Transfer of Salmonella and Campylobacter from stainless steel to romaine lettuce

The degree of transfer of Campylobacter jejuni and Salmonella enterica serovar Typhimurium was evaluated from a stainless steel contact surface to a ready-to-eat food (lettuce). Stainless steel coupons (25 cm2) were inoculated with a 20-microl drop of either C. jejuni or Salmonella Typhimurium to provide an inoculum level of approximately 10(6) CFU/28 mm2. Wet and dry lettuce (Lactuca sativa var. longifolia) pieces (9 cm2) were placed onto the inoculated stainless steel surface for 10 s after the designated inoculum drying time (0 to 80 min for C. jejuni; 0 to 120 min for Salmonella Typhimurium), which was followed by the recovery and enumeration of transferred pathogens (lettuce) and residual surface pathogens (stainless steel coupons). For transfers of Salmonella Typhimurium to dry lettuce, there was an increase from 36 to 66% in the percent transfer of the initial inoculum load during the first 60 min of sampling and then a precipitous drop from 66 to 6% in percent transfer. The transfer of Salmonella Typhimurium to wet lettuce ranged from 23 to 31%, with no statistically significant difference between recoveries over the entire 120-min sampling period. For C. jejuni, the mean percent transfer ranged from 16 to 38% for dry lettuce and from 15 to 27% for wet lettuce during the 80-min sampling period. The results of this study indicate that relatively high numbers of bacteria may be transferred to a food even 1 to 2 h after surface contamination. These findings can be used to support future projects aimed at estimating the degree of risk associated with poor handling practices of ready-to-eat foods.     

Slicing under chlorinated water improves the disinfection of fresh-cut romaine lettuce

The aim of this study was to determine whether the timing or mode of application influences the antimicrobial efficacy of a sodium hypochlorite solution against microorganisms on fresh-cut Romaine lettuce. Lettuce leaves were treated with a solution of sodium hypochlorite containing 70 mg liter(-1) free chlorine prior to slicing (WLS), while submerged in the solution (CWS), or after slicing (PCS), the last being common practice in the fresh-cut industry. Immediate antimicrobial effects were determined from analyses performed directly after treatment, while delayed effects were derived from analysis of packaged samples stored at 4 and 15°C. Experiments were performed with both uninoculated and inoculated whole leaves, using Escherichia coli O157:H7 from a type collection as an inoculum. The CWS treatment provided the greatest initial reductions in aerobic plate counts of E. coli O157:H7 populations, followed by PCS and WLS. The advantage afforded by the CWS approach was maintained over 10 days in storage at 4°C. In addition, it was noted that the visual quality attributes of the fresh-cut lettuce from the CWS approach were better than those from the other two treatments. These results collectively suggest that slicing lettuce under a sanitizer solution could provide better disinfection of fresh-cut Romaine lettuce than the current practice of washing with sanitizer after cutting has taken place.     

Physicochemical stability and virucidal effect of diluted,slightly acidic electrolyzed water against human norovirus

Food Science and Biotechnology - This study aimed to evaluate the virucidal effect and potential use as a disinfectant of undiluted and diluted slightly acidic electrolyzed water (SAEW) on human...     

Transfer of Escherichia coli O157:H7 to romaine lettuce due to contact water from melting ice

Ice can be used to chill romaine lettuce and maintain relative humidity during transportation. Escherichia coli O157:H7 may contaminate water used for ice. The objective of this study was to determine the potential for E. coli O157:H7 contamination of romaine lettuce from either ice contaminated with the pathogen or by transfer from lettuce surfaces via melting ice. In experiment 1, lettuce was spot inoculated with E. coli O157:H7 and chilled with ice prepared from uncontaminated tap water. In experiment 2, water inoculated with this pathogen was frozen and used to ice lettuce. Three heads of lettuce were stacked in each container and stored at 4 or 20 degrees C. After the ice melted, E. coli O157:H7 attachment to and recovery from the lettuce leaves were determined. For experiment 1, the population of E. coli O157:H7 attached to inoculated sites averaged 3.8 and 5.5 CFU/cm2 at 4 and 20 degrees C, respectively. Most of the uninoculated sites became contaminated with the pathogen due to ice melt. For experiment 2, 3.5 to 3.8 log CFU E. coli O157:H7 per cm2 was attached to the top leaf on the first head. After rinsing with chlorinated water (200 microg/ml), E. coli O157:H7 remained on the surface of the top head (1.8 to 2.0 log CFU/cm2). There was no difference in numbers of E. coli O157:H7 recovered from each sampling site at 4 and 20 degrees C. Results show that E. coli O157:H7 can be transferred onto other produce layers in shipping containers from melted ice made of contaminated water and from contaminated to uncontaminated leaf surfaces.     

Listeria monocytogenes在经高氧化还原电位酸性水处理的鲜食莴苣上预测模型的建立

采用高氧化还原电位酸性水(EOW)对接种过单核细胞增生李斯特菌的鲜食莴苣进行处理,研究残留菌在不同温度下的保存期限。建立Gompertz,Logistic和Baranyi初级模型,描述单增李斯特菌在不同温度下的生长情况,对比结果表明,Gompertz模型的判定系数R2=0.9913,能够更好地拟合李斯特菌在各个温度下的生长状况,并得到李斯特菌生长的Gompertz模型生长参数(SGR,LT,MPD)。利用平方根模型对其的最大比生长速率的平方根-温度进行拟合,得到莴苣上单核细胞增生李斯特菌生长的二级模型:SGR=0.015T+0.069。使用判定系数(R2)、均方误差(MSE)、偏差因子(BF)和准确因子(AF)对模型进行验证,结果表明,本研究得出的二级模型能够很好地预测单核细胞增生李斯特菌在相应环境下的生长状况。     

不同电解质电生功能水的电解特性和贮存性能

为扩大电生功能水（EW）的应用范围、提高其制备效率、更好地了解其贮存特性,本文采用NaCl、KCl、CaCl2三种不同电解质制备电生功能水,对其电解特性以及相应的电生功能水贮存特性进行研究,并以KCl为主要研究对象,总结了KCl适合的电解方法和贮存方式:当电解液浓度为0.38g/LKCl+0.0015mol/LHCl时,有效氯产率和所得功能水的稳定性较优;在微酸性范围内,NaCl作为电解质比CaCl2的稳定性要好,与KCl作为电解质相比稳定性和有效氯产率差异不显著;光照、高温加热和顶空都会加速有效氯的损失,所以需要长期贮存时应尽量保证避光、密封。      

Reduction of bacteria on spinach, lettuce, and surfaces in food service areas using neutral electrolyzed oxidizing water

Food safety issues and increases in food borne illnesses have promulgated the development of new sanitation methods to eliminate pathogenic organisms on foods and surfaces in food service areas. Electrolyzed oxidizing water (EO water) shows promise as an environmentally friendly broad spectrum microbial decontamination agent. EO water is generated by the passage of a dilute salt solution ( approximately 1% NaCl) through an electrochemical cell. This electrolytic process converts chloride ions and water molecules into chlorine oxidants (Cl(2), HOCl/ClO(-)). At a near-neutral pH (pH 6.3-6.5), the predominant chemical species is the highly biocidal hypochlorous acid species (HOCl) with the oxidation reduction potential (ORP) of the solution ranging from 800 to 900mV. The biocidal activity of near-neutral EO water was evaluated at 25 degrees C using pure cultures of Escherichia coli, Salmonella typhimurium, Staphylococcus aureus, Listeria monocytogenes, and Enterococcus faecalis. Treatment of these organisms, in pure culture, with EO water at concentrations of 20, 50, 100, and 120ppm total residual chlorine (TRC) and 10min of contact time resulted in 100% inactivation of all five organisms (reduction of 6.1-6.7log(10)CFU/mL). Spray treatment of surfaces in food service areas with EO water containing 278-310ppm TRC (pH 6.38) resulted in a 79-100% reduction of microbial growth. Dip (10min) treatment of spinach at 100 and 120ppm TRC resulted in a 4.0-5.0log(10)CFU/mL reduction of bacterial counts for all organisms tested. Dipping (10min) of lettuce at 100 and 120ppm TRC reduced bacterial counts of E. coli by 0.24-0.25log(10)CFU/mL and reduced all other organisms by 2.43-3.81log(10)CFU/mL.     

酸性电解水用于葡萄杀菌保鲜的试验研究

用不同指标的酸性电解水对葡萄进行处理,对处理后果实的微生物总数、霉菌总数以及腐烂率、脱粒率进行了对比研究,结果显示:经不同指标酸性电解水浸泡处理后,果实表面微生物数量均显著降低,果实的总损失率也明显降低;对比发现,强酸性电解水的防腐保鲜效果最优;葡萄果实采后用酸性电解水处理可以有效的提高其商品价值及食用安全性。     

酸性电解水水解玉米皮提取L-阿拉伯糖的工艺研究

L-阿拉伯糖是一种无热量的天然甜料,可以反竞争性抑制小肠蔗糖酶,阻断蔗糖的吸收,抑制餐后血糖和胰岛素水平的升高。本文以酸性电解水作为催化介质,水解玉米皮提取L-阿拉伯糖,操作简便且环境友好,克服了传统无机酸水解法工艺复杂、对设备要求高、环境污染等问题。通过酸性电解水水解玉米皮单因素实验和正交实验,确定最佳工艺为:酸性电解水p H 2.0,水解温度180℃,水解时间30 min,料液比1∶40(g∶m L)。经验证试验后,L-阿拉伯糖水解得率为15.49%。     

Efficacy of ozonated and electrolyzed oxidative waters to decontaminate hides of cattle before slaughter

The hides of cattle are the primary source of pathogens such as Escherichia coli O157:H7 that contaminate preevisceration carcasses during commercial beef processing. A number of interventions that reduce hide contamination and subsequent carcass contamination are currently being developed. The objective of this study was to determine the efficacy of ozonated and electrolyzed oxidizing (EO) waters to decontaminate beef hides and to compare these treatments with similar washing in water without the active antimicrobial compounds. Cattle hides draped over barrels were used as the model system. Ozonated water (2 ppm) was applied at 4,800 kPa (700 lb in2) and 15 degrees C for 10 s. Alkaline EO water and acidic EO water were sequentially applied at 60 degrees C for 10 s at 4,800 and 1,700 kPa (250 lb in2), respectively. Treatment using ozonated water reduced hide aerobic plate counts by 2.1 log CFU/100 cm2 and reduced Enterobacteriaceae counts by 3.4 log CFU/100 cm2. EO water treatment reduced aerobic plate counts by 3.5 log CFU/100 cm2 and reduced Enterobacteriaceae counts by 4.3 log CFU/100 cm2. Water controls that matched the wash conditions of the ozonated and EO treatments reduced aerobic plate counts by only 0.5 and 1.0 log CFU/100 cm2, respectively, and each reduced Enterobacteriaceae counts by 0.9 log CFU/100 cm2. The prevalence of E. coli O157 on hides was reduced from 89 to 31% following treatment with ozonated water and from 82 to 35% following EO water treatment. Control wash treatments had no significant effect on the prevalence of E. coli O157:H7. These results demonstrate that ozonated and EO waters can be used to decontaminate hides during processing and may be viable treatments for significantly reducing pathogen loads on beef hides, thereby reducing pathogens on beef carcasses.     

Inactivation of Escherichia coli O157:H7, Salmonella and human norovirus surrogate on artificially contaminated strawberries and raspberries by water-assisted pulsed light treatment

This study investigated the inactivation of Escherichia coli O157:H7, Salmonella and murine norovirus (MNV-1), a human norovirus surrogate, on strawberries and raspberries using a water-assisted pulsed light (WPL) treatment. The effects of combinations of WPL treatment with 1% hydrogen peroxide (H₂O₂) or 100 ppm sodium dodecyl sulfate (SDS) were also evaluated. Strawberries and raspberries were inoculated with E. coli O157:H7 and treated by WPL for 5–60 s. E. coli O157:H7 on both strawberries and raspberries was significantly reduced in a time-dependent manner with 60-s WPL treatments reducing E. coli O157:H7 by 2.4 and 4.5 log CFU/g, respectively. Significantly higher reductions of E. coli O157:H7 were obtained using 60-s WPL treatment than washing with 10 ppm chlorine. Compared with washing with chlorine, SDS and H₂O₂, the combination of WPL treatment with 1% H₂O₂ for 60 s showed significantly higher efficacy by reducing E. coli O157:H7 on strawberries and raspberries by 3.3- and 5.3-log units, respectively. Similarly, Salmonella on strawberries and raspberries was inactivated by 2.8- and 4.9-log units after 60-s WPL–H₂O₂ treatments. For decontamination of MNV-1, a 60-s WPL treatment reduced the viral titers on strawberries and raspberries by 1.8- and 3.6-log units, respectively and the combination of WPL and H₂O₂ did not enhance the treatment efficiency. These results demonstrated that the WPL treatment can be a promising chemical-free alternative to chlorine washing for decontamination of berries destined for fresh-cut and frozen berry products. WPL–H₂O₂ treatment was the most effective treatment in our study for decontamination of bacterial pathogens on berries, providing an enhanced degree of microbiological safety for berries.     

Transfer of Listeria innocua from contaminated compost and irrigation water to lettuce leaves

Many foodborne outbreaks of some pathogens such as Escherichia coli O157:H7, Salmonella or Listeria have been associated with the consumption of contaminated vegetables. Contaminated manure and polluted irrigation water are probable vehicles for the pathogens. The aim of this study was to determine the potential transfer of Listeria innocua from soil fertilized with contaminated compost or irrigated with contaminated water to the edible parts of lettuce grown on these soils together with its survival in lettuce and in soil under field conditions during two different seasons. Moreover, its survival on lettuce sprinkled with contaminated irrigation water was evaluated. L. innocua survived in soil samples for 9 weeks at high concentrations, 10⁵ cfu gdw⁻¹ in fall and 10³ cfu gdw⁻¹ in spring. Pathogen survived better in fall, indicating an important influence of temperature and humidity. L. innocua population in lettuce leaves was very high on lettuce leaves after sprinkling, but decreased to undetectable levels at field conditions. There was also transfer of L. innocua from soil contaminated with compost or irrigated with contaminated water to lettuce leaves, mainly to the outer ones. Survival profiles of L. innocua on lettuce and soil samples contaminated either by application of contaminated compost or surface irrigation water was similar. Our results indicated that contaminated compost and contaminated irrigation water can play an important role in the presence of foodborne pathogens on vegetables.     

Application of Cudrania tricuspidata leaf extract as a washing agent to inactivate Listeria monocytogenes on fresh-cut romaine lettuce and kale

The present study aimed to examine the antimicrobial activity of silkworm thorn (Cudrania tricuspidata) leaf extract (CTLE) and its application as a washing agent for fresh-cut romaine lettuce and kale. The antimicrobial activities of CTLE at various concentrations against Listeria monocytogenes were determined using disc diffusion and viable cell count assays, and CTLE exhibited strong inactivation of L. monocytogenes. In particular, after the treatment with 0.4% CTLE, the protein content of L. monocytogenes cells was significantly (P < 0.05) decreased from 507.21 to 254.58 μg mL⁻¹, and damaged cells were observed by scanning electron microscopy. CTLE washing resulted in approximately 2-log reduction of microbial growth, similar to that of 0.01% NaOCl. In addition, CTLE washing did not affect the quality of romaine lettuce and kale. Therefore, these results suggest that CTLE is applicable as a new washing agent for inactivating L. monocytogenes on fresh-cut romaine lettuce and kale.     

强酸性电解水降解对硫磷动力学模型及降解产物

为探明强酸性电解水(Strong acidic electrolyzed water,AcEW)对对硫磷的降解规律,在模拟水环境内进行了降解实验。结果显示,随着反应时间的延长或AcEW的有效氯质量浓度(ACC)的增加,对硫磷的降解效率将增加。AcEW对对硫磷的降解反应符合化学一级反应动力学及二级动力学模型。对硫磷在AcEW(pH3.0、有效氯浓度2 mg/L)中的一级反应动力学方程为ln([parathion]t/[parathion]0)=-0.0099t。通过GC-MS(气相色谱-质谱联用仪)分析,对硫磷被AcEW降解后的产物为对氧磷和4-硝基苯酚。在AcEW中,对硫磷可能的降解途径为对硫磷-对氧磷-4-硝基苯酚-小分子有机物-无机物。     

Use of a common laboratory glassware detergent improves recovery of Cryptosporidium parvum and Cyclospora cayetanensis from lettuce, herbs and raspberries

The success of any protocol designed to detect parasitic protozoa on produce must begin with an efficient initial wash step. Cryptosporidium parvum and Cyclospora cayetanensis oocysts were seeded onto herbs, lettuces and raspberries, eluted with one of four wash solutions and the recovered number of oocysts determined via fluorescent microscopy. Recovery rates for fluorescein thiosemicarbazide labeled C. parvum oocysts seeded onto spinach and raspberries and washed with de-ionized water were 38.4 ± 10.1% and 34.9 ± 6.2%, respectively. Two alternative wash solutions viz. 1M glycine, pH 5.5 and a detachment solution were tested also using labeled C. parvum seeded spinach and raspberries. No statistically significant difference was noted in the recovery rates. However, a wash solution containing 0.1% Alconox, a laboratory glassware detergent, resulted in a significant improvement in oocyst recovery. 72.6 ± 6.6% C. parvum oocysts were recovered from basil when washed with 0.1% Alconox compared to 47.9 ± 5.8% using detachment solution. Also, C. cayetanensis oocysts were seeded onto lettuces, herbs and raspberries and the recovery using de-ionized water were compared to 0.1% Alconox wash: basil 17.5 ± 5.0% to 76.1 ± 14.0%, lollo rosso lettuce 38.3 ± 5.5% to 72.5 ± 8.1%, Tango leaf lettuce 45.9 ± 5.4% to 71.1 ± 7.8% and spring mix (mesclun) 39.8 ± 0.7% to 80.2 ± 11.3%, respectively. These results suggest that the use of Alconox in a wash solution significantly improves recovery resulting in the detection of these parasitic protozoa on high risk foods.     

酸性电解水及其在食品工业中的应用

酸性电解水(AEW)是稀释的盐溶液通过电解槽电解,在阳极生成的具有氧化能力的电解水。其中电解槽的阳极和阴极被隔膜隔开。酸性电解水具有低pH(2.3～2.7)、高氧化还原电位(ORP,>1100mV)和一定的有效氯含量。与传统的消毒剂相比,酸性电解水具有杀菌高效、操作简便、安全环保等优点。作为一种新型的消毒剂,它在医疗、食品加工、农业与环保等行业广泛应用。该文概述了AEW的生成原理与特性、优缺点、杀菌效果与机理。介绍了其在食品工业中的应用以及存在的问题,同时展望了AEW的应用前景。     

Influence of inoculation method, spot inoculation site, and inoculation size on the efficacy of acidic electrolyzed water against pathogens on lettuce

The influence of bacterial inoculation methods on the efficacy of sanitizers against pathogens was examined. Dip and spot inoculation methods were employed in this study to evaluate the effectiveness of acidic electrolyzed water (AcEW) and chlorinated water (200 ppm free available chlorine) against Escherichia coli O157:H7 and Salmonella spp. Ten pieces of lettuce leaf (5 by 5 cm) were inoculated by each method then immersed in 1.5 liters of AcEW, chlorinated water, or sterile distilled water for 1 min with agitation (150 rpm) at room temperature. The outer (abaxial) and inner (adaxial) surfaces of the lettuce leaf were distinguished in the spot inoculation. Initial inoculated pathogen population was in the range 7.3 to 7.8 log CFU/g. Treatment with AcEW and chlorinated water resulted in a 1 log CFU/g or less reduction of E. coli O157:H7 and Salmonella populations inoculated with the dip method. Spot inoculation of the inner surface of the lettuce leaf with AcEW and chlorinated water reduced the number of E. coli O157:H7 and Salmonella by approximately 2.7 and 2.5 log CFU/g, respectively. Spot inoculation of the outer surface of the lettuce leaf with both sanitizers resulted in approximately 4.6 and 4.4 log CFU/g reductions of E. coli O157:H7 and Salmonella, respectively. The influence of inoculation population size was also examined. Each sanitizer could not completely eliminate the pathogens when E. coli O157:H7 and Salmonella cells inoculated on the lettuce were of low population size (10(3) to 10(4) CFU/g), regardless of the inoculation technique.