Local modifications of whey protein isolate powder surface during high temperature storage

• WPI storage at high temperature leads to surface modification.
• Hydrophobic adhesion was higher for aged powders.
• Maillard reaction seems to be the major phenome for surface modification.

Dairy powders are stable ingredients that are frequently stored prior to use. In fact, during powder manufacture, precautionary measures are taken to ensure optimal technological and nutritional functionalities, but during storage, changes in physico-chemical and functional properties of whey protein isolate (WPI) powders were extensively outlined. In the present study, WPI powders were stored at 60 °C and 0.2 water activity for one month and local modifications on particle surface were explored. Atomic force microscopy (AFM), specifically in chemical force microscopy (CFM) mode, was used to follow surface modifications during storage. An increase in surface hydrophobicity was noticed when powders were stored at high temperatures. Complementary techniques such as microscopy and Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) showed a crackled surface and a decrease in the presence of amino acid at surface. Finally, powder browning and fluorescence of components on particle surface suggested that Maillard reaction is the main phenomenon responsible for powder alteration during storage.