Prediction models for the thermal conductivity of aqueous starch Chuan-Liang Hsu 1 * & Dennis R. Heldman 2 1 Department of Food Science, Yuanpei University of Science and Technology, 306 Yuanpei Street, Hsinchu 300, Taiwan 2 Department of Food Science, Rutgers - The State University of New Jersey, 65 Dudley Road, New Brunswick, NJ 08901-8520, USA (Received 30 January 2002; Accepted in revised form 25 January 2004) Summary The objectives of this research were to determine the thermal conductivity of aqueous starch and to develop a theoretical model to predict the thermal conductivity for both granular and gelatinized aqueous starches. Thermal conductivity of starch was experi- mentally investigated as a function of moisture content (55–70%) and temperature (5–45 °C) by using the probe method. Six structural heat conduction models were employed to predict the thermal conductivity. Results indicated that the experimental thermal conductivity increased with increasing moisture content and temperature for both granular and gelatinized starch. The effect of gelatinization on thermal conductivity was small but significant at 5 °C, but insignificant at 25 and 45 °C. Over the moisture and temperature ranges investigated, the thermal conductivity values predicted by the Kopelman (B) and Maxwell models were in close agreement with the experimental values for granular starch, whereas for gelatinized starch, the Maxwell model yielded the lowest standard error with the experimental values. Keywords Gelatinization, granular starch, moisture, temperature. Introduction Most processed foods are subjected to a heat treatment, either heating or cooling, moderate or severe, once or several times. Starch is a typical food component and is appropriate for funda- mental investigation of the heat and mass trans- port properties. The thermal transport properties of starch, such as thermal conductivity, are used in quantitative analysis for various thermal proces- ses, such as heating, cooking, sterilization, drying and extrusion cooking (Drouzas & Saravacos, 1988). The thermal conductivity of starchy foods is a function of its structure, moisture content and temperature (Maroulis et al., 1991). The effects of these variables on the thermal conductivities of granular and gelatinized starch have been investi- gated (Saravacos et al., 1990; Maroulis et al., 1991; Wang & Hayakawa, 1993; Morley & Miles, 1997). Only limited studies have been conducted on the effect of gelatinization on the thermal conductivity of starch although many researchers have attempted to either develop new or use existing models to predict the thermal conductiv- ity of starch during processing (Maroulis et al., 1990, 1991; Morley & Miles, 1997). The objec- tives of this investigation were to: (1) determine the thermal conductivity of starch at various moisture contents and temperatures; (2) investi- gate the effect of gelatinization on the thermal conductivity of starch; and (3) evaluate existing mathematical models and compare the thermal conductivity of starch predicted by them for accuracy. Theoretical Background Thermal conductivity modelling The thermal conductivity of starch has been modelled previously (Kopelman, 1966; Maroulis *Correspondent: Fax: 886-3-5385353; e-mail: clhsu@mail.yust.edu.tw International Journal of Food Science and Technology 2004, 39, 737–743 737 doi:10.1111/j.1365-2621.2004.00840.x Ó 2004 Blackwell Publishing Ltd