Preparation And Characterization Of Edible Films Based On Fish Gelatin

Aiming at promoting the sustainable development of freshwater fishery,much attention has been payed to the comprehensive utilization of the bio-products generated during the freshwater-fish processing.Extracting gelatin from fish processing by-products to prepare the edible packaging films,which can alleviate the pollution to the environment caused by plastic packaging,has became a new way for efficient utilization of fresh-water fish resources.Therefore,edible films were prepared with gelatin from tilapia skin and scales in this study,and then the properties of gelatin films were modified with thermal treatment.In addition,the effect of protein concentration on the properties of gelatin films prepared under high-temperature drying was also investigated.In Chapter 2,edible films based on the gelatin from tilapia scales were prepared.The effects of gelatin extraction temperature and time,along with glycerol concentration on the film properties such as tensile strength?TS?and elongation at break?EAB?were also investigated.TS of films prepared from the scale gelatin which was hardly degraded when extracted at 80oC for0.5 h or 1 h,could reach the highest value at around 44 MPa.With glycerol concentration in the film-forming solution?FFS?increasing,TS and the glass transition temperature?Tg?of films was decreased while EAB was increased,indicating that increasing the glycerol concentration in FFS would lead to the gelatin films a weaker network,thus had an enhancing effect on the extension ability of films.The effects of thermal treatment on the properties of tilapia skin/scale gelatin films were investigated in Chapter 3.Compared to the edible gelatin films from tilapia scales,gelatin films from tilapia skin had relatively lower TS but higher film solubility?FS?.After a high-temperature?100oC and above?thermal treatment on the films for a certain time,the mechanical properties and water resistance ability of tilapia skin gelatin films were enhanced obviously.TS of films were increased with increasing thermal treatment time and temperature.The TS of skin gelatin films was increased by about 46.22%when they were heated for 6 h under 120oC,while the film solubility and protein solubility?PS?were decreased by 44.38%and 40.62%,respectively.Based on the SDS-PAGE patterns of tilapia skin gelatin films and the results of chemical bonding force analysis,it was suggested that during the thermal treatment?100oC and above?on the films,?₁,?₂,?and their aggregations with high molecular weight in gelatin films could be cross-linked with each other through the dehydration condensation reaction between the hydrophilic groups.The changes in the film properties of tilapia scale gelatin films subjected to heat treatment were similar to those of tilapia skin gelatin films,except for the observation of more crosslinkings between gelatin moleculars with 120oC heat treatment for 4 h and 6 h.In the next section of Chapter 4,the effect of protein concentration of FFS on the properties of skin gelatin films dried at high temperature were investigated.The results showed that when the protein concentration of FFS was 5%,the TS of films formed under 100oC was only 13%of that of films formed at room temperature?25oC?,and the FS of the former?33.66%?was significantly higher than that of the latter?22.97%?.The TS of films dried at high temperature was increased with a further increase of the protein concentration of FFS,while the FS decreased gradually.As the protein concentration was increased to 40%,the TS and FS values of films dried at high temperature were nearly close to those of films dried at 25oC.The results of shrinkage ratio,DSC thermograms and FT/IR curves of gelatin films indicated that the hydrogen bonding in gelatin films were enhanced with the protein concentration increasing,and the content of triple-helix structure was increased simultaneously.In conclusion,gelatin extracted from tilapia scales at 80oC for 1 h exhibited excellent film-forming ability,and the edible films prepared with this gelatin had relatively superior mechanical properties and water resistance ability than those of edible films prepared with the skin gelatin extracted at the same conditions.When FFS with the increased protein concentration were dried under 100oC to prepare edible films,the mechanical properties of the resulting gelatin films was similar to that of the films formed at room temperature and even comparable to that of the plastic packaging film OPP?oriented polypropylene?.Furthermore,the mechanical properties and water resistance ability of skin/scale gelatin films could be obviously enhanced with the thermal treatment?100oC and above?on these films.Therefore,the results in this study indicated that edible gelatin films with superior mechanical properties could be prepared from tilapia skin and scales with suitable gelatin extraction and film-formation conditions,which is in favor of the realization of industrial production of fish gelatin films in the future.