Investigation on some physico-chemical properties of Estahban dried fig in order to increase its quality and stability.

Fig is a highly perishable fruit with a very short storage life due to the high amount of low molecular weight carbohydrates and moisture content. Drying is the most common method of fig preservation. It mainly consists of small molecular weight sugars (more than 80%). Stability of these sugars is highly dependent on the storage conditions (temperature and relative humidity). The objective of this study was to assess the effect of storage condition (relative humidity) on the structural stability of dried fig. The static gravimeteric method was used to determine the moisture sorption isotherms of dried fig sample at 5, 25 and 40oC. Dried fig, like most high sugar content materials showed a type I isotherm and the sorption capacity of the sample decreased with increasing the temperature. The glass transition temperature (Tg) and the melting enthalpy ( Hm) of dried figs equilibrated at different relative humidities were measured using differential scanning calorimetry (DSC). The results showed that the glass transition temperature was decreased by increasing moisture content. DSC thermograms revealed that dried fig has semi crystalline structure. The melting enthalpy (∆Hm) associated with the melting of the ordered structure is increasing with relative humidity and reaches its maximum at RH of 45%. At the vicinity of this RH level, the sorption isotherm of dried fig starts a sudden increase. The percentage of crystallisation was measured using x-ray diffraction (XRD). It was revealed that dried fig has semi crystalline structure and the extent of sugar crystallisation increased at the intermediate relative humidity region, as implied by XRD. The same result was observed by measuring Hm, using DSC. Flesh firmness and the energy for penetration were measured using texture analyzer. The results reflected the plasticisation of the structure by water. Flesh firmness and penetration energy were increased with water and then reached a plateau. Also, the results of changes in color of dried fig indicated that the brown color increased with water and reached a plateau. The results of measuring different structural characteristics of dried fig at different relative humidities revealed that the structural changes are intensive at intermediate relative humidities. The impact of different relative humidities on the structural changes was explained in terms of (T_Tg), regardless of whether T or Tg was varied. At a critical relative humidity (intermediate RH), the rate and extent of structural changes reached the maximum values.