G.S. Raouzeos’s research while affiliated with National Technical University of Athens and other places

The effect of ethyl oleate on the drying rates for starches and seedless grapes was investigated in a pilot plant air-dryer. Incorporation of ethyl oleate in unheated pastes of high-amylose starch significantly increased the drying rate during the initial stage of drying but had little effect on the drying rates for granular high-amylopectin starch pastes and gelatinized starches. Dipping grapes in alkali emulsions of ethyl oleate increased significantly the drying rate throughout the drying period.Ethyl oleate may act as a wetting agent, increasing the evaporation rate of water from porous surfaces in the early stages of drying. The initial interphase mass transfer coefficients during the drying of the starches were close to the predicted values for wet surfaces. The acceleration of drying in grapes may be caused by solvent action of ethyl oleate on the skin wax and the grape cell walls.

The drying of Sultana seedless grapes was investigated under intermittent and continuous operating conditions in a laboratory solar installation involving a thermal storage bed and an auxiliary heater. The effect of pretreatment, and of the a i r velocity on the drying rate of the grapes at constant temperature was also studied in relation t o the quality of the dried product.Solar drying of the grapes was accomplished in 30.5 to 60.5 h of intermittent operation, or 19 to 60 h of continuous drying, involving the thermal storage bed and the auxiliary heater. The shortest drying time (19 h ) and the highest quality dried product were obtained with grapes dipped in a hot (80 C ) solution of sodium hydroxide and ethyl oleate, which were dried continuously at 42°C and 2m/s, air temperature and velocity respectively.The mean apparent diffusivity of moisture in raisins at 6o°C and air velocity 2m/s was estimated as 1.0.10-10 m2/s.

The statistical method of factorial design is presented in a thorough analysis of the air-drying of starch gels. The statistical data are used for the development of mathematical models which can predict quantitatively the effect of the important parameters and their interactions on the drying time. Starch gels were chosen as experimental materials because they simulate several food and polymeric materials, and they can be prepared as experimental samples of the desired dimensions and composition.