Exploring Authentic Skim and Nonfat Dry Milk Powder Variance for the Development of Nontargeted Adulterant Detection Methods Using NIR Spectroscopy and Chemometrics

This document provided is the Accepted Manuscript version of a Published Work that appeared in final form in Journal of Agricultural and Food Chemistry, copyright © American Chemical Society, after peer review and technical editing by the publisher. To access the final edited and published work see http://pubs.acs.org/doi/abs/10.1021/jf4023433peer-reviewedA multinational collaborative team led by the U.S. Pharmacopeial Convention is currently investigating the potential of near-infrared (NIR) spectroscopy for nontargeted detection of adulterants in skim and nonfat dry milk powder. The development of a compendial method is challenged by the range of authentic or nonadulterated milk powders available worldwide. This paper investigates the sources of variance in 41 authentic bovine skim and nonfat milk powders as detected by NIR diffuse reflectance spectroscopy and chemometrics. Exploratory analysis by principal component analysis and varimax factor rotation revealed significant variance in authentic samples and highlighted outliers from a single manufacturer. Spectral preprocessing and outlier removal methods reduced ambient and measurement sources of variance, most likely linked to changes in moisture together with sampling, preparation, and presentation factors. Results indicate that significant chemical variance exists in different skim and nonfat milk powders that will likely affect the performance of adulterant detection methods by NIR spectroscopy

Effects of Wet-Blending on Detection of Melamine in Spray-Dried Lactose

During the development of rapid screening methods to detect economic adulteration, spray-dried milk powders prepared by dissolving melamine in liquid milk exhibited an unexpected loss of characteristic melamine features in the near-infrared (NIR) and Raman spectra. To further characterize this “wet-blending” phenomenon, spray-dried melamine and lactose samples were produced as a simplified model and investigated by NIR spectroscopy, Raman spectroscopy, proton nuclear magnetic resonance (¹H NMR), and direct analysis in real time Fourier transform mass spectrometry (DART–FTMS). In contrast to dry-blended samples, characteristic melamine bands in NIR and Raman spectra disappeared or shifted in wet-blended lactose–melamine samples. Subtle shifts in melamine ¹H NMR spectra between wet- and dry-blended samples indicated differences in melamine hydrogen-bonding status. Qualitative DART–FTMS analysis of powders detected a greater relative abundance of lactose–melamine condensation product ions in the wet-blended samples, which supported a hypothesis that wet-blending facilitates early Maillard reactions in spray-dried samples. Collectively, these data indicated that the formation of weak, H bonded complexes and labile, early Maillard reaction products between lactose and melamine contribute to spectral differences observed between wet- and dry-blended milk powder samples. These results have implications for future evaluations of adulterated powders and emphasize the important role of sample preparation methods on adulterant detection

Characterization of Near-Infrared Spectral Variance in the Authentication of Skim and Nonfat Dry Milk Powder Collection Using ANOVA-PCA, Pooled-ANOVA, and Partial Least-Squares Regression

Forty-one samples of skim milk powder (SMP) and nonfat dry milk (NFDM) from 8 suppliers, 13 production sites, and 3 processing temperatures were analyzed by NIR diffuse reflectance spectrometry over a period of 3 days. NIR reflectance spectra (1700–2500 nm) were converted to pseudoabsorbance and examined using (a) analysis of variance-principal component analysis (ANOVA-PCA), (b) pooled-ANOVA based on data submatrices, and (c) partial least-squares regression (PLSR) coupled with pooled-ANOVA. ANOVA-PCA score plots showed clear separation of the samples with respect to milk class (SMP or NFDM), day of analysis, production site, processing temperature, and individual samples. Pooled-ANOVA provided statistical levels of significance for the separation of the averages, some of which were many orders of magnitude below 10^–3. PLSR showed that the correlation with Certificate of Analysis (COA) concentrations varied from a weak coefficient of determination (<i>R</i>²) of 0.32 for moisture to moderate <i>R</i>² values of 0.61 for fat and 0.78 for protein for this multinational study. In this study, pooled-ANOVA was applied for the first time to PLS modeling and demonstrated that even though the calibration models may not be precise, the contribution of the protein peaks in the NIR spectra accounted for the largest proportion of the variation despite the inherent imprecision of the COA values