Effect of Drying on Rheological, Thermal, and Structural Properties of Desert Truffles (Terfezia Claveryi) Powder Dispersions

The effect of drying methods (freeze-drying and tray-drying) on the rheological, thermal and functional properties of truffle flour dispersion was studied. Sieve analysis showed the number of finest particles in the freeze-drying samples were significantly higher than the tray-drying samples whereas no significant difference was observed in the particle size distribution through laser diffraction measurement. The freeze-drying sample had significantly higher water holding capacity, sediment volume fractions, and superior instrumental color values than the tray-drying sample. Upon thermal scanning, two distinct starch-lipid complex melting transitions for the freeze-drying and one for the tray-drying sample were detected. Contrary to differential scanning calorimetric measurement, the oscillatory shear measurement successfully detected a distinct gelatinization temperature for the freeze-drying sample between 64 and 67.6°C. The mechanical rigidity of the dispersion was significantly influenced by the drying method and the freeze-drying sample exhibited the higher mechanical strength over the tray-drying sample throughout the frequency range (0.1 to 10 Hz). Viscoelasticity of the dispersion was estimated by a power-type relationship correlating the elastic modulus and frequency. Various shapes of truffle particles including rod, round, oval, and irregular were observed through the scanning electron microscope. This study provided in-depth knowledge on structural/rheological properties of truffle powder produced by two drying processes.