Investigation of the compositional and structural changes in the proteins of cow milk when processed to cheese

Various treatments applied during dairy processing strikingly affect milk proteins, the major structural determinants, thus causing modifications in some techno-functional and biological properties of the final dairy product. Cheeses, with a variety of types, are mostly consumed processed dairy foods worldwide. The purpose of this study was to investigate the effect of heating, culture/enzyme activity and other treatments on the composition and molecular structure of cow milk proteins during the processing of different cheeses through electrophoresis, chromatography and spectroscopy. Electrophoretic patterns of the samples successfully indicated differences in protein content through process steps and in the final products. Curdling after pasteurization at 85 °C revealed many newborn peptides not detected in raw cow milk and other dairy samples. High and low similarities in peptide profiles of cheeses to that of raw cow milk indicated high-temperature pasteurization-induced unfolding facilitated extensive proteolysis subsequently. Significant conformational changes including loss of α-helices and exposure of β-strands observed in the secondary structure of proteins especially through curdling might offer alterations of reactive/functional groups. In total, pasteurization, curdling, salting, and ripening treatments remarkably altered the content and structure of cow milk proteins through unfolding, denaturation and aggregation, strongly suggesting modified functionality when milk was processed to cheese. •High-temperature pasteurization-induced unfolding facilitated extensive proteolysis.•Remarkable loss of α-helices and exposure of β-strands through curdling via rennet and culture.•Aggregation of milk proteins through curdling followed by disaggregation after ripening.•Numerous peptides varying in size due to heating, enzyme treatment and ripening steps.•Altered protein reactivity/functionality via exposure or burry of relevant groups in dairy process.