Moisture sorption and thermodynamic properties of safflower petals and tarragon Original Research Article

Safflower (Carthamus tinctorius) petals and tarragon (Artemisia dracunculus) are common aromatic and medicinal herbs with centuries of use. Moisture sorption characteristics of safflower petals and tarragon and need to be evaluated since these plants are consumed and stored in their dried forms. The moisture sorption isotherms of safflower petals and tarragon were determined at 15, 25 and 35 °C over a water activity (aw) range of 0.08–0.95, using the static gravimetric method. The sorption data were analyzed using Halsey, Oswin, Brunauer–Emmett–Teller (BET) and Gugghenheim–Anderson–de Boer (GAB) equations. The BET equation was found to be the best model for predicting the equilibrium moisture content of safflower petals and tarragon in the range of water activity 0.06–0.52. For the whole aw range Halsey, Oswin and GAB would be applicable for both products at the temperature range studied. The thermodynamic functions such as isosteric heat of sorption, differential entropy, net integral enthalpy and entropy were evaluated to provide an understanding of the properties of water and energy requirements associated with the sorption behavior. The isosteric heat values decreased with increase in moisture content of the products and approached the latent heat of pure water after around 10% dry basis. The net integral enthalpy of safflower and tarragon samples increased with moisture content to a maximum value of 8.74 and 9.52 kJ mol−1 (respectively) at 6.3% db (around the monolayer moisture content) and then decreased. In a reverse manner, the net integral entropy decreased with increasing moisture content to a minimum value and then increased.