351
gelatin fi lms were amorphous. This was due to the fi lms being dried at room temperature (23 °C), which was below or near the gelation temperatures of mammalian
and warm-water fi sh gelatin solutions and well above the gelation temperature of
cold-water fi sh gelatin solutions. Tensile strength, percent elongation, and puncture
deformation were highest in mammalian gelatin fi lms, followed by warm-water fi sh
gelatin fi lm and then by cold-water fi sh gelatin fi lms. Oxygen permeability values
of cold-water fi sh gelatin fi lms were signifi cantly lower than those for mammalian
gelatin fi lms. These differences were most likely due to higher moisture sorption in
mammalian gelatin fi lms, leading to higher oxygen diffusivity (Avena-Bustillos
et al. 2011 ).
The use of different cross-linking agents has been also reported for fi sh-gelatin
fi lms and their properties (Chiou et al. 2008 , 2009 ). Thus, Yi et al. ( 2006 ) prepared
fi lms using a commercial high molecular weight cold-water fi sh gelatin plasticized
with sorbitol by inducing enzymatic cross-linking with a microbial transglutaminase (MTGase). The tensile strength and oxygen permeability of the MTGasemodifi ed fi lms increased, while elongation decreased. The mechanical and barrier
properties of the gelatin fi lms were explainable in terms of the total free volume of
the fi lm matrix. Thanks to the triple-helix structures present in gelatin molecules,
the gelatin matrix is usually compact, resulting in low oxygen permeability. The
intra and intermolecular covalent bonds formed by MTGase could increase the free
volume of the polymer matrix by hindering helical structure formation. The lower
number of helical structures could decrease the fl exibility of the gelatin matrix,
while the higher degree of cross-linking could increase its strength.
Interestingly, ultraviolet-B radiation can induce cross-linking and improves
physical properties of cold- and warm-water fi sh gelatin gels and fi lms (Otoni et al.
2012 ). Cold- and warm-water fi sh gelatin granules were exposed to ultraviolet-B
radiation for doses up to 29.7 J/cm
2 . Solutions and fi lms were prepared from the
granules. SDS-PAGE and refractive index results indicated there was cross-linking
of gelatin chains after exposure to radiation. It was observed that UV-B treated
samples displayed higher gel strengths, with cold- and warm-water fi sh gelatin having gel strength increases from 1.39 to 2.11 N and from 7.15 to 8.34 N, respectively.
In addition, both gelatin samples exhibited an increase in viscosity for higher UV
doses. For gelatin fi lms, the cold-water fi sh gelatin samples made from irradiated
granules showed greater tensile strength. In comparison, the warm-water gelatin
fi lms made from irradiated granules had lower tensile strength, but better water
vapor barrier properties. This might be due to the UV induced cross-linking in
warm-water gelatin that disrupted helical structures (Otoni et al. 2012 ).
As represented above, a broad variety of fi sh gelatin-based fi lms are examples of
composite- or even multicomposite-containing (Shakila et al. 2012 ) biomaterials.
For example, edible fi lms based on fi sh-skin gelatin incorporated with chitosan and/
or clove essential oil were investigated by Gómez-Estaca and co-workers ( 2009a , b )
and their antimicrobial activity was tested on Lactobacillus acidophilus,
Pseudomonas fl uorescens, Listeria innocua , and Escherichia coli . The fi lms incorporated with the clove essential oil were the most effective, although differences
were observed depending on the biopolymeric matrix in which it was included.
9.1 Fish Gelatin-Based Films
gelatin fi lms were amorphous. This was due to the fi lms being dried at room temperature (23 °C), which was below or near the gelation temperatures of mammalian
and warm-water fi sh gelatin solutions and well above the gelation temperature of
cold-water fi sh gelatin solutions. Tensile strength, percent elongation, and puncture
deformation were highest in mammalian gelatin fi lms, followed by warm-water fi sh
gelatin fi lm and then by cold-water fi sh gelatin fi lms. Oxygen permeability values
of cold-water fi sh gelatin fi lms were signifi cantly lower than those for mammalian
gelatin fi lms. These differences were most likely due to higher moisture sorption in
mammalian gelatin fi lms, leading to higher oxygen diffusivity (Avena-Bustillos
et al. 2011 ).
The use of different cross-linking agents has been also reported for fi sh-gelatin
fi lms and their properties (Chiou et al. 2008 , 2009 ). Thus, Yi et al. ( 2006 ) prepared
fi lms using a commercial high molecular weight cold-water fi sh gelatin plasticized
with sorbitol by inducing enzymatic cross-linking with a microbial transglutaminase (MTGase). The tensile strength and oxygen permeability of the MTGasemodifi ed fi lms increased, while elongation decreased. The mechanical and barrier
properties of the gelatin fi lms were explainable in terms of the total free volume of
the fi lm matrix. Thanks to the triple-helix structures present in gelatin molecules,
the gelatin matrix is usually compact, resulting in low oxygen permeability. The
intra and intermolecular covalent bonds formed by MTGase could increase the free
volume of the polymer matrix by hindering helical structure formation. The lower
number of helical structures could decrease the fl exibility of the gelatin matrix,
while the higher degree of cross-linking could increase its strength.
Interestingly, ultraviolet-B radiation can induce cross-linking and improves
physical properties of cold- and warm-water fi sh gelatin gels and fi lms (Otoni et al.
2012 ). Cold- and warm-water fi sh gelatin granules were exposed to ultraviolet-B
radiation for doses up to 29.7 J/cm
2 . Solutions and fi lms were prepared from the
granules. SDS-PAGE and refractive index results indicated there was cross-linking
of gelatin chains after exposure to radiation. It was observed that UV-B treated
samples displayed higher gel strengths, with cold- and warm-water fi sh gelatin having gel strength increases from 1.39 to 2.11 N and from 7.15 to 8.34 N, respectively.
In addition, both gelatin samples exhibited an increase in viscosity for higher UV
doses. For gelatin fi lms, the cold-water fi sh gelatin samples made from irradiated
granules showed greater tensile strength. In comparison, the warm-water gelatin
fi lms made from irradiated granules had lower tensile strength, but better water
vapor barrier properties. This might be due to the UV induced cross-linking in
warm-water gelatin that disrupted helical structures (Otoni et al. 2012 ).
As represented above, a broad variety of fi sh gelatin-based fi lms are examples of
composite- or even multicomposite-containing (Shakila et al. 2012 ) biomaterials.
For example, edible fi lms based on fi sh-skin gelatin incorporated with chitosan and/
or clove essential oil were investigated by Gómez-Estaca and co-workers ( 2009a , b )
and their antimicrobial activity was tested on Lactobacillus acidophilus,
Pseudomonas fl uorescens, Listeria innocua , and Escherichia coli . The fi lms incorporated with the clove essential oil were the most effective, although differences
were observed depending on the biopolymeric matrix in which it was included.
9.1 Fish Gelatin-Based Films