Melamine Content Research Articles

Rapid quantification models for assessing melamine adulteration in sport nutrition supplements via benchtop and portable NIRS instruments

Sport nutrition supplements (SNS) are vulnerable to adulteration with melamine, artificially augmenting their protein content as determined by conventional assay methodologies. Vibrational spectroscopy techniques are suitable for the detection of adulteration because they allow rapid analysis, require minimal sample preparation, and can perform numerous analyses in a short time. The aim of this study was to develop rapid quantification models for the determination of melamine adulteration in a variety of SNS matrices using NIRS (near-infrared spectroscopy) in combination with multivariate data processing. Moreover, a comparison of benchtop and portable NIR instruments was carried out. Employing a stepwise approach involving OPLS-DA and PLS analysis, matrix discrimination and prediction ability were investigated. The benchtop instrument effectively discriminated among matrices (R2Y = 0.964, Q2 = 0.933), while the portable device, although showing a slightly altered pattern, maintained favorable discrimination capability (R2Y = 0.966, Q2 = 0.931). The quantitative PLS models for each SNS matrix exhibited comparable statistical indicators for both instruments with reasonable errors for melamine content estimation and prediction (RMSEE: 0.3–2.4 %, RMSEP: 0.98–2.99 %). Higher estimation and prediction errors were observed for protein-containing samples in both acquisition modes, probably due to the tendency of protein agglomeration and adhesion to different surfaces, which affects the homogeneity of the powder. Despite data loss due to the narrower spectral range and lower resolution of the portable instrument, all models were found to be suitable for predicting melamine content in sport nutrition supplements.

Lightweight nitrogen‐doped phenolic composites with enhanced thermal ablation‐insulation performance by improving pyrolysis gas blocking effect

AbstractLightweight phenolic ablative composites are considered to be the most reliable materials for thermal protection systems. However, improving the thermal ablation‐insulation performance of heritage phenolic aerogel‐based ablators for extremely complex environments is still necessary. Herein, from the perspective of enhancing the gas‐blocking effect, we design and fabricate a series of needle quartz fiber‐reinforced melamine‐phenolic aerogels (NQF/MPAs) composites by polycondensation of melamine and phenolic in a sol–gel process, followed by ambient drying. The effects of melamine content on the comprehensive performance are analyzed. The prepared nitrogen‐doped phenolic aerogel composites exhibit low density of 440–490 kg/m3, high tensile strength of 36.3–39.1 MPa, and low thermal conductivity of 0.041–0.043 W/(m·K) at room temperature. Simultaneously, the modified composite exhibits excellent high‐temperature insulation property with lower equivalent thermal conductivity of 0.045 W/(m·K) at 1000°C. In arc wind tunnel testing of 130 kW/m2 for 1000 s, the linear recession rates of the composites show a great improvement from 3.7 × 10−6 to 2.5 × 10−6 m/s with the proper introduction of melamine. Furthermore, a one‐dimensional finite element model is stablished, which indicate the introduction of melamine can significantly improve the mass flow rate of pyrolysis gas and the corresponding block factor is enhanced from 0.958 to 0.848.Highlights Economic sol–gel method and ambient drying for composites production. Phenolic aerogel‐based ablative composite with enhanced gas blocking effect. The pyrolysis gas blocking effect is controllable with melamine content. Combined experimental‐simulation approach for ablators designing.

Hierarchical carbon nanotubes-modified heterogeneous composites derived from melamine-mixed ZIF-67/MXene for broadband microwave absorption

In this paper, carbon nanotubes (CNTs) modified TiO2/C/Co@C composites (TiO2/C/Co@C(CNTs)) with good electromagnetic (EM) wave properties were synthesized originated from ZIF-67/MXene composites supplemented with external carbon source melamine by in situ synthesis and high temperature pyrolysis. The effect of the melamine content on the microstructure, EM parameters, and the microwave absorption (MWA) properties of the TiO2/C/Co@C(CNTs) composites was investigated. The results showed that the in-situ grown CNTs were organically connected to the pyrolyzed ZIF-67/MXene derivatives to form a hybrid network structure. The composites achieve the minimum reflection loss (RLmin) value of −47.52 dB at a thickness of 1.5 mm, the effective absorption bandwidth (EAB) of 5.06 GHz at 1.8 mm with the RLmin value of −41.35 dB, and the RLmin value of −52.43 dB at 6.18 GHz. The excellent EM wave attenuation ability of the TiO2/C/Co@C(CNTs) composites covers nearly the entire frequency band of 2–18 GHz with the RLmin value almost less than −30 dB in the thickness of 1.5–5.0 mm. The unique microstructure, dielectric-magnetic synergistic effect, and multiple interfacial polarization optimize the impedance matching. This word proposes a promising new strategy for constructing highly efficient MOF-derived and MXene-based microwave absorbers.

Determination of melamine contamination in milk with various packaging: a risk assessment study.

Melamine is one type of monomer used as starting substance in manufacturing packaging lining in many countries worldwide. Environmental and food contamination is an issue constantly discussed. In the present study, the melamine content in milk samples with three package types was measured by HPLC/UV. Melamine is not a lipophilic compound. Therefore, the selected samples were low-fat milk. The melamine content in various packaged milk, including packet, polyethylene bags, and plastic packaging, is 790 ± 39.8, 50.7 ± 13, and 57.7 ± 24.54ppb, respectively. According to the existing standards, the measured values in all the milk samples were lower than the permitted limits. The risk assessment for adults and children showed that the HQ value for both age groups was less than 1. Therefore, milk consumption will not pose a health risk in terms of contamination with melamine.

Thermal cure kinetics of cold-setting melamine–urea–formaldehyde resins with high melamine content

Thermal cure kinetics of cold-setting melamine–urea–formaldehyde resins with high melamine content

Residual neural networks to quantify traces of melamine in yogurts through image deconvolution

This work combines intelligent algorithms based on transfer learning and residual neural networks (viz., ResNet34) to process and classify optical images of pure and adulterated yogurt samples. This integration aims to detect the presence of melamine in yogurt in concentrations ranging from 1 to 10 ppm. An image database of 1,888 images is used to train the ResNet34, and 212 blinded images to test and validate its performance. The optimized intelligent algorithm is able to classify the images into 21 classes considering the yogurt type and melamine content, obtaining an accuracy of over 94%. These encouraging results certify a simple yet powerful real-time quality control method for producers and distributers to ensure food safety for the final consumers, while pinpointing the source of potential fraudulent procedures.

Facile Preparation and Improved Electrochemical Performance of Oxygen‐Enriched Porous Carbon Materials Based on Diacetal‐Containing Polybenzoxazine

AbstractPorous oxygen‐doped carbon materials based on the copolymers of a diacetal‐type benzoxazine (ACE‐a) and melamine with different ratios are prepared by a facile template‐free method. The oxygen‐rich diacetal structure in ACE‐a allowed for a high oxygen content of 66.2% in surface in these porous carbon materials, and the degradation of the melamine at a high temperature gave an ideal pore structure with a specific surface area of 1383.9 m2 g−1 and a pore capacity of 0.748 cm3 g−1. The electrochemical performances are analyzed by Cyclic voltammetry (CV) and Galvanostatic charge‐discharge (GCD) tests, and the effects of melamine contents and electrolyte types are also investigated. The results suggested that this material possessed specific capacitance of 430 F g−1 in 0.5 M H2SO4 and 194 F g−1 in 6 M KOH (0.5 A g−1), respectively, and showed excellent charge‐discharge behavior and magnification characteristic. Moreover, the copolymerization reactions, crosslinking structures, and degradation process of the benzoxazine/melamine copolymers are studied by differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis‐infrared spectrometry (TGA‐IR), respectively. This kind of oxygen‐enriched porous carbon material has a good applicative prospect in the field of supercapacitor.

Safety level and risk assessment of melamine migration from food contact materials

The residuals of melamine from food contact materials (FCMs) can contaminate into foods. To protect consumer health, the European Union has issued Commission Regulation (EU) No 1282/2011 about specific migration limit (SML) of melamine at 2.5 mg/kg. Therefore, this research was to study the migration of melamine from FCMs which were collected from local markets in 4 regions including Central, Northeast, North and South by using 3% (w/v) acetic acid and high performance - liquid chromatography (HPLC). The extraction method was performed at 70 °C for 2 hours. The amounts of melamine in samples were tested to estimate dietary exposure. The average of melamine content was found at 13.5 mg kg-1 for all types of FCMs. This result had been evaluated for the exposure assessment of melamine and found that various kinds of foods such as rice, fresh milk, beverage and water have high risk depending on food type, age, intake and food packaging used. The highest risk was found in fresh milk for aged 0-3 years and drinking water for aged more than 3 years at 97.5 percentile and eater only. Therefore, the food types with high consumption may have been concerned high risk and avoid misuse of melamine containers in order to prevent a health hazard.

A molecular dynamics study on the miscibility and morphology of polyester blends used in coil coatings

Computational simulations can be used to save on both time and costs, complementing experimental work and providing further guidance. Blends of immiscible polymers induce phase segregation, and in some cases can produce useful multicoat systems. This work uses a range of molecular dynamics simulations methods, including an extended Flory Huggins Interaction Parameter (χ) approach to initially probe the interactions and miscibility between ester monomers commonly used in coil coatings. The work indicates that blends with similar backbone structures or “like with like” show increased miscibility and those with different structures lead to a larger χ value and immiscibility. Further to this, polyester blends with different backbone structures have been coarse grained with MARTINI beads and simulations of 10 μs have been run to identify the morphology of the blends at the mesoscopic level. Finally, simulations of the melamine crosslinker commonly used in polyester formulations are consistent with the previously seen formation of agglomerates at higher melamine content.

Preparation and characterization of a melamine-urea-glyoxal resin and its modified soybean adhesive

Although polyamidoamine-epichlorohydrin (PAE)-modified soybean meal (SM) adhesives exhibit desired bond properties and technological applicability, their commercial application is still limited by the high cost of PAE resin. In this study, a formaldehyde-free crosslinking agent, melamine-urea-glyoxal (MUG) resin for SM adhesive, was developed based on investigations of the effects of melamine content and storage time on the structure and properties of MUG resin and MUG-modified SM adhesive. The test results confirmed that melamine could effectively copolymerize with glyoxal and urea to form an aldehyde-terminated MUG resin that was crosslinkable to soybean protein. The melamine content in MUG had important effects on the bond properties of the SM adhesive, attributed to the incorporation of aromatic triazine rings into the aliphatic urea-glyoxal chains and the greater reactivity and functionality of melamine than urea. However, the addition of melamine at more than 10% led to a shorter storage time of MUG resin and worse bond properties of MUG-modified SM adhesive. Owing to the further reactions of residual aldehyde and amino groups of MUG resin, the water resistance of the MUG-modified SM adhesive decreased with the storage time of the MUG resin. The allowable storage of the optimal MUG-10 resin was 3 weeks to ensure an acceptable bonding quality. Due to the much lower cost of MUG resin than PAE resin, it is beneficial for the wide commercial applications of formaldehyde-free SM adhesives in wood composites.

Fabrication of the cerium dioxide@carbon quasi-aerogels for anti-interference detection of melamine

Improper addition of melamine in milk powder poses a threat to human health, but the interference of complex components makes the trace detection hard. The cerium dioxide@carbon quasi-aerogels (CeO2@C-QAs) with Schottky barrier was successfully prepared to detect melamine in milk powder. The interfacial effects of Schottky barrier on electrochemical detection are studied and find energy barrier can be used as a novel electrochemical driving factor to achieve anti-interference sensing. The highly sensitive detection of melamine was achieved at acidic and alkaline environments. It obtained the good recovery rate and exhibited anti-interference in real milk powder detection. The lowest detection limit (2.19 nM) was much lower than the international safety threshold of melamine content. It affords an inspiring chance to achieve anti-interference electrochemical detection by using the interfacial energy barrier effects.

Visible light activation of photocatalysts formed from the heterojunction of sludge-generated TiO2 and g-CN towards NO removal

The feasibility of preparing TiO2/g-CN heterojunction from Ti-incorporated dried dye wastewater sludge is explored in this study. Two reaction routes of composite formation were evaluated. In the initial approach, one-step calcination of dried sludge and melamine mixture @600 °C was carried out. Detailed morphological and chemical characterizations showed that the one-step calcination route did not create TiO2/g-CN composites; instead, only N-doped anatase TiO2 composites were formed. Moreover, due to the non-uniform composition of organic content in the dried sludge, it was not easy to control the N doping level by varying melamine content (0–100%) in the precursor mix. However, successful formation of anatase TiO2 and g-CN was observed when a two-step calcination route was followed, i.e., via synthesis of anatase TiO2 from dried sludge, and later development of heterojunction by calcining (@550 °C) the TiO2 and melamine mixture. X-ray diffraction along with infrared and X-ray photoelectron spectroscopy verified the effective heterojunction. In addition, maximum atmospheric NO removal under UV and visible light were observed for the prepared composite when the melamine content in the precursor mixture was 70%. After 1 h of UV and visible light irradiation, the best TiO2/g-CN composite removed 25.71% and 13.50% of NO, respectively. Optical characterization suggested that the enhanced NO oxidation under UV/visible light was due to the bandgap narrowing and diminished photogenerated electron-hole recombination.

A Comparison of Adhesion Behavior of Urea-Formaldehyde Resins with Melamine-Urea-Formaldehyde Resins in Bonding Wood

This paper reports a comparison of adhesion behavior of urea-formaldehyde (UF) with those of melamine-urea-formaldehyde (MU) resins in bonding wood by analyzing the results published in literatures. For this purpose, the adhesion behavior of UF resins prepared by blending low-viscosity resin (LVR) with high-viscosity resin (HVR) at five different blending and two formaldehyde/urea (F/U) molar ratios (1.0 and 1.2) was compared with those of two MUF resins synthesized by either simultaneous reaction (MUF-A resins) or multi-step reaction (MUF-B resins) with three melamine contents (5, 10, and 20 wt%). As the blending (LVR:HVR) ratio increased from 100:0 to 0:100, the viscosity and molar mass (Mw and Mn) of the blended UF resins increased while the gelation time decreased. The interphase features such as maximum storage modulus (E′max), resin penetration depth, and bond-line thickness of the UF resins increased to a maximum and then decreased as the blending ratio increased. In addition, both MUF-A and MUF-B resins also showed an increase in the Mw and Mn as the melamine content increased from 5% to 20%. However, the E′max, resin penetration depth, and bond-line thickness of the MUF resins decreased as the molar mass or melamine content increased. These results indicated that the adhesion of UF resins heavily depends on the interphase features while that of the MUF resins highly depends on the cohesion of the resins.

A Method of Measuring Wood Failure Percentage of Wood Specimens Bonded with Melamine-Urea-Formaldehyde Resins Using Image Analysis

Transparent and colorless melamine-urea-formaldehyde (MUF) resins make it difficult to identify the area of wood failure percentage (WFP) in the fracture surface of bonded wood specimens. Therefore, in this study, we develop a method of measuring WFP after the adhesion strength measurement of MUF resins under shear stress. The fractured wood surface of block shear strength (BSS) specimens bonded with cold-setting MUF resins at three melamine contents (20%, 30%, and 40%) was marked black, and then, WFP was accurately measured via image analysis. WFP values measured using this method consistently increased with BSS as the melamine content increased, showing the reliability of this new method. The results suggested that this new method is useful and reliable for measuring the WFP of the fracture surface of wood specimens bonded with colorless adhesives such as urea-formaldehyde, MUF, and melamine-formaldehyde resins.

Generic models for rapid detection of vanillin and melamine adulterated in infant formulas from diverse brands based on near-infrared hyperspectral imaging,

Research has shown that near-infrared hyperspectral imaging (NIR HSI) is an effective rapid-detection tool for milk powder adulteration, but model generality under different adulteration conditions requires further study. Therefore, this study focused on developing generic models for the detection of vanillin and melamine in infant formulas from diverse brands. Three pretreatment algorithms were applied successively to spectrum of each pixel in hyperspectral images. Minimum noise fraction was applied to eliminate interference from brand diversity and extract adulterant information. Partial least squares discriminant analysis (PLSDA) was used to develop a classification model to identify vanillin-rich pixels. The PLSDA model, developed with three optimal wavelengths selected by the successive projections algorithm (SPA), detected vanillin at concentrations as low as 0.01%. Partial least squares regression (PLSR) was applied to establish a quantitative model for melamine. The PLSR model, established with six optimal wavelengths selected by the competitive adaptive reweighting algorithm (CARS), showed excellent predictive capabilities, with a limit of detection of 0.5%. A visual prediction map clearly showed the location of vanillin-rich pixels and melamine content variations spatially. The proposed generic practical method would greatly facilitate the application and promotion of NIR HSI technology in quality inspection for the milk powder market and manufacturers.

Screening , analysis and health impact of melamine residues in milk powder and dry milk infant’s formula by ELISA in Mansoura city, Egypt.

Objective: In recent years, milk and dairy products have been associated with several types of adulterations that have hazard effects onto our health. One of the most famous types of adulteration that rich with nitrogen is melamine. Subsequently, this study aimed to determination the prevalence of melamine in some milk products and analysis it using ELISA. Materials and Methods: Fifty samples of imported and local dry milk infant formula (25 each), and 25 samples of imported milk powder, were purchased from different markets and outlets in Mansoura city, Egypt. Theses samples were closely undertaken and analyzed to stand up on melamine contents of them. Results: The results of the examined samples were matched within the permissible codex alimantarius (1995). The limits of detection for melamine in dry milk infant formula and milk powder were 1 mg/kg and2.5 mg/g, respectively. Conclusion: From our results, we can say that ELISA kits is an effective and more economical tool for analysis of suspected milk samples containing melamine instead of extensive sample preparation or other expensive methods.

Study of the interaction mechanism between hydrophilic thiol capped gold nanoparticles and melamine in aqueous medium

In the last years, intense efforts have been made in order to obtain colloidal-based systems capable of pointing out the presence of melamine in food samples. In this work, we reported about the recognition of melamine in aqueous solution, using gold nanoparticles stabilized with 3-mercapto-1-propanesulfonate (AuNPs-3MPS), with the aim of deepening how the recognition process works. AuNPs were synthesized using a wet chemical reduction method. The synthesized AuNPs-3MPS probe was fully characterized, before and after the recognition process, by both physicochemical (UV–vis, FT-IR, 1H-NMR, DLS and ζ-potential) and morphostructural techniques (AFM, HR-TEM). The chemical and electronic structure was also investigated by SR-XPS. The sensing method is based on the melamine-induced aggregation of AuNPs; the presence of melamine was successfully detected in the range of 2.5−500 ppm. The results achieved also demonstrate that negatively charged AuNPs-3MPS are potentially useful for determining melamine contents in aqueous solution. SR-XPS measurements allowed to understand interaction mechanism between the probe and the analyte. The presence of sulfonate groups allows a mutual interaction mediated by electrostatic bonds between nanoparticles surface thiols and positively charged amino groups of melamine molecules.

Detecting melamine‐adulterated raw milk by using near‐infrared transmission spectroscopy

AbstractChinese national standards regulate that the melamine in infant food should not exceed 1 mg/kg. To quickly and accurately identify whether the melamine in raw milk exceeds the limit, near‐infrared transmission (NIRT) spectra of 220 raw milk samples and 380 melamine‐adulterated raw milk samples were collected over the spectral range of 900–1,700 nm. Different spectral preprocessing and dimension reduction methods were used to preprocess the data of full spectra with 425 wavelengths. The qualitative prediction models of partial least squares discriminate analysis (PLS‐DA) and support vector machine (SVM) were built based on full spectra and reduced data. The results showed that the SVM was better than PLS‐DA in identifying the melamine‐adulterated raw milk whose melamine contents exceeded the limit of 1 mg/kg. The established SVM model using full spectra had the optimal prediction performance with the accuracy rate of 92.67%, sensitivity of 89.09%, and specificity of 94.74%. The study indicates that the raw milk whose melamine contents exceed the limit of 1 mg/kg could be identified by using NIRT spectroscopy.Practical ApplicationsThis study demonstrated that the raw milk whose melamine contents exceed the limit of 1 mg/kg could be identified by using near‐infrared transmission spectroscopy. The results provide technical support and effective information for developing portable instrument to detect melamine‐adulterated raw milk in situ or in field.

Effect of synthesis parameters of cold-setting melamine-urea-formaldehyde resins on the adhesion in wood bonding

This work studied the effect of the synthesis parameters (i.e. synthesis method and melamine content) on the adhesion of cold-setting melamine-urea-formaldehyde (MUF) resins in wood bonding. Two types of cold-setting MUF resins were synthesized: MUF-A resins with three melamine contents (30, 40, and 50 wt%) prepared by the simultaneous reaction of urea, formaldehyde, and melamine, and MUF-B resins with the same melamine levels but synthesized by a sequential reaction process of melamine with formaldehyde and urea. The curing behaviors of both resins were characterized by differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA), and their adhesion performance in the dry and wet states were compared in block-shear strength (BSS) and wood failure (WF) tests. As the melamine content increased, the viscosity and peak temperature (Tp ) of the resins increased. However, MUF-B resins showed lower activation energy (Ea ) than those of MUF-A resins. Dynamic and isothermal DMA scans also showed that MUF-B resins also had greater maximum storage modulus (E′max) than those of MUF-A resins in their neat resins and resins/wood composites, indicating stronger interphase adhesion and cohesion. Lower Tp , lower Ea , and higher E′max, of MUF-B resins than those of MUF-A resins resulted in higher BSS and WF of MUF-B resins in wood bonding. In particular, MUF-B resins with 40% melamine showed the highest BSS and WF. These results indicate that the MUF resin synthesis method is closely related to the adhesion performance in wood bonding.

Preparation of N-doped porous carbons via high internal phase emulsion template

Heteroatom doped porous carbon materials have great application prospects in supercapacitors. In the present study, an approach of preparing N-doped porous carbon (NPC) was proposed from porous poly(resorcinol-formaldehyde-melamine) monoliths which were prepared by high internal phase emulsion (HIPE) template. Melamine was dissolved in the external phase and copolymerized, acting as the N source and porous structure regulator to provide micropore-dominant NPCs. The structure, morphology, specific surface area (SSA), and chemical composition of the samples were systematically studied. With melamine content increasing, N-doping content in NPC increased while the SSA of NPC increased at first and then decreased. When the content of N is 8.42 ​wt%, the obtained NPC showed the highest SSA of about 1670 ​m2 ​g−1. Furthermore, high N doping content could improve the electronic conductivity and provide additional pseudocapacitance of NPC. Under the combined influences of proper N content and high porosity, the prepared NPC electrodes revealed excellent specific capacitance (228.0 ​F ​g−1 at 1.0 ​A ​g−1), favorable circling stability, and prominent rate capability in a three-electrode system with 6 ​M KOH solution as the electrolyte.