Characterising variances of milk powder and instrumentation for the development of a non-targeted, Raman spectroscopy and chemometrics detection method for the evaluation of authenticity

ABSTRACT

There is a need to develop rapid tools to screen milk products for economically motivated adulteration. An understanding of the physiochemical variability within skim milk powder (SMP) and non-fat dry milk (NFDM) is the key to establishing the natural differences of these commodities prior to the development of non-targeted detection methods. This study explored the sources of variance in 71 commercial SMP and NFDM samples using Raman spectroscopy and principal component analysis (PCA) and characterised the largest number of commercial milk powders acquired from a broad number of international manufacturers. Spectral pre-processing using a gap-segment derivative transformation (gap size = 5, segment width = 9, fourth derivative) in combination with sample normalisation was necessary to reduce the fluorescence background of the milk powder samples. PC scores plots revealed no clear trends for various parameters, including day of analysis, powder type, supplier and processing temperatures, while the largest variance was due to irreproducibility in sample positioning. Significant chemical sources of variances were explained by using the spectral features in the PC loadings plots where four samples from the same manufacturer were determined to likely contain an additional component or lactose anomers, and one additional sample was identified as an outlier and likely containing an adulterant or differing quality components. The variance study discussed herein with this large, diverse set of milk powders holds promise for future use as a non-targeted screening method that could be applied to commercial milk powders.

Graphical Abstract

KEYWORDS:

• Skim milk powder (SMP)
• non-fat dry milk (NFDM)
• authentication
• Raman spectroscopy
• chemometrics
• PCA
• variance

Acknowledgements

The authors thank Steven Zbylut, Andrew Mackey, Jianwei Qin, Moon Kim, Kevin Chao, Lucy Botros and Robert Magaletta for discussions on Raman spectroscopy and milk powder evaluation.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

S.R.K. acknowledges the support provided by an appointment to the Research Participation Program at the Center for Food Safety and the Applied Nutrition, administered by the Oak Ridge Institute for Science and Education through an interagency agreement between the US Department of Energy and the US Food and Drug Administration (US FDA).