Instruments, ultrasound, and oils

1. Instruments, ultrasound, and oils Frank PoddProcter Department of Food ScienceUniversity of Leeds 16/11/2002

2. Content • Background • Ultrasound Velocity • Ultrasound Spectrometry • New Developments • Single particle scattering theory • Multiple particle scattering theory • New electronics • New cell design

3. Leeds Food Science Biochemistry Food Processing Eric Dickinson Emulsions Brent Murray Interfaces Malcolm Povey Ultrasound Bronek Wedzicha Small molecule interaction Mike Morgan David Borrill Colloids

4. Instruments within the colloids group • Rheometers, • Brewster angle microscope, Langmuir trough, surface shear rheometers, bubble expansion chambers, • Surface layers, • Simulations, • Confocal microscopy, • Atomic force microscopy, • Acoustic microscopy, • Ultrasound creaming rig, • Ultrasound velocity, • Ultrasound spectroscopy.

5. Liquid oil particle coated with surfactant micelle Ultrasound & Food Emulsions surfactant protein 1 mm Overall ultrasound property depends on: • Continuous phase • Dispersed phase • Surfactant • Droplet shape & • its size distribution Thermal property Viscosity Compressibility

6. Ultrasound VelocityThe Wood equation Bulk modulus Adiabatic compressibility Density

7. Ultrasound Velocity Urick equation Phase volume of jth phase

8. Modified Urick Equation

9. Sound velocity in margarine

10. Detecting adulteration in olive oil? The velocity profile during crystallisation for virgin olive oil shows a smooth curve. This adulterated virgin olive oil displays a spikier velocity curve

11. Crystallization in cocoa butter emulsions

12. Do surfactants affect crystallisation? Plot for 20% v/v WACB oil-in-water emulsion cooled at 5°C / hour. A three stage process occurs with sodium caseinate during the crystallisation: Bulk volume crystallisation initially, Surface crystallisation (the sodium caseinate macromolecule protects the droplets more than Tween 20), Instability stops the sodium caseinate from preventing droplet collisions, thus the crystallisation rate increases.

13. Does crystallisation occur due to micelle transport? Plot of solid content for an 32% v/v n-hexadecane oil-in-water emulsion crystallised at 6°C. In the first 7 days a dialysis tube was used as a barrier to prevent collisions between supercooled liquid and solid droplets. Thereafter, the contents of the dialysis tube were mixed with the liquid.

14. US spectroscopyParticles scatter ultrasound… The effect of scattering can be a frequency dependence in the ultrasonic velocity and attenuation Ultrasound spectroscopy has opened a new dimension in food emulsion study • Rheology • Component analysing • Stability monitoring (flocculation, creaming, coalescences, etc.) • Particle sizing ( particle size distribution, PSD)

15. New Developments @ Leeds(in the ultrasound group) • New stable scattering theory with known error bounds. • Multi-particle theory enabling an estimation of particle spacing. • New US instrumentation • New US sensors

16. Scattering background • Later Epstein and Carhart (J. Acous. Soc. Am. 1953) and Allegra and Hawley (J. Acous. Soc. Am. 1972) developed a model for the attenuation of sound through a suspension of isolated spheres due to thermal and viscous effects. • Ultrasound propagation was first formulated by Lord Rayleigh (The Theory of Sound 1892) . • Although the theory is exact it is prone to numerical difficulties and so an alternative solution technique is required.

17. Results of new single particle scattering theory • Magnitude of error known • Well conditioned numerically • Not constrained to geometry

18. Single Particle System Thermal fields. 1mM particle at 1MHz generates a thermal field of 1mM depth Incident plane wave Reflected wave Transmitted wave Single oil droplet suspended in medium

19. The Multiple Scattering Problem Multiple scattering of the thermal field is different to multiple scattering of the acoustic field. If the particles stay together for the period of the wave thermal fields will scatter coherently. If the particles move in less than this time then the thermal scattering will be incoherent. Oil particle (1mm diameter)in water Thermal field ( 1 mm thick in water at 1 MHz) generated by particle pulsation in the presence of the excitation field

20. Results of new multiple particle scattering theory • Enables the determination of inter-particle spacing?

21. New Cell Design Designed for crystallisation experiments • Small sample volume (2ml) • Low coefficient of thermal expansion • Small heat capacity • High thermal conductivity • Cell designed for high pressure experiments • Choice of transducers - 1MHz to 30MHz frequency range

22. New Electronics • Measure the pulse amplitude in addition to the group velocity • Velocity and attenuation spectrometry • Accurate temperature measurement – detect heat from crystallisation? • Aiming for inline use • Low cost!

23. Monitoring stability and creaming The Acoustiscan builds up a profile of property differences along the cell height. It uses both pitch catch and pulse-echo techniques Colloidal stability can be quantifiably determined using the Acoustiscan. A major factor in colloidal stability is the particle size distribution. This can also be determined ultrasonically, by using the FSUPER for example.

24. FSUPER The FSUPER has several advantages, such as:- • Rapid and accurate measurement • Wide frequency range (1-15MHz) • A small amount of sample required ( ~ 15ml) This type of characterisation can be peformed by the Frequency Scanning Ultrasound Pulse Reflectometer (FSUPER) The particle size distribution can be estimated from the analysis of the frequency dependent ultrasonic velocity and attenuation data. The system can also monitor emulsion stability, measure the amount of surfactant covering the emulsion droplets and identify substances spectroscopically. The method has the potential to characterise emulsions on-line, and in real time.

25. Acknowledgements Many thanks go to Malcolm Povey, Scott Hindle, and Toni Crosthwaite for supplying data and providing help and advice.