High trimethylamine concentration in milk from cows on standard diets is expressed as fishy off-flavour

To establish whether fishy off-flavour observed in cows' milk in Sweden is due to abnormal concentrations of trimethylamine (TMA) in milk, 15 milk samples from 13 cows of the Swedish Red and White breed (SRB) were analysed for this compound using dynamic headspace (DHS) gas chromatography (GC). A mass selective detector (MSD) was used for the qualitative and a flame ionization detector (FID) for the quantitative analyses. Further confirmation was obtained using a solid phase microextraction (SPME) followed by GC-olfactometry (GC-O) and GC-NPD (nitrogen and phosphorus detector). Samples were also evaluated by a two-person organoleptic panel for the presence of fishy off-flavour. Results showed that the seven milk samples with a fish-like taint contained > 1 mg TMA/kg milk, whereas, with a single exception, the seven samples that were judged to be normal did not contain this compound. Furthermore, there were indications of a dose-dependent relationship between TMA concentration and fishy off-flavour score.     

奶粉中铅含量的直接固体分析

本文建立了直接固体进样石墨炉原子吸收光谱测定奶粉中铅含量的新方法,对化学改进剂、石墨炉升温程序等分析参数进行了优化,并详细考察了不同校准方式对分析结果的影响.在优化的参数条件下,本方法对mg级固体样品的分析精密度为5.12%,铅元素的检出限为0.2 Pg.方法用于分析国家一级标准参考物质GBW10017(奶粉),测定值...     

A sensitive determination method for carbendazim and thiabendazole in apples by solid-phase microextraction−high performance liquid chromatography with fluorescence detection

A new analytical method for the determination of carbendazim (MBC) and thiabendazole (TBZ) in apples is reported, based on solid-phase microextraction (SPME) coupling HPLC with fluorescence detection. The main SPME and HPLC experimental conditions were optimized. The apples were first blended and centrifuged. Then, an aliquot of the resulting solution was subjected to SPME on a 60 µm polydimethylsiloxane/divinylbenzene (PDMS/DVB) fibre for 35 min at room temperature with the solution being stirred at 1100 rev min^–1. The extracted pesticides on the SPME fibre were desorbed in the mobile phase into the SPME/HPLC interface for HPLC analysis. The method was linear over the range 0.01–1 mg kg^–1 in apples for both MBC and TBZ, with detection limits of 0.005 and 0.003 mg kg^–1 and correlation coefficients of 0.9995 and 0.9998, respectively. The average recoveries for MBC and TBZ were 91.5 and 92.3% with the relative standard deviations (RSD) of 4.7 and 4.1% at the 0.1 mg kg^–1 level, and 94.6 and 96.1% with RSD of 3.3 and 3.8% at the 0.5 mg kg^–1 level, respectively. The method is simple, sensitive, organic solvent-free and is suitable for the determination of MBC and TBZ in apples.     

气相色谱-氢火焰离子化检测器测定婴幼儿乳粉中37种脂肪酸含量

目的：建立气相色谱-氢火焰离子化检测器测定乳粉中37种脂肪酸含量的分析方法。方法：婴幼儿乳粉样品运用乙酰氯-甲醇法（10%乙酰氯甲醇溶液于80℃±1℃水浴2 h）甲酯化,离心取上清液过0.22μm的有机滤膜后经SP-2560(100 m×250μm×0.2μm)分离,气相色谱法检测,外标法定量。结果：37种脂肪酸甲酯在0.002～0.2 mg/mL浓度范围内线性良好,相关系数均大于0.999,回收率低梯度在85.5%～100.0%之间,中梯度在91.2%～104.2%之间,高梯度在86.8%～103.8%之间,精密度在0.88%～3.81%之间,实际样品测定结果符合相关标准要求。结论：该方法是在国标基础上建立了一种更为快速、分离度更好的脂肪酸检测技术,有很好的实用价值,方法稳定性好,成本低,重现性好,准确度高,适用于婴幼儿乳粉中37种脂肪酸含量的测定。     

Investigation of ascorbigen as a breakdown product of glucobrassicin autolysis in Brassica vegetables

The formation of ascorbigen (ABG), one of the major indole-derived compound of Brassica vegetables, has been studied. An HPLC method developed previously in our laboratory was used to determine ABG precursors, glucobrassicin (GB) and L-ascorbic acid (AA), in intact plant tissues of four nutritionally important vegetable crops belonging to the genus Brassica - white cabbage, cauliflower, Chinese cabbage, and broccoli. The levels of GB varied within the range 25-142 mg kg^-1 and AA contents varied within the range 110-840 mg kg^-1. The amounts of ABG in homogenized Brassica vegetables was found to be between 7 mg kg^-1 and 18 mg kg^-1. The level of GB in the plant material was shown to be the limiting factor in the process of ABG formation. Calculated conversion values expressing the conversion of GB into ABG revealed that only 20-46% of GB present in intact plant tissues was employed in the process of ABG formation. The conversion values increased with decreasing pH values of the vegetable homogenates.     

Fast Determination of Sodium Monofluoroacetate in Liquid Milk and Dairy Powder by Hydrophilic Interaction Liquid Chromatography-Triple Quadrupole Mass Spectrometry

Manufactured sodium monofluoroacetate is a rodenticide with high acute toxicity. A fast and sensitive analytical method in liquid milk and dairy powder was developed both for routine analysis and for fast tackling the terrorist threat. Monofluoroacetate was extracted from liquid milk using acetonitrile and from dairy powder with water and acetonitrile, cleaned using a solid phase extraction (SPE) cleanup procedure with polymeric anion exchange (PAX) cartridge, and measured by hydrophilic interaction liquid chromatography-triple quadrupole mass spectrometry (LC-MS/MS). The conditions for the monofluoroacetate extraction, SPE cleanup, and instrument injection solvent were optimized. A BEH amide chromatographic column with hydrophilic interaction was used to directly separate monofluoroacetate under basic conditions. The limits of detection in liquid milk and dairy powder were 1 and 2 μg kg^-1, respectively. The recoveries at three spiking levels (10, 50, and 200 μg kg^-1) were 72.5–97.6 % with relative standard deviations (RSDs) of 4.7–5.9 % for liquid milk and 70.1–92.8 % with RSDs of 4.7–6.8 % for dairy powder. The method has been applied to analyze sodium monofluoroacetate in dairy products including infant formula.     

Phenols and metals in sugar-cane spirits. Quantitative analysis and effect on radical formation and radical scavenging

A fluorescence-based analytical method for quantification of phenolic compounds in sugar cane spirits (and other distilled alcoholic beverages) was developed. Sample preparation involved reverse-phase solid phase extraction and separation by gradient reversed-phase HPLC with fluorescence detection. Twenty-one Brazilian sugar cane spirits (aged and non-aged cachaça) were analyzed and phenol, guaiacol, o-cresol, p-/m-cresol, 3, 5-xylenol, 4-ethylphenol, 4-ethylguaiacol, 2-ethylphenol, eugenol, (+)-catechin, (-)-epicatechin, and scopoletin quantified. The detection limit was between 0.01 mg l^-1 (eugenol and scopoletin) and 0.1 mg l^-1 [(+)-catechin and (-)-epicatechin]. Kaempferol and quercetin were quantified in the same spirits, together with copper and iron, using HPLC (spectrophotometric detection) and atomic absorption spectroscopy, respectively. Large variations between various spirits were noted: total phenols were between 1.5 and 70 mg l^-1, flavonoids were from below detection to 3.5 mg l^-1, Cu was between 0.04 and 7.0 mg l^-1; and Fe between 0.01 and 0.78 mg l^-1. The tendency of radical formation in the spirits was determined by electron spin resonance spectroscopy using N-t-butyl-!-phenylnitrone spin trapping, and radical scavenging capacity was determined spectrophometrically using the stable 2,2-diphenyl-1-picrylhydrazyl radical as probe. Radical formation depends mainly on the Cu content, while the radical scavenging and antioxidative capacity mainly depends on the flavonoid content. (+)-Catechin and (-)-epicatechin are most important for the antioxidative capacity as confirmed in a model experiment, where oxidation was induced by iron catalysis.     

Simultaneous Determination of Erythromycin,Tetracycline, and Chloramphenicol Residue in Raw Milk by Molecularly Imprinted Polymer Mixed with Solid-Phase Extraction

A rapid, simple, and efficient method was described for the simultaneous determination of three common antibiotic residues including erythromycin, tetracycline, and chloramphenicol in raw milk. A molecular imprinting technique combined with solid-phase extraction (SPE) was used to pretreat the test samples and then simultaneously detected with HPLC. The whole process, only including one step of pretreatment, was able to detect the entire target molecule using specific enrichment and analysis method. The detection was verified by comparison with Chinese standard methods of GB/T 22988-2008, GB/T 22990-2008, and GB/T 29688-2013. The testing lines, accuracy, reproducibility, specificity, and recoveries were evaluated, and calculated values were in line with established standards. The recoveries of erythromycin, tetracycline, and chloramphenicol were 77.82~87.08, 81.02~88.17, and 72.94~83.57%, respectively. By using of this novel solid-phase extraction substrate, the detection limits for erythromycin, tetracycline, and chloramphenicol were 10, 20, and 10 μg kg^?1, respectively. The method was suitable for routine analysis, and the experimental procedure was simplified, with the detection time greatly reduced. This method showed broad application prospects for the detection of antibiotic residues in raw milk.     

Development and single-laboratory validation of an HPLC method for the determination of cyclamate sweetener in foodstuffs

A method for the determination of cyclamate has been developed and single-laboratory validated for a range of foodstuffs including carbonated and fruit-juice drinks, fruit preserves, spreads, and dairy desserts. The method uses the peroxide oxidation of cyclamate to cyclohexylamine followed by derivatization with trinitrobenzenesulfonic acid and analysis by a modified reversed-phase high-performance liquid chromatography-ultraviolet light (HPLC-UV). Cycloheptylamine is used as an internal standard. The limits of detection were in the range 1–20 mg kg^?1 and the analysis was linear up to 1300 mg kg^?1 cyclamic acid in foods and up to 67 mg l^?1 in beverages. Analytical recovery was between 82% and 123%, and results were recovery corrected. Precision was within experimentally predicted levels for all of the matrices tested and Horrat values for the combined standard uncertainty associated with the measurement of cyclamate between 0.4 (water-based drinks) and 1.7 (spreads). The method was used successfully to test three soft drink samples for homogeneity before analytical performance assessment. The method is recommended for use in monitoring compliance and for formal testing by collaborative trial.     

Rapid Determination of Tetracyclines Hydrochloride Using ATR FT-MIR Spectroscopy

Antibiotic residues in animal-derived foods have brought serious threats to human health as well as economic losses to the food industry. Given that analytical methods are crucial but remain limited, a rapid, reliable, and cost-effective method is needed for detecting antibiotic residues. In this paper, a method using attenuated total reflection Fourier transform mid-infrared (ATR FT-MIR) spectroscopy combined with chemometrics was established for the detection of tetracyclines hydrochloride (TCsH). Firstly, TCsH powders were scanned using ATR FT-MIR spectroscopy, and the characteristic peaks of these samples were found in this region. Then, milk samples with different TCsH concentrations (1 to 160 ppb) were measured and were analyzed using principal component analysis (PCA) and partial least squares regression (PLSR) algorithms. The results showed that the kinds of TCsH in milk could not be classified. However, TCsH concentration ranging from 1 to 160 ppb in milk samples was successfully determined with high determination coefficient (R ²) values of 0.88–0.90, low root-mean-square errors values of 9.76–18.2, and high residual predictive deviation (RPD) values close to or greater than 3. These results indicated that ATR FT-MIR spectroscopy could be used to identify TCsH powders based on their unique spectral features, and was suitable for the rapid detection of TCsH concentration in milk.     

Headspace solid-phase micro-extraction gas chromatography method for the determination of methanol in aspartame sweeteners

A headspace solid-phase micro-extraction (HS-SPME) method for the extraction and determination of residual methanol in artificial sweeteners by capillary gas chromatography with flame ionization detection (GC-FID) is described. A manual SPME holder with an 85-µm polyacrylate fibre was used. The optimized conditions for methanol extraction by SPME were: sample agitation, absorption temperature of 30°C, absorption time of 10 min, desorption time of 2 min and sample volume in the vial of 400.0 µl. Under these conditions the calibration graphs were linear in the range 2.50-31.60 mg l^-1, and the precision was good (relative standard deviation 4.9%). The detection limit was 0.40 mg l^-1; the quantification limit was 2.06 mg l^-1.     

鸡蛋、鸡肉及奶粉中22种有机氯农药残留的测定

建立了在鸡蛋、鸡肉和奶粉中同时测定22种有机氯农药残留的方法。样品经乙腈提取、Captiva EMR-Lipid固相萃取柱净化、正己烷复溶后,用气相色谱仪检测,外标法定量。在0.005~0.2 mg/L范围内,22种有机氯农药的质量浓度与其对应的峰面积之间线性关系良好,R²均大于0.995。在0.01、0.02、0.1 mg/kg 3个添加水平下,重复测定6次,22种有机氯农药的回收率均在60%~110%,RSD均小于10%,符合GB 27404—2008的实验室内变异系数要求。该方法能够有效去除鸡蛋、鸡肉和奶粉中的动物脂肪及亲脂性干扰物,方法灵敏度、准确度和精密度均符合农药残留检测的要求,为有效监测鸡蛋、鸡肉和奶粉中有机氯农药残留量提供了一种高效、可靠的分析手段。     

Determination of nitrates in milk by ion-chromatography

A method is described for the determination of nitrates in cow milk, human milk, milk powder or milk-based infant formulae using liquid chromatography on Spheron DEAE and a direct photometric detection (205 nm). The influence of removing proteins by precipitation with Carrez reagent on the accuracy of determination was studied. The proposed method gives identical results with the reference method (photometry after reduction of nitrate to nitrite) but is more rapid. Its limit of determination is 0.5 mg NO3-/l of milk, its reproducibility is 4% (relative standard deviation).     

离子色谱法测定奶粉中的葡萄糖、蔗糖和乳糖

建立高效阴离子交换色谱-脉冲安培检测法测定奶粉中葡萄糖、蔗糖和乳糖的方法。以METROSEP CARB 1(150mm×4.0mm)阴离子交换柱为分离柱,脉冲安培检测,37mmol/L NaOH溶液为淋洗液,以柠檬酸作为蛋白质沉淀剂。葡萄糖、蔗糖和乳糖的线性范围分别为1～40、1～50、1～50mg/L,相关系数分别0.9966、0.9968、0.9985,检出限分别为0.014、0.091、0.083mg/L,精密度为1.10%～4.96%,回收率为90.13%～104.83%。该方法分析时间短,前处理简单,适用于快速测定奶粉中的葡萄糖、蔗糖和乳糖。     

Quality changes in chilled Norway lobster (Nephrops norvegicus) tail meat and the effects of delayed icing

The quality deterioration of Norway lobster (Nephrops norvegicus) tail meat was monitored during ice storage. The K‐value started at 0.7% and reached a value of 39.7% on day 14. Muscle pH followed a sigmoidal pattern that reached a plateau on day 6. Bacterial load and trimethylamine (TMA) increased only after a lag phase to reach considerable levels by day 14 (5.3 log cfu and 10.2 mg (100 g)^?1, respectively). These analytical data were compared with sensory data. Principal component analysis (PCA) indicated that laboratory measures were correlated positively with the smell strength of cooked product (increasingly strong) and negatively with the smell character of raw and cooked product (sour‐ammoniacal in raw and neutral in cooked products), flavour and aftertaste (both increasingly bland–bitter). The effects of icing delays on the quality of tail meat were also evaluated. Changes in K‐values, microbial load, muscle pH and TMA indicated that the delay to icing should be no more than 4 h (at 16 °C) to ensure that quality is not compromised during subsequent post‐harvest storage.     

Assessment of the dietary intake of propylene glycol in the Korean population

An improved method for the analysis of propylene glycol (PG) in foods using a gas chromatography-flame ionisation detector (GC-FID), with confirmation by GC-MS, was validated by measuring several analytical parameters. The PG concentrations in 1073 products available in Korean markets were determined. PG was detected in 74.1% of the samples, in a concentration range from the limit of detection (n.d., 0.39 μg ml^?1) to 12,819.9 mg kg^?1. The Korea National Health and Nutrition Examination Survey (KNHANES) 2011–2013 reported the mean intake levels of PG from all sources by the general population and consumers were 26.3 mg day^?1 (0.52 mg kg^?1 day^?1) and 34.3 mg day^?1 (0.67 mg kg^?1 day^?1), respectively. The 95th percentile intake levels of the general population and consumers were 123.6 mg day^?1 (2.39 mg kg^?1 day^?1) and 146.3 mg day^?1 (2.86 mg kg^?1 day^?1), respectively. In all groups of the general population, breads were the main contributors to the total PG intake. These reports provide a current perspective on the daily intake of PG in the Korean population.     

Classification of the geographical origin of Italian donkey's milk based on differences in inorganic anions

The content of chlorides, nitrites, nitrates, phosphates and sulphates was used to classify 45 donkey's milk samples collected from different Italian regions. A method employing ion exchange chromatography with conductivity detector and chemical suppression was used. The quantitative results indicated phosphates (569.4–1304.4?mg?kg^?1) and chlorides (545.9–1757.9?mg?kg^?1) as being the most abundant anions, followed by sulphates (109.5–200.7?mg?kg^?1). The concentrations of nitrites and nitrates were found to be lower at 5.6 and 5.5?mg?kg^?1 respectively. The data set was subdivided into three groups according to the region of origin of milk, and was statistically evaluated by analysis of variance (ANOVA). Concentrations of chlorides and nitrites showed a significant difference among farms (p?<?0.001). In a first discriminant analysis procedure, functions based on linear combinations of the log _e -transformed element concentrations of anions were generated to classify donkey's milk samples from different regions. In an alternative approach, a three-step discriminant analysis procedure to classify a milk sample was tested. The results obtained led to a correct classification of donkey's milk samples based on their anions content with 91–98% of the samples being correctly classified. The procedure proved to be very simple, so it could be used as an evaluation method for the traceability of donkey's milk, thus defending this unique product against fraud or commercial disputes.     

离子色谱法测定豆奶粉中硝酸盐、亚硝酸盐含量

为了建立离子色谱测定豆奶粉中硝酸盐、亚硝酸盐的含量的方法。样品用去离子水提取,固相萃取后,采用离子色谱法测定豆奶粉中硝酸盐、亚硝酸盐的含量。结果表明：硝酸盐或亚硝酸盐的线性范围分别为1～50、1～25mg/mL,回收率分别为89.3%～98.9%、89.6%～102.0%,检出限分别为0.16、0.11mg/kg。该法灵敏、准确,前处理简单易行,可用于豆奶粉中的硝酸盐、亚硝酸盐含量测定。     

Use of glyceroltriheptanoate as marker for processed animal by-products: development and validation of an analytical method

A recently published European Regulation requires that the artificial marker, glycerol triheptanoate (GTH), be added to processed animal by-product (ABPs) prohibited from entering the food chain. The objective of this new requirement is to allow full traceability and ensure that these materials are disposed of in a proper way. Here, we report the development and single-laboratory validation of an analytical method for the determination of GTH in meat and bone meal plus animal fat. The method comprises three steps: (1) extraction of GTH from the samples with petroleum ether when analysing meat and bone meal or dissolving the sample in n-hexane when analysing fat; (2) clean-up of the extract using commercially available SPE cartridges; (3) determination of GTH by GC/MS or GC with flame ionisation detection (FID). The results of the validation study demonstrated that the relative standard for intermediate precision varied between 2.5 and 8.2%, depending on GTH concentration and the detector utilised. In all cases, the relative recovery rate was above 96%. The limit of quantification was 16 mg kg^?1 (GTH/fat content of the sample) with MS as detector and 20 mg kg^?1 with FID. Moreover, the method has been successfully applied in a second laboratory, indicating its transferability. Considering the minimum GTH concentration in ABPs of 250 mg kg^?1, the method is considered suitable for the intended purpose and can be utilised by EU Member States laboratories for official control and monitoring.     

Simultaneous determination of ammonia,dimethylamine, trimethylamine and trimethylamine-n-oxide in fish extracts by capillary electrophoresis with indirect UV-detection

A capillary electrophoretic method with indirect UV detection is described for simultaneous determination of ammonia, dimethylamine (DMA), trimethylamine (TMA) and trimethylamine-n-oxide (TMAO) in aqueous extracts of fish. A buffer consisting of 4 mM formic acid, 5 mM copper(II)sulfate and 3 mM crown ether 18-crown-6 enabled separation of the analytes in 5–10 min. The use of an extended light path capillary technique resulted in a good sensitivity and repeatability. The linear dynamic range, based on a hydrostatic injection at 50 mbar for 2 s, was from the detection limit to at least 2.5 mM. The detection limit for ammonia, DMA, TMA, and TMAO was less than 0.04 mM, corresponding to 2 mg nitrogen per 100 g fish. As an extra benefit, the method also provided a quantitative determination of potassium, sodium, calcium and magnesium ions.