title: Raman spectroscopy as an effective screening method for detecting adulteration of milk with small nitrogen-rich molecules and sucrose.
abstract: Adulteration of milk for commercial gain is acknowledged as a serious issue facing the dairy industry. Several analytical techniques can be used to detect adulteration but they often require time-consuming sample preparation, expensive laboratory equipment, and highly skilled personnel. Here we show that Raman spectroscopy provides a simple, selective, and sensitive method for screening milk, specifically for small nitrogen-rich compounds, such as melamine, urea, ammonium sulfate, dicyandiamide, and for sucrose. Univariate and multivariate statistical methods were used to determine limits of detection and quantification from Raman spectra of milk spiked with 50 to 1,000 mg/L of the N-rich compounds and 0.25 to 4% sucrose. Partial least squares (PLS) calibration provided limit of detection minimum thresholds <200mg/L (0.02%) for the 4 N-rich compounds and <0.8% for sucrose, without the need for surface-enhanced Raman spectroscopy. The results show high reproducibility (7% residual standard deviation) and 100% efficiency for screening of milk for these adulterants.
authors.affiliation: MacDiarmid Institute for Advanced Materials and Nanotechnology, New Zealand; The Photon Factory, The University of Auckland, 23 Symonds St., Auckland, 1142 New Zealand; School of Chemical Sciences, The University of Auckland, 23 Symonds St., Auckland, 1142 New Zealand. Electronic address: m.nieuwoudt@auckland.ac.nz.
authors.forename: M K
authors.initials: MK
authors.lastname: Nieuwoudt
authors.affiliation: Fonterra Research & Development Centre, Private Bag 11029, Palmerston North, New Zealand.
authors.forename: S E
authors.initials: SE
authors.lastname: Holroyd
authors.affiliation: The Dodd Walls Centre for Photonic and Quantum Technologies, New Zealand; Department of Physics, The University of Auckland, 23 Symonds St., Auckland, 1142 New Zealand.
authors.forename: C M
authors.initials: CM
authors.lastname: McGoverin
authors.affiliation: MacDiarmid Institute for Advanced Materials and Nanotechnology, New Zealand; The Photon Factory, The University of Auckland, 23 Symonds St., Auckland, 1142 New Zealand; School of Chemical Sciences, The University of Auckland, 23 Symonds St., Auckland, 1142 New Zealand; The Dodd Walls Centre for Photonic and Quantum Technologies, New Zealand; Department of Physics, The University of Auckland, 23 Symonds St., Auckland, 1142 New Zealand.
authors.forename: M C
authors.initials: MC
authors.lastname: Simpson
authors.affiliation: MacDiarmid Institute for Advanced Materials and Nanotechnology, New Zealand; School of Chemical Sciences, The University of Auckland, 23 Symonds St., Auckland, 1142 New Zealand.
authors.forename: D E
authors.initials: DE
authors.lastname: Williams
mesh_terms: D000818:Animals; D002138:Calibration; D008892:Milk / Q000737:chemistry*; D009584:Nitrogen / Q000032:analysis; D017672:Nitrogen Compounds / Q000032:analysis; D015203:Reproducibility of Results; D013059:Spectrum Analysis, Raman / Q000379:methods*; D013395:Sucrose / Q000032:analysis; D014227:Triazines / Q000032:analysis
chemical_list: D017672:Nitrogen Compounds; D014227:Triazines; D013395:Sucrose; C011907:melamine; D009584:Nitrogen
keywords: Raman spectroscopy; milk adulteration; nitrogen-rich molecules; sucrose