Innovative Food Science and Emerging Technologies 5 (2004) 199–204 1466-8564/04/$ - see front matter  2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.ifset.2004.02.001 Dielectric spectroscopy–a new method for particle size- and fraction-determination M. Regier *, H. Schubert , H.P. Schuchmann a, b a Institute of Process Engineering, Federal Research Centre for Nutrition, Haid-und-Neu-Str. 9, D-76131 Karlsruhe, Germany a Institute of Food Process Engineering, University of Karlsruhe, Kaiserstr. 12, D-76131 Karlsruhe, Germany b Received 8 August 2003; accepted 21 February 2004 Abstract Important parameters, that define the physical properties of dispersed systems, are the fractions of the constituents and their particle size. Both, the fraction and the particle size have effects on the dielectric properties of the dispersion. Therefore, dielectric spectroscopy between 0.5 MHz and 6 GHz has been investigated to determine these quantities from the dispersion’s spectra. Using the principal component analysis it has been demonstrated that this technique works for oil-in-water emulsions as an example for fluid dispersed systems.  2004 Elsevier Ltd. All rights reserved. Keywords: Dispersions; Emulsions; Particle size determination; Fraction determination; Dielectric spectroscopy Industrial relevance: Particle size of dispersed phases has a marked influence on product properties of fluid dispersed systems. Currently, conventional measurement techniques do not allow in- or online measurement which would be of great value during production. This work presents an attempt to measure particle size and the fractions of the constituents simultaneously. The dielectric properties of oil-in-water emulsions were used to determine oil and salt fraction as well as mean droplet size by analysing the whole dielectric spectrum by a principal component analysis approach. This allows short measurement and analysis time in the order of seconds. 1. Introduction Fluid dispersed systems such as suspensions and emulsions are common in the food industry. Prominent examples are milk, mayonnaise, dressings, spreads or margarine. Many physical properties (for example the rheological or the sensory properties) of dispersions are strongly dependent on the concentrations of constituents. In practice these food emulsions consist of more than oil and water. Beside an emulsifier, often more ingredients like salts are added. The particle size of the dispersed phase also has a strong influence on the product properties. However, conventional measurement techniques such as phase separation for oil-volume-fraction-determination or laser diffraction for particle size measurement cannot be applied in- or online which in term would be of interest for production. *Corresponding author. Tel.: q49-721-6625263; fax: q49-721- 6625-303. E-mail address: marc.regier@bfe.uni-karlsruhe.de (M. Regier). For example the phase separation by drying or cen- trifugation is a rather long process, while laser diffrac- tion only works with strongly diluted systems (Kissa, 1999). Meeting the task of a fast quality control of disper- sions during production, a new inyonline measurement technique was developed based on dielectric spectros- copy combined with the principal component analysis. This statistical analysis was first used in behavioural sciences and has been previously applied successfully in various spectroscopical techniques (Malinowski & Howery, 1980). In this work, the use of this method to measure simultaneously both, the particle size and the fractions of the constituents (Regier, Danner & Schubert, 2002) is presented. 2. Materials and methods 2.1. Investigated systems As model systems for the fraction determination oil- in-water emulsions of 10–60% oil volume fraction and