Evaluating protein quantification methods in long-life dairy and plant-based milk alternatives.

Routine protein quantification in plant-based milk alternatives is essential for nutritional labelling and quality control. This study compared UPLC-UV amino acid analysis, elemental, Bradford assay, Raman spectroscopy, and ATR-FTIR for protein determination in bovine and plant-based milks. UPLC-UV provided detailed protein measurements but was labor-intensive and time-consuming. Elemental analysis offered rapid and robust estimates but lacked specificity for protein-derived nitrogen. The Bradford assay showed variability depending on the calibration standard, supported by circular dichroism findings indicating inconsistent performance. Raman spectroscopy, using 785 nm excitation, was limited by fluorescence interference in complex milk matrices. ATR-FTIR demonstrated strong potential as a fast, simple, and easy method for protein estimation, achieving high linearity (R2 = 0.997) with minimal sample preparation. Effective water subtraction and optimised calibration improved its performance despite matrix complexity. Although further matrix-matched calibration and validation are required, ATR-FTIR shows considerable promise for routine industrial protein analysis and food science applications.