Development and validation of a front-face fluorescence spectroscopy-based method to determine casein in raw milk

A front-face fluorescence spectroscopy (FFFS)-based method for measuring casein in raw milk was developed and validated. Calibration samples (n _cal = 20) with different casein contents (0.36–3.7%) were prepared by mixing ultrafiltered retentate (2 × concentrate) and permeate at different ratios. A principal component regression model was developed using the calibration fluorescence spectra, showing a useful prediction power based on a residual prediction deviation of 3.1. The calibration model was independently validated using 20 raw milk samples. The FFFS-based method showed a root mean square error of prediction of 0.15% and 6.7% relative prediction error. A larger sample size should be included in the future to further validate the method and potentially implement it for routine measurement of casein levels in raw milk.