intermolecular forces along polymer chains, thereby
‘softening’ film structure, decreasing tensile strength and
increasing elongation (Gennadios et al., 1993). Shaw
et al. (2002) revealed reduction in tensile strength and
increased water vapour pressure of whey protein isolate
films with increase in plasticiser content. The water
solubility is an important property for edible films.
Potential application to high moisture foods demands
water resistance, but use as edible packaging may
require high solubility (Stuchell & Krochta, 1994).
Water solubility of RBP films at pH 9.5 was higher
than that at pH 3.0, which is similar to the observation
of Gnanasambandam et al. (1997). Increased protein
solubility and higher pH may be the probable reason for
this.