脉冲强光对大肠杆菌的灭活效果及其动力学模型的建立

为研究脉冲强光对大肠杆菌的杀菌效应,试验以大肠杆菌ATCC 8739为对象,研究了不同生长期、pH和温度对脉冲强光杀菌效果的影响,并对其杀菌动力学进行Linear和Weibull模型拟合。结果表明:培养了6 h的对数期大肠杆菌对脉冲强光处理最为敏感,处理1 s能够降低(2.31±0.16)lg cfu/mL。pH和温度对脉冲强光杀菌效果有很大影响,介质温度在35~45 ℃,pH4.0~6.0或pH8.0都能促进脉冲强光的灭活作用。不同脉冲距离和时间下,Linear和Weibull模型都能够很好地拟合脉冲强光对大肠杆菌的杀菌效果(R²>0.99),且Weibull模型更为精确,但杀菌效果最终取决于辐射通量(可通过调节脉冲距离和脉冲时间改变)。总之,脉冲强光技术可以作为一种有效杀灭大肠杆菌的非热杀菌技术,其杀菌过程符合Linear和Weibull模型,且Weibull更为精确,该模型可以为饮用水消毒提供参考。     

响应面优化脉冲强光对煎饼表面大肠杆菌的杀菌效果

采用脉冲强光对煎饼表面进行杀菌处理,研究脉冲强光对煎饼表面大肠杆菌的杀菌效果。在单因素试验基础上,利用响应面分析方法建立大肠杆菌数量降低对数值的二次多项数学模型,利用模型对脉冲能量、脉冲次数和脉冲距离及其交互作用进行分析。结果表明：脉冲强光可有效杀死煎饼表面的大肠杆菌,优化条件为脉冲能量500 J、次数40 次、距离10.9 cm,此时脉冲强光对煎饼表面大肠杆菌的数量可减少2.15 个对数值,提高了煎饼的货架期及食用安全性。     

脉冲强光对煎饼中细菌的杀菌效果的研究

煎饼在包装和贮藏过程中易受微生物的二次污染,严重影响其食用安全性,采用脉冲强光杀菌技术可有效杀死煎饼中的微生物。结果表明:脉冲能量为400J、次数20次、距离10.9cm、频次2次/s,在此优化条件下脉冲强光对煎饼中细菌杀菌率达到99.4%。     

脉冲强光对煎饼中细菌的杀菌效果的研究

煎饼在包装和贮藏过程中易受微生物的二次污染,严重影响其食用安全性,采用脉冲强光杀菌技术可有效杀死煎饼中的微生物。结果表明:脉冲能量为400J、次数20次、距离10.9cm、频次2次/s,在此优化条件下脉冲强光对煎饼中细菌杀菌率达到99.4%。      

脉冲磁场对大肠杆菌和金黄色葡萄球菌杀灭效果的验研究

通过试验,考察了脉冲磁场对于大肠杆菌和金黄色葡萄球菌杀灭效果的影响.试验结果表明,脉冲数(杀菌时间)和磁场强度对两株菌的杀菌效果影响显著,脉冲数增至20以后,杀菌效果趋于稳定;脉冲数对杀菌效果的影响大于磁场强度.     

响应面法优化脉冲强光杀灭干豆腐大肠杆菌条件的研究

采用响应面法对影响脉冲强光杀灭干豆腐大肠杆菌效果的因素进行研究,得出影响大肠杆菌灭菌率的顺序为:照射时间脉冲强光能量照射距离;最佳灭菌条件为:脉冲强光能量300J,照射距离10cm,照射时间15s,此条件下的灭菌率可达98.29%。     

脉冲强光对大肠杆菌的杀菌实验研究

脉冲强光杀菌是一种新兴的冷杀菌技术,自制脉冲强光杀菌装置,光脉冲的脉冲宽度为20μs,最大输入能量为644J.使用该装置对大肠杆菌进行杀菌实验,对脉冲强光的杀菌影响因素进行研究.结果表明,脉冲强光对大肠杆菌的杀菌效果十分显著,输入电压2500V时,闪照4次能达到完全致死.各因素对脉冲强光杀菌效果影响的主次顺序是:闪照次数>输入电压>菌液透光率>菌液厚度.此外,杀菌菌液的物理性质对杀菌效果有较大影响.     

自动控制脉冲强光杀菌装置的研制

采用单片机控制技术，研制了自动控制脉冲强度杀菌装置。每个光脉冲的输入能量可达６００～２２００Ｊ；光脉冲宽度经测定小于８００μＳ。３０个光脉冲能使大肠杆菌减少５个数量级，４０个光脉冲以使蛋白酶的活力钝化９０％，脉冲强光杀菌可事负透明塑料薄膜包装的切片面包的保存期延长１倍以上，脉冲强光杀菌是一种很有发展前途的冷杀菌技术。     

脉冲强光杀菌装置设计的初步研究

脉冲强光杀菌是一种新兴的冷杀菌技术，本试验设计脉冲强光杀菌的发生电路，对电路进行了初步的设计研究，使用双电源脉冲发生电路提供能量，使电路简单化，并达到预期效果。     

脉冲磁场对大肠杆菌和金黄色葡萄球菌杀灭效果的试验研究

通过试验,考察了脉冲磁场对于大肠杆菌和金黄色葡萄球菌杀灭效果的影响。试验结果表明,脉冲数(杀菌时间)和磁场强度对两株菌的杀菌效果影响显著,脉冲数增至20以后,杀菌效果趋于稳定;脉冲数对杀菌效果的影响大于磁场强度。     

脉冲强光对大肠杆菌的杀菌作用

采用自主研制的脉冲强光杀菌装置,通过对大肠杆菌的杀菌试验,研究脉冲强光的杀菌影响因素.结果表明脉冲强光对大肠杆菌有明显的杀菌效果,各因素对脉冲强光杀菌效果影响的主次顺序是闪照次数＞光照强度＞菌液透光率＞菌液厚度.在光照强度0.5 J/cm2,菌液厚度3.4 mm,菌液透光率100,闪照16次能达到完全致死.此外,杀菌菌液的物理性质对杀菌效果有较大影响.     

Inactivation of Staphylococcus aureus in milk using flow-through pulsed UV-light treatment system

ABSTRACT:  This study investigated the efficacy of pulsed UV-light for continuous-flow milk treatment for the inactivation of Staphylococcus aureus , a pathogenic microorganism frequently associated with milk safety concerns. Pulsed UV light is an emerging technology, which can be used for the inactivation of this pathogen in milk in a relatively short time. Pulsed UV light damages the DNA of the bacteria by forming thymine dimers that lead to bacterial death. The effect of sample distance from the quartz window of the UV-light source, number of passes, and flow rate was investigated. A response surface methodology was used for the design and analysis of experiments. Milk was treated at 5-, 8-, or 11-cm distance from a UV-light strobe at 20, 30, or 40 mL/min flow rate and treated up to 3 times by recirculation of milk to assess the effect of the number of passes on inactivation efficiency. Log₁₀ reductions varied from 0.55- to 7.26-log₁₀ CFU/mL. Complete inactivation was obtained in 2 cases and no growth was observed following an enrichment protocol. Predicted results were in agreement with the experimental data. Overall, this work demonstrates that pulsed UV-light has a potential for inactivation of milk pathogens.     

脉冲强光杀菌在水处理中的应用

介绍了饮用水生产中的杀菌方法及存在的主要问题,介绍了脉冲强光杀菌原理,并展望了该方法在水处理的广阔应用前景。     

Inactivation of E. coli K12 in apple juice by high voltage pulsed electric field

Pulsed Electric Field (PEF) technology is an emerging non-thermal food preservation technique that has mainly been applied to improve the shelf life of such foods as bread, milk, orange juice, apple juice and liquid eggs. It involves the application of pulses of high voltage to liquid or semi-solid materials, placed between two electrodes at ambient, sub-ambient, or slightly above ambient temperature. The voltage is typically in the range 20–80 kV/cm, and may be applied in the form of exponentially decaying, square wave, oscillatory, or in some cases, bipolar (instant-charge-reversal) pulses. In the present work, the effect number of pulses on the inactivation of E. coli K12 in apple juice was studied at two different voltages, namely 20 and 40 kV/cm and the number of pulses was varied from 0 to 100. The results indicate that the regulatory requirement of 5-log reduction in microbial count for food safety purposes could only be achieved with 40 kV/cm applied voltage and 100 pulses. The experiments were carried out at 20 °C and the maximum temperature rise was 2 °C.     

Inactivation of E. coli O157:H7 on blueberries by electrolyzed water, ultraviolet light, and ozone

Increased interest in blueberries due to their nutritional and health benefits has led to an increase in consumption. However, blueberries are consumed mostly raw or minimally processed and are susceptible to microbial contamination like other type of fresh produce. This study was, therefore, undertaken to evaluate the efficacy of electrostatic spray of electrolyzed oxidizing (EO) water, UV light, ozone, and a combination of ozone and UV light in killing Escherichia coli O157:H7 on blueberries. A 5-strain mixture of E. coli O157:H7 were inoculated on the calyx and skin of blueberries and then subjected to the treatments. Electrostatic EO water spray reduced initial populations of E. coli O157:H7 by only 0.13 to 0.24 log CFU/g and 0.88 to 1.10 log CFU/g on calyx and skin of blueberries, respectively. Ozone treatment with 4000 mg/L reduced E. coli O157:H7 by only 0.66 and 0.72 log CFU/g on calyx and skin of blueberries, respectively. UV light at 20 mW/cm2 for 10 min was the most promising single technology and achieved 2.14 and greater than 4.05 log reductions of E. coli O157:H7 on the calyx and skin of blueberries, respectively. The combination treatment of 1 min ozone and followed by a 2 min UV achieved more than 1 and 2 log additional reductions on blueberry calyx than UV or ozone alone, respectively. PRACTICAL APPLICATION: Outbreaks of foodborne illnesses have been associated with consumption of fresh produce. Many methods for removing pathogens as well as minimizing their effect on quality of treated produce have been investigated. UV technology and its combination with ozone used in this study to inactive E. coli O157:H7 on blueberries was found effective. Results from this study may help producers and processors in developing hurdle technologies for the delivery of safer blueberries to consumers.     

UV Inactivation of E. coli in Liquid Egg White

Liquid egg white is currently pasteurized using heat; however, this treatment damages the functional properties of the egg. In this study, a nonthermal ultraviolet light (UV) system was developed to pasteurize liquid egg white. The system consisted of low-pressure mercury bulbs surrounded by UV transparent tubing. Egg white was inoculated with Escherichia coli K12 and pumped through the UV system at a flow rate of 330 ml/min. The effects of treatment time (0 to 160 s), temperature (30 to 50 °C), and egg white pH (7 to 9) on the inactivation of E. coli were investigated. The population of E. coli in egg white was reduced by 4.3 log after being exposed to UV at 50 °C for 160 s. Inactivation was linearly dependent on treatment time and was adequately described using first-order kinetics (r ² of 0.94). The electrical energy of the process was calculated to be 44 J/ml. Inactivation was directly dependent on temperature and inversely dependent on pH. Nonthermal UV processing has the potential to improve the safety and functional properties of liquid egg white. Mention of trade names or commercial products in this publication is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the US Department of Agriculture.     

Inactivation kinetics and factors of variability in the pulsed light treatment of Listeria innocua cells

Pulsed light (PL) treatment can effectively reduce microbial populations in clear substrates and on surfaces, but its effectiveness varies as a function of substrate or treatment-related factors. For PL to be successfully adopted by the food industry, all factors of influence, as well as the inactivation kinetics for the microorganisms of concern, must be elucidated. In this study, the inactivation kinetics of Listeria innocua and the effect of inoculum size on PL inactivation were investigated. Stainless steel coupons (50.8 by 101.6 mm) of defined surface properties and transparent glass chamber slides (25.4 by 50.8 by 10 mm) were each inoculated with 1 ml of aqueous suspensions of L. innocua containing inoculum populations of up to 10(9) CFU. The thickness of the liquid layer in the glass slides was 1.16 mm. The inoculated substrates were exposed to PL treatment of up to 17 J/cm2 in a static PL chamber equipped with a pulsed Xenon lamp. Survivors were recovered and enumerated by both standard plate counting and most-probable-number procedures. The data indicated that in clear liquids, PL resulted in more than a 6-log reduction of L. innocua after a 12-J/cm2 treatment, regardless of the initial inoculum size. For the stainless steel surfaces, less than a 4-log reduction after a 12-J/cm2 treatment and a noticeable effect of substrate characteristics and inoculum size on inactivation were observed. The survivor curves showed pronounced tailing for all substrates used in the study. The Weibull model accurately predicted the survivor ratios for the PL treatment of L. innocua in clear liquids, with a shape and scale parameter of 0.33 and 3.01, respectively. The Weibull model resulted in significant overestimation of PL effectiveness for the stainless steel substrates, where the influence of various substrate properties and inoculum level on inactivation was significant.     

脉冲强光对大肠杆菌细胞膜损伤及胞内酶活性的影响

通过脉冲强光处理对数生长期大肠杆菌细胞悬液,研究菌体细胞膜通透性及胞内酶活性的变化.结果表明,蛋白质的漏出量及丙二醛的生成量均随大肠杆菌存活率的下降而增加,在处理电压1 500 V、闪照次数32次的条件下,蛋白质漏出量为13.03 μg/mL,丙二醛生成量为2.76 nmol/L,对氯化钠的耐受性明显低于对照组(P＜0.01).此外,胞内酶活性与处理前相比均有所降低,超氧化物歧化酶活性最低降至83.78%,过氧化氢酶活性最低降至76.92%.因此,细菌屏障结构破坏所造成的细胞膜渗透压及通透性改变,可使细菌胞内物质发生改变,甚至导致菌体死亡,羟自由基可能对致死细胞的协同作用有一定的意义.     

Inactivation kinetics of Escherichia coli by pulsed electron beam

ABSTRACT:  A novel and compact low-energy (keV) high-power pulsed electron beam (e-beam) that utilizes a secondary emission electron gun (SEEG) was designed and constructed. Escherichia coli JM 109 at a concentration of 10⁶ CFU/mL was spread-plated on Luria-Bertani (LB) medium and subjected to the SEEG e-beam. The e-beam was administered as 1 or 5 pulses. The duration of a single pulse was constant at 5 μs, e-beam current density was constant at 25 mA/cm², and e-beam energy varied between 60 and 82.5 keV. Following treatment with the SEEG e-beam, survivors of the irradiated E. coli samples were enumerated by a standard 10-fold dilution and spread-plated. The survivor curves were plotted on logarithmic scale as a function of e-beam dose. The D ₁₀-values were calculated as a negative reciprocal of the slope of the survivor curves. The D ₁₀-values for E. coli inactivated with 1- and 5-pulse SEEG e-beam were 0.0026 and 0.0217 Gy, respectively. These D ₁₀-values were considerably lower than published D ₁₀-values for E. coli inactivated with conventional high-energy continuous e-beam, likely due to shorter exposure time ( t ), greater current density ( J ), and a pulse mode of the SEEG e-beam. The SEEG e-beam showed promising results for microbial inactivation in a nonthermal manner; however, due to low energy of the SEEG e-beam, current applications are limited to surface decontamination. The SEEG e-beam may be an efficient processing step for surface inactivation of food-borne pathogens on ready-to-eat products, including fresh and leafy vegetables.