7 th TAE 2019 17 - 20 September 2019, Prague, Czech Republic SELECTED RHEOLOGICAL PROPERTIES OF SOME TOMATO KETCHUPS Peter HLAVÁČ 1 , Monika BOŽIKOVÁ 1 , Zuzana HLAVÁČOVÁ 1 1 Department of Physics, Faculty of Engineering, Slovak University of Agriculture in Nitra Abstract This article is focused on monitoring and evaluation of rheological properties of tomato ketchups. Influence of temperature in range (5 – 30) °C and short storage time was investigated. Dependencies of rheological properties on temperature and storage time were evaluated by the regression equations and the coefficients of determination. Ketchup is a non-Newtonian material, so apparent viscosity was measured using digital rotational viscometer Anton Paar DV-3P. Densities of samples were deter- mined according to definition. Apparent viscosity of samples decreased exponentially with increasing temperature, so the Arrhenius equation is valid. Ketchup’s apparent fluidity was increasing exponen- tially with the temperature. We also found out that apparent viscosity had decreased with storage time and on the other hand apparent fluidity was increasing with storage time, which can be caused by structural changes in samples during storing. Temperature dependencies of ketchup densities were sufficiently characterized by decreasing linear function in measured temperature range. Key words: ketchup; rheological parameters; density; temperature, dependency. INTRODUCTION Precise knowledge of physical quantities of materials is required at controlled processes in manufac- turing, handling and holding. For the quality evaluation of food materials it is important to know their physical properties particularly, mechanical (Kubík et al., 2017), rheological and thermophysical (Glicerina et al., 2013). Tomatoes are often consumed in fresh state, but several varieties are pro- cessed into various products such as tomato sauce, soup, paste, puree, juice, ketchup and salsa. Au- thors noted that several studies had investigated the benefits of tomatoes in reducing the risk of heart disease, improving bone health, and decreasing the risk of cancer ( Tan & Kerr, 2015). The industrial processing of tomatoes leads to a great variety of output products. Some of the most relevant are the following: concentrated tomato products, either as puree or paste depending on the percentage of natu- ral soluble solids; pizza sauce, from peels and seeds; tomato powder, as dehydrated concentrated to- mato; peeled tomato, either whole or diced; ketchup, tomato sauce seasoned with vinegar, sugar, salt and some spices, etc. (Ruiz Celma et al., 2009). New design of experimental double piston filament stretching apparatus that can stretch fluids to very high extensional strain rates was presented by Mackley et al. (2017). Authors had used high speed photography for determination of filament defor- mation and breakup profiles of a strategically selected range of fluids including low and higher viscos- ity Newtonian liquids together with a viscoelastic polymer solution, biological and yield stress fluids at extensional strain rates in excess of 1000 s −1 . Mackley et al. (2017) had also reported that numerical modelling can be used with the fluids correct rheological characterization to gain physical in-sight into how rheologically complex fluids deform and breakup at very high extensional deformation rates. Chandrapala et al. (2012) had stated that ultrasonic pulses in combination with rheological measure- ments could be used at the solids concentration determination in various highly concentrated and in- dustrial food suspensions (tomato, vegetable and pasta sauces, seafood chowder, strawberry yoghurt, cheese sauce with vegetables). Low intensity ultrasound-based techniques could be used during the detection and identification of foreign bodies in food products (e.g. tomato ketchup) (Chandrapala et al., 2012). The rheological behaviour of some food dispersions were investigated and modelled with the Herschel–Bulkley model by Herrmann et al. (2013). Several rheologic parameters were studied in dependency on composition of various ingredients (fats, carbohydrates, proteins, water). The effects of manothermosonication or thermal treatment on tomato pectic enzymes and tomato paste rheological properties were compared by Vercet et al. (2002). The quality of tomato concentrate was studied by Fadavi et al. (2018) using ohmic vacuum, ohmic, and conventional-vacuum heating methods. Authors had indicated that ohmic heating under vacuum condition had a good effect on quality during the con- centration of tomato juice and that vacuum condition decreased the time required for processing and 165