Non-targeted detection of milk powder adulteration by 1H NMR spectroscopy and conformity index analysis

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 even at 5% w/w of spiking, 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.