Prediction of thermal conductivity and specific heat of native maize starch and comparison with HMT treated starch
Résumé
Specific heat (Cp) and effective thermal conductivity (λ) of native maize starch (NS) were measured by DSC and transient heat transfer method, respectively, at different moisture contents and temperatures. The dependency of temperature (T) and moisture content (W) on the two parameters were investigated. The thermophysical properties of treated starch (TS) by four hydrothermal processes (RP-HMT, IV-HMT, DV-HMT and FV-HMT) were measured and compared to native strach. Hydrothermal treatments were performed at 3 bars (133°C) for 10 min. For Cp and λ measurements, moisture content varied for NS from 5 to 21.5% d.b. and from 8.8 to 25% d.b., respectively, and was fixed at 6% d.b. for TS. Empirical models were developed to specific heat and effective thermal conductivity, using a multiple regression algorithm with subsequent statistical analysis. The proposed models for NS based on T and W predict Cp and λ with a mean absolute error of 3.5% and 1.3%, respectively. Large differences in specific heat were observed between TS and NS. In a temperature range of 40 to 160°C, Cp values varied from 1.964 to 2.699 for NS and 1.380 to 2.085 (J.g-1.°C-1) for TS. In contrast, the conductivity of NS was almost identical to that of treated starch by FV-HMT, followed in an increasing order by those treated by DV-HMT, RP-HMT, and IV-HM processes.
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