。     

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.     

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.     

Properties of anaerobically digested and composted municipal solid waste assessed by linking soil mesofauna dynamics and nitrogen modelling

We have studied the effect of anaerobically digested (ADMSW) and composted municipal solid waste (CMSW) on mineralization and foodweb dynamics to verify the hypothesis that ADMSW would immobilize N right after addition to soil in contrast to addition with CMSW. Another hypothesis was that the mesofauna (enchytraeids and microarthropods) would stimulate N release from the decomposer community. We measured excretion of -N and urea-N from the mesofauna and hypothesized that enchytraeids would release urea. ADMSW and CMSW were amended to pots with sandy loam and barley. The pots were divided into treatments with or without mesofauna. Mesofauna, plant N and biomass, soil N and ergosterol (fungal biomass) were measured over a 113-day period of four equidistant samplings. Soil respiration, N mineralization and N release by the mesofauna were modelled from concurrent studies. ADMSW- and CMSW-treated soils initially (<20 days) immobilized N. The amendments did not increase plant growth substantially, and this was probably due to N-limitation in the early stages of plant growth. Enchytraeid abundance was about three times higher in ADMSW- than CMSW-treated soils, indicating that ADMSW contained more labile compounds, bacteria, and microfauna. The mesofauna did not affect N-content, but the cumulated -N excreted by the mesofauna was estimated to be substantial and about one-fifth of total plant N in ADMSW. An explanation for this discrepancy might be that in the absence of the mesofauna, other members of the detrivore and microbivore community performed the mesofauna’s function. Neither enchytraeids nor microarthropods excreted urea.     

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,     

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,     

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,     

Assessing the effectiveness of conservation measures: Resolving the “wicked” problem of the Steller sea lion

“Wicked” problems are those that are complex and that change when solutions are applied. Many conflicts in conservation fall into this category. The study approached the problem of how to constrain the apparent wickedness of a problem in the conservation management of a species by using simple empirical indicators to carry out iterative assessment of the risk to a population and to document how this risk evolves in relation to the addition of new data and the implementation of management actions. Effects of high levels of uncertainty within data and also concerning population structure were examined through stochastic simulation and by exploration of scenarios. Historical trends in the example used, the Steller sea lion, showed rapid declines in abundance in some regions during the 1980s. The current total population is 130,000-150,000 Steller sea lions through Alaska and British Columbia and this number has been stable since about 1990 in spite of regional differences in population dynamics. Regional differences in the sequence of changes in the number of pups and non-pups, suggested that an internal re-distribution of juveniles could have happened between 1980 and 1990. Current productivity also appears close to the long-term mean. Stochastic population projection using various scenarios showed that, based upon this history, the risk of extinction for the population has declined and is below reasonable thresholds for considering the population to be endangered. The trends in risk suggest that management actions taken since 1990 have probably been effective. Consequently, the conservation management objectives for the Steller sea lion are probably being met. The approach provides a mechanism, based upon experience and scenario analysis, for exploring future policy options and may help to constrain the debate amongst stakeholders about the cost-benefit trade-offs associated with different options.     

Soil-profile distribution of primary and secondary plant-available nutrients under conventional and no tillage

Nutrient distributions under no tillage (NT) compared with conventional disk-and-bed tillage (CT) management in the warm, humid region of the southeastern USA need to be assessed so that future placement, quantity, and type of fertilizers can be altered, if necessary, to efficiently match crop demands. We determined soil-profile distributions of pH, N, P, S, K, Ca, Mg, Na, Zn, Fe, Mn, and Cu to a depth of 0.9 m at the end of 8.5 years of continuous CT and NT management on a Weswood silty clay loam (fine, mixed, thermic Fluventic Ustochrept) in southcentral Texas. Most dramatic changes occurred within the 0–0.05 m depth, where soil under NT had lower pH, Fe, and Cu than under CT, but greater P, K, Zn, and Mn. Greater P and K under NT than under CT also occurred below the till-zone (0.15–0.3 m). At a depth of 0–0.3 m, soil under NT contained greater amounts of extractable P, K, Zn, Fe, Mn, and Cu than under CT. Nitrogen fertilization had little effect on nutrient distributions, except resulting in greater extractable K at 0–0.05 m and greater nitrate at 0–0.15 m. Few changes in soil-profile distributions were observed for extractable S, Ca, Mg, and Na. Long-term continuous use of NT on this fine-textured, high-fertility (except for N) soil had no apparent adverse effects on nutrient distributions relative to CT, but enhanced conservation and availability of P, K, Zn, Fe, Mn, and Cu near the soil surface where crop roots proliferate.     

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.