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

Abstract

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 (H 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 H 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.

Effects of the Adulteration Technique on the Near-Infrared Detection of Melamine in Milk Powder

“…This wavenumber upshift could arise from a chemical interaction, such as H bonding, of melamine to proteins and/or lactose in SMP or melamine protonation during the spray-drying process . This chemical shift has also been reported by Yakes et al in model systems containing only lactose and melamine . Raman spectra of 0.33% melamine (Supplemental Figure 5 of the Supporting Information) were more intense in DB than in WB samples.…”

“…38 This chemical shift has also been reported by Yakes et al in model systems containing only lactose and melamine. 28 Raman spectra of 0.33% melamine (Supplemental Figure 5 of the Supporting Information) were more intense in DB than in WB samples. As also indicated by the PLM analysis, this can be attributed to differences in melamine concentration distributions that inherently arise from the dry-and wet-blending methods.…”

“…25,42 Temporal changes have been observed in the 1 H NMR spectra of melamine admixtures with lactose. 28 Solid-state NMR studies are required to more satisfactorily explore hypotheses regarding melamine H bonding and chemical adduct formation.…”

“…This investigation is related to a companion NIR study using only melamine and lactose in a parallel experimental model system. 28…”

“…The objectives of the current study were to (1) determine the effect of the spiking technique on the NIR spectrum of melamine in dry milk powder, (2) identify causes of spectral variation between wet- and dry-blended samples, and (3) illustrate their potential effects on the targeted and non-targeted detection of melamine in SMP. This investigation is related to a companion NIR study using only melamine and lactose in a parallel experimental model system …”