Effect of ionic strength on inactivation kinetics of Escherichia coli O157:H7 by electron beam in ground beef, chicken breast meat, and trout fillets

The ionic strengths (IS) of ground beef, chicken meat, and trout fillets were modified to intermediate and highest with 3.5% and 7.0% NaCl, respectively. The samples with modified and unaltered (native) IS were inoculated with Escherichia coli O157:H7 and subjected to electron beam (e‐beam). The water activity (a_w) of the meat samples were 1.0, 0.96–0.97, and 0.94 for native, intermediate, and highest IS. The D₁₀‐values were calculated from survivor curves. The D₁₀‐values for E. coli ranged from 0.19 kGy in trout (highest IS) to 0.31 kGy in beef and chicken (highest IS). Regardless of the meat type, the increased resistance of E. coli to e‐beam was only observed at the highest IS. The difference of the D₁₀‐value for E. coli in samples at intermediate and native IS was insignificant. Regardless of the IS, the E. coli in trout was most sensitive, while the difference of E. coli resistance to e‐beam in ground beef and chicken meat was insignificant.     

Effect of water activity on the inactivation kinetics of Escherichia coli O157:H7 by electron beam in ground beef, chicken breast meat, and trout fillets

Water activity (a_w) of ground beef, chicken breast meat, and trout fillets was modified to intermediate (a_w 0.98–0.99) and lowest (a_w 0.94–0.96) levels. The meat samples with modified and unaltered (native, a_w 1.00) a_w were inoculated with Escherichia coli O157:H7 and subjected to electron beam (e‐beam). Survivor curves were plotted and the D₁₀‐values were calculated. The D₁₀‐values ranged from 0.22 kGy for trout at native a_w to 0.33 kGy for beef at intermediate, and chicken and trout at lowest a_w. Regardless of the species, a_w reduction increased E. coli resistance to e‐beam, suggesting that even small depletion of unbound water from food increases survival. The difference of the D₁₀‐values between the samples at intermediate and lowest a_w was insignificant. E‐beam could be used before a_w‐reducing techniques are applied to food products. However, this would require stringent microbial control following e‐beam processing. The ‘tailing’ of survivors was observed for some samples with reduced a_w.     

Temperature Effect on Inactivation Kinetics of Escherichia coli O157:H7 by Electron Beam in Ground Beef, Chicken Breast Meat, and Trout Fillets

ABSTRACT:  Ground beef, boneless skinless chicken breast meat, and boneless skinless trout fillets were inoculated with Escherichia coli O157:H7 and incubated to approximately 10⁹ colony forming units per gram (CFU/g). Following incubation, temperature of the meat samples was equilibrated to −20, 4, and 22 °C. The meat samples at different temperatures were subjected to one-sided electron beam (e-beam) with fixed energy at 10 million electron volts (MeV) and doses at 0 (control), 0.5, 1.0, 2.0, 2.5, and 3.0 kGy. The survivors were enumerated using a standard spread-plating method. The survivor curves were plotted on logarithmic scale as a function of e-beam dose for each meat sample subjected to e-beam at different temperatures. The D -values were calculated as a negative reciprocal of the slope of the survivor curves. The D -values for E. coli ranged from 0.22 to 0.35 kGy in trout at 4 °C and chicken at −20 °C, respectively. The D -values were different between meat types. Regardless of temperature, E. coli in chicken had highest D -value followed by beef and trout. The D -values for E. coli in frozen samples were higher than D -values in samples irradiated at 4 and 22 °C regardless of species. Although there were numerical differences between D -values for samples subjected to e-beam while chilled (4 °C) or frozen (−20 °C), they were statistically insignificant. Water radiolysis is considered as an indirect mechanism for microbial inactivation. Therefore, while the physical state of water (frozen or unfrozen) in foods seems the major contributor to microbial inactivation by e-beam due to water radiolysis, product temperature most likely plays a minor role.     

Effect of pH on Inactivation of Escherichia coli K12 by Sonication, Manosonication, Thermosonication, and Manothermosonication

ABSTRACT:  The effect of pH on inactivation of Escherichia coli K12 by sonication at 100 kPa/40 °C, manosonication (MS) at 400 kPa/40 °C, thermosonication (TS) at 100 kPa/61 °C, and manothermosonication (MTS) at 400 kPa/61 °C at acoustic energy density of 3 W/mL and 6 W/mL was investigated. Five linear and nonlinear kinetic models were used to examine the inactivation kinetics. At all pH levels, the inactivation rates of E. coli K12 in a buffer by TS and MTS were significantly higher than those by sonication and MS. A 5 log reduction of E. coli K12 population by TS and MTS was achieved in 0.5 and 0.25 min, respectively. With an initial count of 10⁸ CFU/mL, no colonies were detected at pH 3 after a 0.25-min MTS treatment. The lethal effect of MTS was enhanced at low pH (pHs 3 and 4), whereas at nonlethal temperature of 40 °C, no increased killing was observed. Regardless of pH, the treatment by MTS, TS, and MS exhibited a rapid initial reduction followed by tailing-off on the inactivation curves. The biphasic linear, log-logistic, and modified Gompertz kinetic models allowed better fitting of the inactivation data for MTS, TS, and MS treatments than the 1st-order and Weibull models. The survival counts of sonication-treated E. coli K12 at all pH levels fitted well to a 1st-order kinetic model.     

高强脉冲电场对食品中大肠埃希氏菌基因水平传递的影响

目的:探讨高强脉冲电场对大肠埃希氏菌的基因获得及水平传递中的作用。方法:采用接合转移试验,研究了PEF强电场作用对大肠埃希氏菌基因水平传递的影响,并以未经处理的标准菌株为对照,通过PCR方法进行基因检测分析。结果:所有经PEF处理的菌株均由正常的接合转移率42.4%～68.5%上升到100%。PCR检测结果显示,所得接合子中int基因的扩增产物大小仍为923bp,与正常未处理int基因大小一致。结论:PEF处理使得细菌接合转移率明显提高,PEF处理对传递到接合子中的基因未能产生影响。     

Inactivation of Escherichia coli K12 by pulsed UV light on goat meat and beef: microbial responses and modelling

The objective of this study was to investigate the efficacy of pulsed UV light (PUVL) in inactivating Escherichia coli K12 on goat meat and beef surfaces. Inactivation studies were conducted for 5 to 60 s at three distances from the light source (4.47, 8.28 and 12.09 cm) in the PUVL chamber. Predictive models using regression and artificial neural networks (ANN) were developed to quantify log reductions. Pulsed UV light was more effective on beef than goat meat. Maximum log reductions of 1.66 and 1.74 CFU mL⁻¹ rinse solution were achieved on goat meat and beef, respectively, at 4.47 cm distance for 60 s. Escherichia coli K12 reduction increased significantly with increasing treatment time and closer distance from the light source. In general, both ANN and regression models effectively described inactivation of E. coli K12. Predictive models describing PUVL inactivation kinetics of E. coli K12 can be used for process optimisation in meat industry.     

Inactivation of Escherichia coli by Carbon Dioxide under Pressure

Thermal inactivation of Escherichia coli was studied under CO₂ pressures of 1.2, 2.5, and 5 MPa at 25, 35, and 45°C. Two phases were observed in the destruction curves. The earlier stage was characterized by a slow rate of inactivation, which increased sharply at the later stage. An increase of pressure and/or temperature enhanced the antimicrobial effects of CO₂ under pressure. The effects on cell structure were studied by scanning electron microscopy and the specific mechanism of action appeared to be related to enzyme inactivation.     

食品中大肠杆菌的快速检测方法

大肠杆菌是人及各种动物肠道中的正常寄居菌,食物或水中大肠杆菌的检出意味着直接或间接的近期粪便污染。大肠杆菌作为饮水、食品等的粪源性污染卫生细菌学指标;而且他在外界存活时间与一些主要肠道病原菌相近,它的出现也可能预示某些肠道病原菌（如沙门氏菌、志贺氏菌）的存在。大肠杆菌是国际上公认的卫生监测指示菌,因此大肠杆菌的检测技术显得十分重要,相应出现了大量的大肠杆菌的各种检测方法。     

Inactivation of Escherichia coli on almonds using nonthermal plasma

ABSTRACT:  This study was carried out to investigate the applicability of nonthermal plasma (NTP) technology for the pasteurization of almonds. Almonds were spiked with various levels of Escherichia coli by dipping the almonds in E. coli culture broth followed by drying. The spiked almonds were treated with NTP under different treatment conditions. The pattern of the microorganisms reduction by NTP was analyzed. NTP was found to be effective on reduction of E. coli on almond evidenced by almost 5-log reduction after 30-sec treatment at 30 kV and 2000 Hz. The NTP bactericidal effect on E. coli inoculated on almond increased with the applied voltage and the frequency. The NTP reduction followed the 1st-order reaction kinetics, and the reduction rate constants varied with almond types and grades. The E. coli cells at logarithmic phase were more sensitive to the NTP than those at stationary and declining phases.     

酶底物法快速检测食品中的大肠埃希氏菌

目的将水质检验的酶底物法用于食品检验,探索酶底物法是否能快速检测食品中的大肠埃希氏菌。方法测定食品样品,比较酶底物法与传统鉴定法结果的一致性。结果传统方法检出24份阳性和8份阴性,酶底物法检出25份阳性和7份阴性。实验结果进行X~2检验,结果无显著性差异(X~2=0.087,P0.05)。32份样品MPN值结果一致,8份样品MPN值有差异,其中7份样品酶底物法的MPN值大于传统法。结论酶底物法可用于食品中大肠埃希氏菌的快速检测,具有快捷简便、特异性高的优势。     

Effect of Meat Binding Formulations on Thermal Inactivation of Escherichia coli O157:H7 Internalized in Beef

ABSTRACT:  This study evaluated the effects of meat binding or restructuring formulations, including salt/phosphate, algin/calcium, Activa™RM, and Fibrimex®, with or without 0.27% (wt/wt) lactic acid, on thermal inactivation of internalized Escherichia coli O157:H7 in ground beef, serving as a model system for restructured products. Ground beef batches (700 g; approximately 5% fat) were mechanically mixed with a 5-strain composite of E. coli O157:H7 (7 log CFU/g) and then with the restructuring formulations. Product portions (30 g) were extruded into plastic test tubes (2.5 × 10 cm) and stored at 4 °C (18 h), before heating to 60 or 65 °C in a circulating water bath to simulate rare or medium-rare doneness of beef, respectively. Cooking to 60 or 65 °C reduced ( P < 0.05) bacterial counts of control samples by 1.8 and 3.2 log CFU/g, respectively. Thermal destruction at 60 °C was not different ( P > 0.05) among all treatments and the control. At 65 °C, greater ( P < 0.05) thermal inactivation of E. coli O157:H7, as compared to the control, was obtained in samples treated with lactic acid alone (reductions of 4.9 log CFU/g), whereas for all other treatments, microbial destruction (reductions of 2.2 to 4.5 log CFU/g) was comparable ( P > 0.05) to that of the control. Cooking weight losses were lower ( P < 0.05) in salt/phosphate samples (<1%) compared to other formulations and the control (7.4% to 15.9%). Findings indicated that, under the conditions examined, restructuring of beef with salt/phosphate, algin/calcium, Activa™RM, or Fibrimex® did not affect inactivation of internalized E . coli O157:H7 in undercooked (60 or 65 °C) samples, whereas inclusion of lactic acid (0.27%) in nonintact beef products enhanced pathogen destruction at 65 °C.     

Ultraviolet inactivation kinetics of Escherichia coli and Yersinia pseudotuberculosis in annular reactors

Terrorist threats have precipitated the need for information on the ultraviolet (UV) resistance of potential biothreat agents in food processing, such as Yersinia pestis. The objective of this study was to characterize the resistance of the Yersinia species to UV treatment using a single-lamp annular UV reactor. A novel method is proposed to measure the inactivation kinetics of Yersinia pseudotuberculosis, a surrogate of Y. pestis. This proposed method can overcome the disadvantages of the traditional collimated beam approach for liquids with high absorptive properties, such as liquid foods. As a reference, an inactivation rate of Escherichia coli K12 in caramel model solutions was measured first. Both first-order and series-event inactivation models were used to fit UV inactivation data. For the series-event model, an inactivation constant of k(SE)= 0.675 cm(2)/mJ and threshold n= 4 were obtained for E. coli K12 with the coefficient of determination R(2)= 0.987 and the standard deviation of log(10) reductions sigma(y)= 0.133. For Y. pseudotuberculosis, k(SE)= 0.984 cm(2)/mJ and n= 3 were obtained with R(2)= 0.972 and sigma(y)= 0.212. In contrast, for the first-order inactivation model, the first-order inactivation constant k(1)= 0.325 cm(2)/mJ with R(2)= 0.907 and sigma(y)= 0.354 was found for E. coli; and k(1)= 0.557 cm(2)/mJ with R(2)= 0.916 and sigma(y)= 0.402 was obtained for Y. pseudotuberculosis. Based on R(2), sigma(y), and the maximum absolute and relative errors, the series-event inactivation model describes the UV inactivation kinetics of Y. pseudotuberculosis and E. coli better than the first-order model. It is apparent that Y. pseudotuberculosis is less resistant to UV light than E. coli K12.     

生物传感器检测食源性大肠杆菌O157:H7研究新进展

近年来, 生物传感器因具有快速、简便、灵敏度高、低成本等优势被广泛应用到临床检测、环境监测等领域。该技术在食品安全领域也逐步得到重视, 尤其在病原微生物的快速检测方面。本文从免疫识别和核酸识别两方面简要介绍生物传感器技术检测食源性大肠杆菌O157:H7研究的最新进展, 对生物传感器技术存在的问题及未来的研究方向进行了总结及展望。     

冷冻鱼糜制品中大肠杆菌生长动力学模型的构建

以冷冻鱼糜制品为原料将大肠杆菌接种到鱼糜制品中,托盘包装后分别在5、10、15、20、25和85℃贮藏。并应用Curve Expert1.3软件拟合不同温度下大肠杆菌的生长情况。结果表明,修正的Gompertz方程能较好地描述不同温度下大肠杆菌在鱼糜制品中的生长动态,温度对大肠杆菌生长参数μmax(最大比生长速率)和λ(延滞时间)的影响,采用平方根模(Belehradek)描述呈良好线性关系。85℃用失活模型Linear的拟合较好。通过13℃和18℃下大肠杆菌的生长对构建的Gompertz模型进行了验证,并经数学检验参数偏差值和准确值计算,偏差度分别为0.938、0.956,准确度为1.034、1.083,表明所建立模型是有效的。      

Inactivation of Escherichia coli with Power Ultrasound in Apple Cider

The use of acoustic energy to secure apple cider safety was explored. Inactivation tests were performed with Escherichia coli K12 at 40 °C, 45 °C, 50 °C, 55 °C, and 60 °C with and without ultrasound, followed by a validation test with E. coli O157:H7 at 60 °C. The cell morphology was observed with environmental scanning electron microscopy for samples treated at 40 °C and 60 °C. Physical quality attributes of the apple cider (pH, titratable acidity, °Brix, turbidity, and color) were compared for treated samples. The inactivation tests showed that sonication increased E. coli K12 cell destruction by 5.3‐log, 5.0‐log, and 0.1‐log cycles at 40 °C, 50 °C, and 60 °C, respectively. The additional destruction due to sonication was more pronounced at sublethal temperatures. At the lethal temperature of 60 °C, the rate of death by ultrasound was not significantly different compared with the thermal‐alone treatment. The inactivation of E. coli K12 with heat was described by 1st‐order kinetics, especially at 50 °C and 60 °C. For ultrasound treatments, concave upward survival curves were observed, which had a shape factor in the range of 0.547 to 0.720 for a Weibull distribution model. Extensive damage for ultrasound treated E. coli K12 cells, including cell perforation, was observed. Perforation is a unique phenomenon found on ultrasound‐treated cells that could be caused by liquid jets generated by cavitation. Titratable acidity, pH, and °Brix of the cider were not affected by ultrasound treatment. Minor changes in color and turbidity for ultrasound treated samples, especially for sonication at 40 °C for 17.7 min, were observed.     

食品中大肠杆菌生物检测方法的研究进展

大肠杆菌是人类及各种动物肠道中的正常寄居菌,一旦食品、饮用水被检测出含有E.coli就意味着食品可能直接或间接受到了粪便的污染.大肠杆菌是国际上公认的卫生监测指示菌.近年来,由于大肠杆菌引起的食品安全事件频发,严重危害人类健康,研发大肠杆菌快速检测以及防控技术具有重要意义.本文就近几年大肠杆菌感染引发的食品安全事件、生物检测技术等方面的论文做一综述.     

蔬菜中大肠杆菌O157的分离与鉴定

对武汉市售蔬菜(50份)进行大肠杆菌O157的检验,经过新生霉素-EC增菌液增菌、免疫磁珠富集、选择性平板培养和血清学鉴定,从一份生菜中筛出1株O157阳性菌株EC9.23。PCR鉴定该菌毒力基因,stx1、stx2、rfbO157基因均为阳性,hly、eae、fliCH7基因均为阴性。说明从武汉市售蔬菜中可检出携带志贺毒素基因的O157菌株。     

动物性食品源大肠杆菌质粒介导喹诺酮的耐药机制研究

本研究以动物性食品源大肠杆菌为研究对象,采用琼脂二倍稀释法调查菌株对抗生素的药物敏感性,通过PCR扩增及产物测序检测质粒介导喹诺酮耐药(PMQR)基因的分布以及喹诺酮耐药决定区(QRDR)靶基因突变,旨在更好的了解食源性大肠杆菌对喹诺酮类药物产生耐药性的分子机制。645份动物性食品样品中共检出大肠杆菌179株,总检出率为27.7%。179株动物性食品源大肠杆菌对15种抗生素均表现出不同程度的耐药性,其中对四环素、链霉素、萘啶酸和复方新诺明的耐药水平较高。PMQR基因阳性菌株共14株,占受试菌株的7.8%,其中有11株能通过接合转移将PMQR基因转移至受体菌中。QRDR靶位突变在PMQR阳性菌株中普遍存在,介导菌株对喹诺酮的高水平耐药。研究结果表明,动物性食品可能成为耐药菌株的潜在"蓄水池",并通过食物链将耐药性传递给人类,从而引起人类的感染以及耐药菌株的流行。     

高压均质对芒果汁中大肠杆菌的杀菌动力学

为预测高压均质(high pressure homogenization,HPH)对芒果汁中大肠杆菌的杀菌作用,进行了压力40~190 MPa、进料温度20~60℃和均质次数1~5次的HPH实验,并运用Weibull模型对杀菌致死曲线进行动力学分析。研究表明:随压力、进料温度和均质次数的升高,HPH对芒果汁中大肠杆菌的杀菌效果增强。50℃HPH处理芒果汁,压力由40 MPa升高至190 MPa时,大肠杆菌降低量由0.46(lg(CFU/mL))增加至5.16(lg(CFU/mL)),达到美国食品药物管理局规定的非热加工杀菌卫生安全要求;70 MPa HPH处理芒果汁,进料温度由20℃升高至60℃时,大肠杆菌降低量由0.34(lg(CFU/mL))增加至5.02(lg(CFU/mL));20℃、190 MPa HPH处理芒果汁,均质次数由1增加至4时,大肠杆菌降低量由1.73(lg(CFU/mL))增加至5.15(lg(CFU/mL))。通过Weibull模型拟合杀菌致死曲线,并对模型进行简化,发现简化的Weib ull模型在20~50℃、40~190 MPa均质1次和20~40℃、190 MPa均质1~5次时拟合性较好(R~20.92)。简化的Weibull模型可用于预测进料温度-压力和进料温度-均质次数的杀菌效果,可为芒果汁的HPH生产过程中微生物安全性的控制提供理论依据。     

Inactivation of Escherichia coli O157:H7 and Listeria monocytogenes inoculated on raw salmon fillets by pulsed UV-light treatment

The efficacy of pulsed UV‐light to inactivate of Escherichia coli O157:H7 and Listeria monocytogenes Scott A on salmon fillets was investigated in this study by evaluating the effects of treatment times and distance from the UV strobe. The sterilization system generated 5.6 J cm^?2 per pulse at the lamp surface for an input voltage of 3800 V and three pulses per second. Skin or muscle side inoculated salmon fillet (8 cm × 1.5 cm) in a Petri dish was placed on shelf at three different distances from the UV strobe; 3, 5, and 8 cm. At each distance, the pulsed UV‐light treatment was performed for 15, 30, 45, and 60 s. For E. coli O157:H7, maximum log₁₀ reduction was 1.09 log₁₀ CFU g^?1 on muscle side at 8 cm for 60‐s treatment, whereas 0.86 log₁₀ CFU g^?1 reduction on skin at 5 cm for 30‐s treatment. For L. monocytogenes Scott A, maximum reduction was 1.02 log₁₀ CFU g^?1 at 8 cm for 60‐s treatment on skin side, whereas 0.74 log₁₀ CFU g^?1 reduction on muscle at 8 cm for 60‐s treatment. The fillet's surface temperature increased up to 100degrC within 60‐s treatment time. Therefore, some fish samples were overheated after 30 and 45 s at 3‐ and 5‐cm distances from light source, respectively, which resulted in visual colour and quality changes. Overall, this study demonstrated that about one log reduction (c. 90%) of E. coli O157:H7 or L. monocytogenes could be achieved at 60‐s treatment at 8 cm distance without affecting the quality.