EFFECTS OF GLYCEROL ON THE DRYING OF GELATIN AND SUGAR SOLUTIONS

ABSTRACT

The water diffusion coefficients D of gelatin, sucrose arid maltodextrin solutions were determined from the isothermal drying (desorption) rates as a function of water content u ( 0.1 < u < 1.0 ) and temperature (303, 323K) for various glycerol contents ( W_G = 0 – 0.43 kg-glycerol/kg-total solid). When W_G was above 0.2, D increased especially at low water contents (u < 0.25). The desorption isotherms were measured for the same systems. The equilibrium water content at a given water activity A_w decreased with an increase in W_G when A_w < 0.5. This indicates that adding glycerol weakens the water-solute interaction especially at low water contents. Glycerol also softened gelatin films and resulted in loss possibilities of surface cracks during drying.

Key Words:

• water diffusivity
• drying rate
• gelatin
• sugar solutions
• plasticizer
• desorption isotherm