Modelling the inactivation of Listeria monocytogenes and Salmonella typhimurium in simulated egg wash water

The inactivation of Listeria monocytogenes Scott A and Salmonella typhimurium in synthetic egg washwater was studied under varying conditions of temperature (38°C to 46°C), egg solids (0%, 2%), pH (9·5 to 10·5) and chlorine concentration (0 to 10 μg ml^-1 [ppm]) using a full factorial design. Survival was measured as the logarithm of the time required for a 4-log reduction in viable counts. Both pathogens were significantly affected by temperature and the presence of egg, while the survival of S. typhimurium was significantly reduced by pH and chlorine alone. Both pathogens were affected by second order interactions involving egg and either pH or chlorine. Egg was the most significant factor, reducing the survival of L. monocytogenes while promoting the survival of S. typhimurium. Two linear equations were derived to describe the decrease in survival of L. monocytogenes and S. typhimurium as a function of the 4 factors. These equations were used to estimate conditions which would reduce the time for a 4-log reduction in viable counts to <30 min. In the absence of egg solids, chlorine (20 μg ml^-1) can be used to control L. monocytogenes and S. typhimurium using moderate temperature (42°C) and pH (10·5). When egg is present in wash water, increased temperature (47·4°C) and pH (10·8) are required.     

A survey of food-borne pathogens in free-range poultry farms

A survey of the occurrence of Campylobacter, Salmonella, Listeria and Shiga toxin-producing E. coli was performed on 60 flocks of free-range chicken from 34 farms in the Basque Country (Northern Spain). Campylobacter was the most prevalent of the four pathogens, isolated in 70.6% of the farms, followed by L. monocytogenes (26.5%), and Salmonella (2.9%). No E. coli O157 or other STEC were isolated. In total 48 flocks from 26 farms were positive for at least one pathogen: 31 of them for a single pathogen (64.6%), and 17 for more than one species (35.4%). C. coli was more prevalent than C. jejuni (15 vs. 13 farms), and both species of Campylobacter were found in 3 farms. L. monocytogenes isolates were identified as serotype 4b complex, and the only Salmonella isolated was serovar Enteritidis. flaA PCR-RFLP performed on 91 Campylobacter isolates (36 C. jejuni and 55 C. coli) yielded 26 patterns, with higher diversity among the C. jejuni isolates. More than one pattern was found in 11 farms, and in 8 of them several patterns were found within the same flock. The findings of the present study suggest that the free-range rearing conditions described herein might have an advantageous effect on diminishing Salmonella but not on Campylobacter or L. monocytogenes flock contamination.     

HACCP在冷却牛肉生产中控制微生物的应用

根据危害分析与关键控制点系统原理,对冷却牛肉加工过程中主要环节可能存在的微生物危害进行分析,确立关键控制点、关键限值、监控方法及纠偏措施,构建规范的HACCP质量管理体系,从而有效消除、预防或最大限度地降低冷却牛肉生产过程中的微生物危害,确保产品质量。     

Survival of Salmonella in waste egg wash water

Waste wash waters from chicken egg-processing facilities can harbor high densities of bacteria, including salmonellae. For this study, we enumerated total coliforms, Escherichia coli, and Salmonella spp. in the egg wash waters of a large egg producer. We then determined how long these organisms would survive at temperatures of 5, 15, and 25 degrees C. We found that the fraction of salmonellae surviving over time at a given temperature was comparable to the fraction of indicator organisms that survived. We also found that the survival of these organisms varied with temperature, with 16, 8, and < 2 days being required for a 90% reduction of Salmonella in waste wash water held at 5, 15, and 25 degrees C, respectively. Finally, we noted that the response of laboratory-derived cultures to environmental stresses mimics the response of the indigenous microbial population, but individual cells within that population may survive for longer periods than laboratory-cultured strains.     

冷却猪肉供应链中微生物污染研究

研究冷却猪肉供应链的屠宰、运输、销售等过程中微生物的变化情况,分析各环节微生物污染的主要污染源,指出影响冷却猪肉安全的主要因素.     

Roles of oxidation-reduction potential in electrolyzed oxidizing and chemically modified water for the inactivation of food-related pathogens

This study investigates the properties of electrolyzed oxidizing (EO) water for the inactivation of pathogen and to evaluate the chemically modified solutions possessing properties similar to EO water in killing Escherichia coli O157:H7. A five-strain cocktail (10(10) CFU/ml) of E. coli O157:H7 was subjected to deionized water (control), EO water with 10 mg/liter residual chlorine (J.A.W-EO water), EO water with 56 mg/liter residual chlorine (ROX-EO water), and chemically modified solutions. Inactivation (8.88 log10 CFU/ml reduction) of E. coli O157:H7 occurred within 30 s after application of EO water and chemically modified solutions containing chlorine and 1% bromine. Iron was added to EO or chemically modified solutions to reduce oxidation-reduction potential (ORP) readings and neutralizing buffer was added to neutralize chlorine. J.A.W-EO water with 100 mg/liter iron, acetic acid solution, and chemically modified solutions containing neutralizing buffer or 100 mg/liter iron were ineffective in reducing the bacteria population. ROX-EO water with 100 mg/liter iron was the only solution still effective in inactivation of E. coli O157:H7 and having high ORP readings regardless of residual chlorine. These results suggest that it is possible to simulate EO water by chemically modifying deionized water and ORP of the solution may be the primary factor affecting microbial inactivation.     

Trends in microbial control techniques for poultry products

Fresh poultry meat and poultry products are highly perishable foods and high potential sources of human infection due to the presence of several foodborne pathogens. Focusing on the microbial control of poultry products, the food industry generally implements numerous preventive measures based on the Hazard Analysis and Critical Control Points (HACCP) food safety management system certification together with technological steps, such as refrigeration coupled to modified atmosphere packaging that are able to control identified potential microbial hazards during food processing. However, in recent years, to meet the demand of consumers for minimally processed, high-quality, and additive-free foods, technologies are emerging associated with nonthermal microbial inactivation, such as high hydrostatic pressure, irradiation, and natural alternatives, such as biopreservation or the incorporation of natural preservatives in packaging materials. These technologies are discussed throughout this article, emphasizing their pros and cons regarding the control of poultry microbiota and their effects on poultry sensory properties. The discussion for each of the preservation techniques mentioned will be provided with as much detail as the data and studies provided in the literature for poultry meat and products allow. These new approaches, on their own, have proved to be effective against a wide range of microorganisms in poultry meat. However, since some of these emergent technologies still do not have full consumer's acceptability and, taking into consideration the hurdle technology concept for poultry processing, it is suggested that they will be used as combined treatments or, more frequently, in combination with modified atmosphere packaging.     

Application of propidium monoazide-qPCR to evaluate the ultrasonic inactivation of Escherichia coli O157:H7 in fresh-cut vegetable wash water

The efficacy of sanitizing technologies in produce or in vegetable wash water is generally evaluated by plate count in selective media. This procedure is time consuming and can lead to misinterpretations because environmental conditions and sanitizing processes may affect bacterial growth or culturable capability. Thus, the aim of this study was to determine the applicability of a propidium monoazide real-time PCR (PMA-qPCR) method to monitor the inactivation by ultrasound treatment of foodborne bacteria in fresh-cut vegetable wash water. To this aim, lettuce wash water was artificially inoculated with Escherichia coli O157:H7 (10⁶ CFU/mL) and treated by means of a continuous ultrasonic irradiation with a power density of 0.280 kW/L. Quantification data obtained by PMA-qPCR and plate counts were statistically similar during the viability reduction of 99.996% which corresponds to 4.4 log reductions. Further reductions of E. coli O157:H7 were not detected by the PMA-qPCR method due to the limit of detection of this technique (20 CFU/mL). Inactivation data obtained by both techniques successfully fitted a linear model, giving no significant differences in kinetic parameters. These results indicate that the PMA-qPCR method is a suitable technique for evaluating ultrasonic disinfection of vegetable wash water, being able to distinguish between live and dead bacteria.     

冷鲜鸡冷藏保存过程中菌群结构变化分析

研究壳聚糖和ε-聚赖氨酸对肉食杆菌细胞结构和细胞保护酶的作用,探讨其对肉食杆菌的抑菌作用机制。采用肉汤稀释法测定壳聚糖和ε-聚赖氨酸对肉食杆菌的最小抑菌浓度（minimal inhibitory concentration,MIC）,由细菌生长曲线、电导率、胞外核酸、胞外蛋白、碱性磷酸酶（alkaline phosphatase,AKP）活力等指标,并结合扫描电子显微镜（scanning electron microscopy,SEM）观察,综合评价壳聚糖和ε-聚赖氨酸对肉食杆菌的作用机制;通过测定细胞保护酶（超氧化物歧化酶（superoxide dismutase,SOD）和过氧化氢酶（catalase,CAT））的活力变化分析其氧化应激反应参与情况。结果表明：壳聚糖和ε-聚赖氨酸对肉食杆菌的MIC分别为0.1953和 0.1563 mg/mL,经MIC和2MIC的壳聚糖和ε-聚赖氨酸处理后,菌体细胞内成分（AKP酶、蛋白质、核酸和离子）发生渗漏,CAT和SOD酶活力呈显著下降趋势（P<0.05）,且壳聚糖和ε-聚赖氨酸质量浓度与酶活力呈负相关关系。由扫描电镜观察得出,壳聚糖能使菌体变形且内容物渗出,ε-聚赖氨酸则使菌体出现褶皱和扭曲变形,细胞表面生成孔洞。综上所述,壳聚糖和ε-聚赖氨酸均能通过破坏细胞壁、损伤细胞膜、产生氧化应激反应等机制来抑制肉食杆菌的生长。

     

Model of inactivation of Campylobacter jejuni in poultry scalding

The purpose of this study was to develop a model of inactivation of Campylobacter jejuni in industrial scalding of chickens. Models can be used as a guide for broiler slaughterhouse operations for reducing levels of C. jejuni contamination on broiler carcasses. Mean concentrations of C. jejuni in terms of colony forming units (CFU) in scald tank water and in carcass rinse solution after scalding were 2.90 ± 0.07 and 3.86 ± 0.11 LogCFU/mL, respectively. Scald tank water temperature, flow rate, pH, and total solids in scalding process water were 54.15 ± 0.2 °C, 172.0 ± 8.4 L/min, 8.0 ± 0.01, and 2565 ± 114.3 mg/L, respectively. Inactivation models were developed by using mass balances and literature data for inactivation kinetics, of Campylobacter and the Arrhenius equation. Results of the inactivation models of scalding process indicate that high temperature and short time (less than 2 min) of scalding process were effective in reducing the number of viable cells. For this experimental data more than 50% of the Campylobacter are inactivated on surfaces of the chickens. The model fits the experimental data well and the values of the estimated parameters provide insight for this process. The model can be used for process design and potential process modifications.     

Occurrence of selected foodborne pathogens on poultry and poultry giblets from small retail processing operations in Trinidad

We conducted a study to determine quantitatively and qualitatively the presence of Campylobacter spp., Escherichia coli, staphylococci, total coliforms, total aerobic bacteria, and Salmonella on broiler carcasses from selected small retail processors in Trinidad. We used standard media and procedures for detection and quantification. All carcass and weep samples were positive for aerobic bacteria, E. coli, total coliforms, and staphylococci. Significant differences in the mean counts of aerobic bacteria were observed for samples of carcass (P = 0.001), weep (P = 0.038), and liver and heart (P = 0.017). There was a significant difference (P < 0.05) in the prevalence of E. coli and Campylobacter for liver and heart samples and gizzard samples across various areas (health divisions) in Trinidad and for Campylobacter jejuni and Campylobacter coli for offal samples. The prevalence of Salmonella in carcass, drip, gizzard, and liver and heart samples was 7.3, 3.1, 2.1, and 1.0%, respectively, and three serotypes, Salmonella Kiambu (53.8%), Salmonella Kentucky (38.5%), and Salmonella Mbandaka (7.7%) were isolated. Of the six groups of microbes considered with respect to sale activity, the differences in the prevalence of Campylobacter in medium-activity sale shops (95.8%) and low-activity sale shops (83.3%) and the mean counts of staphylococci for medium-activity sale shops (5.5 +/- 0.9) and low-activity sale shops (5.1 +/- 0.8) were statistically significant (P < 0.05). Carcasses rinsed in a stagnant system had a significantly higher (P < 0.05) prevalence (92.3%) and mean count per milliliter (3.1 +/- 0.7) for Campylobacter compared with 77.8% and 2.7 +/- 0.7 for shops that rinsed with constantly running water. The frequency of rinse water change significantly (P = 0.04) affected the prevalence of Salmonella on carcasses. It is recommended that a quality control system be introduced for these shops, particularly with respect to evisceration and rinsing practices.     

冷鲜鸡货架期微生物预测系统的构建

利用修正的Gompertz方程建立冷鲜鸡货架期动力学模型,使用皮尔森相关系数描述微生物参数与冷鲜鸡货架期准确度的相关性,利用Visual Basic语言编写形成冷鲜鸡货架期微生物预测系统,并对其进行实际样品验证。结果表明:冷鲜鸡中肠杆菌、热死环丝菌与菌落总数的腐败阙值分别为4.433,2.735,5.141lg(CFU/g);修正的Gompertz方程与平方根模型R2>0.94;肠杆菌、热死环丝菌、菌落总数的皮尔森系数分别为0.992 3(P<0.01),0.992 7(P<0.01),0.995 1(P<0.01),表明肠杆菌、菌落总数和热死环丝菌均与冷鲜鸡腐败相关,并且与菌落总数相关性最高;VB语言编写的冷鲜鸡货架期微生物预测系统软件的最大相对误差<9%,可快速获得不同贮藏温度下冷鲜鸡的货架期。     

Contribution of wine components to inactivation of food-borne pathogens

ABSTRACT:  Wine is a complex solution containing several components with several likely antimicrobial properties. Low pH (3.0 to 4.0), high organic acid content (titratable acidity ≥6.0 g/L tartaric acid), relatively high ethanol (10% to 15%), and potentially high total sulfur dioxide (0 to 300 ppm) may contribute to inactivation of food-borne pathogens when exposed to wine. The objective was to determine the effect of these 4 parameters on reducing populations of Escherichia coli ( E. coli ) O157:H7 and Staphylococcus aureus . A factorial design was used to test variables (pH, titratable acidity, sulfur dioxide, ethanol) in combinations of low, medium, and high levels. Suspension tests were performed to compare the efficacy of 81 treatments with controlled exposure time of 20 min. Staphylococcus aureus was significantly more resistant to wine treatment than E. coli O157:H7. Stepwise regression analysis of S. aureus inactivation revealed the ordered impact of pH, molecular sulfur dioxide, titratable acidity, and ethanol concentration. Selected analysis of E. coli inactivation revealed the importance of pH and ethanol in predicting inactivation. Total and free sulfur dioxide were not predictive of inactivation of either pathogen. Wine-based solutions may have application as surface disinfectants for food surfaces and food contact equipment. Wine destined to be used as a disinfectant could be enhanced by increasing any of the parameters tested in this study; however, lowering the pH would be the most effective and would likely enhance the efficacy of the other parameters. Additional wine components such as volatile acidity and phenolics were not evaluated but may also contribute to the antimicrobial properties of wine.     

冷鲜猪肉产品出水问题的初探

冷鲜肉也称冷却肉,是指严格执行检疫制度宰杀后的温热畜肉,迅速经过各种方法使其温度降至0~4℃(此温度高于肉组织的冰点而避免冻结),并在后续的分割加工、流通和零售过程中始终处于不超过7℃的冷却链控制下的生鲜肉[1].冷鲜肉的保质期一般可达7~14d.冷鲜肉以其新鲜、肉嫩、味美、营养、卫生的优点受到越来越多消费者的喜好.     

Radiation inactivation of foodborne pathogens on frozen seafood products

Foodborne illness due to consumption of contaminated seafood is, unfortunately, a regular occurrence in the United States. Ionizing (gamma) radiation can effectively inactivate microorganisms and extend the shelf life of seafood. In this study, the ability of gamma irradiation to inactivate foodborne pathogens surface inoculated onto frozen seafood (scallops, lobster meat, blue crab, swordfish, octopus, and squid) was investigated. The radiation D(10)-values (the radiation dose needed to inactivate 1 log unit of a microorganism) for Listeria monocytogenes, Staphylococcus aureus, and Salmonella inoculated onto seafood samples that were then frozen and irradiated in the frozen state (-20°C) were 0.43 to 0.66, 0.48 to 0.71, and 0.47 to 0.70 kGy, respectively. In contrast, the radiation D(10)-value for the same pathogens suspended on frozen pork were 1.26, 0.98, and 1.18 kGy for L. monocytogenes, S. aureus, and Salmonella, respectively. The radiation dose needed to inactivate these foodborne pathogens on frozen seafood is significantly lower than that for frozen meat or frozen vegetables.     

超高压对双孢蘑菇的杀菌效果和动力学的研究

以细菌总数、大肠菌群、酵母菌和霉菌数为对象,研究了超高压(High hydrostatic pressure,HHP)处理对双孢蘑菇(Agaricus bisporus)的杀菌效果和杀菌动力学。双孢蘑菇在300、400、500、600MPa压力下,室温下分别用HHP处理2.5～25min。结果表明:随压力的升高和时间的延长,杀菌效果增强;霉菌、酵母对压力较为敏感,400MPa处理2.5min可将其全部杀死;300MPa处理2.5min可完全杀灭双孢蘑菇中的大肠菌群。应用Weibull模型对不同处理条件下双孢蘑菇的杀菌效果进行拟合,拟合动力学曲线的决定系数R2均大于0.97,拟合效果较好。提出了双孢蘑菇的HHP杀菌的最优杀菌工艺参数,即600MPa处理5min,该条件即可以有效杀灭双孢蘑菇中的微生物。     

鲢鱼糜漂洗液中蛋白质分析与回收

对鲢鱼糜不同漂洗阶段的漂洗液中蛋白质含量和组成进行分析,采用调节鱼糜漂洗液pH值法和褐藻胶絮凝法对第1次漂洗液(WS-Ⅰ)中蛋白质进行回收,并对回收蛋白组成进行分析。结果表明,3次漂洗液中蛋白质含量分别为12.37 mg/mL(WS-Ⅰ),3.12 mg/mL(WS-Ⅱ),1.75mg/mL(WS-Ⅲ)。通过SDS-PAGE电泳可知,WS-Ⅰ中蛋白组分的分子量主要为20.1～97.2kDa,有少量低于20.1kDa的蛋白组分。处理pH和温度对蛋白回收率有显著影响,蛋白质的回收率在pH 5.0左右达到最高,且蛋白回收率在4～30℃范围内随温度增加而增加。采用调节pH法结合褐藻胶絮凝法可进一步提高蛋白回收效果,在pH 5.0条件下,按100mg/L添加1%褐藻胶溶液时,蛋白回收率最高,为70.25%。