Milk protein and peptide profiles under different heat loads: Molecular analysis

Heat treatment induces structural changes in milk proteins, thus affecting the processing suitability of milk powder. Identifying new molecular markers of heat load helps to develop rapid and efficient approaches to milk powder assessment. This study utilized molecular analysis to investigate the impact of thermal treatment on the proteome and peptidome of skim milk. The skim milk samples were subjected to heat treatment at 70, 80, and 90°C for 30 s, while skim milk maintained at 45°C served as control. Two-dimensional electrophoresis made it possible to separate and evaluate protein structural changes. Peptide identification relied on matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS), preceded by trypsinolysis. A combination of Raman spectroscopy and principal component analysis visualized the heat-induced spectral responses to evaluate the potential of Raman spectroscopy for tracing the thermal history of milk powder. High pasteurization temperature reduced the number of protein fractions. MALDI-TOF MS identified 30 peptides belonging to seven major milk proteins. Peptide fragments of αS1-casein and β-casein were absent in the control but present in the experimental samples, indicating heat-induced protein transformation. The intermolecular interactions and disruption of the secondary structure of proteins resulted in differences in the isoelectric points. Raman spectroscopy revealed heat-induced changes in the wavenumber ranges of 900–1097, 1328–1437, and 1475–1546 cm–1, attributed to the transformed carbohydrate and proteomic milk profiles. The principal component analysis made it possible to visualize the differences and identify the regions that make the highest contribution to the response. Raman spectroscopy proved to be a reliable technique for developing and validating a rapid approach to assess the degree of heat load in milk.