浓香型白酒酒醅微生物与酯类成分关联性定量模型的建立

为研究浓香型白酒出窖酒醅微生物与酯类成分的定量关系，该研究通过高通量测序分析浓香型白酒出窖酒醅优势微生物属的相对丰度，使用气相色谱-质谱联用法（GC-MS）测定酒醅中主要酯类成分的相对含量，并以优势微生物属为自变量，主要酯类物质为因变量，对建模变量进行两轮筛选，建立两者的偏最小二乘（PLS）数学模型。结果表明，经变量筛选后得到的模型包含11种酯类物质和16种优势微生物属；模型主成分个数为3时，所保留的变量均能够用选取的主成分进行解释；所得模型能够解释92.6%的自变量信息和89.4%的因变量信息，预测率为0.679，质量良好，该模型可以定量解释出窖酒醅微生物与酯类之间的关联性。     

Development of novel method for screening microorganisms using symbiotic association between insect (Coptotermes formosanus Shiraki) and intestinal microorganisms

It is becoming increasingly difficult to isolate novel useful microorganisms from the natural environment using conventional screening methods based on pure culture techniques. A novel method for screening microorganisms in symbiotic association with insects was developed. This method involves the following two steps. In the first step, the existence of desired microorganisms that grow well by degrading difficult-to-degrade materials in the gut of insects is detected using the survivability of insects as an indicator. In the second step, the desired microorganisms are selected from the surviving insects. The second step is based on an idea that the guts of insects act as continuous-culture systems whereby microorganisms that cannot degrade diet components are washed out whereas those that can degrade diet components are retained and made to multiply in the gut. Coptotermes formosanus Shiraki was fed with an artificial diet containing phenol as a model of lignin-derived and difficult-to-degrade compound. Each C. formosanus feeding on an artificial diet containing 100 mg/l phenol had different levels of adaptation to the toxicity of phenol. About 20% of C. formosanus fed with an artificial diet containing 100 mg/l phenol died within a few days whereas others survived for more than 10 d. The structure of the intestinal microorganisms of the surviving C. formosanus fed with the 100 mg/l phenol artificial diet gradually changed and was very different from that of the bacterial communities obtained from the enrichment culture of wood-feeding C. formosanus using an artificial medium containing phenol as a sole carbon source. Furthermore, Only three species (as DGGE band) were detected from the gut of wood-feeding C. formosanus, whereas 200 times more phenol-degrading microorganisms were detected in the gut of C. formosanus feeding on a phenol artificial diet. Out of these nine species (as DGGE band) of phenol-degrading microorganisms were isolated. The screening method developed in this study can also be applied to various insects, leading to the isolation of various microorganisms that can degrade difficult-to-degrade compounds.     

A suitable model of microbial survival curves for beer pasteurization

Published isothermal inactivation data indicated that beer can undergo under- or over-processing depending on the target log reduction and the shape of the survival curve of a microorganism if traditional first-order model is used. This was demonstrated for a mold, yeasts and lactic acid bacteria by use of a more flexible and convenient model than the first-order model, namely Weibull model. The parameters of the Weibull model can be reduced from two to one with a very a slight loss of goodness-of-fit. The validity of the proposed model should also be checked for mixed populations of microorganisms in beer and non-isothermal treatments for beer. Beer can be the first product to validate the proposed model in industrial base since it has been free from problems with pathogenic microorganisms. If the model provides the requirements then it can also be used in other food products. This will minimize the energy expenditure for pasteurization and provide minimal processing to achieve a better food quality.     

Influence of Microbial Growth on the Redox Potential of Fermented Cucumbers

ABSTRACT:  Commonly, pH measurements are used during the production of fermented cucumbers to indirectly monitor growth of lactic acid bacteria (LAB) and acid production. Redox potential (E_h) measurements, which are determined by the potential of an electron to reduce an acceptor, could serve as an alternative tool to monitor the progress of fermentation allowing the detection of the metabolic activity and/or growth of LAB and other microorganisms. Pasteurized and inoculated jars of cucumbers were observed to better understand how the E_h changes during the cucumber fermentation and how it could be used as a monitoring tool. Jars of diced, brined cucumbers were pasteurized and inoculated with microbes previously isolated from fermented cucumbers including Lactobacillus plantarum , Zygosaccharomyces globiformis , and Enterobacter aerogenes . Although an initial decrease in E_h was observed for all microorganisms, distinctive trends in E_h occurred when these organisms were inoculated. After a 2-wk fermentation period, the E_h (Ag/AgCl, 3 M KCl) in jars inoculated with L. plantarum , Z. globiformis , and E. aerogenes was at +453 ± 55, +104 ± 5, and –156 ± 73 mV, respectively. Cucumbers inoculated with a mixture of L. plantarum and Z. globiformis had a terminal E_h value of +202 ± 24 mV, which was between that found for the individual microorganisms. L. plantarum dominated the E_h trend when inoculated along with E. aerogenes with a final E_h of +411 ± 72 mV. The results showed that changes in E_h continued after pH measurements became stable. Thus E_h measurement can provide a tool to continuously monitor microbial growth during the course of cucumber fermentations.     

A PREDICTIVE MODEL FOR HIGH-PRESSURE CARBON DIOXIDE INACTIVATION OF MICROORGANISMS

The Weibull model, which is commonly used for thermal inactivation of microorganisms in literature, was used to describe microbial inactivation by high-pressure carbon dioxide (HPCD). The number of parameters of the model was reduced from two to one in order to avoid interrelationship of these parameters with a slight loss of goodness-of-fit. A second-order polynomial function fulfilling a number of constraints was proposed for the secondary modeling of the time-constant parameter of the reduced Weibull model. This function consists of both pressure and temperature and therefore can be used for HPCD treatments.

PRACTICAL APPLICATIONS

The application of any new technology in food preservation requires a reliable model that accurately describes and predicts the inactivation data of microorganisms. In principle, the methodology presented here could be used to describe and predict the survival data for high-pressure carbon dioxide inactivation of microorganisms at least for some pressure and temperature ranges if the isobaric/isothermal survival curves of these microorganisms are linear, concave upward or downward.     

Modeling UV-induced inactivation of microorganisms on surfaces

A model is presented to account for inactivation by UV light of microorganisms on the surfaces of solid materials. In the model, the surface is divided into a discrete number of zones, each having a characteristic exposure factor (alpha). This is the ratio of UV intensity actually "seen" by the microorganism to that incident on the surface. Application of the model requires inactivation data obtained under conditions where the surface microorganisms are fully exposed to incident UV (alpha = 1) as well as kinetic inactivation data for the same microorganisms actually present on the surface of interest during UV irradiation. The kinetics in question may apply either to a single species or to the characteristic microflora associated with a particular material. Standard nonlinear programming techniques were used to determine the number of zones among which the microorganisms are distributed, the alpha for each zone, and the fraction of the microbial population present in each zone. The model was applied to data previously published by Gardner and Shama for UV inactivation of Bacillus subtilis spores on the surfaces of filter papers and also to the data of Stermer et al. for UV irradiation of beef. Good representation of the kinetics was obtained, and a maximum of three zones was required to adequately represent the experimental data. One direct application of the model is that it yields quantitative information about the UV fluences necessary to achieve specified reductions in microbial viability.     

Characterizing bioaerosol risk from environmental sampling

In the aftermath of a release of microbiological agents, environmental sampling must be conducted to characterize the release sufficiently so that mathematical models can then be used to predict the subsequent dispersion and human health risks. Because both the dose-response and environmental transport of aerosolized microbiological agents are functions of the effective aerodynamic diameter of the particles, environmental assessments should consider not only the total amount of agents but also the size distributions of the aerosolized particles. However, typical surface sampling cannot readily distinguish among different size particles. This study evaluates different approaches to estimating risk from measurements of microorganisms deposited on surfaces after an aerosol release. For various combinations of sampling surfaces, size fractions, HVAC operating conditions, size distributions of release spores, uncertainties in surface measurements, and the accuracy of model predictions are tested in order to assess how much detail can realistically be identified from surface sampling results. The recommended modeling and sampling scheme is one choosing 3, 5, and 10 μm diameter particles as identification targets and taking samples from untracked floor, wall, and the HVAC filter. This scheme provides reasonably accurate, but somewhat conservative, estimates of risk across a range of different scenarios. Performance of the recommended sampling scheme is tested by using data from a large-scale field test as a case study. Sample sizes of 10-25 in each homogeneously mixed environmental compartment are sufficient to develop order of magnitude estimates of risk. Larger sample sizes have little benefit unless uncertainties in sample recoveries can be reduced.     

Modelling homogeneous and heterogeneous microbial contaminations in a powdered food product

The actual physical distribution of microorganisms within a batch of food influences quantification of microorganisms in the batch, resulting from sampling and enumeration by microbiological tests. Quantification may be most accurate for batches in which microorganisms are distributed homogeneously. However, when the distribution is non-homogeneous, quantification may result in an under-, or overestimation. In the case of pathogens being non-homogeneously distributed, this heterogeneity will impact on public health. Enumeration data are commonly modelled by the Lognormal distribution. Although the Lognormal distribution can model heterogeneity, it does not allow for complete absence of microorganisms. Studies that validate the appropriateness of using Lognormal or other statistical distributions are scarce. This study systematically investigated laboratory and industrial scale batches of powdered infant formula, modelled the enumeration data using a range of statistical distributions, and assessed the appropriateness of individual models. For laboratory scale experiments, batches of milk powder were contaminated by distributing similar numbers of cells of Cronobacter sakazakii either homogeneously throughout a batch of milk powder or by distributing the cells in a localised part of the batch. Each batch was then systematically sampled and the distribution determined by enumerating the samples. By also enumerating the remainder of the batch, a balance could be made of the total number of microorganisms added and of the number retrieved from a batch. Discrete, as well as continuous statistical distributions, were fitted to enumeration data and the parameters estimated by Maximum Likelihood. The data were fitted both as censored and uncensored data. Enumeration data obtained for an industrial batch of powdered infant formula were investigated in this way as well. It was found that Normal, Poisson and Zero-Inflated Poisson distributions fitted the data sets very poorly. In case of homogeneous contamination, there was not a notable difference between the ability of Negative Binomial, Poisson-Lognormal, Weibull, Gamma, and Lognormal distributions to model the data. Overall, either the Negative Binomial distribution or the Poisson-Lognormal distribution fitted the data best in the 10 batches studied, especially when part of a data set contained zeros and/or the numbers were low. The Negative Binomial fitted the laboratory batches best and the Poisson-Lognormal fitted the industrial batch best.     

鸡肉中沙门氏菌和背景菌群生长动力学模型

本研究通过一级模型和二级模型描述鸡肉样品中沙门氏菌和背景菌群的生长动力学模型。用两种沙门氏菌血清型（鼠伤寒沙门氏菌（CICC22956）和肠炎沙门氏菌（CICC21482））的混合物接种到鸡肉样品中,分别将其在8、12、16、20、25、30、33、37、40、43 ℃下恒温培养。除了8 ℃以外,在其他温度下都可以观察到沙门氏菌和背景菌群的生长。将12～43 ℃下得到的微生物生长数据分别用一级模型Huang模型、Baranyi模型进行拟合,根据方差分析的结果,两种一级模型在模拟鸡肉样品中沙门氏菌和背景菌群的生长精确度方面没有显著差异（P＞0.05）,均适合描述鸡肉样品中沙门氏菌和背景菌群的生长。采用3 个二级模型（Ratkowsky平方根模型、Huang平方根模型和Cardinal模型）描述温度对鸡肉样品中沙门氏菌和背景菌群生长速率的影响。Cardinal模型低估了低温下微生物的生长速率,Huang平方根模型预测的沙门氏菌最低（7.81 ℃）和最高（49.67 ℃）生长温度与文献报道更为接近。Ratkowsky平方根模型描述的温度范围较广,更适合描述菌种复杂的背景菌群的生长速率。本研究结果可对食品工业和监管机构预测鸡肉样品中沙门氏菌的生长以及肉制品中该微生物安全风险评估提供科学依据。     

A mathematical model for bacterial inactivation

The first order kinetic model, the Buchanan model and Cerf's model, can model a linear survival curve, a survival curve with a shoulder and a survival curve with a tailing, respectively. However, they are not suitable for fitting a sigmoidal survival curve. The three models were integrated into a new model that was capable of fitting the four most commonly observed survival curves: linear curves, curves with a shoulder, curves with a tailing (biphasic curves) and sigmoidal curves. The new model was compared with the Whiting-Buchanan model using the survival curves of Staphylococcus aureus. The goodness-of-fit of the proposed model is practically as good as that of the Whiting-Buchanan model. Compared with the Whiting-Buchanan model, the proposed model has a more mechanistic background. Since for non-linear survival curves, such as biphasic and sigmoidal curves, the t(m-D) value (the time required for an m-log-cycle reduction of microorganisms under a given condition) cannot be estimated accurately by the existing or traditional method, a new method is also proposed to predict accurately the t(m-D) value for non-linear survival curves.     

Environmental microbes can speciate and cycle arsenic

Naturally occurring arsenic is found predominantly as arsenate [As(V)] or arsenite [As(III)], and can be readily oxidized or reduced by microorganisms. Given the health risks associated with arsenic in groundwater and the interest in arsenic-active microorganisms, we hypothesized that environmental microorganisms could mediate a redox cycling of arsenic that is linked to their metabolism. This hypothesis was tested using an As(V) respiring reducer (strain Y5) and an aerobic chemoautotrophic As(II) oxidizer (strain OL1 ) both isolated from a Superfund site, Onondaga Lake, in Syracuse, NY. Strains were grown separately and together in sealed serum bottles, and the oxic/anoxic condition was the only parameter changed. Initially, under anoxic conditions when both isolates were grown together, 2 mM As(V) was stoichiometrically reduced to As(III) within 14 days. Following complete reduction, sterile ambient air was added and within 24 h As(III) was completely oxidized to As(V). The anoxic-oxic cycle was repeated, and sterile controls showed no abiotic transformation within the 28-day incubation period. These results demonstrate that microorganisms can cycle arsenic in response to dynamic environmental conditions, thereby affecting the speciation, and hence mobility and toxicity of arsenic in the environment.     

Predictive Modeling of the Growth of Lactobacillus Viridescens under Non-isothermal Conditions

Food spoilage by microorganisms is a major problem that can generate large economic losses to industries, making critical the application of technologies for predicting shelf life, aiming to obtain products with higher quality. The Lactic Acid Bacteria (LAB), including Lactobacillus viridescens, are among the main groups of microorganisms responsible for spoilage of refrigerated meat products, vacuum packed and under modified atmosphere. The growth of the LAB can be predicted by mathematical models, which describe the influence of various environmental factors (such as non-isothermal conditions) on microbial growth. The objective of this study was to obtain a mathematical model able to predict the growth of L. viridescens in non-isothermal conditions in culture medium (MRS broth). Six isothermal growth curves (at 4, 8, 12, 16, 20 and 30̊C) were described by Baranyi and Roberts model and the dependence of maximum specific growth rate (μ_max) parameter on the temperature was described by square root secondary model. The model was validated using L. viridescens experimental data in the temperature ranging from 6 to 10°C and 5 to 11°C, changing every 12 and 24h, respectively. The results showed that it was possible to predict safely (bias factor greater than 1) the growth of L. viridescens in MRS broth under non-isothermal conditions. The observed prediction deviations may have been caused by abrupt temperature changes, generating intermediate adaptation phases.     

微生物合成共轭亚油酸机理的研究进展

相比于共轭亚油酸（CLA）的化学合成,微生物合成CLA与化学法具有培养灵活、对设备要求低、产物分离简单等优势。主要讨论了微生物合成CLA的研究进展,亚油酸（LA）能被微生物转化的原因,以及微生物合成CLA的机理。CLA的合成机理从微生物在动物瘤胃内混合发酵代谢LA和单一微生物在体外合成CLA两方面进行阐述。     

Modelling the interactions between Lactobacillus curvatus and Enterobacter cloacae. II. Mixed cultures and shelf life predictions

The modelling approach presented in this study can be used to predict when interactions between microorganisms in homogenous systems occur. It was tested for the interaction between Lactobacillus curvatus and Enterobacter cloacae. In this binary system, L. curvatus produces lactic acid which decreases the pH in the system. The pH decrease was found to be the main limiting factor of growth of both E. cloacae and L. curvatus. This resulted in E. cloacae reaching its final concentration earlier when compared to its growth in pure culture. The models consisted of a set of first order ordinary differential equations describing the growth, consumption and production rates of both microorganisms. The parameters for these equations were obtained from pure culture studies and from literature. These equations were solved using a combination of analytical and numerical methods. The prediction of growth in mixed culture using parameters from pure culture experiments and literature were close to the experimental data. Both model predictions and experimental validation indicated that interaction occurs when the concentration of L. curvatus reaches 10(8) cfu/ml. At that moment in time, the pH had decreased to inhibiting levels. These concentrations of microorganisms (10(8) cfu/ml) do occur in fermented products where interactions obviously are important. In nonfermented foods however, this level of microorganisms indicate that spoilage has occurred or is about to start. Microbial interactions can therefore be neglected when predicting shelf life or safety of food products in most cases.     

膳食纤维及短链脂肪酸对肠道微生物组成的影响

膳食纤维是一类不能被胃肠道分解的碳水化合物，但它可以被肠道微生物降解成短链脂肪酸。膳食纤维和短链脂肪酸对机体的代谢和健康具有重要的保健功能。本文概括了膳食纤维的类型和来源不仅影响肠道微生物的组成和功能，还影响着宿主与微生物之间的相互作用。重点阐述了膳食纤维能够通过肠道微生物产生短链脂肪酸的机制，进一步探讨了短链脂肪酸、阿魏酸、琥珀酸等对肠道微生物的组成、多样性的影响。     

Determination of thermal inactivation kinetics of microorganisms with a continuous microflow apparatus

Use of a continuous microflow submerged microcoil (CSMC) apparatus was compared with the capillary tube (CT) method for measuring the thermal inactivation kinetics of Pseudomonas fluorescens at 61 degrees C for 3 to 29 s. Inocula were continuously pumped through a microbore (< or = 0.0762 cm inside diameter) thin-walled stainless steel capillary tube submerged in a heated oil bath. The heating time was set by changing the flow rate, tube dimensions, or both. With the use of microthermo-couples, the time for the inocula to reach within 1 degree C of the set temperature was <3 s, and shorter than that with capillary tubes or vials. Inactivation curves (61 degrees C) for P. fluorescens prepared by the CSMC method were not different from curves prepared by the CT method, as determined by analysis of variance (P > 0.05). Inactivation of Bacillus cereus spores (105 degrees C) and native microflora found in raw milk (72 degrees C) over heating times of 3 to 42 s were determined by CSMC. CSMC can measure thermal inactivation kinetics of microorganisms efficiently and simply at high temperatures and in short times. Survivors can be enumerated in 1-ml volumes of heat-treated samples, making it useful for determining inactivation kinetics of low numbers of microorganisms, such as those found in high-quality raw milk. Inactivation kinetics were generally more accurately described by the Weibull function (R2 > or = 0.97) than the linear kinetic model.     

Biokinetic parameter estimation for degradation of 2,4,6-trinitrotoluene (TNT) with Pseudomonas putida KP-T201

The purpose of this study is to determine the biodegradation kinetics of 2,4,6-trinitrotoluene (TNT) by a newly isolated microorganism. Hundreds of microorganisms were isolated from explosives-contaminated soil in Korea. Examination of culture tests revealed that a few species of microorganisms have good ability to degrade TNT. The most efficient one was selected and identified as Pseudomonas putida KP-T201. Biodegradation of TNT was tested in a batch reactor using a pure culture of P. putida KP-T201. The effect of different concentrations of TNT on the rate of bacterial biodegradation was investigated. The Haldane equation seems to be an adequate expression for the cell growth data, and the kinetic constants obtained were mu(m)=0.65 h(-1), K(S)=0.62 mgl(-1), and K(i)=115 mgl(-1). The dependence of the bacterial specific growth rate on the concentration of TNT could be explained as a conventional model of substrate inhibition.     

黄瓜贮藏中微生物信息三维荧光判别及其数量监控模型构建

为实现黄瓜贮藏过程中基于微生物内源荧光信息的微生物数量变化情况的快速实时监控,并为腐败预判提供依据,在不同贮藏时间对黄瓜表面进行三维荧光信息采集。运用多项式插值方法去除原始光谱中的瑞利散射,并进行Savitzky-Golay多项式平滑降噪处理。采用核心一致诊断（core consistency diagnostic,CORCONDIA）法对组件数进行估计,以避免黄瓜在贮藏过程中表面微生物自身的代谢作用对样本荧光信号的分析造成干扰。运用交替三线性分解（alternating trilinear decomposition,ATLD）算法,按该组件数对三维荧光矩阵进行分解,获得不同组件的相对激发强度光谱、相对发射强度光谱和相对浓度阵。解析结果表明：通过CORCONDIA法在函数值大于60%的前提下,确定组件数为4。以ATLD算法分解出的4 个组件中,组件1和组件3呈现特殊双峰结构,其特征激发-发射光谱与微生物主要内源荧光物质,即类色氨酸和类酪氨酸的荧光指纹图谱吻合,且组件1所代表的类色氨酸具有较高的荧光量子产率。运用荧光区域积分法对组件1的特征光谱中高激发类色氨酸和低激发类色氨酸区域的荧光总量进行定量分析,并用多元逐步回归方法构建了标准化区域积分值与微生物数量间的函数关系。回归分析结果显示,采用二元四次逐步回归方法构建的回归模型决定系数R2可达98.309 8%。采用1 个未参与模型建立的样本对预测模型进行检测,获得微生物数量的相对误差为1.037 1%。结论：在对黄瓜表面荧光光谱中微生物信息判别的基础上,可以实现黄瓜贮藏过程中基于微生物三维荧光信息的微生物数量变化监控模型的构建,为实时监控腐败进程提供依据。     

In vivo measurement of the surface energy of human fingernail plates

The surface energy of the human nail plate is expected to influence the adhesion of microorganisms (and subsequent colonization and infections) as well as that of medicines (and subsequent drug permeation) and of cosmetics. The aim of the study was therefore to measure the surface energy of nail plates in vivo. The surface energy of healthy human fingernails (untreated, hydrated and abraded) and of hoof membranes (often used as a model for the nail plate) was estimated from contact angle measurements of liquids (water, formamide, diiodomethane and glycerol) on the nail plate and subsequent computation using the Lifshitz-van der Waals/acid-base (LW-AB) approach. The surface energy of untreated fingernail plates was found to be 34 mJ m(-2) . Most of this total energy was from the apolar Lifshitz-van der Waals component. When the polar component of the surface energy was analysed, the electron donor component was considerably larger than the electron acceptor one. Hydrating the nail plate had no significant influence on the surface energy. In contrast, abrasion caused a small, but statistically significant increase in the apolar surface energy component. The surface energy of bovine hoof membrane was similar to that of the fingernail plate. We conclude that the human fingernail plate is a low-energy surface and that bovine hoof membranes may be used as a substitute for the nail plate in certain experiments.     

PCR技术在食源性致病微生物快速检测中的应用

PCR(Polymerase Chain Reaction)即聚合酶链式反应,是一种体外快速扩增基因或DNA序列的方法。食源性致病微生物是影响食品质量和安全的主要因素之一,建立和完善食品中致病微生物快速检测技术具有重要的现实意义。PCR技术以其自身的灵敏度高、特异性强、速度快等优点作为食源性致病微生物检测的关键技术在食品中得到广泛的应用。本文简要介绍PCR技术的基本原理,及其在几种食源性致病微生物如沙门氏菌、金黄色葡萄球菌、单核细胞增生李斯特氏杆菌、致病性大肠杆菌及其他一些有害微生物检测中的应用,并分析了PCR技术在食源性致病菌检测的实际应用中存在的一些问题及对此项技术的展望,这将有力促进我们今后更好地研究应用PCR技术检测食品中食源性致病微生物。