FUNCTIONAL AND BIOACTIVE PROPERTIES OF COLLAGEN AND ...

formation and stabilisation (Townsend & Nakai, 1983). In this respect, the foam capacity of gelatin
from farmed giant catfish was found to be higher than that from calf skin, the difference possibly
being due to the higher content of hydrophobic amino acid residues in the former. Moreover, the
almost 4 times greater viscosity of the farmed giant catfish skin gelatin was also one of the main
reasons for its better foam stability (Jongjareonrak et al., 2010).
4.3.- Film-forming properties
Gelatin has been extensively studied on account of its film-forming ability and its usefulness as an
outer film to protect food from drying and exposure to light and oxygen (Arvanitoyannis, 2002).
Furthermore, there is an important trend in favour of the use of biodegradable films made from edible
biopolymers from renewable sources to combat the environmental impact of plastic waste
(Tharanathan, 2003). The highly hygroscopic nature of gelatin is its main drawback when considering
the use of gelatin films as protective barriers, because they tend to swell or dissolve when in contact
with the surface of foodstuffs with high moisture content. Consequently, the current trend in
designing gelatin-based biodegradable materials for food packaging or biomedical applications is
focused on developing films with improved mechanical and water resistance properties, by combining
gelatin with biopolymers with different characteristics, such as lipids (Bertan, Tanada-Palmu, Siani,
& Grosso, 2005; Pérez-Mateos, Montero & Gómez-Guillén, 2009; Limpisophon, Tanaka, & Osako,
2010), soy protein isolates (Cao, Fu, & He, 2007; Denavi, Pérez-Mateos, Añón, Montero, Mauri, &
Gómez-Guillén, 2009), polysaccharides as gellan (Lee, Shim, & Lee, 2004), konjac glucomannan
(Li, Kennedy, Jiang, Xie, 2006), chitosan (Arvanitoyannis, Nakayama & Aiba, 1998) pectins (Liu,
Liu, Fishman & Hicks, 2007; Farris et al., 2009), new hydrophobic or hydrophilic plasticizers
(Andreuccetti, Carvalho, & Grosso, 2009; Cao, Yang, & Fu, 2009), synthetic polymers such as
poly(vinyl) alcohol (Carvalho et al., 2009) or polyethylene (Haroun, Beherei, & Abd El-Ghaffar,
2010a), as well as cross-linking agents, such as glutaraldehyde (Bigi, Cojazzi, Panzavolta, Rubini, &
Roveri, 2001), TGase or 1-ethyl-3-(3-dimethylamino-propyl) carbodiimide (EDC) (Yi, Kim, Bae,
Whiteside, & Park, 2006; Kolodziejska & Piotrowska, 2007).
The effect on film properties of gelatin attributes, especially from fish origin, was reviewed recently
by Gómez-Guillén et al. (2009). The molecular weight distribution and amino acid composition,
which are the main factors influencing the physical and structural properties of gelatin, are also
believed to play a key role in the mechanical and barrier properties of the resulting films. Weaker and
more deformable films are normally obtained when low-molecular weight fragments predominate in a
given gelatin preparation, which may be caused by protein heat degradation during the water
extraction step (Muyonga, Cole & Duodu, 2004a) or during the evaporation step (Carvalho et al.,
2008). Furthermore, films made using a lower-molecular weight gelatin were found to be more
plasticized, as a result of the higher plasticizer:biopolymer molar ratio (Thomazine, Carvalho &
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