A chitosan solution of 1% (w/v) was prepared by dissolving an
appropriate amount of chitosan in 1% acetic solution (v/v). Chitosan
solution was mixed with a proper amount of starch (see experimental
design). The mixture was constantly stirred and heated
from room temperature (approximately 25 C) to 90 C, where it
was kept for 5 min. The mixture was cooled down to room temperature
before 1% (w/v) of a plasticizer (glycerol or glucose) and 1%
(w/v) of a surfactant (Tween®-20 or Tween®-80) were added. Afterward,
the mixture was homogenized by using an ultraturrax
(Polytron, Switzerland) at 11,000 rpm for either 0.5 or 4 min.
Twenty mL of the prepared solution were transferred to a Petri dish
of 7 cm diameter. The Petri dish was left in a chamber (SCI Finetech
Co., Korea) at 30 C, 60% relative humidity for 24 h