| Tilapia is the most important economic fish in the south coastal of China.Its products are often exported overseas in the form of packaged fish fillets.This kind of export method makes tilapia produce a large number of by-products like skin.How to improve the economic benefits of these by-products is a problem.The development of high-quality gelatin and gelatin products is an effective technological means for increasing the value of these resources.Generally,gelatin have good film-forming properties and biodegradability,which has received great attention as packaging substrate in the field of packaging.Therefore,in this study,tilapia skin was used as the raw material,firstly,gelatin of different quality was regulated and prepared,and its physicochemical properties were analyzed.Secondly,gelatin films were prepared by different Bloom with(or without)transglutaminase(TGase)and the basic properties of these films were compared.Finally,thinking of the characteristics of anthocyanins exhibiting different colors at different pH values,a pH-sensitive function was successfully prepared by the above gelatin film-forming solution.The anthocyanins-gelatin composite film are evaluated for their sensitivity to pH by contacting withifferent acid and alkaline media.The main findings are as follows:1.Study on physicochemical properties of Tilapia Gelatin(TSG)with different Extraction conditions.The extraction yield of TSGs obtained from different extraction conditions ranged from 11.67%to 41.91%(dry weight),the imino content ranged from 190 to 199/1000 residues;the results of SDS-PAGE profiles showed that the TSG obtained at the extraction temperature of 45 ? has a higher molecular weight distribution(>100 kDa);the band intensity of ?-chains and cross-linked components were dramatically decreased when use higher temperature or lower pH,which indicated that the high temperature or acidic extraction environment decreased the molecular weight of TSG.The gel strength of TSGs were obtained and ranged 127.7?382.3 g;the TSG of higher molecular weight corresponds to a higher gel strength.All gelatin solution can form a gel at 4 ? but only gelatin obtained at an extraction temperature of 45 ? can set a gel at room temperature.This result shows that the effect of temperature on TSG gel is more significant than pH.Rheological results show that different gelling temperature and melting temperature of TSG gels distributed in the range of 17.64?25.08 0C and 24.76?31.29 ?.In addition,at the same extraction temperature,the emulsifying capacity of gelatin was acquired at pH 5 is significantly higher than that of pH 3.2.Effects of Gelatin with different Bloom and TGase on Gelatin film.When the concentration of TGase added was 0.5%(w/w),gelatin film with 280 g Bloom can achieve higher tensile strength(15.3 Mpa).Gelatins with higher Bloom values had more triple-helix structures in its film.Compared to gelatin with 245 and 160 g Bloom values,gelatin film with 280 g Bloom value has a lower moisture content and water vapor transmission rate,and higher tensile strength,but a lower elongation at break than the film prepared by 245 g Bloom.Gelatin films prepared by different Bloom gelatins are completely dissolved in water.After TGase modification,the water solubility of films prepared with different Bloom values all decreased significantly(as low as 33.8%),and the corresponding X-ray diffraction peak at 20 = 7.5° also decreased,but the mechanical properties improved,especially the tensile strength of the gelatin film obtained by 280 g Bloom value was significantly increased.3.Preparation and characterization of active and intelligent films incorporated with anthocyanins.Under the conditions of pH 3,7 and 11,using anthocyanins from red cabbage,black grape peel and purple sweet potato,the resulting anthocyanin gelatin composite film(GL-RC,GL-BP and GL-PP)were all thinner.Among them,there were significant differences in ?E*between GL-RC and GL-BP produced in these three pH.The three composite films obtained at pH 3 and pH 7 have obvious color changes after contact with acid,alkaline gas and liquid,among which the color change of GL-BP was most obvious at pH 7;only GL-RC and GL-BP made at pH 3 have a color change in contact with semi-solids.Compared with the control film(GL),thickness and water vapor transmission of the three anthocyanin composite film increased;the water content of GL-RC and GL-BP decreased slightly,but there was no significant change in GL-PP;Compared with pH 3,anthocyanin composite film prepared of pH 7 and pH 11 had better water resistance and mechanical properties;the water solubility of GL-RC was 25.3%and the tensile strength was 20.7 Mpa when prepared at pH 7.The addition of anthocyanins also provided a certain degree of antioxidant activity for the composite films,but no antibacterial activity;the DPPH radical capacity of the GL-BP prepared under the pH 3 can reach 87.4%,and the DPPH radical capacity is basically stable within 48 h. |
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