Proteomic analysis of temperature-dependent changes in stored UHT milk

Area of Science:

• Food Chemistry
• Protein Chemistry
• Analytical Chemistry

Background:

• Ultra-high temperature (UHT) processing alters milk proteins, and subsequent storage can induce further molecular changes.
• Understanding these changes is crucial for maintaining milk quality and predicting shelf-life.

Purpose of the Study:

• To investigate molecular modifications in milk proteins during storage of UHT-treated milk.
• To characterize protein changes induced by different storage temperatures using advanced analytical techniques.

Main Methods:

• Two-dimensional electrophoresis (2-DE) was employed to separate and visualize protein modifications.
• Matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) mass spectrometry was used for protein identification and characterization.
• Samples were stored at 4 °C, 28 °C, and 40 °C for two months.

Main Results:

• Three primary changes were observed: non-disulfide cross-linking of caseins, deamidation of α(S1)-casein, and lactosylation of whey proteins (β-lactoglobulin and α-lactalbumin).
• The extent of these modifications increased with higher storage temperatures.
• Mass spectrometry confirmed deamidation sites and identified lactosylation on specific lysine residues of whey proteins.

Conclusions:

• Storage temperature significantly impacts the molecular integrity of UHT-treated milk proteins.
• These findings provide insights into protein degradation pathways during milk storage.
• Further analysis is needed to fully elucidate cross-linking mechanisms and deamidation sites, particularly due to the complexity of phosphorylated caseins.