Characterization of some functional properties of edible films based on muscle proteins of Nile Tilapia

Recently, it was observed that the myofibrillar as well as the sarcoplasmatic proteins obtained from fish are capable to form films. The objectives of this work was to elaborate and to characterize the water vapor permeability (WVP), the color and opacity, the mechanical properties, and the viscoelastic properties of films made with muscle proteins of Nile Tilapia (Oreochromis niloticus). The proteins were obtained by finely grinding the fish muscle, followed by separation of the connective tissue and freeze-drying after liquid nitrogen freezing. The films were prepared from filmogenic solutions (FS) by the casting technique, as follows: 1 g of protein/100 g of FS, 15-65 g of glycerin/100 g of protein, pH = 2.7 (acetic acid) and FS thermal treatment of 40, 65 and 90 degreesC/30 min. The WVP was determined by a gravimetric method, and the color and opacity of the films were determined with a colorimeter (model MiniScan XE, HunterLab). The mechanical properties, force and elongation at puncture, were determined with the help of a texturometer (model TA.XT2i, TA Instruments), at 25 degreesC. The viscoelastic properties were determined by dynamic mechanical analysis, with a DMA2980 apparatus (TA Instruments) operating in the frequency scanning mode, at 30 degreesC, with the viscoelastic properties being calculated at 1 Hz. It was observed that the WVP increased with the concentration of glycerin (C(g)) as expected and that an increase in temperature of FS thermal treatment also caused an increase in the WVP of the films. The color and the opacity of the films decreased with C(g) and were proportional to the thermal treatment temperature of the FS. In general, it was observed that increasing the C(g) provoked linear reduction of puncture force and an increase on the elongation at break, due to its plasticizer effect. It was also observed that increasing the C(g) caused depression on both the storage and loss moduli values but increased the tan delta. The presence of sarcoplasmatic proteins did not affect the quality of functional properties of films based on muscle proteins of Nile Tilapia. (C) 2003 Elsevier Science Ltd. All rights reserved.