349
with a novel solution (An et al. 2010 ). The introduction of PLLA remarkably improved
the mechanical properties of the gelatin membranes. With a combination of good
biocompatibility and mechanical properties, fi sh gelatin/PLLA blending non-woven
mats are considered to be very promising in the area of tissue regeneration.
Recently, Qazvini et al. ( 2012 ) reported on the development of “ self-healing fi sh
gelatin/sodium montmorillonite biohybrid coacervates ”. Complex coacervation
driven by associative electrostatic interactions was studied by these authors in mixtures of exfoliated sodium-montmorillonite (Na
+ -MMT) nanoplatelets and fi sh gelatin, at a specifi c mixing ratio and room temperature. Structural and viscoelastic
properties of the coacervate phase were investigated as a function of pH by means
of different complementary techniques. Independent of the technique used, the
results consistently showed that there is an optimum pH value at which the coacervate phase shows the tightest structure with highest elasticity. The solid-like coacervates showed an obvious shear-thinning behavior and network fracture, but
immediately recovered back into their original elastic character upon removal of the
shear strain. The nonlinear mechanical response characterized by single step stress
relaxation experiments revealed the same trend for the yield stress and isochronal
shear modulus of the coacervates. As a function of pH, the modulus has a maximum
at pH 3.0 and lower values at 2.5 and 3.5 pHs, followed by a very sharp drop at pH
4.0. Finally, small-angle X-ray scattering (SAXS) data confi rmed that at pHs lower
than 4.0 the coacervate phases were dense and structured with a characteristic length
scale (ξ(SAXS)) of ~7–9 nm. Comparing the ξ(SAXS) with rheological characteristic
length (ξ(rheol)) estimated from low-frequency linear viscoelastic data and network
theory, it was concluded that both the strength of the electrostatic interactions and
the conformation of the gelatin chains before and during of the coacervation process
are responsible for the structure and rigidity of the coacervates (Qazvini et al. 2012 ).
9.1 Fish Gelatin-Based Films
Gelatin applications in foods are derived largely from its gelation and fi lm-forming
properties, which are a consequence of an extended, fi brous tertiary structure and a
triple helical cross-linked quaternary structure (Simon-Lukasik and Ludescher
2004 ). In gelatin, the triple-helical fold can involve segments of several different
chains. As a result of these interchain cross-links, a network is formed with interstitial space for water. As gelatin gels age, water is excluded and the protein matrix
condenses into a rubbery fi lm that vitrifi es upon drying (Simon-Lukasik and
Ludescher 2004 ). Recently, Carvalho et al. ( 2008 ) reported that adding a concentration step by evaporating at 60 °C before spray drying the gelatin from Atlantic halibut ( Hippoglossus hippoglossus ) skin resulted in sizeable differences in the physical
properties of the corresponding fi lms. Differences in the mechanical behaviour of
these fi lms were attributed to slight differences in the molecular weight distributions
of the two types of gelatin, caused by protein heat degradation during the evaporation step. As a result, these authors concluded that gelatin having a predominance of
lower-molecular weight fractions underwent greater plasticization by the added
9.1 Fish Gelatin-Based Films
with a novel solution (An et al. 2010 ). The introduction of PLLA remarkably improved
the mechanical properties of the gelatin membranes. With a combination of good
biocompatibility and mechanical properties, fi sh gelatin/PLLA blending non-woven
mats are considered to be very promising in the area of tissue regeneration.
Recently, Qazvini et al. ( 2012 ) reported on the development of “ self-healing fi sh
gelatin/sodium montmorillonite biohybrid coacervates ”. Complex coacervation
driven by associative electrostatic interactions was studied by these authors in mixtures of exfoliated sodium-montmorillonite (Na
+ -MMT) nanoplatelets and fi sh gelatin, at a specifi c mixing ratio and room temperature. Structural and viscoelastic
properties of the coacervate phase were investigated as a function of pH by means
of different complementary techniques. Independent of the technique used, the
results consistently showed that there is an optimum pH value at which the coacervate phase shows the tightest structure with highest elasticity. The solid-like coacervates showed an obvious shear-thinning behavior and network fracture, but
immediately recovered back into their original elastic character upon removal of the
shear strain. The nonlinear mechanical response characterized by single step stress
relaxation experiments revealed the same trend for the yield stress and isochronal
shear modulus of the coacervates. As a function of pH, the modulus has a maximum
at pH 3.0 and lower values at 2.5 and 3.5 pHs, followed by a very sharp drop at pH
4.0. Finally, small-angle X-ray scattering (SAXS) data confi rmed that at pHs lower
than 4.0 the coacervate phases were dense and structured with a characteristic length
scale (ξ(SAXS)) of ~7–9 nm. Comparing the ξ(SAXS) with rheological characteristic
length (ξ(rheol)) estimated from low-frequency linear viscoelastic data and network
theory, it was concluded that both the strength of the electrostatic interactions and
the conformation of the gelatin chains before and during of the coacervation process
are responsible for the structure and rigidity of the coacervates (Qazvini et al. 2012 ).
9.1 Fish Gelatin-Based Films
Gelatin applications in foods are derived largely from its gelation and fi lm-forming
properties, which are a consequence of an extended, fi brous tertiary structure and a
triple helical cross-linked quaternary structure (Simon-Lukasik and Ludescher
2004 ). In gelatin, the triple-helical fold can involve segments of several different
chains. As a result of these interchain cross-links, a network is formed with interstitial space for water. As gelatin gels age, water is excluded and the protein matrix
condenses into a rubbery fi lm that vitrifi es upon drying (Simon-Lukasik and
Ludescher 2004 ). Recently, Carvalho et al. ( 2008 ) reported that adding a concentration step by evaporating at 60 °C before spray drying the gelatin from Atlantic halibut ( Hippoglossus hippoglossus ) skin resulted in sizeable differences in the physical
properties of the corresponding fi lms. Differences in the mechanical behaviour of
these fi lms were attributed to slight differences in the molecular weight distributions
of the two types of gelatin, caused by protein heat degradation during the evaporation step. As a result, these authors concluded that gelatin having a predominance of
lower-molecular weight fractions underwent greater plasticization by the added
9.1 Fish Gelatin-Based Films