evaluation of the physical stability of garlic powder dried by freeze and cabinet drying

sorption isotherm and thermal properties of powders were used for determining stability during storage. garlic slices with 2 mm thickness were dried, using two methods of freeze and cabinet drying. the results showed that, the density, loss of pyruvate and color changes of the freeze dried powder were less than those of the cabinet dried powder. sorption isotherm curves of the both garlic powders changed slightly up to 0.40 water activity and increased drastically at higher water activity values. the glass transition temperature of freeze dried powder with 50.36 ºc at 6.98 % moisture content was more than cabinet dried powder with 44.5 ºc at 7.68 % moisture content. the glass transition temperatures of the powders decreased with increasing in their moisture contents. the critical condition for the storage of garlic powder was the water activity higher than 0.55 and the temperatures above 35 ºc that increased the risk of moisture absorption and agglomeration of the garlic powder.