Search

Adulteration/unintentional contamination of milk with melamine could have negative health and economic implications especially in the developing countries due to insufficient laboratory support and surveillance. This paper presents an Isotope Dilution Liquid Chromatography-Mass Spectrometry (ID LC-MS) method developed for detection of melamine in powdered milk. The rapid sample preparation involved dissolution of 1g of milk powder in 2.5% formic acid, precipitation of protein with acetonitrile, spiking of samples with melamine (triamine-15N3) at 200 µg L–1 and detection of intrinsic 14N-melamine molecular ratio to the spike. The isotope dilution calibration procedure was free from matrix effects, unlike other methods where the detector sensitivity can fluctuate up to several orders of magnitude. Limit of detection of the method was 13 µg kg–1, and the recovery of melamine at 50, 100, and 250 µg kg–1 was 78.7–126.3%. The method was used to determine melamine levels in 22 milk powder products (local and imported) available in Sri Lanka. Melamine was detected in all the samples (range = 0.33–0.96 mg kg–1). Full cream milk powders (both local and imported) contained melamine in the range of 0.39–0.84 mg kg–1, and various health and pregnancy formulas contained <0.5 mg kg–1 of melamine. Two imported infant formula samples contained the highest levels of melamine (0.96 and 0.94 mg kg–1). Although these melamine levels are below the regulatory limit in Sri Lanka (1 mg kg–1), a monitoring programme would ensure consumer safety. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Food Safety & Quality is the property of Journal of Food Safety & Quality Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Melamine adulteration is a fraudulent practice to increase the protein content of food in some areas of the world. In 2008, many babies in China suffered from serious illness and death because of melamine-tainted powdered infant formula. The issue prompted researchers to develop methods on detecting melamine in milk powder. Optical spectroscopy technologies have been proven to be effective in identifying and quantifying food contaminants. To provide useful information for future researches, the widely used optical spectroscopy technologies, such as near-infrared, middle-infrared, Raman, fluorescence, terahertz, hyperspectral imaging technology, etc., were introduced briefly. Then the applications of these optical spectroscopy technologies in determining melamine-adulterated milk powder in the last decade were reviewed. Meanwhile, the potential advantages and limitations of these technologies were put forward, and some suggestions for future researches in detecting melamine-adulterated milk powder were given. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Food Safety & Quality is the property of Journal of Food Safety & Quality Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Food Safety & Quality is the property of Journal of Food Safety & Quality Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Food Research & Development is the property of Food Research & Development Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A novel analytical method for melamine in milk powder has been developed and exploited with three-dimensional (3D) magnetic molecularly imprinted polymers (MMIPs) combining with liquid chromatography-tandem mass spectrometry. The 3D MMIPs were synthesized with graphene-carbon nanotube hybrid composite as carrier which can increase the accessible surface area. The products were characterized, and the binding affinity was investigated by isothermal absorption, kinetic adsorption and selective adsorption. The results showed that the 3D MMIPs exhibited high adsorption capacity with maximum adsorption capacity of 123.1 mg g −1 , fast adsorption rate (10 min) and high selectivity toward melamine. Various affecting extraction parameters were evaluated. The limit of detection was 0.00045 mg kg −1 and the recoveries were ranged from 90.3% to 95.7%. The precisions (RSDs) were lower than 4.7%. This method was applied for analyzing six milk powder samples. The result was in agreement with that obtained by the state standard method used in China. [ABSTRACT FROM AUTHOR]

Forty samples of milk powder purchased in Uruguay were analysed to assess melamine (MEL) levels. Trichloroacetic acid and acetonitrile were used to extract and precipitate milk proteins previously to clean up of the samples by solid-phase extraction and then were determined by liquid chromatography coupled to ultraviolet detection. The limit of detection (LOD) and limit of quantification (LOQ)of MEL were 0.006 and 0.019 mg kg−1, respectively. Milk was fortified with MEL at three levels, producing average recoveries higher than 83.8%. The values for positive samples ranged from 0.017 to 0.082 mg kg−1. Nine samples were positive. Three of them had concentrations between LOD and LOQ. The mean MEL contamination was 0.028 mg kg−1. Consumption of milk powder containing these levels of MEL does not constitute a health risk for consumers. [ABSTRACT FROM AUTHOR]

Milk is a vulnerable target for economically motivated adulteration. In this study, a line-scan high-throughput Raman imaging system was used to authenticate milk powder. A 5 W 785 nm line laser (240 mm long and 1 mm wide) was used as a Raman excitation source. The system was used to acquire hyperspectral Raman images in a wave number range of 103–2881 cm–1 from the skimmed milk powder mixed with two nitrogen-rich adulterants (i.e., melamine and urea) at eight concentrations (w/w) from 50 to 10,000 ppm. The powdered samples were put in sample holders with a surface area of 150 ×100 mm and a depth of 2 mm for push-broom image acquisition. Varying fluorescence signals from the milk powder were removed using a correction method based on adaptive iteratively reweighted penalised least squares. Image classifications were conducted using a simple thresholding method applied to single-band fluorescence-corrected images at unique Raman peaks selected for melamine (673 cm–1) and urea (1009 cm–1). Chemical images were generated by combining individual binary images of melamine and urea to visualise identification, spatial distribution and morphological features of the two adulterant particles in the milk powder. Limits of detection for both melamine and urea were estimated in the order of 50 ppm. High correlations were found between pixel concentrations (i.e., percentages of the adulterant pixels in the chemical images) and mass concentrations of melamine and urea, demonstrating the potential of the high-throughput Raman chemical imaging method for the detection and quantification of adulterants in the milk powder. [ABSTRACT FROM AUTHOR]

The sensitive and accurate detection of trace water in solid food products is of great significance for the protection of their stability and quality. Herein, a novel crystalline COF TAPT-BPTA with fluorescence was prepared via Schiff-base condensation reaction between 4,4′,4″-(1,3,5-Triazine-2,4,6-triyl)trianiline (TAPT) and 2,5-bis(2-propyn-1-yloxy)-1,4-benzenedicarboxaldehyde (BPTA). The fluorescence of TAPT-BPTA was sensitive to trace water and can be quenched due to the disruption of intermolecular charge transfer (ICT) process by water molecules. Hence, COF TAPT-BPTA was successfully applied for sensing of trace water in common organic solvents including acetone, acetonitrile, THF and DMF with rapid response (less than 3 s) and good sensing ranges (0.05–20 v/v% for acetone, 0.10–25 v/v% for THF, 0.05–15 v/v% for ACN, and 0.05–10 v/v% for DMF). The limit of detection of water in acetone, ACN, DMF, THF were 0.0585%, 0.0631%, 0.0185% and 0.0718% (v/v), respectively. Additionally, using TAPT-BPTA as signal probe and tris(2,2′-bipyridyl)ruthenium (II) dichloride with red fluorescent as reference, a ratiometric fluorescent sensor was prepared and successfully used for the sensing of trace water in milk powder samples. [Display omitted] • Highly crystalline 2D COF TAPT-BPTA with fluorescent was prepared at room-temperature. • The fluorescence of TAPT-BPTA can be quenched by trace water due to the block of ICT effect. • A ratiometric sensor was proposed for the detection of trace water in organic solvents and milk power sample. • Satisfactory sensing range, good sensitivity and rapid response were obtained. [ABSTRACT FROM AUTHOR]

A new magnetic molecularly imprinted polymer was coupled with ultra high performance liquid chromatography and tandem mass spectrometry for the selective determination of melamine in milk powder. The magnetic molecularly imprinted polymer has been prepared by using carbon nanotubes as the matrix, Fe3O4 particles as the magnetic ingredient, melamine as the template molecule, methacrylic acid as the functional monomer, ethylene glycol dimethacrylate as the cross-linker and polyvinylpyrrolidone as the dispersant. The polymer was characterized with scanning electron microscopy, Fourier transform infrared spectroscopy and a physical property measurement system. The isothermal adsorption, kinetics adsorption, and selectivity were studied to evaluate the rebinding properties of the magnetic molecularly imprinted polymer. Various parameters affecting the extraction efficiency such as the amount of polymer, extraction time, and eluting solution were evaluated. The limit of detection was 0.00075 mg/kg. The relative standard deviations of the intraday and interday precision are 0.4-2.7 and 2.3-5.1%, respectively. The proposed method was successfully applied to determine melamine in different milk powder samples from different provenances, and satisfactory recoveries of 89.0-95.6% were obtained. This method has great significance for quality control and is simple and suitable for the rapid determination of melamine in milk powder. [ABSTRACT FROM AUTHOR]

Since 2008, the detection of the adulterant melamine (2,4,6-triamino-1,3,5-triazine) in food products has become the subject of research due to several food safety scares. Near-infrared (NIR) hyperspectral imaging offers great potential for food safety and quality research because it combines the features of vibrational spectroscopy and digital imaging. In this study, NIR hyperspectral imaging was investigated for quantitative evaluation of melamine particles in nonfat and whole milk powders. Melamine was mixed into milk powders in a concentration range of 0.02–1.00% (w/w). A NIR hyperspectral imaging system was used to acquire images (938–1654 nm) of melamine powder, whole milk powder, nonfat milk powder, and mixtures of melamine and each of the milk powders. Two optimal bands (1447 nm and 1466 nm) were selected by a linear correlation algorithm with pure milk and pure melamine. Band ratio (B 1447/1466 ) images coupled with a single threshold were used to create resultant images to visualize identification and distribution of the melamine adulterant particles in milk powders. The identification results were verified by spectral feature comparison between separated mean spectra of melamine pixels and milk pixels. Linear correlations (r) were found between the number of pixels identified as containing melamine and melamine concentration in nonfat milk and whole milk powders, which were 0.980 and 0.970 or higher, respectively. The study demonstrated that the combination of NIR hyperspectral imaging and simple band ratioing was promising for rapid quantitative analysis of melamine in milk powders. [ABSTRACT FROM AUTHOR]

The increasingly common application of the near-infrared (NIR) hyperspectral imaging technique to the analysis of food powders has led to the need for optical characterization of samples. This study was aimed at exploring the feasibility of quantifying penetration depth of NIR hyperspectral imaging light for milk powder. Hyperspectral NIR reflectance images were collected for eight different milk powder products that included five brands of non-fat milk powder and three brands of whole milk powder. For each milk powder, five different powder depths ranging from 1 mm-5 mm were prepared on the top of a base layer of melamine, to test spectral-based detection of the melamine through the milk. A relationship was established between the NIR reflectance spectra (937.5-1653.7 nm) and the penetration depth was investigated by means of the partial least squares-discriminant analysis (PLS-DA) technique to classify pixels as being milk-only or a mixture of milk and melamine. With increasing milk depth, classification model accuracy was gradually decreased. The results from the 1-mm, 2-mm and 3-mm models showed that the average classification accuracy of the validation set for milk-melamine samples was reduced from 99.86% down to 94.93% as the milk depth increased from 1 mm-3 mm. As the milk depth increased to 4 mm and 5 mm, model performance deteriorated further to accuracies as low as 81.83% and 58.26%, respectively. The results suggest that a 2-mm sample depth is recommended for the screening/evaluation of milk powders using an online NIR hyperspectral imaging system similar to that used in this study. [ABSTRACT FROM AUTHOR]

• Acrylated citric acid based polimeric sensor was used for the first time for melamine determination. • The novel sensor presented high sensitivity for very low concentration of melamine up to 2.32 × 10−10 mol L−1. • The response time of the sensor was really short (less than 60 sec.). • The sensor can be applied to determine the melamine adulteration in milk powder. Melamine selective acrylate citric acid (ACA) based polymeric membrane sensor was prepared by radical polymerization method and the sensor was characterized. The sensor showed a selective fluorescent response to melamine (λ ex /λ em = 388/425 nm). The sensor response is linear in the concentration range of 3.96 × 10−9 to 7.93 × 10−8 mol L−1, the optimum pH value is 6.0 and response time is less than 1 min. Limit of detection (LOD) and limit of quantification (LOQ) were calculated as 2.32 × 10−10 mol L−1 and as 7.74 × 10−10 mol L−1, respectively. The sensor showed great selectivity towards melamine in the presence of a large number of molecules and ions. The performance of sensor was also confirmed by determining of melamine in milk powder sample and the results were compared with HPLC results and acceptable results were obtained. As a conclusion, the results revealed that the proposed sensor is an interesting alternative for melamine determination. [ABSTRACT FROM AUTHOR]

Milk and its products are important and widely traded food commodities, which made them the target for adulteration. Fourier Transform Infrared spectroscopy (FTIR) is one of the most widely used methods to identify chemical contaminations and determine their concentrations. In the present work, two-dimensional correlation spectroscopy (2D-COS) was applied to analyse FTIR spectra of milk powder having different concentration of melamine. With the help of sequential order analysis, the FTIR band at 815 cm−1 was determined as the most qualified FTIR band for carrying quantitative analysis. It is recommended to perform 2D-COS and determine the sequential order of intensity change among all peaks of the contamination. This is to establish the appropriate bands for quantitative analysis, and help to improve the values of analytical parameters. • FTIR spectrum of milk powder was examined for melamine adulteration. • 2D-COS-FTIR and the sequential analysis were used to determine a quantitative band. • The band at 815 cm−1 was the most qualified band for quantitative analysis. • The proposed method is particularly important when dealing with new adulterations. • FTIR combined with 2D-COS are powerful tools in milk powder adulteration. [ABSTRACT FROM AUTHOR]

Poly(caffeic acid) polymer was immobilized onto the surface of a glassy carbon electrode via electropolymerization. Voltammetry shows a signal related to the two-electron oxidation of the immobilized hydroquinone groups in the caffeic acid monomer units. The modified electrode in aqueous solution shows complexation of the electrogenerated o-quinone species with melamine thus allowing in the electrochemical detection of melamine by recording the shift in potential of the oxidation signal of the polymer. Melamine detection was investigated in pure aqueous solutions and in the presence of milk powder solutions and the proposed analytical method of melamine detection in milk powder was applied successfully with an average recovery of ca. (91±7.9)%. [ABSTRACT FROM AUTHOR]

We have synthesized silver nanoparticles (AgNPs) decorated with α-cyclodextrin (CD) by using the traditional silver mirror reaction in the presence of CD. The CD-AgNPs were used as substrate in surface-enhanced Raman spectroscopy (SERS) for determining melamine. The intensity of the Raman band of melamine at 704 cm was used to determine melamine in milk and milk powder. The use of CD-AgNPs as the SERS substrate rather than classical silver nanoparticles makes the method more sensitive in giving an enhancement by a factor of up to ~ 10 in scattering efficiency. The effects of the volume of solutions (of CD-AgNPs, NaCl, NaOH, melamine) and of mixing time were optimized. The standard addition method was employed for quantitative analysis. The correlation coefficient of the calibration plot is 0.9995, and the limit of detection is 3.0 μg L. The method was successfully applied to the determination of melamine in milk and milk powder, with relative standard deviations of <10 % and recoveries between 89 and 104 %. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

A sensitive ELISA method was developed based on a monoclonal antibody to detect melamine in milk powder. Two haptens were prepared using the melamine structural analogue, 2-chloro-4, 6-diamino-1, 3, 5-triazine. The obtained antibody belonged to the IgG1κ family and had high affinity for melamine (affinity constant was 3.09×109). The antibody could also recognise cyromazine (cross-reactivity was 131%) and had low cross-reactivity toward the haptens. The effects of pH, ionic strength and organic solvents on ELISA performance were evaluated. The lowest IC50value (6.0±0.55 ng/mL) and the limit of detection in milk powder, 50 ng/g, were achieved under optimised conditions. Milk powder spiked at two levels of melamine (100 ng/g and 500 ng/g) was analysed with this ELISA method. Good recovery was obtained (76.2±7.3% at the 100 ng/g spiked level and 91.4±5.0% at 500 ng/g). [ABSTRACT FROM PUBLISHER]

A pilot study (APMP.QM-P19) of the Asia Pacific Metrology Program for the determination of melamine at two different levels in milk powder was organized in 2010. It was the first interlaboratory comparison programme in measuring melamine in food matrices for metrology institutes in the region. Melamine was chosen as the target analyte because of the recent crises that happened in 2007 and 2008 had caused substantial concern from consumers, food manufacturers, policy makers on food safety and the food testing communities. The objectives of APMP.QM-P19 were to evaluate the testing capability of participants on the quantification of trace level melamine in milk and milk products and to investigate the degree of equivalence with respect to the assigned values. In total, 19 laboratories (11 metrology institutes and eight food testing institutes) enrolled in the study. Analytical techniques reported by participants included liquid chromatography with ultra-violet and tandem mass spectrometry, gas chromatography with high-resolution mass spectrometry and enzyme-linked immunosorbent assay. Dispersion of analytical data in the two test materials was significant, and normal Gaussian distribution of data was not observed. The median was agreed to be used as the assigned values in the programme. Metrology institutes who employed isotope dilution mass spectrometry technique were found to give more consistent results and higher degree of equivalence than others. The performance of most of the food testing institutes was not satisfactory, and they were encouraged to have a thorough review of their validation procedure and estimation of uncertainty. [ABSTRACT FROM AUTHOR]

Melamine made headlines in September 2008 because it was found to be the contaminant responsible for the deaths of several infants and making many more sick. Determination of trace melamine is very important. Therefore, in this work a novel, sensitive and reliable method was developed using differential pulse polarography. The most suitable buffer system was found to be Britton-Robinson (B-R) buffer, pH 11.2. The melamine peak in this medium appeared at about −50 mV, it responded well to standard additions and high reproducibility was obtained. The calibration graph was linear in the concentration range of melamine from 1.0 to 66.4 μM with a correlation coefficient of 0.999. The limit of detection (LOD) and limit of quantification (LOQ) were obtained as 0.3 and 1.0 μM, respectively. The current was characterized as being adsorption-controlled process. The proposed method was successfully applied to the determination of melamine in spiked milk and milk powder. The linear dynamic ranges observed for melamine concentration in milk and milk powder samples were between 1-58 and 10-57 μM, respectively. The sufficiently good recoveries and low standard deviations for the data reflect the high accuracy and precision of proposed differential pulse polarographic method. [ABSTRACT FROM AUTHOR]

We report here a simple and easy electrochemical approach for sensitive detection of non‐electroactive melamine using a disposable screen printed carbon electrode (SPCE) with uric acid as the recognition element. It is based on the competitive adsorptive behavior of melamine at the preanodized SPCE causing suppression in the oxidation current of uric acid. A linear range up to 126 ppb with a detection limit of 1.6 ppb (S/N=3) is achieved at the preanodized SPCE by differential pulse voltammetry. The electrochemical method is successfully applied to detect the melamine content in tainted milk powder and dog food. [ABSTRACT FROM AUTHOR]

Abstract: A high-performance micellar electrokinetic capillary chromatography with amperometric detection (MECC–AD) method for the fast determination of melamine (MM), occasionally used to increase the apparent protein content of milk products, has been developed. Method development involved optimisation of the working electrode, the running buffer system and acidity, the concentration of sodium dodecyl sulphate (SDS), the separation voltage, the applied potential and the sample injection time. Under the optimum conditions, MM can be well separated from its co-existing interferences in real-world samples within 9min at the separation voltage of 20kV in a 8mmol/L SDS/20mmol/L H3BO3–Na2B4O7 running buffer (pH 7.4). Satisfactory recovery (83.3–105.5%), repeatability of the peak current (3.2%) and migration time (3.8%), and the limit of detection (2.1×10−6 g/mL) for the method were achieved. This proposed procedure has been successfully used for the determination of MM in milk products. [Copyright &y& Elsevier]

Abstract: The use of fast semi-automated method employing direct analysis in real time (DART) ion source coupled to time-of-flight mass spectrometry (TOFMS) for analysis of melamine (MEL) and cyanuric acid (CYA) in milk powder and milk based products has been demonstrated in this study. Simple sample extraction procedure employing methanol–5% aqueous formic acid mixture, which enabled disruption of melamine–cyanurate complex, was followed by direct, high-throughput (30s per run) examination of sample extracts spread on a glass rod by mass spectrometry under ambient conditions, without any prior chromatographic separation. After optimization of instrument parameter settings, limits of detection (LODs) 170 and 450μgkg−1 were achieved for MEL and CYA, respectively. In the final phase of study, the possibility of minimizing spectral interference, thus improving method performance characteristics through the use of ultrahigh resolving power offered by Orbitrap based mass analyzer is demonstrated. [Copyright &y& Elsevier]

Abstract: Melamine adulterant in milk powder was detected using a portable compact Raman spectrometric system. Melamine-free milk powder from a domestic brand was used as blank control after verification by HPLC tandem mass spectrometry. Melamine fortified in milk powder was identified with good reproducibility by two characteristic vibration modes at 673 and 982cm−1. The intensity of the first mode was used to quantify melamine adulterant in milk powder. A detection limit (DL) of 0.13% and a good partial least squares (PLS) analysis model were obtained. As a fast-screening scheme, the method could be suitably applied to on-site quality control of dairy products and market surveillance. [Copyright &y& Elsevier]

Capillary electrophoretic (CE) technique was developed for a rapid determination of melamine. The optimized separations were carried out in 50 mmol/l tris(hydroxymethyl) aminomethane-phosphate electrolyte (pH 2.5) using a capillary coated with a poly(diallyldimethylammonium chloride)/poly(sodium-4-styrenesulfonate) bilayer and direct UV detection at 214 nm. The calibration curve was linear in the concentration range 0.2-10.0 mg/l for melamine with correlation coefficients higher than 0.9997. The detection limit was 0.06 mg/l. The proposed method was applied for a rapid determination of melamine in milk powder samples. The recovery tests established for real samples were within the range 93.5-104%. [ABSTRACT FROM AUTHOR]

Background: A major food safety incident in China was made public in September 2008. Kidney and urinary tract effects, including kidney stones, affected about 300,000 Chinese infants and young children, with six reported deaths. Melamine had been deliberately added at milk-collecting stations to diluted raw milk ostensibly to boost its protein content. Subsequently, melamine has been detected in many milk and milk-containing products, as well as other food and feed products, which were also exported to many countries worldwide. Objectives: The melamine event represents one of the largest deliberate food contamination incidents. We provide a description and analysis of this event to determine the global implications on food and feed safety. Discussions: A series of factors, including the intentional character of the milk contamination, the young age of the population affected, the large number of potentially contaminated products, the global distribution of these products, and the delay in reporting led this event to take on unexpected proportions. This incident illustrated the complexity of international trade of food products and food ingredients that required immediate actions at international level. Conclusion: Managing food-safety events should be done internationally and early on as soon as multinational consequences are expected. Collaboration between food-safety authorities worldwide is needed to efficiently exchange information and to enable tracking and recalling of affected products to ensure food safety and to protect public health. [ABSTRACT FROM AUTHOR]