Emergence of methicillin-resistant Staphylococcus aureus (MRSA) ST8 in raw milk and traditional dairy products in the Tizi Ouzou area of Algeria

Staphylococcus aureus is one of the leading causes of food-borne illness worldwide. Raw milk and dairy products are often contaminated with enterotoxigenic strains of this bacterium. Some of these strains carry antimicrobial resistance, leading to a potential risk for consumers. The aim of this study was to characterize S. aureus strains circulating in raw milk and traditional dairy products for carriage of staphylococcal enterotoxin (se) genes and antimicrobial resistance. Overall, 62 out of 270 samples (23%) were contaminated with S. aureus, and 69 S. aureus strains were identified. We studied the enterotoxin genes using 2 multiplex PCR targeting 11 se genes. Seventeen (24.6%) isolates carried one or more genes encoding for staphylococcal enterotoxins. The most commonly detected se genes were seb and sep, followed by seh, sea, and see. Using the disk diffusion method, we found that resistance to penicillin G and tetracycline was the most common. Eleven isolates of methicillin-resistant S. aureus (MRSA) carried the mecA gene. All MRSA isolates belonged to the same spa type (t024) and sequence type (ST8), and carried the seb and sep enterotoxin genes. However, none of them carried the Panton Valentine leukocidin gene (lukF/S-PV). The presence of enterotoxigenic S. aureus strains, including MRSA, in raw milk and dairy products, raises a serious public health concern, because these strains may cause food poisoning outbreaks, be disseminated to the population, or both.     

微波消解-原子荧光检测乳制品中铅的方法

研究了微波消解-原子荧光检测乳制品中铅的方法。采用微波消解法对样品进行前处理,原子荧光法中用的载流剂为质量分数2%的盐酸,还原剂为KBH4+K3Fe3(CN)6+NaOH。该方法检出限为0.021μg/L,相对标准偏差为2.15%,回收率在93%~98%之间。与GB5009.12-2010[1]第二法氢化物原子荧光光谱法相比,处理时间缩短了约12 h。该方法具有简单、快速、灵敏度高的特点。     

Enantiomeric fraction of selected chiral polychlorinated biphenyls in cow, goat, and ewe milk and dairy products by heart-cut multidimensional gas chromatography: first results

The concentration of the most relevant polychlorinated biphenyl (PCB) congeners has been determined in milk and dairy products (i.e., cheese and yogurt, from cow, goat, and ewe). In addition, the enantiomeric composition of 11 atropisomeric PCB has been determined for the first time in this type of product, using heart-cut multidimensional gas chromatography and 2 enantioselective columns for the unambiguous determination of both enantiomers. Results showed a deviation from the racemic composition for PCB 135, 136, 176, 171, and 183 in the samples analyzed. Whereas PCB 135, 136, and 176 showed an enrichment of the first eluted enantiomer, congeners 171 and 183 showed an enrichment of the first or second eluted enantiomer depending on the dairy product and species. The remaining congeners analyzed (PCB 84, 91, 95, 132, 149, and 174) did not present a clear enrichment of any of the enantiomers. Therefore, differences in the enantiomeric composition of some of the target atropisomeric PCB have been found among the 3 species and among the milk samples and the related dairy products analyzed. Enantioselective species-dependent processes, as well as enantioselective processes carried on by microorganisms during the fermentation and ripening in the latter could be possible explanations for the differences observed. However, changes in the enantiomeric composition are still not well understood, and further investigation in this direction is recommended.     

乳及乳制品中动物水解蛋白L-羟脯氨酸的检测技术

介绍了检测乳及乳制品中L-羟脯氨酸的常用方法,主要包括高效液相色谱法、高效液相色谱-质谱联用法、氨基酸自动分析仪测定法,毛细管电泳-激光诱导荧光检测法和分光光度法,并对今后乳及乳制品中动物水解蛋白检测技术的发展趋势进行了分析。     

HPLC测定原料乳与乳制品中三聚氰胺质量分数的不确定度评定

建立高效液相色谱法测定测定原料乳与乳制品中三聚氰胺质量分数的不确定度评定方法,采用GB/T22388-2008高效液相色谱法测定测定原料乳与乳制品中三聚氰胺质量分数。建立数学模型,根据《测量不确定度评定与表示》(JJF1059—1999)中有关规定评估其不确定度。结果表明,按数学模型计算奶粉中三聚氰胺质量分数为2.70mg/kg,扩展不确定度为0.064mg/kg,结果表达为(2.70±0.064)mg/kg。该方法建立的数学模型合理、可靠。     

西藏乳及发酵乳制品中乳酸菌与酵母菌分布

西藏当地牦牛乳及发酵乳制品中的微生物分布备受科研人员的关注,而且重点多集中在其中的乳酸菌和酵母菌。本文对西藏当地乳及乳制品中乳酸菌与酵母菌的分布做了详细的介绍,包括原料乳、曲拉和藏灵菇乳中的乳酸菌和酵母菌的研究现状,并对今后的发展趋势做了分析。      

Aflatoxins in dairy cow feed,raw milk and milk products from Turkey

This study aims to detect aflatoxins (AFs) in dairy cow feed, milk and milk products using a high-performance liquid chromatography coupled with fluorescence detection (HPLC-FLD) method. All the validation parameters met the method performance criteria of the European Union. The samples comprised 76 dairy cow feeds and 205 milk and milk products (including yoghurt and yoghurt-based beverage, ayran). AFs were present in 26.3% of the feed samples. Two feed samples exceeded the maximum limit (ML) of 5 µg kg^?1 for AFB₁ as established by the EU. Nineteen milk samples (21.1%) contained aflatoxin M₁ (AFM₁) of which three exceeded the EU ML of 0.05 µg l^?1. In addition, only two yoghurt samples and one ayran sample contained AFM₁, but the levels were lower than the EU ML.     

Concentration of furfuryl alcohol in fluid milk,dried dairy ingredients,and cultured dairy products

Maillard reactions occur in dairy products during heat treatment. Furfuryl alcohol (FA) may be found in dairy products as a result of Maillard reactions. The recent posting in California Proposition 65 indicates that FA may be carcinogenic, and for this reason it is crucial to accurately measure FA concentrations in dairy products. The objective of this study was to identify an extraction and quantitation method for FA from dairy products and to determine FA concentrations in milk, dairy powders, and cultured dairy products. Solvent-assisted flavor extraction, solid-phase microextraction, stir bar sorptive extraction with gas chromatography-mass spectrometry and triple quadrupole mass spectrometry were compared for recovery of FA. Internal standards for the quantitation of FA (2-methyl-3-heptanone, furfuryl-d₅ alcohol, 2,5-dimethylphenol, 5-methyl-2-furfuryl alcohol, and 5-methyl furfural) were also compared. Subsequently, fluid milk [high temperature, short time (HTST) and ultrapasteurized], whey protein isolates (3 mo–4 yr), whey protein concentrates (3 mo–4 yr), whole milk powders (1 yr), high and low heat skim milk powders (SMP; 0–8 yr), milk protein isolates (3 mo–3 yr), milk protein concentrates (3 mo–3 yr), Cheddar cheese (mild, medium, sharp, and extra sharp), mozzarella cheese (whole and part skim), cottage cheese (nonfat, low fat, and full fat), sour cream (nonfat, low fat, and full fat), traditional yogurt (nonfat, low fat, and full fat), and Greek-style yogurt (nonfat; n = 139 products total) were evaluated. Furfuryl alcohol was extracted from products by headspace solid-phase microextraction followed by gas chromatography-triple quadrupole mass spectrometry using a ZB-5ms column (30 m × 0.25 mm × 0.25 µm; Phenomenex Inc., Torrance, CA). Furfuryl-d₅ alcohol was used as an internal standard. Each food was extracted in triplicate. Ultrapasteurized milks had higher levels of FA than HTST milks (122.3 vs. 7.350 µg/kg). Furfuryl alcohol concentrations ranged from 0.634 to 26.55 µg/kg in whey protein isolates, 2.251 to 56.19 µg/kg in whey protein concentrates, 11.99 to 121.9 µg/kg in milk protein isolates, and 8.312 to 49.71 µg/kg in milk protein concentrates, and concentrations increased with powder storage. High heat SMP had higher concentrations of FA than low heat SMP (11.8 vs. 1.36 µg/kg) and concentrations increased with storage time. Concentrations of FA in Cheddar and mozzarella cheese ranged from 2.361 to 110.5 µg/kg and were higher than FA concentrations in cottage cheese or sour cream (0.049–1.017 µg/kg). These results suggest that FA is present at higher levels in dairy products that have been subjected to higher temperatures or have been stored longer. Sour cream and cottage cheese had lower levels of FA. Compared with other studies on food products with reported levels of FA, such as coffee (200–400 µg/g), dairy products have very low levels of FA.     

Lead excretion in milk of accidentally exposed dairy cattle

Lead (Pb) exposure in dairy cattle is associated with economic losses due to mortality and treatment costs, but with production animals there is also risk to the human food chain. The first objective of this study was to quantify the Pb concentration in milk from Pb-exposed cattle. The second objective was to correlate blood and milk Pb concentrations from individual cows. The third objective was long-term monitoring to determine the duration of milk contamination after exposure ceased. A dairy herd of more than 100 cows was accidentally exposed to Pb-contaminated feed. Milk and blood were collected for Pb analysis. Serial collection of milk samples continued for 2.5 years. The initial concentration of Pb in bulk tank milk was 0.0999 mg l^–1. The highest milk Pb concentration from an individual cow was 0.4657 mg l^–1 and the highest blood Pb concentration was 1.216 mg l^–1. One milk sample collected at the end of the study (day 922) contained 0.0117 mg Pb l^–1 of Pb. The calculated relationship between milk (y) and blood (x) Pb concentration was ln(y) = 3.4(x) – 2.21 (R² = 0.98).     

蛋白质组学技术及其在乳及乳制品中的应用研究进展

蛋白质组学技术是近年来生命科学研究的重要工具,在食品、医学及动植物研究领域具有独特优势。利用蛋白质组学技术研究乳及乳制品,深入阐明其中蛋白质的表达及动态变化已成为当前的研究热点。该文主要综述了蛋白质组学的概念、常用技术及应用领域,重点介绍蛋白质组学在乳及乳制品领域,特别是在乳脂肪球膜蛋白、乳清蛋白、乳及乳制品加工过程以及干酪制品中的研究应用,探讨了目前乳及乳制品蛋白质组学研究中存在的问题与局限,并对蛋白质组学及其在乳及乳制品中的应用前景进行了总结与展望,为应用蛋白质组学技术深入研究乳及乳制品提供了理论依据。     

牛奶及奶制品中雌激素残留和检测的研究

牛奶在人类日常饮食结构中占有重要位置。近年来随着对环境雌激素研究的深入,牛奶中的雌激素问题越来越引起人们的关注。有研究表明,现代商业牛奶中雌激素含量显著上升。本文阐述了雌激素的分类及应用,并对牛奶和奶制品中雌激素残留状况,可能危害及检测方法进行了综述。     

乳及乳制品中抗寄生虫药检测研究进展

抗寄生虫药是牛羊等产奶动物养殖过程中必不可少的投入品。这些药物经牛羊吸收代谢后, 容易残留在牛羊奶及其他动物组织中, 给消费者造成安全隐患。我国食品安全国家标准规定了牛羊奶中21种抗寄生虫药的最大残留限量值, 科研工作者们也建立了多种检测方法。本文对2018~2023年牛羊奶中抗寄生虫药的检测方法进行综述, 简要对比电化学传感器法、表面增强拉曼光谱法、胶体金免疫试纸条法、液相色谱-质谱法、液相色谱-高分辨质谱法的优缺点, 并对抗寄生虫药检测方法的发展方向进行了讨论和展望, 为乳及乳制品中抗寄生虫药的定性筛查和定量检测提供技术参考。     

Cadmium and lead in cocoa powder and chocolate products in the US Market

Cocoa powder and chocolate products are known to sometimes contain cadmium (Cd) and lead (Pb) from environmental origins. A convenience sample of cocoa powder, dark chocolate, milk chocolate, and cocoa nib products was purchased at retail in the US and analysed using inductively coupled plasma mass spectrometry to assess Cd and Pb concentrations. Cd and Pb were evaluated in relation to the percent cocoa solids and to the reported origin of the cocoa powder and chocolate products. Cd ranged from 0.004 to 3.15 mg/kg and Pb ranged from <LOD to 0.38 mg/kg. Cd and Pb were significantly correlated with percent cocoa, with correlations varying by product type and geographic origin. Geographic variation was observed for Cd, with higher Cd concentrations found in products reported as originating from Latin America than from Africa. The influence of percent cocoa solids and cocoa origin on Cd levels are relevant to international standards for Cd in chocolate products.     

Effect of dietary phosphorus on performance of lactating dairy cows: milk production and cow health

The objective of this study was to measure cow response to feeding of two dietary concentrations of P, one of which was close to recent National Research Council requirements, and the other of which was well in excess of the requirement. Diets containing 0.37 or 0.57% P (dry basis) were fed to Holstein cows for the first 165 d of lactation, and occasionally longer until cows were confirmed pregnant approximately 60 d after insemination. At calving, cows were randomly assigned to experimental diets. The number of cows completing a minimum of 165 d of lactation was 123 for the 0.37 and 124 for the 0.57% P groups. Cows were housed in a stanchion barn and fed one of two transition diets, each formulated to contain one of the P treatments for the first 3 wk of lactation, and then cows were moved to a free-stall barn where the experimental diets were group fed. Milk production, milk fat, and milk protein averaged 35.1 kg/d, 3.92%, and 2.90% for the 0.37% P diet, and 34.9 kg/d, 3.98%, and 2.91% for the 0.57% P diet. None of these measures were different between treatments. Blood serum P concentrations on d 50 and 100 of lactation averaged 6.1 and 6.2 mg/dL for the 0.37% P diet, and 6.8 and 6.9 mg/dL for the 0.57% P diet. No treatment differences were detected in milk production, cow health, or body condition score.     

乳与乳制品中四种动物源性成分鉴定方法的研究

目的 针对小众乳与乳制品的掺假的现象,构建乳与乳制品中动物源性成分检测方法。方法 设计合成了牛、羊、驴、水牛的特异引物探针,优化乳与乳制品中核酸提取方法,对设计的荧光PCR方法进行了特异性、灵敏度、适用性进行验证。结果 该方法对于常见动物物种具有较强特异性和灵敏度,牛、羊、驴、水牛的检测灵敏度分别为0.001、0.01、0.01、0.01 ng。此外,该方法适用性较强,在各类乳与乳制品样品中均能检出标识动物源性成分和掺伪动物源性成分。结论 本研究构建的检测方法,特异性、灵敏度、检出限等指标均能满足日常实验需要,可为监管与检验提供有力的技术支撑。     

乳及乳制品中矿物质元素检测方法的研究进展

乳及乳制品中矿物质元素的种类和含量是评价其营养质量的关键指标,选择出高效、灵敏、快捷的矿物质元素检测方法,在乳及乳制品的科研、生产、贸易等方面显得尤为重要。文章首先讨论乳及乳制品中矿物质元素检测的前处理方法,然后比较乳及乳制品中矿物质元素的检测方法,包括火焰原子吸收光谱法、石墨炉原子吸收光谱法、氢化物原子吸收光谱法、原子荧光光谱法、原子发射光谱法、电感耦合等离子质谱法、免疫分析法、中子活化分析法、伏安溶出法、酶抑制法等方法,最后总结各种方法的优缺点,旨在为乳及乳制品中矿物质元素检测方法的应用、研究和发展提供参考。     

Investigation of the migration of triclabendazole residues to milk products manufactured from bovine milk,and stability therein,following lactating cow treatment

Triclabendazole (TCB) is a flukicide used in the treatment of liver fluke in cattle; however, its use is currently prohibited in lactating dairy cows. In this study, following administration of 10% Fasinex (triclabendazole, Novartis Animal Health UK Ltd., Camberley, UK) the milk of 6 animals was used to manufacture dairy products, to ascertain if TCB residues in milk migrate into dairy products. The detection limit of the ultra-high-performance liquid chromatography-tandem mass spectrometry method used was 0.67 μg/kg. The highest concentrations of TCB residue measured, within the individual cow milk yield, was 1,529 ± 244 µg/kg (n = 6), on d 2 posttreatment. Days 2 and 23 posttreatment represented high and low residue concentrations, respectively. At each of these 2 time points, the milk was pooled into 2 independent aliquots and refrigerated. Milk products, including cheese, butter, and skim milk powder were manufactured using pasteurized and unpasteurized milk from each aliquot. The results for high residue milks demonstrated that TCB residues concentrated in the cheese by a factor of 5 (5,372 vs. 918 µg/kg for cheese vs. milk) compared with the starting milk. Residue concentrations are the sum of TCB and its metabolites, expressed as keto-TCB. Residues were concentrated in the butter by a factor of 9 (9,177 vs. 1,082 μg/kg for butter vs. milk) compared with the starting milk. For milk, which was separated to skim milk and cream fractions, the residues were concentrated in the cream. Once skim milk powder was manufactured from the skim milk fraction, the residue in powder was concentrated 15-fold compared with the starting skim milk (7,252 vs. 423 µg/kg for powder vs. skim milk), despite the high temperature (185°C) required during powder manufacture. For products manufactured from milk with low residue concentrations at d 23 posttreatment, TCB residues were detected in butter, cheese, and skim milk powder, even though there was no detectable residue in the milk used to manufacture these products. Triclabendazole residues were concentrated in some milk products (despite manufacturing treatments), exceeding residue levels in the starting milk and, depending on the storage conditions, may be relatively stable over time.     

乳和乳制品中无机砷测定方法的探讨

目的 对原子荧光光谱法测定乳和乳制品中无机砷的方法中仪器的工作参数、还原剂浓度选择等条件进行了探讨。方法 通过一系列实验选出了测定最佳条件。结果 在选定的最佳仪器条件下检出限为0.22 ng/mL、回收率为98%~105%、相对标准偏差为1.38%。结论 本方法具有灵敏度高、重现性好、准确性高等特点, 适合用于分析乳和乳制品中无机砷的含量。     

乳及乳制品中残留青霉噻唑酸钾的检测方法

通过分光光度法检测乳及乳制品中青霉素钾的主要酶解产物青霉噻唑酸钾,间接检测了乳及乳制品中是否添加过β-内酰胺酶。通过实验该方法的工作曲线相关系数为0.9997,检测限为2.5 mg/L,回收率在93.2%～106.3%之间,RSD为2.9%～4.5%。在30组样品中应用效果良好,表明该方法简单、快速准确、灵敏度高,适用于乳及乳制品中青霉噻唑酸钾残留量的检测。     

高效液相色谱法测定乳与乳制品中双氰胺的残留

建立了乳与乳制品中双氰胺残留的高效液相色谱测定方法.采用水-乙腈提取样品、氨基色谱柱分离、紫外检测器检测、外标法定量测定双氰胺残留.该方法的检出限为牛奶0.01mg/kg,乳粉为0.05 mg/kg(均为质量分数),线性范围为0.25.0 mg/L,并确定了回归方程,相关系-R2=0.9998,样品加标回收率在90％~8％,相对标准偏差为1.2％~2.3％.该法具有样品处理简单方便,灵敏度高,分析时间短等优点,可以满足乳与乳制品中双氰胺残留的测定.