Prediction of Thermal Conductivity and Specific Heat of Native Maize Starch and Comparison With HMT Treated Starch

Abstract

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. These processes differ by the water content, temperature and processing time used. The two major hydrothermal processes largely cited by the literature that modify the physicochemical properties of starch, without destroying the granules are annealing [1-3] and Heat-Moisture Treatment (HMT) [4][5][6][7]. Annealing process occurs under large excess of water (50 to 60%) and relatively low temperatures, below the gelatinization temperature while HMT process is conducted under restricted moisture content (10-30%) and higher temperatures (< 140°C), above its glass transition temperature and below the gelatinization temperature for times of few minutes [8] to hours [7,[9][10]. As the HMT treatments lead to more or less significant changes in the structure and the functional properties of starches, many works were focused on the study of physicochemical properties of starch granules after HMT treatment but limited investigations are available on the effect of these treatments on changes in thermophysical properties and taking into account modifications of structural properties. Starch is considered as a reactive porous media, composed of a discontinuous solid phase which plays an important role in internal transports by canalizing flows and developing the thermophysical bonds with the fluid phases [11]. In presence of water and temperatures above 60°C, the physico-chemical properties of starch change due to modifications in its semi-crystalline structure. Bahrani et al. [12] have already shown during the steaming of standard maize starch (SMS) by three HMT processes that the heating of starch granules is the result of transfer of latent heat of steam condensation by direct contact with saturated...

Energy efficiency and physical integrity of maize grains subjected to continuous and intermittent drying

“…During the tempering time, the variations in temperature and relative humidity of the intergranular air were not higher than 5 °C and 2%, respectively (Figure 4), after reaching the equilibrium, resulting in better insulation of the expanded polystyrene box, whose thermal conductivity is about seven times higher than that of maize grains (Suleiman & Rosentrater, 2016;Leila et al, 2019).…”

“…The expanded polystyrene box with capacity of 100 L was resized to have the following dimensions: 0.51, 0.30 and 0.16 m for length, width and height, respectively, reducing the volume to 24.48 L (24.48 x 10 -3 m 3 ) (Figure 2). With this adjustment, a 0.15 m thickness was adopted on all sides, including the upper and lower parts, equivalent to a thickness of 1.011 m in the mass of grains, considering the thermal conductivities of the material (0.02 W m -1 ºC -1 ) and of the product at the temperature and moisture content during the tempering (0.16 W m -1 ºC -1 ) (Suleiman & Rosentrater, 2016;Leila et al, 2019).…”

Effects of Different Processing Techniques and Sol-Gel Coating on Physical Properties of Starch and Clay-Based Biocomposite Material

“…The C measures the ability of a biocomposite material to conduct heat and is useful for the control of the multiple changes during food processes. The apparent C value of starch dispersions raises with temperature, and strongly dependent on the temperature and moisture content (Aklouche et al, 2019). The C value of native starch was 1.638 Jg -1 K -1 whereas it was 1.87 Jg -1 K -1 for the pregelatinized cornstarch (Mariam et al, 2008).…”

Microscopy of maize grains subjected to continuous and intermittent drying

“…Agronomy, v. 44, e54906, 2022 10 −3 m 3 ) (Figure 2), and 0.150-m thick insulation made of expanded polystyrene on all sides. It resulted in an equivalent layer of maize grains of 1.011 m, considering the thermal conductivity of the insulating material (0.024 W m −1 °C−1 ) and the maize grains under the temperature and moisture content conditions during the rest (0.1618 W m −1 °C−1 ) (Suleiman & Rosentrater, 2016;Leila et al, 2019;Chai & Chen, 2010).…”