J. Phys. IV France 125 (2005) 807-810
DOI: 10.1051/jp4:2005125186

Photoacoustic and optothermal studies of tomato ketchup adulterated by the red beet (Beta vulgaris)

D. Bicanic¹, E. Westra¹, J. Seters¹, S. van Houten¹, D. Huberts¹, I. Colic-Baric², J. Cozijnsen³ and H. Boshoven<sup>1

1</sup>  Laser Laboratory for Photothermal Science, Biophysics Division, Department of Agrotechnology and Food Sciences, Wageningen University, Dreijenlaan 3, 6703 HA Wageningen, The Netherlands
²  Food Quality and Nutrition, Faculty of Food Technology and Biotechnology, Zagreb University, Pierotijeva 6, 1000 Zagreb, Croatia
³  Food Chemistry, Department of Agrotechnology and Food Sciences, Wageningen University, Bomenweg 2, 6703 HD Wageningen, The Netherlands

Abstract
Photoacoustic (PA) spectroscopy and optothermal window (OW) technique were used to explore their potential to detect red beet added as a colorant to tomato ketchup. The associated changes of colour resulting in the changes of absorbance (and hence of PA and OT signals) were monitored in the 500 nm region corresponding to the absorption maximum of lycopene. Both methods were shown capable of quantifying about 1% of red beet (by mass) in the mixture of ketchup and red beet.

© EDP Sciences 2005