Sorption isosteric heat for some medicinal and aromatic plants

In this study, sorption isosteric heat for some medicinal and aromatic plan ts was determined by the application of the Clausius-Clapeyron equation to sorption isotherms. Above the moisture contents of 0.14 d.b., the latent he at of vaporization of free water is not significantly different from the so rption isosteric heats for peppermint, marjoram, muscat, cardamom, chamomil e and cloves, and above moisture contents of 0.10 d.b. for thyme and corian der. Sorption isosteric heats for peppermint, daphne, marjoram, muscat, car damom, chamomile, cloves and coriander, thyme are higher for moisture conte nts below 0.12 and 0.10 d.b., respectively. Fennel and anise have the small est sorption isosteric heat values among the selected medicinal and aromati c plants. There is no significant difference between the sorption isosteric heat of fennel and latent heat of vaporization of water. Among the selecte d medicinal and aromatic plants, cinnamon and ginger have the highest sorpt ion isosteric heats for the moisture contents from 0.19 to 0.05 d.b. The ra tios between the sorption isosteric heat and the latent heat of vaporizatio n of free water Q(st)/L-r for cinnamon and ginger are calculated as 1.29 an d 1.27 at moisture content of 0.10 d.b., respectively. These are the highes t ratios of those obtained for all the tested crops. The predicted sorption isosteric heat values are found to be considerably higher for cloves and l ower for cinnamon than those of published sorption isosteric heat values fo r these crops. These differences ranged between 3.8 and 14.2%, depending on the plant species and moisture content. (C) 2001 Silsoe Research Institute .