The heterogeneity of the film matrix created by fatty
acid incorporation probably led to weakened intermolecular interactions
and a consequent decrease in the TS of the emulsified films.
No significant difference (P > 0.05) in UTS was observed between
PGP and PGP–C16 films at concentrations of 2% and 4%, whereas
the UTS of all PGP–C18 films were significantly (P < 0.05) lower
than that of the PGP film. Interestingly, increasing C18 concentration
had a positive effect on UTS, which increased with the addition
of more C18. Consistent with this observation, Rhim et al. (1999) reported
that the UTS of soy protein–fatty acid films decreased at low
concentrations of fatty acids because of poor interactions between
protein and fatty acids, but increased at fatty acid concentrations
>20%. They argued that the increase in the ratio of fatty acid/protein
beyond this point strengthened films because fatty acids are
solid at room temperature.