| Gelatin is a kind of biopolymer,which is partially hydrolyzed from collagen.Except tryptophan,gelatin contains almost all essential amino acids and has high nutritional value.It is widely used in modern manufacturing and processing of food,medicine,cosmetics,etc.because of unique functional properties(good hydrophilicity,emulsification,film-forming,gelling,water-holding,etc.).However,the research of fish gelatin has become a hotspot in recent years due to the restriction of dietary habits and the risk of potential animal pathogenic carriers.Fish gelatin has similar functional properties to mammalian gelatin,so fish gelatin could be an effective substitute for mammalian gelatin.However,compared with mammalian gelatin,fish gelatin has lower content of proline and hydroxyproline,resulting in poor emulsifying properties,which limits scope of application.In this thesis,three kinds of fish scales were regarded as raw materials.The gelatin was extracted by acid method and the obtained gelatin was phosphorylated.The influence of external conditions on the emulsifying properties of fish scale gelatin was studied,aiming to improve the emulsifying properties of fish scale gelatin.Finally,the phosphorylation-induced fish scale gelatin was applied to the preparation of yogurt,discussing its practical application value.The main conclusions were as follows:(1)In order to study the changes of physical and chemical properties of different fish scale gelatin,the chemical structure of fish scale gelatin was analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis(SDS-PAGE),fourier transform infrared spectroscopy(FTIR)and fluorescence spectroscopy.The effect of phosphorylation on the emulsifying properties of fish scale gelatin was also discussed.Fourier transform infrared spectroscopy and endogenous fluorescence spectroscopy showed that the structure of the three fish scale gelatins changed.After phosphorylation for 1 h,the surface hydrophobicity index of the three fish scale gelatins increased by 36.72,31.42 and 111.67,the emulsifying activity index increased by 115.86,155.22 and 45.52 m~2/g,and the emulsifying stability index increased by98.37,256.77 and 169.61 min,respectively.The results indicated that phosphorylation could be used as a method to produce fish scale gelatin with improved emulsifying properties.(2)The effects of different external conditions(p H,temperature and salt ion concentration)and storage time on the emulsifying properties of fish scale gelatin were studied.The results showed that the emulsifying activity of fish scale gelatin was the highest when the p H was 7.0,but the emulsion was the most unstable.The emulsification activity of phosphorylated fish scale gelatin was the lowest at 60℃.The phosphorylated fish scale gelatin emulsion was extremely unstable at temperatures above 60℃,especially at 80℃.When the salt ion concentration was in the range of 0-50 mmol/L,the emulsifying activity of phosphorylated fish scale gelatin increased,and when the salt ion concentration was in the range of 0-300mmol/L,the emulsifying stability of fish scale gelatin decreased.With the prolongation of storage time,the particle size of the fish scale gelatin emulsion gradually increased,and from the 5th to the 7th day,the emulsion appeared delamination,indicating that the stability of the emulsion system was destroyed.(3)Using commercial gelatin as a reference,phosphorylated fish scale gelatin was applied in yogurt production,and the p H,titratable acidity,color and water holding capacity of yogurt were measured.And its texture properties,microbial content and sensory properties was analyzed.Results showed that the taste,smoothness,texture state and stability of phosphorylated fish scale gelatin yogurt were better than commercial fish scale gelatin yogurt,and its hardness,viscosity and water holding capacity were acceptable.This study provided theoretical guidance and technical support for the application of fish scale gelatin in yogurt. |
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