Transactions of the ASABE Vol. 50(2): 597−604 E 2007 American Society of Agricultural and Biological Engineers ISSN 0001−2351 597 TECHNICAL NOTE: THERMAL PROPERTIES OF CHICKPEA FLOUR, ISOLATED CHICKPEA STARCH, AND ISOLATED CHICKPEA PROTEIN S. Emami, L. G. Tabil, R. T. Tyler ABSTRACT. Thermal properties (thermal conductivity, specific heat, and thermal diffusivity) of chickpea flour, isolated starch, and isolated protein at different temperatures and bulk densities were studied. Thermal conductivity was measured using the line heat source method and calculated using the maximum slope method. Specific heat was measured using differential scanning calorimetry (DSC). Thermal diffusivity was calculated using thermal conductivity, specific heat, and bulk density values. Prediction models were obtained to determine the thermal properties of samples as a function of experimental variables. Thermal conductivity of all three samples showed a linear relationship with temperature and bulk density. Specific heat had a linear relationship with the temperature and moisture content of the sample. Thermal diffusivity of samples had a negative linear relationship with bulk density. Keywords. Food powder, Line heat source, Maximum slope, Starch, Thermal properties. hickpea grains contain high and valuable protein (12.4% to 30.6%) and carbohydrates (52.4% to 70.9%) (Chavan et al., 1986). Starch constitutes the majority of the carbohydrates. Therefore, chickpea grains can be used as raw material for the produc- tion of starch and protein fractions that can be used as ingredi- ents in food processing (Neves and Lourenco, 1995; Tian et al., 1999), including human food, pet food, and animal feed as well as in non-food products (Sánchez-Vioque, et al., 1999). Starch is especially utilized in industries such as min- ing, paper, cosmetics, and pharmaceuticals for binding, siz- ing, dyeing, filling, etc. (International Starch Institute, 2003). Thermal properties of foodstuffs, including specific heat, thermal conductivity, and thermal diffusivity, are important considerations in the design, calculation, modeling, and opti- mization of food processing operations involving heat trans- fer, such as freezing, thawing, cooking, drying, pasteurization, and sterilization (Nesvadba, 1982; Drouzas and Saravacos, 1988; Drouzas et al., 1991). This information can also be used in the study of packaging and shelf-life of the product. Thermal properties of some food materials are avail- able in the literature; however, those of processed materials with different compositions and porosities in a non-homoge- nous structure are more difficult to predict or find in the liter- ature and need to be measured using experimental methods (Drouzas et al., 1991). Submitted for review in May 2006 as manuscript number FPE 6471; ap- proved for publication by the Food & Process Engineering Institute Divi- sion of ASABE in January 2007. The authors are Shahram Emami, ASABE Member Engineer, Gradu- ate Student, and Lope G. Tabil, ASABE Member Engineer, Associate Professor, Department of Agricultural and Bioresource Engineering, and Robert T. Tyler, Professor, Department of Applied Microbiology and Food Science, University of Saskatchewan, Saskatoon, Canada. Corresponding author: Lope G. Tabil, Department of Agricultural and Bioresource Engi- neering, University of Saskatchewan, 57 Campus Dr., Saskatoon, SK S7N 5A9 Canada; phone: 306-966-5317; fax: 306-966-5334; e-mail: lope.t- abil@usask.ca. Thermal conductivity measurement can be conducted us- ing different techniques. Transient techniques include the line heat source method, which is the most widely used meth- od for food materials (Rahman, 1995) because it is simple, quick, accurate, low cost, and usable for any geometry of a sample (Wang and Hayakawa, 1993; Rahman, 1995). The line heat source method started with Van der Held and Van Drunen (1949), who used a high thermal conductivity probe. An internal heater wire runs the length of the probe, with a thermocouple in the middle of its length (Mohsenin, 1980). The remaining space in the probe is filled with high thermal conductivity paste. The probe is inserted into a sample having a uniform temperature and heated at a constant rate. The tem- perature adjoining the line heat source is measured using the thermocouple. After a brief period, the slope resulting from the plot of the natural logarithm of time versus temperature is determined. Thermal conductivity is affected by sample moisture, temperature, and bulk density (Drouzas and Sara- vacos, 1988; Lan, 2000). Specific heat of an agricultural material can be measured or predicted using: (1) the method of indirect mixtures, (2) determination of the foodstuff’s composition followed by applying prediction equations that calculate the specific heat, or (3) differential scanning calorimetry (DSC) (Nesvadba, 1982; Singh and Goswami, 2000). Among these methods, DSC is the most accurate (Yang et al., 2002). It has been uti- lized to investigate thermodynamic properties of legume flours or their fractions (Colonna et al., 1982; Sosulski et al., 1985; Zeleznak and Hoseney, 1987; Davydova et al., 1995; Kerr et al., 2000; Ratnayake et al., 2001). Specific heat is af- fected by moisture content and temperature and increases al- most linearly with increasing moisture content (Drouzas et al., 1991; Singh and Goswami, 2000; Lan et al., 2000). Thermal diffusivity can be measured by different tech- niques, including the transient heating technique, a line heat source thermal conductivity probe with an auxiliary thermo- couple, the transient heating computer technique, and experi- mental measurement of thermal conductivity, specific heat, and bulk density (Rao and Rizvi, 1995). The latter, an indirect C