Institut for Fysik og Astronomi

PhD project: Improvement of texture in milk based products by use of high intensity ultrasound

University: Aarhus University, Faculty of Science and Technology

Department: Department of Food Science

Main supervisor: Lars Wiking, PhD, Ass. Prof.

Project supervisor: Marianne Hammershøj, PhD, Ass. Prof.

Project term: 01.08.2011 – 31.07.2014

Master’s degree: MSc in Molecular Biology, Aarhus University                 

Background

High intensity ultrasound (HIU) has in recent years proven, in laboratory scale, to be a promising technique to modify the microstructure of e.g. crystallized fat and protein networks. Ultrasound is defined as any sound of frequencies greater than the upper limit of human hearing, i.e. above 16 kHz up to 10 MHz, and HIU, also referred to as power ultrasound, operates with frequencies ranging from 20-100 kHz and intensities of 10-1000 W/cm². 

Studies of anhydrous milk fat have shown that treatment with HIU results in quantitatively less fat crystals and hence higher viscosity. It is shown that for cocoa butter, ultrasound can be used to modify the polymorphic forms of fat crystals, which affect the structure determining e.g. the color and the texture of the product. It is therefore hypothesized that the production time at the dairy can be reduced significantly by using ultrasound treatment to control crystal formation.

In food systems where proteins form networks, the functional properties such as texture of the gel network and its water holding capacity are important parameters. Several studies indicate that HIU treatment increase the rheological parameters describing firmness, strength and the water holding capacity in systems with milk and whey protein concentrate, although the mechanistic reasons are not clear.

Aim

The aim is to understand the effect of HIU on fat crystallization and clarify ultrasonic application in building protein networks in dairy products. We hypothesize that the texture of lipid and protein networks can be improved as consequence of modified microstructures by using HIU as a new technology.

Research outline

The project will focus on two systems representing nearly pure lipid and pure protein foods, i.e. anhydrous milk fat and whey protein concentrate, respectively. Various effect, time and temperature combinations of ultrasound treatment will be applied to these products and the impact on the microstructure will be studied. Macroscopic properties, such as texture, stability towards liquid syneresis and processing yield will be analyzed. Furthermore, on the molecular level, interactions such as hydrophobic interactions and/or disulfide bridges are studied. Finally, a holistic understanding of how HIU affects the macroscopic properties including the underlying mechanisms on microstructure and molecular levels will be described.