Assessment of measurement uncertainty for quantitative methods of analysis: comparative assessment of the precision (uncertainty) of bacterial colony counts

An interlaboratory trial was made, by three analysts in each of the 19 laboratories, of three International Standards Organisation (ISO) colony count methods for aerobic organisms (ACC), Enterobacteriaceae (ECC) and Escherichia coli (EcCC). All tests were done in duplicate and were further replicated by plating both on culture media supplied by the organisers and on each laboratory's own choice of culture media. In order to avoid any influence of food matrix on the results, the inoculum for each test was a freeze-dried ampoule of a standardised mixed culture. After collation of test results, individual data sets were examined for obvious non-consistency, and colony counts for each individual test were determined both as simple and 'weighted' mean values. The derived colony counts were then log(10)-transformed and examined statistically. Estimates of repeatability and reproducibility for each set of results were derived and used to calculate the parameters for the uncertainty of measurement. Estimated values of the uncertainty of reproducibility and repeatability for the ACC ranged, respectively, from 9.3 to 12.1% and 2.0 to 3.9% of the mean log(10) colony count, depending on the specific culture media, the method of deriving the mean count and the statistical procedure employed. Similarly, estimates of the uncertainty of reproducibility and repeatability for the ECC ranged, respectively, from 14.0 to 17.4% and 4.1 to 6.7%. The estimates of uncertainty of reproducibility and repeatability for the EcCC data ranged, respectively, from 21.1 to 30.9% and 6.7 to 15.4%. Whilst the uncertainty estimates for the ACC data conform to long-held views on the repeatability and reproducibility of microbial count data, the estimates for the ECC and EcCC are considerably greater. It was notable that no benefits were seen in the use of the weighted mean as compared to simple mean colony count. The importance of uncertainty estimates of colony count data in the assessment of the microbiological quality of foods is discussed.     

Alkaloids in food: a review of toxicity,analytical methods,occurrence and risk assessments

Food Science and Biotechnology - Alkaloids have been utilized by humans for years. They have diverse applications in pharmaceuticals. They have been proven to be effective in treating a number of...     

气相色谱法检测食品中的抗氧化剂BHA、BHT和TBHQ及不确定度评定

建立了运用气相色谱法同时测定食品中抗氧化剂丁基羟基茴香醚(BHA)、二丁基羟基对甲酚(BHT)和特丁基对苯二酚(TBHQ)含量的方法,对该方法的线性范围、检出限、精密度、回收率等指标进行了考察。结果表明,该方法能准确检测食品中的抗氧化剂含量。同时建立了食品中BHA含量不确定度的评定方法,分析了不确定度的来源,建立评估的数学模型,计算出不确定度的各主要分量。结果表明,影响检测结果不确定度的主要因素为样品的回收率。     

食品中硝基呋喃类药物及其代谢物残留检测技术的研究进展

硝基呋喃类药物及其代谢产物因具有强毒性和致癌副作用, 已引起了国际社会的高度重视。本文综述了该类药物及其代谢物在食品中残留的检测方法的最新研究进展, 分析了硝基呋喃类药物及其代谢物残留各检测方法的优缺点, 并对该类药物检测方法进行了展望。     

Comparison study of validation parameters and measurement uncertainty of rapid analytical methods for piperine in black pepper by ultraviolet spectroscopy and high-performance liquid chromatography

Food Science and Biotechnology - Piperine, one of the main constituents of black pepper, is an important marker of black pepper quality because of its bio-activity and characteristic flavour....     

Hyperspectral imaging and machine learning in food microbiology: Developments and challenges in detection of bacterial,fungal, and viral contaminants

Hyperspectral imaging (HSI) is a robust and nondestructive method that can detect foreign particles such as microbial, chemical, and physical contamination in food. This review summarizes the work done in the last two decades in this field with a highlight on challenges, risks, and research gaps. Considering the challenges of using HSI on complex matrices like food (e.g., the confounding and masking effects of background signals), application of machine learning and modeling approaches that have been successful in achieving better accuracy as well as increasing the detection limit have also been discussed here. Foodborne microbial contaminants such as bacteria, fungi, viruses, yeast, and protozoa are of interest and concern to food manufacturers due to the potential risk of either food poisoning or food spoilage. Detection of these contaminants using fast and efficient methods would not only prevent outbreaks and recalls but will also increase consumer acceptance and demand for shelf-stable food products. The conventional culture-based methods for microbial detection are time and labor-intensive, whereas hyperspectral imaging (HSI) is robust, nondestructive with minimum sample preparation, and has gained significant attention due to its rapid approach to detection of microbial contaminants. This review is a comprehensive summary of the detection of bacterial, viral, and fungal contaminants in food with detailed emphasis on the specific modeling and datamining approaches used to overcome the specific challenges associated with background and data complexity.     

Onion cells after high pressure and thermal processing: comparison of membrane integrity changes using different analytical methods and impact on tissue texture

Two different analytical methods were evaluated for their capacity to provide quantitative information on onion cell membrane permeability and integrity after high pressure and thermal processing and to study the impact of these processing treatments on cell compartmentalization and texture quality. To determine changes in cell membrane permeability and/or integrity the methodologies utilized were: (1) measurement of a biochemical product, pyruvate, formed as a result of membrane permeabilization followed by enzymatic activity and (2) leakage of electrolytes into solution. These results were compared to previously determined methods that quantified cell viability and 1H-NMR T(2) of onions. These methods allowed for the monitoring of changes in the plasma and tonoplast membranes after high pressure or thermal processing. High pressure treatments consisted of 5 min holding times at 50, 100, 200, 300, or 600 MPa. Thermal treatments consisted of 30 min water bath exposure to 40, 50, 60, 70, or 90 °C. There was strong agreement between the methods in the determination of the ranges of high pressure and temperature that induce changes in the integrity of the plasma and tonoplast membranes. Membrane rupture could clearly be identified at 300 MPa and above in high pressure treatments and at 60 °C and above in the thermal treatments. Membrane destabilization effects could already be visualized following the 200 MPa and 50 °C treatments. The texture of onions was influenced by the state of the membranes and was abruptly modified once membrane integrity was lost. PRACTICAL APPLICATION: In this study, we used chemical, biochemical, and histological techniques to obtain information on cell membrane permeability and onion tissue integrity after high pressure and thermal processing. Because there was strong agreement between the various methods used, it is possible to implement something relatively simple, such as ion leakage, into routine quality assurance measurements to determine the severity of preservation methods and the shelf life of processed vegetables.     

Technical note: Determination of acidity in whole raw milk: comparison of results obtained by two different analytical methods

In Argentina, one analytical method is usually carried out to determine acidity in whole raw milk: the Instituto Nacional de Racionalización de Materiales standard (no. 14005), based on the Dornic method of French origin. In a national and international regulation, the Association of Official Analytical Chemists International method (no. 947.05) is proposed as the standard method of analysis. Although these methods have the same foundation, there is no evidence that results obtained using the 2 methods are equivalent. The presence of some trends and discordant data lead us to perform a statistical study to verify the equivalency of the obtained results. We analyzed 266 samples and the existence of significant differences between the results obtained by both methods was determined.     

Folate-binding protein in milk: a review of biochemistry, physiology, and analytical methods

Folate-binding protein (FBP) was discovered in cow's milk around 40 years ago. Bovine FBP belongs to a family of several folate-binding proteins. In milk, it is a soluble whey protein with the ability to sequester folate from blood plasma. Bovine FBP is a well-characterized protein in terms of amino acid sequence and binding characteristics. Affinity and binding kinetics towards various folate forms have been intensively studied because they are crucial in using bovine FBP as an analytical tool. Shortly after the identification of bovine FBP, a competitive protein-binding assay for measuring serum and blood folate concentrations was introduced. Another analytical application of bovine FBP is in affinity chromatography, as a clean-up/concentration step for analysis of folates in foods and biological samples by liquid chromatographic methods. Concentrations of FBP in milk and dairy products have been determined by ELISA and Surface Plasmon Resonance-biosensor techniques. Since the initial reports of FBP in cow's milk, its physiological role has been discussed, especially regarding its effects on folate absorption from milk and dairy products. This review summarizes recent biochemical, analytical, food science, and nutritional advances regarding folate-binding protein in milk.     

Knowledge,attitudes, and perceptions of dairy farmers regarding antibiotic use: Lessons from a developing country

In lower- and middle-income countries, uncontrolled use of antibiotics is causing antimicrobial resistance, affecting both animal welfare and public health. Meanwhile, studies on antibiotic use in these countries are limited. A crucial step to limit the spread of antimicrobial resistance (AMR) is to examine the use of these drugs and identify its determinants. The aim of our study, the first of its kind in Lebanon, was to assess dairy farmers' knowledge and awareness of antimicrobial use (AMU) and AMR. For this, 18 farmers from different regions, educational backgrounds, experience levels, and herd sizes were interviewed. Results showed that owners of larger farms were more aware of AMU and AMR, and trying to implement preventive actions, whereas nonsystematic antimicrobial use was prevalent among the smaller farms. Mastitis and laminitis were the most treated diseases, and antibiotics used were oxytetracycline, penicillin, streptomycin, and florfenicol. Overall, antibiotic use was found as a preventive measure and a treatment of nonbacterial diseases. Irregular uses were linked to easy access of farmers to antibiotics, interrupted relations with veterinary authorities, and lack of self-assessment and inspection. Lebanese dairy farmers and owners reported feeling disadvantaged in their local trade field, facing illegal competition and unauthorized farms and industries, and lacking support from the government. Training and awareness programs must be implemented, and policies and regulations must be set, to reduce antibiotic use and hinder the spread of AMR in Lebanon.     

Univariate and multivariate modelling of flavour release in chewing gum using time-intensity: a comparison of data analytical methods

Sensory properties of chewing gum were measured using time-intensity (TI) methodology to record responses from assessors. Studying the information retrieved from a total of 800 TI curves, old and new data analysis methods were compared. These included the normalization method developed by Liu and MacFie, and ad hoc curve parameter retrieval, Principal Components Analysis (PCA) and ANOVA Partial Least Squares Regression (APLSR) methods. Two alternative methods have been developed for handling the multiple sources of variation in the data, including a dual PCA method and PARAllel FACtor analysis 2 (PARAFAC2) multiway analysis. A comparison of the different methods is conducted and the advantages of the different methods highlighted. All methods provide valuable interpretations of the time-intensity data and lead to similar conclusions. The multiway analysis provides a comprehensive overview of the data, but more experience with different datasets is needed to provide definite advices as to which methods are preferable.     

Motives for food choice: a comparison of consumers from Japan, Taiwan, Malaysia and New Zealand

With increasing emphasis on understanding consumer preferences in export markets, particularly in Asia, there is a need to determine those factors that influence food choice in other cultures. The Food Choice Questionnaire (FCQ), which assess the relative importance of nine factors thought to be important motives in food choice: Health, Mood, Convenience, Sensory Appeal, Natural Content, Price, Weight Control, Familiarity, andEthical Concern, was administered to groups of female consumers in Japan, Taiwan, Malaysia, and New Zealand. The Food Neophobia Scale was also administered in New Zealand, Taiwan and Japan. There was agreement between Taiwanese and (ethnically Chinese) Malaysian consumers in the most important food choice factors: Health, Natural Content, Weight Control andConvenience. In contrast, Price was most important for Japanese consumers and Sensory Appeal for New Zealand consumers. Familiarity was rated as least important by all countries, and Ethical Concern was also considered unimportant by all countries except Japan, where it was rated as relatively important. Older consumers generally gave higher ratings. Differences between consumer groups were also shown in the degree of neophobia. These data are important in demonstrating differing motives for food choice cross-culturally, and also provide indications of which food claims may be useful in promoting choice in the countries studied.     

Quantification of beef,pork, chicken and turkey proportions in sausages: use of matrix-adapted standards and comparison of single versus multiplex PCR in an interlaboratory trial

Quantitative PCR methods for the determination of beef, pork, chicken and turkey proportions in sausage were tested in an interlaboratory trial. Twelve different laboratories analysed six meat products each made of different compositions of beef, pork, chicken and turkey. Two kinds of calibrators were used: sausages of known proportions of meat and DNA from muscle tissue. Results generated using calibration sausages were more accurate than those resulting from the use of muscle tissue DNA. Regardless of the method used (either multiplex or single PCR), when using calibration sausages, it was always possible to quantify the proportions of meats in the unknown samples (in the range of 0.5–80%) with high precision and accuracy.     

Testing for bias between the Kjeldahl and Dumas methods for the determination of nitrogen in meat mixtures, by using data from a designed interlaboratory experiment

Bias between the Dumas and the Kjeldahl methods for the determination of protein nitrogen in food was studied by conducting an interlaboratory study involving 40 laboratories and 20 different test materials. Biases were found to be small and statistically significant only for the chicken test materials, where a bias of 0.020 ± 0.004% m/m was detected.     

两种不同检测方法分析不同类型天然和人工染菌食品中菌落总数的比较研究

目的：验证分析测试片检测不同类型食品菌落总数计数的适用性。 方法：与传统国标平板计数方法平行比较,应用测试片检测肉制品、面食、冷饮、奶制品、豆制品、果蔬和坚果7大类70份天然食品,以及以最常见的两种食源性微生物金黄色葡萄球菌和大肠埃希菌作为标准菌株,制备22的份不同食品基质的人工染菌样品。所有检测结果使用两种不同数据方法进行处理分析,以此探讨不同方法检测结果的相关性。 结果：依据ISO 16140-2 2016推荐的数据处理分析方法发现测试片和国标平板计数方法检测不同类型天然和人工染菌食品样品的菌落总数结果对数值差值的平均值均小于0.5;同时、单因素方差分析结果也证实两种方法检测结果无显著性差异（P>0.05）,相关系数高达0.938,不同方法检测结果之间呈正相关。以此发现本研究随机选择食品中菌落总数最高的分别为豆沙春卷、京酱肉丝和鲜猪皮。 结论：本研究证实测试片对不同类型食品菌落总数检测结果与国标平板计数方法结果一致性好,并且具有简单、快捷、易于标准化的优点,适用于不同层级食品承检机构。     

Microgradients in bacterial colonies: use of fluorescence ratio imaging, a non-invasive technique

Fluorescence ratio imaging is a non-invasive technique for studying the formation of microgradients in immobilised bacterial colonies. These gradients can be quantified easily when combined with the gel cassette system designed at the Institute of Food Research, Norwich, UK. Colonies of Lactobacillus curvatus were observed using this technique and relevant pH gradients were present when the colonies reached a diameter of about 100 microm. These pH gradients were due to production of lactic acid by L. curvatus cells in the colonies. The spatial resolution of the images was about 1.5 microm (scale of bacterial cells) and therefore very suitable for observing local effects in colonies which ranged in sizes from 1 to 500 microm.     

多环芳烃对农作物的影响及在食品中的来源、污染状况与检测分析

多环芳烃是一类持久性的有机污染物,对农作物的影响具有“双刃剑”效应,可对作物生长产生负面影响,也可起到提质增产的作用。该类物质具有致癌、致畸、致突变等毒性,广泛存在于食品、特别是烟熏食品中,过量摄入将严重危害人体健康。许多国家通过制定严格的限量标准、加强检验检测等措施对食品中的多环芳烃进行防控,但随着工业化的快速发展,煤、石油等燃料的大量使用,其食品污染问题依然突出,在食品中仍普遍被检出,已成为影响食品安全的主要风险来源之一,关于食品中多环芳烃的污染来源、监测分析和检测技术等方面的研究也日益增多。本文通过查阅近年来国内外发表的文献,概述了多环芳烃对农作物的影响,分析了食品中多环芳烃的来源和污染状况,从样品前处理和测定分析方面,综述了食品中多环芳烃的主要检测技术,评述了其优缺点,并提出了今后研究工作的建议,以期为同类研究提供参考。     

Stability of dietary 5-formyl-tetrahydrofolate and its determination by HPLC: a pilot study on impact of pH, temperature and antioxidants on analytical results

5-Formyltetrahydrofolate (5-HCO-H₄folate) is one of the main naturally occurring forms of folic acid in foods, but its determination is complicated because of its high susceptibility to interconversion and oxidative degradation. The present study investigated the stability of 5-HCO-H₄folate at different pH and temperatures and with different antioxidants to find optimal conditions for protection of 5-HCO-H₄folate from interconversion and oxidation during sample pre-treatment and analysis by HPLC or LC-MS. The pH of buffers during sample pre-treatment and purification was found to be crucial, especially in the absence of antioxidants. To reduce losses of 5-HCO-H₄folate during sample pre-treatment, the use of two antioxidants, ascorbic acid in combination with 2-mercaptoethanol or 2,3-dimercapto-1-propanol, and pH close to neutral were found to be of great importance. During the chromatographic analysis, the use of moderate acidic buffers in the mobile phase with pH above 3 and shorter retention times of folates, preferably below 15 min, might minimise the losses of 5-HCO-H₄folate. The results of the present study clearly demonstrated that the interconversion of 5-HCO-H₄folate to 5,10-methenyltetrahydrofolate at acidic pH should be taken into account when developing HPLC methods for folate determination.     

Aflatoxins in food: occurrence, biosynthesis, effects on organisms, detection, and methods of control

Aflatoxins are secondary metabolites produced by species of Aspergilli, specifically Aspergillus flavus and Aspergillus parasiticus. These molds are ubiquitous in nature and grow on a variety of substrates, thereby producing aflatoxins. Aflatoxins are of great concern due to their biochemical and biological effects on living organisms. In this article, the occurrence of aflatoxins, their biosynthesis, factors influencing their production, their effects on living organisms, and methods of detection and control in food are reviewed. Future areas of research involving mathematical modeling of factors influencing aflatoxin production and alternative methods of control, such as modified atmosphere packaging, are also discussed.