Performance characteristics and estimation of measurement uncertainty of three plating procedures for Campylobacter enumeration in chicken meat

In this work, we present an intra-laboratory study in order to estimate repeatability (r), reproducibility (R), and measurement uncertainty (U) associated with three media for Campylobacter enumeration, named, modified charcoal cefoperazone deoxycholate agar (mCCDA); Karmali agar; and CampyFood ID agar (CFA) a medium by Biomérieux SA. The study was performed at three levels: (1) pure bacterial cultures, using three Campylobacter strains; (2) artificially contaminated samples from three chicken meat matrixes (total n=30), whereby samples were spiked using two contamination levels; ca. 10(3)cfuCampylobacter/g, and ca. 10(4)cfuCampylobacter/g; and (3) pilot testing in naturally contaminated chicken meat samples (n=20). Results from pure culture experiment revealed that enumeration of Campylobacter colonies on Karmali and CFA media was more convenient in comparison with mCCDA using spread and spiral plating techniques. Based on artificially contaminated samples testing, values of repeatability (r) were comparable between the three media, and estimated as 0.15log(10)cfu/g for mCCDA, 0.14log(10)cfu/g for Karmali, and 0.18log(10)cfu/g for CFA. As well, reproducibility performance of the three plating media was comparable. General R values which can be used when testing chicken meat samples are; 0.28log(10), 0.32log(10), and 0.25log(10) for plating on mCCDA, Karmali agar, and CFA, respectively. Measurement uncertainty associated with mCCDA, Karmali agar, and CFA using spread plating, for combination of all meat matrixes, were +/-0.24log(10)cfu/g, +/-0.28log(10)cfu/g, and +/-0.22log(10)cfu/g, respectively. Higher uncertainty was associated with Karmali agar for Campylobacter enumeration in artificially inoculated minced meat (+/-0.48log(10)cfu/g). The general performance of CFA medium was comparable with mCCDA performance at the level of artificially contaminated samples. However, when tested at naturally contaminated samples, non-Campylobacter colonies gave similar deep red colour as that given by the typical Campylobacter growth on CFA. Such colonies were not easily distinguishable by naked eye. In general, the overall reproducibility, repeatability, and measurement uncertainty estimated by our study indicate that there are no major problems with the precision of the International Organization for Standardization (ISO) 10272-2:2006 protocol for Campylobacter enumeration using mCCDA medium.     

The contribution of sampling uncertainty to total measurement uncertainty in the enumeration of microorganisms in foods

Random samples of each of several food products were obtained from defined lots during processing or from retail outlets. The foods included raw milk (sampled on farm and from a bulk-milk tanker), sprouted seeds, raw minced meat, frozen de-shelled raw prawns, neck-flaps from raw chicken carcasses and ready-to-eat sandwiches. Duplicate sub-samples, generally of 100 g, were examined for aerobic colony counts; some were examined also for counts of presumptive Enterobacteriaceae and campylobacters. After log(10)-transformation, all sets of colony count data were evaluated for conformity with the normal distribution (ND) and analysed by standard ANOVA and a robust ANOVA to determine the relative contributions of the variance between and within samples to the overall variance. Sampling variance accounted for >50% of the reproducibility variance for the majority of foods examined; in many cases it exceeded 85%. We also used an iterative procedure of re-sampling without replacement to determine the effects of sample size (i.e. the number of samples) on the precision of the estimate of variance for one of the larger data sets. The variance of the repeatability and reproducibility variances depended on the number of replicate samples tested (n) in a manner that was characteristic of the underlying distribution. The results are discussed in relation to the use of measurement uncertainty in assessing compliance of results with microbiological criteria for foods.     

Sampling methods for microbiological analysis of red meat and poultry carcasses

Microbiological analysis of carcasses at slaughterhouses is required in the European Union for evaluating the hygienic performance of carcass production processes as required for effective hazard analysis critical control point implementation. The European Union microbial performance standards refer exclusively to the excision method, even though swabbing using the wet/dry technique is also permitted when correlation between both destructive and nondestructive methods can be established. For practical and economic reasons, the swab technique is the most extensively used carcass surface-sampling method. The main characteristics, advantages, and limitations of the common excision and swabbing methods are described here.     

On-line measurements in pig carcass classification: Repeatability and variation caused by the operator and the copy of instrument

For nearly all pigs slaughtered in the EU, the lean meat content is assessed on-line at the slaughter line. The assessment is made indirectly by an instrument performing a number of informative measurements including the thickness of back fat as one of the most important and common measurements. Several types of instruments are used for making the measurements. The quality of the calibration (the prediction ability) has to be approved by the EU Commission. However, the maintenance of instruments, training of operators, working conditions and other factors influencing the routine are quite as important for the accuracy as the calibration. As a part of an EU funded project, partners representing thirteen European countries have investigated the instruments used in their countries focusing on the precision of indirect measurements. The preconditions have differed considerably between the countries resulting in a wide range of estimates of the repeatability and the reproducibility (precision) of fat and muscle thickness. Totally, there have been three different types of manual instruments - invasive probe instruments from three manufacturers, non-invasive ultrasound and callipers. Furthermore, the precision of two automatic instruments with respect to lean meat content has partly been estimated. Even though neither the aim nor the design of the experiments was set for a direct comparison between different instruments, none of them seemed to deviate notably from the others with respect to the precision of fat thickness. In this study, the only investigated influencing factors were the variations in operators and copies of instruments. Generally, the variations between operators were more important than the variation between copies of the same type of instrument.     

分光光度法测定白砂糖中淀粉含量的重复性和再现性研究

测定白砂糖中的微量淀粉是对白砂糖质量控制,进而是对澄清饮料絮凝问题进行控制的手段之一。本研究采用分光光度计在580nm处测定“淀粉-碘复合物”含量的方法来对白砂糖中微量淀粉进行测定,并用标准加入法验证了方法的准确性,回收率在97％以上,变异系数小于0．02。同时研究了该法的重复性和再现性,采用8个白砂糖样品在4个不同实验室的不同仪器上进行测定,采用柯克伦检验和格拉布斯检验对数据的有效性进行检验,并利用测量系统分析（Measurement Systems Analysis,MSA）对方法进行评价。结果表明,该法测定的准确性高,重复性及再现性均符合要求．可作为内部白砂糖原料验收的检测方法及澄清饮料絮状沉淀控制的验证方法之一。     

微生物法测定乳粉中叶酸的不确定度评定

目的 评定微生物法测定乳粉中叶酸的不确定度.方法 按照GB 5009.211—2014《食品安全国家标准食品中叶酸的测定》规定的微生物法对婴儿配方乳粉中叶酸含量进行测定,根据CNAS-CL01-G003:2019要求,依据GB/Z 22553—2010和JJF 1059.1—2012,分析测定过程中影响检验结果的因素主...     

Direct determination of the total fat content of butter and edible oil emulsions — an international collaborative study

A standard operating procedure for the direct determination of fat in butter and edible oil products involved the extraction of the fat from the sample, separation of the solvent–fat phase from the serum phase and transfer of the solvent–fat phase to a fat-collecting vessel. The solvent was removed by distillation or evaporation and the mass of extracted matter was determined gravimetrically. This method was studied collaboratively involving 13 laboratories and eight samples to determine precision estimates. Estimates of repeatability and reproducibility were 0.23 g per 100 g and 0.45 g per 100 g, respectively. The method is recommended for adoption as an international reference method.     

A procedural approach for the identification of sources of uncertainty associated with GM quantification and real-time quantitative PCR measurements

Estimation of measurement uncertainty is important as it provides objective evidence that an assay or instrument is ‘fit for purpose’, and is a requirement for accreditation to ISO17025. Technological developments within the bioanalytical laboratory have progressed rapidly in the past few years. However, the measurement science associated with these technologies has not yet fully matured. The provision of a full measurement uncertainty budget is often difficult because of a lack of standardised approaches and the constraints associated with time, finances and expertise. A procedural approach for the identification of factors that can account for measurement uncertainty in quantification of genetically modified (GM) ingredients using real-time quantitative PCR is presented here. This example illustrates an approach for the identification of factors that can be applied to related assays concerned with GM quantification, can be utilised as part of existing uncertainty approaches, and can provide the basis for making quantitative estimates of uncertainty that will contribute towards a full measurement uncertainty budget.     

卫生纸柔软度的测定及不确定度评估

探讨了在质检过程中卫生卷纸试样的尺寸大小与柔软度测定结果的比例对应关系,并进行柔软度测量过程中的不确定度评定。     

Effects of preparation methods on the microbiological safety of home-dried meat jerky

Historically, drying meats to produce jerky was conisidered to be a safe preservation process and the convenience and flavor of jerky has made it a popular food product for home food preservers. Recent outbreaks of foodborne illness related to both home-dried and commercially manufactured jerky have raised concerns about the safety of the product. Some traditional home recipes and drying processes were shown to be inadequate to destroy Escherichia coli O157, Salmonella, Staphylococcus aureus, and Listeria monocytogenes in both whole-muscle and ground-meat jerky. Several research studies have identified processes such as precooking meats before drying, usingacidic marinades, cooking meats after drying, or some combination of these treatments that can destroy pathogens of concern to produce microbiologically safe and palatable meat jerky at home.     

分光光度法测定肉制品中亚硝酸盐含量的不确定度评定

目的 对分光光度法测定肉制品中亚硝酸盐含量的不确定度进行评定。方法 通过建立不确定度评定数学模型, 分析并计算各不确定度分量, 从而得出合成不确定度和扩展不确定度。结果 肉制品中亚硝酸盐含量6.01 mg/kg, 扩展不确定度为0.25 mg/kg (95%, k=2)。结果表明, 用分光光度法测定肉制品中亚硝酸盐时, 其测量不确定度主要来源于标准曲线制备过程, 特别是标准曲线系列显色定容过程, 而样品称量和样液样液定容引入的不确定度可以忽略不计。结论 该评定方法可为分光光度法测定肉制品中亚硝酸盐含量的测量不确定度评定提供参考。     

不同计算方法评定大麦中水分含量测定不确定度研究

用不同计算方法进行大麦中水分含量测量不确定度的评定并进行比较。分析了整个检测实验过程产生的不确定度,给出扩展不确定度以及最终结果表示11.04%±0.39%(k=2)。并且分析了产生不确定度的主要来源,为有效地控制大麦中水分含量测量的质量提供了理论依据。      

A comparison of wet-dry swabbing and excision sampling methods for microbiological testing of bovine, porcine, and ovine carcasses at red meat slaughterhouses

A comparison of wet-dry swabbing and surface tissue excision of carcasses by coring was undertaken. Samples from 1,352 bovine, 188 ovine, and 176 porcine carcasses were collected from 70 separate visits to commercial slaughterhouses operating under normal conditions. The mean total aerobic viable bacterial counts (TVCs) for all species sampled by excision was 5.36 log units, which was significantly greater than the 4.35 log units measured for swabbing. Poorly correlated linear relationships between swab- and excision-derived bacterial numbers from near-adjacent carcasses were observed for all three animal species. R2 values for least squares regressions for bovine, ovine, and porcine carcasses were 0.09, 0.27, and 0.21, respectively. The reasons why it was not possible to calculate a factor that allowed the interconversion of bacterial numbers between samples collected by each sampling method were investigated. Uncertainty associated with laboratory analyses was a contributing factor because the geometric relative standard deviations measured for TVCs were 0.174 and 0.414 for excision and swabbing, respectively. Uneven distribution of bacteria at identical sampling sites on near-adjacent carcasses on processing lines was also a contributory factor. The implications of these findings for process control verification were investigated by intensive sampling for 13 weeks in three commercial slaughterhouses. As many as 4 log units of difference in TVCs were observed in duplicate samples collected within a narrow timeframe from near-adjacent carcasses on the processing line. We conclude that it might not be appropriate to institute corrective actions in slaughterhouses on the basis of a single week's test results.     

A risk microbiological profile of the Australian red meat industry: risk ratings of hazard-product pairings

A risk profile of microbial hazards across the supply continuum for the beef, sheep and goat meat industries was developed using both a qualitative tool and a semi-quantitative, spreadsheet tool, Risk Ranger. The latter is useful for highlighting factors contributing to food safety risk and for ranking the risk of various product/pathogen combinations. In the present profile the qualitative tool was used as a preliminary screen for a wide range of hazard-product pairings while Risk Ranger was used to rank in order of population health risk pairings for which quantitative data were available and for assessing the effect of hypothetical scenarios. 'High' risk hazard-product pairings identified were meals contaminated with Clostridium perfringens provided by caterers which have not implemented HACCP; kebabs cross-contaminated by Salmonella present in drip trays or served undercooked; meals served in the home cross-contaminated with Salmonella. 'Medium' risk hazard-product pairings identified were ready-to-eat meats contaminated with Listeria monocytogenes and which have extended shelf life; Uncooked Comminuted Fermented Meat (UCFM)/Salami contaminated with Enterohaemorrhagic E. coli (EHEC) and Salmonella; undercooked hamburgers contaminated with EHEC; kebabs contaminated by Salmonella under normal production or following final "flash" heating. Identified 'low' risk hazard-product pairings included cooked, ready-to-eat sausages contaminated with Salmonella; UCFM/Salami contaminated with L. monocytogenes; well-cooked hamburgers contaminated with EHEC. The risk profile provides information of value to Australia's risk managers in the regulatory, processing and R&D sectors of the meat and meat processing industry for the purposes of identifying food safety risks in the industry and for prioritising risk management actions.     

The bacterial quality of red meat and offal in Casablanca (Morocco)

The present study aimed to evaluate the bacteriological quality of beef (n = 52), lamb (n = 52) and beef offal (n = 52) marketed in Casablanca, Morocco. Meat and offal samples (n = 156), were collected randomly from butcheries, supermarkets, and slaughterhouses. Two sampling periods were considered, one during the hot season and the second one during the cold season. The samples were analyzed for the presence of the following bacteria: Escherichia coli, coagulase-positive Staphylococcus, Clostridium perfringens, Salmonella, and Listeria monocytogenes. Results indicated that counts of the aerobic plate count, and fecal coliforms were particularly high in all the samples analyzed. E. coli, coagulase-positive Staphylococcus and C. perfringens were detected in 37.8, 16, and 4.5% of the meat samples, respectively. Neither Salmonella nor L. monocytogenes were isolated from meat samples. Approximately 26.9% of beef, 34.6% of lamb and 28.8% of beef offal samples contained bacteria above the maximum limits established by the Moroccan regulatory standards for meat and meat products. Seasonality and the distribution location significantly (p < 0.05) affected bacterial populations: the hot season and butcheries appeared to be cases where the highest populations of bacteria in meat were observed. These high levels of microbiological contamination attest the poor hygienic quality of meat and offal, possibly due to uncontrolled processing, storage, and handling of these products.     

UPLC-MS/MS法检测肉制品中克伦特罗残留量的不确定度评定

建立了UPLC-MS/MS法检测肉制品中克伦特罗残留量的不确定度评定方法,分析了肉制品中克伦特罗残留量的测定过程中供试品重复性测量、标准曲线拟合残差、标准品溶液的配制、供试品溶液的配制、分析仪器等因素对测定的不确定度的影响。结果表明,按照JJF1059-1999《测量不确定度评定与表示》对各不确定度分量合成和扩展,当置信概率为95%,包含因子k=2,其扩展相对不确定度为16.08%。通过对不确定度的分析,发现标准曲线拟合残差是不确定度的主要来源,并由此提出了质量控制改进方法。该研究对于肉制品中克伦特罗残留量测量的不确定度标准制定具有一定的示范意义。      

电感耦合等离子体质谱法测定肉制品中总砷的不确定度评定

目的评定电感耦合等离子体质谱法(inductively coupled plasma mass spectrometry,ICP-MS)测定肉制品中总砷含量的不确定度。方法依据CNAS-GL06:2006《化学分析中不确定度的评估指南》和JJF1135-2005《化学分析测量不确定度评定》,通过建立不确定度数学模型,采用微波消解-ICP-MS测定肉制品中的总砷含量,分析该方法测量不确定度的主要来源,并评定各标准不确定度的分量。结果在肉制品的总砷含量测定中,当样品的总砷含量为0.120 mg/kg,其扩展不确定度为0.008 mg/kg(k=2),结果表示为(0.120±0.008)mg/kg。结论用ICP-MS进行测量时,主要不确定度来源于样品的重复性测定、标准物质及配制、标准曲线拟合,通过降低可控不确定度来提高测量结果的准确度,该质量控制手段可用于合理地体现测定结果的可靠程度。     

Rapid dye reduction tests for the determination of microbiological quality of meat

Rapid dye reduction tests have been developed to determine the quality of meat. Three chemical indicators, resazurin and two tetrazolium compounds, were used to correlate the microbial numbers and reduction times in meat samples. Twenty-five surface samples from sheep carcasses were subjected to each reduction test. Total viable counts given were obtained at 37°C. Resazurin reduction time was 90–120 min when the bacterial counts ranged from 1.5×10⁶ to 7.7×10⁶/cm². Samples showing bacterial counts between 1.5×10⁶ and 6.0×10⁶/cm² reduced tetrazolium (NBT) in 360–390 min whereas samples containing bacterial counts of 2.1×10⁶/cm² took 420–450 min to reduce iodophenyl nitrophenyl tetrazolium (INT) dye. Regression equations relating the number of organisms per cm² and reduction time were applied to predict the microbiological quality of meat samples from reduction time data. Among the three dyes, resazurin gave the lowest reduction time.     

食品微生物检验样品的采集和制备

通过对样品采集和制备的介绍,保证所检样品的代表性和一致性,提高对整批产品的判定结果的准确率.     

A microbiological screening method for the indication of irradiation of frozen poultry meat

A microbiological screening method for the detection of irradiation of frozen poultry meat was developed on the basis of the combined use of total cell count by the direct epifluorescent filter technique (DEFT) and viable cell count by the aerobic plate count method (APC). Samples of ground, deboned poultry leg were irradiated or not with dose levels of 3, 5 and 7 kGy using an electron beam accelerator. All samples were frozen before the irradiation treatment. The average values of the differences between DEFT and APC counts in control samples and those irradiated with doses of 3, 5 and 7 kGy were 1.14 log units for control samples, and 3.16, 3.68 and 3.79 log units for the irradiated samples. A difference of at least 2 log units can therefore be considered as a limit value indicating probable irradiation treatment necessitating further investigations.

---

Anwendung eines mikrobiologischen Unterscheidungsverfahrens zum Nachweis der Bestrahlung von gefrorenem Hühnerfleisch

Zusammenfassung Es wurde ein mikrobiologisches Verfahren zum Nachweis der Bestrahlung von tiefgefrorenem Hühnerfleisch auf der Basis kombinierten Einsatzes direkter Epifluoreszenzfiltertechnik (DEFT) und Kolonieauszählung (APC) entwickelt. Die Proben - knochenfreie, zerkleinerte Hühnerschenkel - waren entweder unbestrahlt oder mit einem Elektronenbeschleuninger mit Dosen von 3, 5 bzw. 7 kGy bestrahlt worden. Alle Proben waren vor der Bestrahlung eingefroren worden. Die Mittelwerte der Differenzen zwischen den DEFT- und den APC-Ergebnissen betrugen bei den unbestrahlten Proben 1,14 logarithmische Einheiten und bei den mit 3, 5 bzw. 7 kGy bestrahlten Proben 3,16, 3,68 bzw. 3,79 logarithmische Einheiten. Die Differenz von wenigstens zwei logarithmischen Einheiten kann als Grenze für die Möglichkeit eines Nachweises eventueller Bestrahlung betrachtet werden und macht weitere Untersuchungen erforderlich.