Your browser doesn't support javascript.
Mostrar: 20 | 50 | 100
Resultados 1 - 6 de 6
Mais filtros

Base de dados
Intervalo de ano de publicação
J Agric Food Chem ; 67(31): 8425-8430, 2019 Aug 07.
Artigo em Inglês | MEDLINE | ID: mdl-31322874


In recent years, non-targeted methods have been a popular "buzz" phrase in food fraud detection. Using analytical instrumentation techniques, non-targeted methods have been developed and applied in many food and agricultural situations. However, confusion and misstatements remain regarding how the methods are used. This perspective will discuss the definitions related to non-targeted testing, the procedure of developing and validating methods, the techniques and data analysis, and opportunities and challenges regarding the use of this class of analytical methods. The perspective seeks to provide readers with the latest information regarding recent advances in the use of non-targeted methods.

Análise de Alimentos/métodos , Contaminação de Alimentos/análise , Cromatografia Líquida/métodos , Eletroforese Capilar/métodos , Análise de Alimentos/instrumentação , Humanos , Espectroscopia de Ressonância Magnética/métodos , Espectrometria de Massas/métodos
J Agric Food Chem ; 65(28): 5799-5809, 2017 Jul 19.
Artigo em Inglês | MEDLINE | ID: mdl-28617599


The United States Pharmacopeial Convention has led an international collaborative project to develop a toolbox of screening methods and reference standards for the detection of milk powder adulteration. During the development of adulterated milk powder reference standards, blending methods used to combine melamine and milk had unanticipated strong effects on the near-infrared (NIR) spectrum of melamine. The prominent absorbance band at 1468 nm of melamine was retained when it was dry-blended with skim milk powder but disappeared in wet-blended mixtures, where spray-dried milk powder samples were prepared from solution. Analyses using polarized light microscopy, Raman spectroscopy, dielectric relaxation spectroscopy, X-ray diffraction, and mass spectrometry indicated that wet blending promoted reversible and early Maillard reactions with lactose that are responsible for differences in melamine NIR spectra between wet- and dry-blended samples. Targeted detection estimates based solely on dry-blended reference standards are likely to overestimate NIR detection capabilities in wet-blended samples as a result of previously overlooked matrix effects arising from changes in melamine hydrogen-bonding status, covalent complexation with lactose, and the lower but more homogeneous melamine local concentration distribution produced in wet-blended samples. Techniques used to incorporate potential adulterants can determine the suitability of milk reference standards for use with rapid detection methods.

Análise de Alimentos/métodos , Contaminação de Alimentos/análise , Leite/química , Triazinas/análise , Animais , Bovinos , Lactose/análise , Pós/química , Espectroscopia de Luz Próxima ao Infravermelho/métodos
Appl Spectrosc ; 71(2): 308-312, 2017 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-27329831


A portable Raman system with an immersion fiber optic probe was assessed for point-of-collection screening for the presence of adulterants in liquid milk. N-rich adulterants and sucrose were measured in this proof-of-concept demonstration. Reproducibility, limit of detection range and other figures of merit such as specificity, sensitivity, ratio of predicted to standard deviation, standard error of prediction and root mean squared error for cross validation were determined from partial least squares (PLS) and partial least squares with discriminant analysis (PLS-DA) calibrations of milk mixtures containing 50-1000 ppm (parts per million) of melamine, ammonium sulphate, Dicyandiamide, urea and sucrose. The spectra were recorded by immersing the fiber optic probe directly in the milk solutions. Despite the high scattering background which was easily and reliably estimated and subtracted, the reproducibility for four N-rich compounds averaged to 11% residual standard deviation (RSD) and to 5% RSD for sucrose. PLS calibration models predicted the concentrations of separate validation sets with standard errors of prediction of between 44 and 76 ppm for the four N-rich compounds and 0.17% for sucrose. The sensitivity and specificity of the PLS-DA calibration were 92% and 89%, respectively. The study shows promise for use of portable mini Raman systems for routine rapid point-of-collection screening of liquid milk for the presence of adulterants, without the need for sample preparation or addition of chemicals.

Contaminação de Alimentos/análise , Leite/química , Análise Espectral Raman/métodos , Sulfato de Amônio/análise , Animais , Guanidinas/análise , Limite de Detecção , Reprodutibilidade dos Testes , Sacarose/análise , Triazinas/análise , Ureia/análise
J AOAC Int ; 99(1): 26-9, 2016.
Artigo em Inglês | MEDLINE | ID: mdl-26823162


Proteins are a key nutritional component of both powdered milk and infant formula types of product, and reliable methods for their determination are important for manufacturing and international trade. In this review, we distinguish between methods used for determining protein quality for nutrition purposes and those used for determining chemically defined protein. The former methods cover the ability of a dietary protein source to meet human nutritional requirements for the indispensable amino acids. The latter are chemical methods for the determination of total protein and can be divided into three broad types: total nitrogen determination, direct protein determination, and indirect protein determination. Current techniques and recent developments in each are reviewed.

Laticínios/análise , Fórmulas Infantis/química , Proteínas/análise , Animais , Humanos , Lactente
J Dairy Res ; 81(3): 340-9, 2014 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-25052435


The objective of this study was to estimate heritability and crossbreeding parameters (breed and heterosis effects) of various fatty acid (FA) concentrations in milk fat of New Zealand dairy cattle. For this purpose, calibration equations to predict concentration of each of the most common FAs were derived with partial least squares (PLS) using mid-infrared (MIR) spectral data from milk samples (n=850) collected in the 2003-04 season from 348 second-parity crossbred cows during peak, mid and late lactation. The milk samples produced both, MIR spectral data and concentration of the most common FAs determined using gas chromatography (GC). The concordance correlation coefficients (CCC) between the concentration of a FA determined by GC and the PLS equation ranged from 0.63 to 0.94, suggesting that some prediction equations can be considered to have substantial predictive ability. The PLS calibration equations were then used to predict the concentration of each of the fatty acids in 26,769 milk samples from 7385 cows that were herd-tested during the 2007-08 season. Data were analysed using a single-trait repeatability animal model. Shorter chain FA (16:0 and below) were significantly higher (P<0.05) in Jersey cows, while longer chain, including unsaturated longer chain FA were higher in Holstein-Friesian cows. The estimates of heritabilities ranged from 0.17 to 0.41 suggesting that selective breeding could be used to ensure milk fat composition stays aligned to consumer, market and manufacturing needs.

Bovinos/genética , Ácidos Graxos/análise , Leite/química , Animais , Cromatografia Gasosa/veterinária , Feminino , Hibridização Genética/genética , Característica Quantitativa Herdável , Espectrofotometria Infravermelho/veterinária
J Agric Food Chem ; 55(8): 2791-6, 2007 Apr 18.
Artigo em Inglês | MEDLINE | ID: mdl-17378579


Near-infrared (NIR) spectroscopy calibrations that will allow prediction of the solid fat content (SFC) of milk fat extracted from butter by one measurement during manufacture were developed. SFC is a measure of the amount of the solid fraction of fat crystallized at a temperature expressed as a percentage (w/w). At-line SFC determinations are currently performed by nuclear magnetic resonance (NMR) spectroscopy, which involves a 16 h delay period for tempering of the milk fat at 0 degrees C prior to the SFC measurements, from 0 to 35 degrees C in a series of 5 degrees C increments. The NIR spectra (400-2500 nm) were obtained using a sample holder maintained at 60 degrees C. Accurate predictions for the SFC (%) were developed by principal component analysis (PCA) and partial least-squares (PLS) regression models to relate the NIR spectra to the corresponding NMR values. The independent validation samples (N = 22) had a standard error of prediction (SEP) of 0.385-0.762% for SFC between 0 and 25 degrees C, with SFC reference values ranging between 70.42 and 8.96% with a standard deviation range of 3.36-1.47. The low bias (from -0.351 to -0.025), the slopes (0.935-1.077), and the excellent predictive ability (R2; 0.923-0.978) supported the validity of these calibrations.

Manteiga/análise , Gorduras/análise , Leite/química , Espectroscopia de Luz Próxima ao Infravermelho , Animais , Espectroscopia de Ressonância Magnética , Nova Zelândia