Effect of Storage Relative Humidity on Physical Stability of Dried Fig

Modeling the rheological properties of currant paste as a function of plasticizers concentration, storage temperature and time and process temperature

The steady and dynamic shear rheological properties of currant paste samples as a function of storage temperature (15, 25 and 35 °C) and time (180 days) and plasticizers content (water and/or glycerol) have been evaluated. Apparent viscosity (η_a) has been found to be significantly increased with prolonged storage, implying possible structural changes, and decreased with the increase in storage temperature and the addition of water or/and glycerol. Flow behavior index and consistency index were determined by fitting the resulting experimental data to a power law equation with high values of correlation coefficients (R² ≥ 0.912). Furthermore, the combined effect of storage temperature, time and plasticizers concentration on the apparent viscosity was described adequately by a proposed empirical model, with low standard relative errors (SRE ≤ 0.011). Additionally, the viscoelastic properties were significantly affected by all evaluated parameters in the same way as in apparent viscosity while both moduli (G' and G″) were modeled sufficiently (R² ≥ 0.884) as power functions of oscillatory frequency. The heat treatment (heating from 25 to 100 °C and cooling back with a rate of 10 °C/min) applied has proved sufficient to reverse the observed storage effects. Moreover, the modified Cox-Merz rule was satisfactorily applied to describe the correlation between the apparent viscosity and the complex viscosity.

Fig extract drying: The relationship between the main operating parameters of a pilot-scale spray dryer and product specifications

This study aims to optimize extraction and drying conditions of fig syrup. Drying was done in a pilot scale two‐fluid nozzle spray dryer. A total of 27 experiments were conducted with varying inlet air temperatures, air flow rates, and also a maltodextrin (MD)‐ low methoxyl pectin (LMP) ratios. While feed rate, feed temperature, and compressed air flow rate of the atomizer were kept constant. The results of differential scanning calorimetry revealed that high levels of glucose and fructose in the extract resulted in a low glass transition temperature of fig syrup. By an increase in the inlet air temperature, the powder bulk density decreased. However, the MD:LMP ratio and the air flow rate were not significantly effective (p < 0/05) in changing the bulk density. SEM micrographs of spray‐dried particles and particle size distribution analysis showed that particles were largely in a range of 5 to 50 μm. The best powders were obtained at an inlet air temperature of 170°C.