CHARACTERISTICS OF GELATIN BIOFILMS IN RELATION TO DRYING PROCESS CONDITIONS NEAR MELTING

ABSTRACT

Biofilms are edible films formed from biopolymers. In the casting process technique, the biofilm is obtained by the drying of a colloidal solution in the final process stage The aim of this work was to analyse the drying process of gelatin based biofilms, in room frontier conditions. The biofilms were prepared initially by dissolving gelatin in water and adding sorbitol as plasticizer. The filmogenic solution was dried in an automatic drier under various drying conditions, for 1mm film: air temperature (T= 35, 40 and 45 °C), relative humidity (ϕ= 60 and 75 %) and air velocity (v= 3m/s). The drying kinetics was measured for 15, 30 and 45 % sorbitol concentrations. Sorption isotherms at 25, 35 and 45 °C were determined for the 15% sorbitol concentration films by the static gravimetric method. The glass transition and the melting temperature for various moisture contents were determined with a Differential Scanning Calorimeter TA 2010. The results showed an unusual behaviour for temperature dependence: decreasing drying kinetics with increasing air temperature. Also separation of gelatin and sorbitol were seen when the temperature increased. This phenomenon occurs when the film temperature during the drying process gets close to the melting temperature of the film.

Key Words:

• edible films
• biopolymers
• quality