Effect of Storage Relative Humidity on Physical Stability of Dried Fig

Abstract

The objective of this study was to assess the effect of storage condition (relative humidity) on the structural stability of dried fig. Moisture sorption isotherms of dried fig were obtained at 5, 25 and 40C. 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 (T g) and the melting enthalpy (ΔH m) of dried figs equilibrated at different relative humidities were measured using differential scanning calorimetry (DSC). The percentage of crystallization was measured using wide angle X-ray diffraction (WAXD). It was revealed that the extent of sugar crystallization increased at the intermediate relative humidity region, as implied by WAXD. The same result was observed by measuring ΔH m using DSC. The impact of different relative humidities on the sugar crystallization was explained in terms of (T − T g). Practical Applications Fig is mostly used in dried form. Low molecular weight sugars are the major component of fig solid. The physical states of these sugars play an important role in stability of dried fig during storage. Changes in water content as a function of storage condition may lead to undesired physical properties in dried fig which is of great importance for its structure and quality. Water has a great plasticization effect on this fruit and distresses its T g. Crystallization of amorphous sugars is the most important issue for physical instability of dried fig and other dried fruits with high-sugar contents during storage. The rate and extent of this phenomenon increase at intermediate relative humidities and can be described in term of T − T g. The present results showed that intermediate storage relative humidities are critical for the physical stability of dried fig during storage.