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Food Science and Technology International
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Rheological Characteristics of Juniperus drupacea Fruit Juice (pekmez) Concentrated by Boiling

M. Akbulut

Department of Food Engineering, Faculty of Agriculture, Selcuk University, 42031 Konya, Turkey, makbulut{at}selcuk.edu.tr

H. Çoklar

Department of Food Engineering, Faculty of Agriculture, Selcuk University, 42031 Konya, Turkey

G. Özen

Department of Food Engineering, Faculty of Agriculture, Selcuk University, 42031 Konya, Turkey

Rheological parameters of Juniperus drupacea fruit pekmez were evaluated using a rotational viscometer at 10, 20, 30, 40, and 50 °C and at concentrations of 62.8, 68.9, 72.0, and 75.2% total soluble solids. The flow characteristics of Juniperus drupacea fruit pekmez were described by the power law and Herschel—Bulkley models. The Herschel—Bulkley model was found to be the best to describe the rheological property with the coefficient of determination higher than 0.993. Juniperus drupacea pekmez exhibited a time-independent shear thickening behavior. The effect of temperature on viscosity can be described by means of an Arrhenius equation. Depending on the soluble solid contents, the activation energies for flow of diluted samples vary from 78.23 to 60.38 kJ/mol. The effect of soluble solids on viscosity can be described by an exponential equation. Experimental data were fitted to several models in order to describe the effect of temperature and soluble solid content. The combined effect of temperature and soluble solid content on viscosity was also formulated.

Key Words: Juniperus drupacea • pekmez • power law • Herschel—Bulkley • fruit juices

Food Science and Technology International, Vol. 14, No. 4, 321-328 (2008)
DOI: 10.1177/1082013208097193
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