Evidence of low-density water to high-density water structural transformation in milk during high-pressure processing

•In-situ ultrasound measurements allow evidencing water structural transformation.•The transformation pressure in pure water is 275 MPa at room temperature.•LDW-to-HDW transformation also occurs in complex aqueous systems under pressure.•The transformation pressure was the same for water, milk and sodium caseinate.

The objective of this research was to check whether the observed low-density water (LDW) to high-density water (HDW) transformation does take place or not in a complex aqueous system like those involved in high pressure processing of food. In-situ measurements of speed-of-sound up to 640 MPa were used for this purpose. After validation of the methodology in liquid water at 25 °C, LDW-to-HDW transformation was also evidenced in sodium caseinate solution and milk samples. The transformation pressure was always observed at 275 MPa. Since water plays a key role in most biochemical transformations, the occurrence of a LDW-HDW transition should be taken into account for understanding the complex component interactions in milk and other related systems under pressure.Industrial relevanceOpportunities exist for the industry to use pressure as a tool for texturing dairy products. Process parameter choice to obtain a given texture is tricky due to the complexity of milk component interactions under pressure. As a main component in foods, water structural transformation under pressure should not be ignored by experts in the field.