Detection of urea adulteration in packaged milk samples using spatially-offset Raman spectroscopy

Abstract

Urea adulteration in milk is very rampant worldwide and its consumption can cause serious health hazards. Raman spectroscopy, because of its molecular-specificity, is a powerful analytical tool for biochemical assessment of the urea content in unpackaged milk samples. However, milk is commonly sold in packaged form. Hence, we report the development of a depth sensitive technique “inverse spatially-offset Raman spectroscopy” in combination with a multivariate statistical algorithm for the quantification of the urea adulteration in packaged milk samples. Limit of detection (LOD) and limit of quantification (LOQ) values were found to be 0.22 g/L and 0.67 g/L respectively. Hence, the method suitably detects all urea concentrations above the permissible limit of 0.70 g/L. For example, sample with urea concentration 0.75 g/L, have low Percentage Absolute Error (PAE) of ∼6 %, indicating that the urea concentration can be predicted with a high accuracy of ∼94 % using the developed technique. Further, the prediction accuracy follows an inverse relationship with the thickness of packaging material. The developed technique demonstrates quantification of urea in packaged milk samples, thereby advocating its potential for in-situ monitoring of urea adulteration in a milk production and packaging facility, as well as in the local vending outlets.