Reduction of Pathogens Using Hot Water and Lactic Acid on Beef Trimmings

Beef trimmings from young or mature beef cattle were obtained commercially. Trimmings within age type then were inoculated with about 6.0 log₁₀ CFU/mL of rifampicin-resistant. Escherichia coli O157:H7 and Salmonella typhimurium (ATCC 13311) were randomly assigned to 1 of 3 treatments (control; 95 °C hot water alone, or with 2% L-lactic acid). After treatment, trimmings were ground, held for 0, 14, 28, or 42 d in chub packages at 4 °C, and total aerobic plat counts, E. coli O157:H7, and S. typhimurium counts were determined. Non-inoculated trimmings were also treated and samples were evaluated for pH, fat, moisture, TBA, meat color by colorimeter, and meat color, and odor by trained sensory panels. Trimmings treated with water or hot water plus lactic acid reduced levels of E. coli O157:H7 and S. typhimurium and tended to be darker after treatment. Meat odor in the final product was not affected by treatment.     

Hydrogen production from rotten dates by sequential three stages fermentation

This study was devoted for H₂ production from rotten fruits of date palm (Phoenix dactylifera L.) by three fermentation stages. A facultative anaerobe, Escherichia coli EGY was used in first stage to consume O₂ and maintain strict anaerobic conditions for a second stage dark fermentative H₂ production by the strictly anaerobic Clostridium acetobutylicum ATCC 824. Subsequently, a third stage photofermentation using Rhodobacter capsulatus DSM 1710 has been conducted for the H₂ production. The maximum total H₂ yield of the three stages (7.8 mol H₂ mol⁻¹ sucrose) was obtained when 5 g L⁻¹ of sucrose was supplemented to fermentor as rotten date fruits. A maximum estimated cumulative H₂ yield of the three stages (162 LH₂ kg⁻¹ fresh rotten dates) was estimated at the (5 g L⁻¹) sucrose concentration. These results suggest that rotten dates can be efficiently used for commercial H₂ production. The described protocol did not require addition of a reducing agent or flashing with argon which both are expensive.     

乙醇提取柚子皮中总黄酮条件及其抑菌分析

对乙醇提取柚子皮中总黄酮的影响因素作了探讨，确定了乙醇提取黄酮的条件为：水浴温度70℃、乙醇体积浓度50％、提取时间2．0h、固液比1g：25mL，该条件下测得总黄酮的提取率为4．39％。该提取物对大肠杆菌有一定的抑制效果，对酵母菌几乎没有抑制作用。     

Hydrogen production and metabolic flux analysis of metabolically engineered Escherichia coli strains

Escherichia coli can produce H₂ from glucose via formate hydrogen lyase (FHL). In order to improve the H₂ production rate and yield, metabolically engineered E. coli strains, which included pathway alterations in their H₂ production and central carbon metabolism, were developed and characterized by batch experiments and metabolic flux analysis. Deletion of hycA, a negative regulator for FHL, resulted in twofold increase of FHL activity. Deletion of two uptake hydrogenases (1 (hya) and hydrogenase 2 (hyb)) increased H₂ production yield from 1.20 mol/mol glucose to 1.48 mol/mol glucose. Deletion of lactate dehydrogenase (ldhA) and fumarate reductase (frdAB) further improved the H₂ yield; 1.80 mol/mol glucose under high H₂ pressure or 2.11 mol/mol glucose under reduced H₂ pressure. Several batch experiments at varying concentrations of glucose (2.5–10 g/L) and yeast extract (0.3 or 3.0 g/L) were conducted for the strain containing all these genetic alternations, and their carbon and energy balances were analyzed. The metabolic flux analysis revealed that deletion of ldhA and frdABdirected most of the carbons from glucose to the glycolytic pathway leading to H₂ production by FHL, not to the pentose phosphate pathway.     

Peracetic acid‐enhanced photocatalytic and sonophotocatalytic inactivation of E. coli in aqueous suspensions

BACKGROUND: Although chlorination is an effective and widely employed method of water disinfection, it suffers serious drawbacks such as the formation of toxic chlorinated by‐products. Therefore, other disinfection technologies have been researched and developed, including advanced oxidation. RESULTS: The efficacy of heterogeneous photocatalysis and sonophotocatalysis induced by UV‐A irradiation and low frequency (24–80 kHz) ultrasound irradiation in the presence of TiO₂ as the photocatalyst and peracetic acid (PAA) as an additional disinfectant to inactivate E. coli in sterile water was evaluated. PAA‐assisted UV‐A/TiO₂ photocatalysis generally leads to nearly complete E. coli inactivation in 10–20 min of contact time with the extent of inactivation depending on the photocatalyst type and loading (in the range 100–500 mg L^?1) and PAA concentration (in the range 0.5–2 mg L^?1). The simultaneous application of ultrasound and UV‐A irradiation in the presence of TiO₂ and PAA prompted further E. coli inactivation. CONCLUSIONS: The proposed advanced disinfection technology offers complete E. coli inactivation at short treatment times and low PAA doses. Copyright © 2010 Society of Chemical Industry     

Construction of self‐organized free‐standing TiO2 nanotube arrays for effective disinfection of drinking water

BACKGROUND: In this study, the efficacy of disinfection surface water using anodic TiO₂ films was investigated. The as‐prepared photocatalyst demonstrated excellent photocatalytic disinfection of E. coli cells. Free‐standing and self‐organized TiO₂ nanotube arrays were synthesized via a facile electrochemical anodization method, prior to calcination. RESULTS: Over 95% of the initial 10⁶ cpu mL^?1 E. coli cells were inactivated within 50 min of UV‐A photocatalytic disinfection, despite the influence of various ionic species and organic compounds commonly present in groundwater. This was justified by the unique double‐walled nanotubular structure of the TiO₂ photocatalyst, which provided efficient delocalization of electron carriers and promoted anti‐recombination of photogenerated pairs of electrons and holes. Based on the experimental results obtained, cations enhanced the overall disinfection process while anions had an inhibitory effect on disinfection rates. CONCLUSION: The photocatalyst exhibited high efficiency in terms of photocatalytic disinfection of E. coli cells present in groundwater. It is deemed promising for applications in drinking water treatment owing to its superior disinfection performance, as well as high settleability, which promotes recovery and reuse of the catalyst. Copyright © 2010 Society of Chemical Industry     

Effect of high shear stress on microbial viability

Escherichia coli and Saccharomyces cerevisiae suspensions were submitted to controlled shear stress. Above a threshold value shear stress induced a decrease in micro‐organism viability. The threshold of shear stress efficiency depended on the micro‐organisms, being between 1292 Pa and 2770 Pa for S cerevisiae, and about 1250 Pa for E coli. Above 1810 Pa, E coli cells were disrupted whereas the S cerevisiae cells remained intact. The higher the cellular concentration, the greater the rate of decrease in viability. Viability loss was influenced by the number of passages through the experimental shear stress device and by exposure time. © 2001 Society of Chemical Industry     

丁香酚对多重耐药大肠杆菌的抑菌活性及其作用机制研究

为研究丁香酚对多重耐药大肠杆菌(Multidrug-resistant Escherichia coli,MDR E.coli)的抑菌活性,利用微量二倍稀释法和琼脂扩散法确定丁香酚对多重耐药大肠杆菌的最低抑菌浓度(Minimum inhibitory concentration,MIC)和最低杀菌浓度(Minimum bactericidal concentration,MBC),并利用紫外分光光度法、考马斯亮蓝法等方法初步分析其作用机制。结果表明,丁香酚对MDR E.coli的MIC和MBC分别为2.50 mg/mL和5.00 mg/mL;丁香酚可延长MDR E.coli迟缓期进入对数生长期的进程,改变菌体结构,增加菌株可溶性蛋白的含量和胞外核酸的量,增大菌体培养液中的电导率,对MDR E.coli具有较强的抑菌作用,这些作用可能归因于丁香酚对其细胞结构的破坏。本研究为临床有效缓解或解决多重耐药大肠杆菌的耐药、感染和致死率等问题提供新的思路、新途径,并为其在医药和食品开发领域的应用奠定理论基础。     

Ag沉积N、S掺杂改性P25材料对大肠杆菌的抑菌性研究

为扩展纳米TiO_2光谱响应范围,提高其可见光催化抗菌性能,本文以商业纳米TiO_2为原料,采用Ag化学沉积,N、S非金属元素掺杂制备改性P25抑菌材料(Ag-P25、Ag-N-P25、Ag-S-P25),研究这三种材料在可见光下对大肠杆菌的抑菌效果。研究表明,三种抑菌材料对大肠杆菌均有良好的抑制效果,其抑菌率随光照时间延长而不断上升。三种材料抑菌效果的强弱顺序为:Ag-S-P25、Ag-N-P25、Ag-P25。当光照时间为100min时,三者对大肠杆菌的抑菌率均达100%,与纯P25的抑菌率(79%)相对比,提高了21%。通过扫描电镜观察和提取菌体质粒DNA的电泳检测表明,三种材料对大肠杆菌菌体造成破坏,引起DNA泄漏,导致菌体死亡。通过研究讨论改性P25材料对大肠杆菌的灭活机理,可为具有抗菌功能的新型保鲜材料的研究开发提供理论和实验依据。     

响应面试验优化乌梅熊果酸提取工艺及其对大肠杆菌的抑制作用

采用响应面法优化超声提取乌梅熊果酸的最佳条件。在单因素试验基础上,选择乙醇体积分数、料液比和超声时间为影响因素,以乌梅熊果酸提取量为响应值进行响应面分析;并研究了乌梅熊果酸对大肠杆菌的抑制作用。结果表明,乌梅熊果酸提取最佳工艺条件为乙醇体积分数71%、料液比3∶44（g/mL）、超声时间2.5 h,在此条件下提取量为（12.61±0.13）mg/g。乌梅熊果酸对大肠杆菌最低抑菌浓度为0.25 mg/mL;高剂量组（0.5 mg/mL）处理后与对照组相比,细胞壁和细胞膜通透性增加,培养液蛋白质含量、核酸大分子物质含量、Ca2＋浓度和总漏出率分别增加了28、1.5、7 倍和0.8 倍;扫描电镜观察菌体有明显变形或破碎现象,表明乌梅熊果酸对大肠杆菌生长具有抑制作用。