The Codex Alimentarius guidelines on the application of general principles of food hygiene to the control of Listeria monocytogenes in ready-to-eat foods

This is a summary of the contents of the Codex Guidelines on the control of Listeria monocytogenes in ready-to-eat (RTE) foods and its three Annexes, including a short introduction to the Codex Alimentarius.     

Prevention of travel-related foodborne diseases: Microbiological risk assessment of food handlers and ready-to-eat foods in northern Italy airport restaurants

The focus of this study was to assess the hygienic standards of 44 foodservice facilities located in three Italian International Airports (with an output ranging from 100 to 800 meals a day), by monitoring the microbiological quality and safety of foods ready for consumption (n = 773), food contact surfaces (n = 302), and food handlers (n = 287). The hygienic standard of surfaces was sufficiently high. Only 7.9% of surfaces did not conform with advisory standards in terms of total coliforms, and 2.6% were found to be contaminated with Enterococcus spp. at ≥1.0 log₁₀ CFU/cm². The hygienic standard of washed and disinfected hands of food workers was not adequately high: the total bacterial count and coagulase positive Staphylococci exceeded the satisfactory limit in 8.4% and 3.5% of cases, respectively. The microbial analysis of foods examined showed an absence of Listeria monocytogenes and Salmonella spp. Food sample analyses highlighted a percentage of samples that did not conform to microbial reference standards: Staphylococcus aureus non-conforming percentages ranged from 2.3% for “fully cooked food” to 9.2% for “raw fruit and vegetables”; Escherichia coli, from 0.0% for “raw fruit and vegetables” to 6.1% for “cooked and uncooked foods”; total coliforms from 14.3% for “fully cooked food” to 79.8% for “cooked and uncooked food”. In conclusion, the results suggest that more effort is needed in the application of HACCP principles. In order to prevent travel-related foodborne infections, various changes in the timing of food preparation and holding temperatures are needed, together with further training of food handlers.     

A comparison between the discrete Poisson-gamma and Poisson-lognormal distributions to characterise microbial counts in foods

The choice of statistical distributions characterising microbial counts is essential in risk assessment and risk management. While the lognormal distribution has been long used to directly model the microbial data obtained from food samples, it does not allow for complete absence of microorganisms in a sample. Within a heterogeneous Poisson theoretical interpretation, a gamma or a lognormal population distribution for the unknown microbial concentration and a Poisson measurement distribution produces a discrete Poisson-gamma (λ, 1/k) or a Poisson-lognormal (μ,σ) distribution of observed plate counts. The capability of both distributions to deal with clustering was compared using six data sets of variable proportion of zero counts: total viable counts, coliforms and Escherichia coli on pre-chill and post-chill beef carcasses. Whereas the Poisson-lognormal distribution fitted better to the high counts data sets, the Poisson-gamma distribution represented the low counts data sets (13–81% zero counts) by far better than the Poisson-lognormal – which invariably tended to have a longer tail, an overestimated mean log and a lower predicted probability of zero counts. The inverse close relationship between the observed proportion of zero counts in the data set and the fitted dispersion factor 1/k suggested the possibility of obtaining a first approximation of 1/k by this means. Finally, in absence of zero counts, it was demonstrated that fitting a Poisson-lognormal to the observed plate count data can be closely approximated by the common practice of fitting a simple normal distribution to the back-calculated ‘unobserved’ mean concentrations in log CFU/g.     

The food safety impact of the Codex sampling plans for Listeria monocytogenes in ready-to-eat foods: An empirical case study applying the FAO/WHO sampling plan tool

Sampling plans are specified by the Codex Alimentarius Commission microbiological criteria for Listeria monocytogenes in ready-to-eat foods. This case study evaluates the direct food safety impact of the Codex sampling plans as estimated by the FAO/WHO web-based microbiological sampling plan analysis tool under different assumptions about the pathogen distribution, test procedures, and the fraction of lots tested. The case study uses L. monocytogenes concentration data available for deli-type salads to empirically illustrate application of the sampling tool. The results indicate that the estimated impact of the sampling plans is dependent on the partitioning of total observed variance into its within- and between-lot components. The presence-absence based sampling plan is relatively insensitive to the substantial uncertainty and variability of the sensitivity of the reference method for detection of L. monocytogenes. The analytical sample size for enumeration impacts the ability of the concentration-based sampling plan to discriminate between compliant and non-compliant lots. Reducing the frequency of lot testing dramatically changes the statistical properties of the sampling schemes. Skip-lot sampling places greater importance on compliance assurance than on the direct, curative impact of lot acceptance sampling.     

Investigation of the food value chain of ready-to-eat chicken and the associated risk for staphylococcal food poisoning in Tshwane Metropole,South Africa

The objective of the study was to better understand the informal markets for ready-to-eat (RTE) chicken in Tshwane Metropole, Gauteng Province, South Africa, and in particular the links between the formal and informal sector. As part of this, we assessed the risk of a common food poisoning (staphylococcal) through consumption of RTE chicken sold by informal vendors. We used participatory risk assessment, a novel approach to understanding food safety in data scarce environments to collect information. Structured interviews and focus group discussions with informal vendors (n = 237) were conducted to understand poultry value chains for informal RTE chicken, business operation and hygiene practices. Samples (n = 100) of RTE were collected from informal vendors in six major taxi ranks. Staphylococcus aureus counts were determined using 3M™ Petrifilm™ plates. Data collected in this present study plus information obtained from reviewing of literature, were used to develop a stochastic risk model. The number of colonies which were too numerous to count (TNTC) was artificially modeled.A mapping of the informal food value chain revealed that there are four possible value chains and that chicken spilled over from formal to informal markets. The prevalence of S. aureus in RTE chicken samples (44%; 90% CI: 36.1%–52.2%) was high. The mean S. aureus counts in the ready to eat chicken was 10^3.6 (90%CI: 10^3.3–10^3.9), and the risk of purchasing chicken of unsatisfactory quality (>10³ cfu/g) was 32.9% (90%CI: 25.5%–40.4%). The probability of food poisoning due to consumption of RTE chicken contaminated with staphylococcal enterotoxin was estimated to be 1.3% (90% CI: 0%–2.7%). Sensitivity analysis showed that the probability of S. aureus having the enterotoxin gene was the most sensitive parameter for food poisoning. This was followed by S. aureus concentration in RTE chicken and lastly the prevalence of S. aureus in ready-to-eat chicken.This study demonstrates the existence of a strong link between formal and the informal market. In view of the low risk observed, the relevant authorities in Tshwane should continue to support the informal sale of RTE chicken. However, there is still a need for provision of hygiene training to reduce the concentration levels of S. aureus on the RTE chicken, and to promote the sale of safer affordable source of protein for the large urban poor population in South Africa. This will also help secure the opportunities for employment associated with the trade.     

Temperature increase of foods in car trunk and the potential hazard for microbial growth

This study assessed the potential microbial hazard posed by temperature increases on refrigerated and frozen food stored in car trunk exposed to sunlight. The internal temperatures in the trunk and of food items (egg, milk, tofu, fresh meat, and frozen meat) stored in it during summer were measured at 10 min intervals for up to 3 h (12:00 PM to 15:00 PM). Trunk temperature steadily increased from 32.3 °C up to 41.5 °C, with longer exposure times. Food temperature also increased substantially during this period, reaching 33.5 °C (frozen meat), 35.3 °C (milk), 35.6 °C (tofu), 37.0 °C (egg), and 38.4 °C (fresh meat). Cloud cover and solar radiation affected car and food temperature, with lower cover and higher radiation associated with higher food temperatures (7.1 °C higher in the car trunk when compared to a situation of extensive cloud cover and low radiation, and 6.9 °C higher for eggs, 5.9 °C for milk, 5.0 °C for tofu, and 7.4 °C and 5.5 °C for fresh and frozen meat, respectively). The temperature of refrigerated foods (egg, milk, and fresh meat) reached 20 °C within 40 min (tofu: 60 min) and 30 °C within 90–110 min (tofu: 130 min). The temperature of frozen meat reached to danger zone (5–60 °C), which is associated with bacterial growth, after 90 min. Consumers should therefore realize the importance of time–temperature control, particularly in warm and sunny weather. Purchased foods should be transferred to a refrigerated environment as fast as possible, and the car trunk should be avoided. The present results can be used for consumer education, contributing to the recognition of the importance of food safety.     

Effect of pH on the effectiveness of whey protein/glycerol edible films containing potassium sorbate to control non-O157 shiga toxin-producing Escherichia coli in ready-to-eat foods

Potassium sorbate (PS) (0.5%, 1.0% and 1.5% w/w) was included into whey protein concentrate (WPC)/glycerol (Gly) edible films at pH 5.2 and 6.0. The films inhibited or retarded the growth of Shiga toxin-producing Escherichia coli (STEC) pathogens in both diffusion and barrier tests. Bacterial growth inhibition was dependent on PS content at both pH values. PS release was not affected by pH. Scanning electron microscopy (SEM) was used to analyze the microstructure of the films and gain a better understanding of their optical parameters. Acidic control films (pH 5.2) prepared without PS were the least transparent. SEM micrographs confirmed the greater structural heterogeneity of these films, coinciding with opacity. The incorporation of PS into WPC/Gly films improved transparency and produced a smoother surface than acidic control ones. The utilization of active packaging based on whey proteins and organic acids to control and prevent the dissemination of STEC pathogens may be an effective, safe, ecological and relatively inexpensive alternative to be used in the food packaging industry.     

Advances with intelligent on-line retort control and automation in thermal processing of canned foods

This paper presents a review of recent developments over the past 10 years that have further advanced the state of the art in improving food safety, quality and manufacturing efficiency in the canned food industry worldwide. The review focuses initially on retort control systems, and the various approaches that have been taken to help canned food processors accomplish on-line correction of unexpected process deviations, the major cause of lost productivity. Important features of each approach are discussed, along with suggested industry applications that would be appropriate for each method. The review also describes recent advances in industrial automation, including new retort systems for flexible and semi-rigid retortable packages, and automated materials handling systems for loading and unloading of batch retorts. The review concludes with a discussion of future trends to be expected in the industry.     

Emergency food control assistance for the prevention and control of cholera in Latin America

The cholera epidemic, which first struck Peru in early 1991, spread to several countries in the region causing serious public health problems and affecting the food production sector, food consumption and exports. This paper summarizes the technical assistance provided by FAO to attempt to stem the spread of the epidemic.     

生物聚合物深部调剖技术室内及矿场应用研究

为了探讨老油田高含水后期生物聚合物深部调剖的可行性,将代谢产出生物聚合物的菌种及其营养液连续注入地层,封堵裂缝及大孔道,扩大注水波及体积。对菌种及其代谢产出生物聚合物特性进行了研究,分析了岩心注入能力、聚合物产出能力及封堵调剖机理。通过油井堵水、水井深部调剖矿场试验的跟踪监测和动态分析,确定了生物聚合物深部调剖效果的主要影响因素。室内物理模拟驱油试验结果表明,这种方法能提高原油采收率9%,矿场油井堵水增油647t。对注水井深部调剖后,周围油井含水率下降7.7%～64%,有效期达12～20个月。生物聚合物深部调剖设备简单,施工简便,有效期长,成本低,具有良好应用前景。     

Improving the control of food production in catering establishments with particular reference to the safety of salads

Food production in four school kitchens was checked in order to improve food safety by establishing a self-regulated control system based on good manufacturing practices (GMPs) and as an introduction to hazard analysis and critical control points (HACCP). A form, which referred to different aspects such as the cleanliness of the installations, personnel hygiene and the prevention of cross-contamination, was used to obtain the necessary data. Furthermore, foods thought to be of high risk were periodically collected for microbiological analysis. Samples for microbiological examination were taken from cutting boards, tables, machines, knives and ingredients (on-line sampling). We used the results as a basis to train foodhandlers to improve the safety of salad preparation, in accordance with GMPs, observing that hygiene improvement depended on chlorine levels in the rinsing water. We also designed several controls for raw materials, cold storage, freezers and available chlorine levels in water. At the end of the study period, we observed a decrease in microbial populations of examined samples, which indicated that the knowledge of hygiene practices on the part of foodhandlers represents a critical control point, as defined by the EC Directive 93/43/EEC on Hygiene of Food Stuffs.     

Effectiveness of two sanitation procedures for decreasing the microbial contamination levels (including Listeria monocytogenes) on food contact and non-food contact surfaces in a dessert-processing factory

The aim of this study was to determine the presence and persistence of Listeria monocytogenes (LM) after using two sanitization protocols in different parts of a dessert-processing factory. The sampling for LM detection was performed: a) on various food contact and non-food surfaces; b) after and before treatment using two different sanitization protocols. LM was not detected on food contact surfaces while its identification was restricted to non-food contact surfaces (mostly the floor). Both sanitizing protocols managed to reduce the LM load (as well for the rest of the microbial parameter studied) but not to eradicate the microorganism completely.     

An assessment of the value of documenting food safety in small and less developed catering businesses

Current legislation requires food businesses to identify and control food hazards by focussing on critical factors which directly affect the safety of food. This study, commissioned by the Food Standards Agency (FSA) compares the standards of food hygiene in seventy food premises operating either documented or undocumented hazard analysis systems within the Derby City Council boundary.Food hygiene standards were evaluated from purchase of foodstuffs to service of meals to customers. Scores were awarded for the implementation of controls integral to hazard analysis, based on epidemiological data. The only stages in production where a significant difference in standards existed was during preparation and cooking. That is, the standards of hygiene were better during preparation and cooking in those premises with documented hazard analysis systems compared to those operating undocumented systems. The findings highlight problems associated with ineffective monitoring of temperatures, particularly at cooking and cross contamination resulting from poor cleaning practices.The study has important implications for future development of hygiene legislation, particularly if Government is committed to require 30% of UK food businesses to implement full HACCP by April 2004.     

Recent Experiences with Listeria monocytogenes in New Zealand and development of a food control risk-based strategy

A risk-based strategy for Listeria monocytogenes has been developed by New Zealand Food Safety Authority. Incidents of L. monocytogenes in ready-to-eat foods reported to the regulatory authority were analysed to identify common factors that contributed to the contamination. In addition, the current regulatory framework and available food industry guidance were reviewed to prepare a strategy that will provide a consistent and informed approach to managing the risk of L. monocytogenes. Also recognised is the future impact of an aging population and an increase in the availability and range of chilled ready-to-eat foods that should be integrated into the strategy if an objective of ‘no increase in the reported incidence of foodborne listeriosis after five years’ is to be achieved.     

Restaurant business operators' knowledge of food hygiene and their attitudes toward official food control affect the hygiene in their restaurants

We surveyed the knowledge and attitudes of restaurant business operators (RBOs) with respect to their restaurants' hygiene. A total of 82 RBOs were interviewed and a hygiene evaluation was performed in each of the restaurants by one researcher. Fifty-six food control officials responded to an electronic questionnaire. Based on our results, positive correlations exist between hygiene knowledge of the RBOs, their attitudes toward food hygiene and official food control, and their restaurants' hygiene level. Proper justification of control measures used by food control officials and a negotiative approach appear to be highly important for improving restaurant hygiene.     

兴城地区火山岩储层孔洞裂缝发育与产能关系研究

对油气储层的产能进行定性或定量评价一直是勘探开发的一项基本任务。针对徐深气田兴城地区火山岩储层类型多样,孔隙结构复杂,储层非均质性强的特点,在对研究区火山岩储层地质及试气资料分析的基础上,应用常规和成像测井资料,论述了总孔隙度、次生孔隙度、次生发育厚度、孔洞裂缝发育程度等参数与产能的关系。并利用上述参数建立了火山岩储层产能评价标准。在实际应用中取得了比较满意的效果,对今后天然气火山岩储层的产能预测和气田开发部署具有较高的参考价值。     

纵波特性与岩石含水饱和度关系的实验研究

岩石中的纵波首波幅度和速度的变化不仅与岩性、孔隙度、渗透率等因素有关，而且与岩石孔隙中的流体类型及其饱和条件有着非常密切的关系。本文在实验室超声条件下，就取心样品含水饱和度与纵波首波幅度、速度的关系进行了实验研究和机理分析，结果表明它们之间存在非线性关系。     

小气顶低幅构造强底水油藏剩余油分布主控因素

曹妃甸油田群河流相底水油藏是渤海海域已开发的一类重要油藏类型,采用不规则水平井井网开发,目前大多数油藏已进入中、高含水阶段,但采收率偏低,亟需理清剩余油分布规律和主控因素,指导油田下步综合调整。曹妃甸油田群新近系馆Ⅲ油组下段储量大、开发井多,是一个已进入高含水开发期的小气顶低幅构造强底水油藏。通过静态地质资料和动态生产资料相结合,认为微构造形态和小断距断层等构造因素、河漫滩成因夹层、油水界面差异、油田早期开发理念、目前开发井网等5大因素控制了研究区剩余油分布。在以第2期夹层为界的上、下开发层系中,剩余油分布具有一定规律性。上开发层系剩余油主要分布在油环井网不完善区域,下开发层系剩余油主要分布在油藏西部的油水界面较低及井网不完善区域、中部的水平生产井和气油界面之间、第4期主力夹层下部构造高部位以及距开发井较远的断层附近。     

塔里木盆地塔中-巴楚地区侵入体温度场演化特征及其与油气储层的关系

通过对塔中-巴楚地区奥陶系钻遇侵入体的岩石学、地球化学分析以及数值模拟等的详细研究,探讨了其热效应及对碳酸盐岩储层发育的影响。研究发现,塔中-巴楚地区碳酸盐岩中的层状侵入体为紫苏辉长岩和辉绿岩,紫苏辉长岩主要矿物有拉长石和紫苏辉石,副矿物有磷灰石等,辉绿岩主要矿物组合以单斜辉石和基性斜长石为主。地球化学分析表明,辉长岩的SiO₂含量介于44.58%～45.39%,K₂O+Na₂O含量为3.91%～4.67%,Na₂O/K₂O含量比为2.16～4.23,属碱性系列;稀土元素配分模式属轻稀土元素富集型,LaN/YbN比值为5.010～5.980,铕异常参数δEu值为0.910～1.002,Eu负异常很弱甚至没有Eu异常。塔中-巴楚地区层状侵入体热能传输理论模型与计算表明,层状侵入体温度的影响范围是有限的,侵入体对碳酸盐岩储层的热影响范围与其厚度密切相关,厚度越大影响范围越大。