The film thickness increased from 0.0166 (±0.0003) mm
for the 5% WPI film to 0.0232 (±0.0012) mm for the 7%
WPI film and to 0.0447 (±0.0003) mm for the 9% WPI film
(Fig. 1). The difference in thickness was significant
(p < 0.05) in all comparisons of films made from the different
concentrations of WPI. This behavior is as a result of
the protein concentration of WPI solution, when the concentration
was high. The WPI-based film thickness values
were lower than those reported by Vachon, Yu, Yefsa,
Alain St-Gelais, and Lacriox (2000) with thicknesses of0.05 to 0.06 ± 0.002 mm for the same material but crosslinked
by heating and irradiation. However, the values
were much higher than those reported by Simelane and
Ustunol (2005) who noted a thickness value of
0.14 ± 0.02 mm. This was due to differences in film-forming
solution formulations and procedures used.
At the same protein concentrations, films prepared with
a different ratio of plasticizer showed different values in
thickness. The thickness increased slightly when the glycerol
amount was increased in film-forming solution. Generally
WPI:Gly ratio did not significantly affect the film
thickness.
Thickness affects the drying kinetics of the liquid filmforming
dispersion, which may cause differences in film
structure (Debeaufort & Voilley, 1995). A high film thickness
produces an increase in WVP. Therefore, control of
this parameter is crucial.