Philippine Science Letters
vol. 4 | no. 1 | 2011
published online April 20, 2011


Effect of pretreatment and geometry on the thermophysical properties of raw ubi (Dioscorea alata L.)

by Cresel F. Noche, Dennis V. Cantre, and Floirendo P. Flores*

Institute of Food Science and Technology, College of Agriculture, University of the Philippines Los Baños, College, Laguna, Philippines 4031



Ubi (Dioscorea alata L.) is a tropical root crop in the Philippines that can be processed into powder for use in manufacturing several food products such as ice cream, ubi jam, among others. The thermophysical properties of ubi need to be determined and compared to prediction equations to understand and optimize the heat transfer in processing ubi. This study was conducted to determine the effect of two pretreatments (sulfite dipping and steaming) and two sample geometries (parallel and perpendicular) on the thermophysical properties (apparent density, specific heat, thermal conductivity, and thermal diffusivity) of raw ubi (Hinaligi variety). Apparent density (r) was measured by liquid displacement method. Results (944.0 – 1092.5 kg m-3) showed that pretreatment had negligible effect. Specific heat (Cp) was determined using the method of mixtures. Cp values (3.44 – 4.07 kJ kg-1 ºC-1) varied minimally with pretreatment and approximated theoretical values. The heated probe method was used to measure thermal conductivity (k). Thermal conductivity of steamed samples (0.426 W m-1°C-1) approximated predictive equations using perpendicular geometry, while that of raw (0.382 W m-1°C-1) and sulfite dipped samples (0.379 W m-1°C-1) correlated better with equations based on parallel geometry. Results of this study can be used to design efficient heat processes for ubi.

*Corresponding author
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Submitted: May 19, 2010
Revised: April 4, 2011
Accepted: April 6, 2011
Published:April 20, 2011
Editor-in-charge: Eduardo A. Padlan
Rex B. Demafelis
Kevin F. Yaptenco