Non-targeted detection of milk powder adulteration by 1H NMR spectroscopy and Conformity Index Analysis

Authors: BERGANA, MARTI - Us Pharmacipeia (USP); ADAMS, KRISTI - Us Pharmacipeia (USP); Harnly, James - Jim; MOORE, JEFFREY - Us Pharmacipeia (USP); XIE, ZHOUHONG - Us Pharmacipeia (USP)

Submitted to: Journal of Food Composition and Analysis
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/19/2019
Publication Date: 4/23/2929
Citation: Bergana, M., Adams, K., Harnly, J.M., Moore, J., Xie, Z. 2020. Non-targeted detection of milk powder adulteration by 1H NMR spectroscopy and conformity index analysis. Journal of Food Composition and Analysis. https://doi.org/10.1016/j.jfca.2019.01.016.
DOI: https://doi.org/10.1016/j.jfca.2019.01.016

Interpretive Summary: Proton NMR spectra of powdered milk samples were examined for irregularities by comparison with authentic samples with no predetermined targeted contaminants. This non-targeted method for classifying authentic and adulterated skim and nonfat dry milk powders (MP) was tested using eight known adulterants. Adulteration was detected at the lowest concentrations (= 0.005 – 0.05% w/w) for samples containing nitrogen-rich, small molecules (melamine and dicyandiamide). An NMR peak associated with ammonium sulfate was not observed; however, adulteration was indirectly detected at 5% w/w via matrix effects on milk metabolites. Adulteration by soy protein isolate and whey protein concentrate was not detected, which was attributed in part to poor protein solubility. In all, 6 of the 8 adulterants were detected. These results provide a successful proof of concept that proton NMR combined with conformity index analysis can support MP authentication and detect adulteration.

Technical Abstract: A non-targeted method for classifying authentic and adulterated skim and nonfat dry milk powders (MP) by solution-state, high-field 1H NMR spectroscopy and conformity index analysis has been developed. Authentic MP samples from the global market and synthetically-adulterated MP samples involving eight adulterants were used in a pre-validation study. Adulteration was detected at the lowest concentrations (= 0.005 – 0.05% w/w) for samples containing nitrogen-rich, small molecules (melamine and dicyandiamide). For urea, a milk metabolite, and for sucrose and maltodextrin, the detection thresholds were higher (= 0.5% w/w). An NMR peak associated with ammonium sulfate was not observed; however, adulteration was indirectly detected at 5% w/w via matrix effects on milk metabolites. Adulteration by soy protein isolate and whey protein concentrate was not detected, which was attributed in part to poor protein solubility. These results provide a successful proof of concept that 1H NMR combined with conformity index analysis can support MP authentication and detect adulteration.