| Nowadays,most of the world's commercial gelatins are derived from the skin and bone of pigs and cattle.However,there is an urgent to find a new material to replace mammalian gelatin due to the food safety caused by infectious diseases such as “porcine plague” and “mad cow disease” and the eating habits of religious believers such as Islam.Although fish gelatin is recognized as the best alternative to mammalian gelatin,it has a small share of the market.The main reason is the low melting temperature and melting temperature of fish gelatin,which makes it impossible to replace mammalian gelatin in some applications.Therefore,based on the current status of gelatin,this paper first modified fish gelatin with ?-polyglutamic acid(?-PGA)to study the effects of ?-PGA modification on the gel properties,rheological properties and structural properties of fish gelatin for providing a theoretical basis for the development of high-quality fish gelatin.The main conclusions of this paper are summarized as follows:(1)The effects of ?-PGA concentrations and pH when ?-PGA exists on the gel properties(gel strength,melting temperature and texture characteristics)of fish gelatin were studied.With the increase of ?-PGA concentration,the gel strength and melting temperature of fish gelatin increased first and then stabilized.The hardness,adhesiveness and chewiness increased first and then decreased,while the elasticity and cohesion did not change significantly.When the ?-PGA concentration was 0.04%,the gel strength,melting temperature,hardness,tackiness,and chewiness peaked,respectively.The effect of pH was studied when the concentration of ?-PGA was 0.04%.It was found that the gel strength,melting temperature,hardness,adhesiveness and chewiness of fish gelatin increased first and then decreased with the increase of pH value,which reached the maximum values of 681.13 g,30.03 ° C,1229.794 g,1153.55 g and 1058.70 g at pH 5,respectively.(2)The effect of fish gelatin modified with different concentration of ?-PGA and pH of ?-PGA when ?-PGA exists on the rheological properties of fish gelatin was studied.The results showed that ?-PGA modification could significantly affect the G' and G'' values of fish gelatin,and the rheological properties of fish gelatin were improved.When the ?-PGA concentration is 0.04% and the pH is 5,the gelation point temperature and the melting point temperature of the fish gelatin can be improved,and the gel strength is also improved under this condition.(3)?-PGA can significantly improve the gelation and rheological properties of fish gelatin.In this paper,Raman spectroscopy,X-ray diffraction and atomic force microscopy were used to study the changes of chemical force,spiral structure and microstructure of fish gelatin during gelation.As the concentration of ?-PGA increased,the electrostatic interaction increased,and the hydrophobic interaction decreased.Strong hydrogen bonds force was showed when the ?-PGA concentrations were 0.04% and 0.06% in the fish gelatin system.When the ?-PGA concentration was increased from 0% to 0.04%,more phenolic hydroxyl groups of tyrosine residue tended to form hydrogen bonds with the protein.However,as the ?-PGA concentration is further increased to 0.1%,hydrogen bonds of phenolic hydroxyl groups with water molecules were enhanced.As the pH increased,the electrostatic interaction increased,while the hydrophobic interaction first increased and then decreased,and when pH was 5,the hydrophobic interaction reached the maximum.And hydrogen bonding had a tendency to decrease first and then increase.It found that pH would affects the formation of triple helices during gelation and had a significant effect on the nanostructure of fish gelatin. |
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