Abstract
The aim of this work is to model the thin layer convective drying kinetics of 'Ameclyae' prickly pear seed variety and to evaluate the effects of drying conditions on the quality of extracted seed oil, specifically alpha-tocopherol content. Drying experiments were carried on following a full 2(3) factorial design using a vertical drying tunnel. The study is restricted to a particular particle size and a particular seed bed of height 0.5 cm, of effective porosity around 0.4 and of initial moisture content on dry basis equal to 1.2 (+/- 0.01) kg/kg. The temperature range was 45 to 70 degrees C, relative humidity range was 15-30% and air velocity was 1 and 2 m/s. The experimental drying curves were fitted to different semi-theoretical drying models proposed in the literature. The Midilli-Kucuk model was found with satisfaction describing the seed air drying curves with a correlation coefficient of 0.999 and a standard error of 0.01. For each drying condition, the extraction of fixed oil seeds was performed at cold using liquid/solid separation method. The oil quality was evaluated on the basis of the alpha-tocopherol content. The alpha-tocopherol was identified and quantified by high-performance liquid chromatography (HPLC-UV). According to the experimental results, it was found that drying air velocity is the most important factor influencing the concentration of alpha-tocopherol, whereas the effects of temperature and relative humidity were lower. The increase of the velocity from 1 m/s to 2 m/s reduced the alpha-tocopherol concentration by about 25%. The convective drying of thin layer of seeds at soft air conditions, drying temperature of 45 degrees C, relative humidity of 15% and air velocity of 1 m/s give the optimal quality of extracted oil in terms of alpha-tocopherol content. Characterization of the morphologic structure of seeds was also performed by SEM.