Thermal and Dielectric Properties of Sweetpotato Puree

Pureeing of sweetpotato (SP) is carried out to enhance the conversion of the roots into value-added products. During processing, production and home utilization, the puree is often heated (conventional cooking or microwaved), hence the need to measure the corresponding properties of SP puree. Thermal (specific heat, thermal conductivity, density, and thermal diffusivity) and dielectric properties (dielectric constant and dielectric loss factor) of SP puree were determined within a temperature range of 5 to 80 C. Increase in temperature increased the specific heat (3.70–3.78 kJ=kg K), thermal conductivity (0.52–0.78 W=m K), and thermal diffusivity (1.98 10 – 4.25 10 m=s) of SP puree. The density (705–485 kg=m) of the puree decreased with temperature. Both temperature and frequency (900–2500 MHz) significantly affected the dielectric constant (60.5–73.0) and dielectric loss factor (16.5–29.5) of SP puree. At the two frequencies (915 and 2450 MHz) used in industrial food processing, calculations showed that the penetration depth was not significantly affected by temperature at 2450 MHz, while at 915 MHz, the penetration depth decreased with temperature. *Correspondence: O. O. Fasina, Biosystems Engineering Department, Auburn University, Auburn, AL 36849, USA; Fax: 334-844-3530; E-mail: [email protected]. INTERNATIONAL JOURNAL OF FOOD PROPERTIES Vol. 6, No. 3, pp. 461–472, 2003 DOI: 10.1081=JFP-120021459 1094-2912 (Print); 1532-2386 (Online) Copyright # 2003 by Marcel Dekker, Inc. www.dekker.com 461