Drying kinetics and allicin potential in garlic slices during different methods of drying

Drying kinetics of garlic cloves was investigated by drying 5 mm thick slices in air, vacuum, and nitrogen atmosphere. The drying coefficient and lag factor were estimated from the slope and intercept of the moisture ratio time plot based on a model by Dincer-Hussain. Both drying coefficient and lag factor increased with increasing drying temperature. The diffusivity estimated from the Fick's law of diffusion and Dincer-Hussain's model differed, because Fick's law assumes negligible external mass transfer, whereas Dincer-Hussain's model considers both internal and external mass transfer resistance. Allicin, which is rapidly produced by the action of alliinase on alliin when fresh tissue is crushed, is the main biologically active phytochemical of garlic. Air drying at 50°C, vacuum drying at 50 and 60°C, nitrogen atmosphere drying at 40°C gave lowest losses of allicin potential. In general, the loss of allicin potential increased with increasing drying temperature, and drying below 50°C should be the best drying condition for the retention of allicin potential. This could be due to higher retention of alliinase activity during lower temperature drying. The loss of allicin potential decreased with the increase of slice thickness. This may be explained by lower structural damage and by lower shrinkage in the case of thicker slices.