Study On The Protein Modification Techniques Improving The Physicochemical Properties Of Fish Gelatin And Its Application

Gelatin is a natural peptide polymers,which is produced from the hydrolysis of collagen,and widely used in food and pharmaceuticals industries because of its unique physicochemical properties.Nowadays,about 98.5% of the world commercial gelatin is produced from skins,bones and hides of pig and cow.However,the applications of mammalian gelatin have been limited because this gelatin may be contaminated by pathogenic vectors as well as religious restrictions,and are unacceptable to consumers with strict adherence to vegetarianism throughout the world.It becomes more and more significant to explore mammalian gelatin replacer to meet consumer's requirements and solve the shortage of gelatin raw material in the world.Fish gelatin has been regarded as an alternative to mammalian gelatin,due to its similar functional properties.Nevertheless,the main problem of the technique is that fish gelatin possesses inferior rheological,gel properties and emulsion stability,which limit its application in food and pharmaceutical industries.Based on the weakness of physicochemical properties and applications of fish gealtin,two main parts were performed in this study: Various protein modification methods were used to improve rheological behavior,gel and emulsion properties of fish gelatin to produce high quality fish gelatin products,which could replace mammalian gelatin totally;Based on the improvements of functional properties of fish gelatin,modified fish gelatin were used in dairy models to evaluate how it affect quality of dairy products.The main results are following:(1)MTGase and pectin was used to modify fish gelatin to evaluate the optimal modification method by the comparison study of rheological behaviors,gel and structural properties of modified fish gelatin.MTGase and pectin could improve melting temperature,hardness,gelation and melting points as well as viscosity,but higher contents of MTGase and pectin could decrease gel strength of fish gelatin.The modification of MTGase and pectin could hinder the formation of triple-helix during gelation,and destroy left-helix of gelatin.MTGase modification could not change nanostructure of fish gelatin,but produce denser gel network;pectin could change nanostructure of fish gelatin,while high content of pectin could weak gel network.In conclusion,MTGase modification showed better rheological behaviors and higher gel properties than those of pectin modification.(2)Pectin and enzyme complex modification was used to overcome the phenomenon of weak gel by the high contents of MTGase and pectin.We used 0.06%(w/v)MTGase and various contents of pectin(0.1-1.6%,w/v)to modify fish gelatin by evaluating the changes of rheological behavior,gel and structural properties of modified fish gelatin.Pectin and MTGase complex modification could sharply improve gel strength,melting temperature and rheological behaviors,and complex modified fish gelatin presented similar gel strength,gelation and melting points with mammalian gelatin as pectin was 0.8%.Pectin and MTGase complex modification hinder the formation of triple-helix and decrease gelation rates,but sharply increase viscosity.The complex modification cover the chromophore groups on the gelatin molecule,forming soluble “super-molecular”,strengthen the gel network.All in all,pectin and MTGase complex modification could overcome the defect that higher contents of MTGase and pectin could weak gel network.Therefore,pectin and MTGase complex modification could be used as a method to produce high quality of fish gelatin that replace mammalian gelatin.(3)The phosphorylation time was used to modify fish gelatin to change the multifunctional and structural properties of fish gelatin.The shorter time of phosphorylation could improve gel strength,gelation and melting points of fish gelatin.Nevertheless,phosphorylation could decrease viscosity and gelation rates with hindering the formation of triple-helix.Scanning electron microscopy and atomic force microscopy revealed that longer time of phosphorylation resulted in looser gel network with more aggregation.Longer phosphorylation time could stabilize fish gelatin emulsions,and endowed emulsions with smaller particle size and lower coefficient viscosity,but higher ?-potential values.These results suggested that phosphorylation could be applied to obtain fish gelatin with varying functional properties suitable for numerous industrial application.(4)Glycation was used to modify fish gelatin and improve its emulsion stability as well as application in coffee as “coffee whitener”.Glycation could decrease particle size and viscosity of fish emulsion,but contributed to improvements of emulsion stability.New tribological model was developed to evaluate the storage time influence tribology of emulsion,showing that glycation could endow emulsion better lubrication as well as give coffee good appearance and lubrication.Glycation fish gelatin emulsion could replace milk in coffee drinks theoretically.(5)In order to overcome the weakness of fish gelatin in yoghurt products and meet the requirements of low fat yoghurt,various fish gealtin-polysaccharide complex systems were bulit.The preparation of fish gelatin-polysaccharide systems presented high stability.The tribological properties of fish gelatin-polysaccharide systems were affected by the ratios of fish gelatin to polysaccharide,showing lowest lubrication than those of fish gelatin and polysaccharide systems.The complex of fish gelatin-polysaccharide could improve viscosity and gel network of yoghurt,endowing yoghurt high lubrication,and the addition of fish gelatin-xanthan gum could endow yoghurt better mouthfeel.