Preparation Of Soy Protein And Crosslinked Corn Starch/Nano-TiO₂ Packaging Film And Application Of Cherry Tomatoes Preservation

Soy protein isolate film,as a natural "green packaging material",shows its own unique advantages in many biodegradable natural polymer film materials.However,the application of soy protein isolate film in the field of food packaging has been greatly limited due to its poor mechanical properties and barrier properties.Therefore,it is considered to add other substances into the film to improve the performance of the composite film.The composite film made of corn starch,which is modified by cross-linking agent has excellent comprehensive performance.Also,the corn starch product is low and easy to obtain,and when it is mixed with soy protein isolate to form a film,major molecules can be well bonded.Although the performance of protein film is improved,there is still room for improvement when the addition of nano materials are added.When nano-TiO₂ is incorporated into packaging materials,they will provide inhibition of foodborne microorganisms while increasing the overall performance of the packaging film.Therefore,when the modified corn starch and the nano titanium dioxide are added into the soy protein isolate film,the comprehensive performance of the composite film can be effectively improved.At the same time,it can improve the fresh-keeping ability of fruits and vegetables and prolong the shelf life of foods.This subject mainly studies the modification of corn starch with epichlorohydrin as crosslinking agent.At the same time,the mechanical properties,barrier properties,micro-properties and practical application in food packaging of soy protein isolate composite film with modified corn starch and nano-TiO₂ were studied.The modified corn starch was prepared by single factor test and orthogonal test.Then,the soy protein isolate composite film was prepared by single factor analysis and response surface optimization test,and the performance and microscopic characterization of the composite film were analyzed.The changes of sensory properties,weight loss rate,hardness,soluble solid content and ascorbic acid content of cherry tomatoes,which were packaged with pure soy protein isolate composite and soy protein isolate composite film in the experiment,were determined.According to these data,the effect of keeping fresh was evaluated.The main contents and results of the study are as follows:?1?The effect of the addition of EPI,the addition of Na OH,the reaction time and the reaction temperature on the performance of the modified corn starch was studied.The primary and secondary relations of each factor influence were: EPI content > Na OH content > reaction temperature > reaction time.The best parameters for preparing MCS were: the addition of EPI was2.0 m L,Na OH 0.6 g,the reaction temperature was 50? and the reaction time was 4 h.?2?The tensile strength,elongation at break,water vapor permeability,oxygen permeability,carbon dioxide permeability,and water solubility?WS?of the soy protein isolate composite film were used as detection indexes.The effects of each single factor including soy protein isolate?SPI?addition,MCS addition,nano-TiO₂ addition and glycerol addition on the performance of the composite film were determined by comprehensive score.On the basis of the previous single factor experiment,the comprehensive score was taken as the index.Through the response surface optimization test,the primary and secondary relations of each factor influence were: SPI addition amount > MCS addition amount > nano TiO₂ addition amount > glycerin addition amount.The optimal film formation parameters of SPI/MCS/Nano-TiO₂ composite film were: SPI addition amount was 3.601 g/100 m L,MCS addition amount was 2.000 g/100 m L,nano TiO₂ addition amount was 0.077 g and glycerin addition amount was 1.050 g/100 m L.Repeat the test 3 times according to the optimal component conditions predicted by the model.The performance of SPI/MCS/nano-TiO₂ composite film was obtained: TS was?11.64±0.187?MPa,EB was?38.14±1.064?%,oxygen permeability was?5.68±0.034?mg·m^-2·h^-1,carbon dioxide permeability was?7.65±0.093?mg·m^-2·h^-1,WVP was?3.94±0.045?gmm/m²d·k Pa,WS was?24±0.153?% and the comprehensive score was 0.761±0.008.On this basis,the regression model of the comprehensive score and components: SPI addition amount,MCS addition amount,nano-TiO₂ addition amount and glycerin addition amount were established as follows:K=0.75+0.059A+0.0006667B+0.025C+0.024D+0.008500AB-0.012AC-0.021AD-0.009BC-0.014BD-0.065CD-0.14A²-0.13B²-0.11C²-0.077D²?3?The performance and microstructure of six-group composite films?A: pure SPI film,B:SPI/CS composite film,C: SPI/MCS composite film,D: SPI/nano-TiO₂ composite film,E:SPI/CS/nano-TiO₂ composite film,F: SPI/MCS /Nano-TiO₂ composite film?were studied.The MCS and nano-TiO₂ molecules reacted chemically with the SPI molecules in the SPI composite film matrix,which changed the intermolecular interactions in the composite film.The surface properties and light blocking properties of SPI/MCS/nano-TiO₂ composite film were better than those of the other five composite films.It is indicated that the compatibility of each component in the film forming matrix was better.SPI/MCS/nano-TiO₂ composite film had the strongest hydrophobic performance.It is indicated that the interaction between molecules in the SPI composite film was enhanced by the addition of MCS and nano-TiO₂ molecules,and the structure of the composite film was denser and the performance of the composite film was better.?4?The application of pure SPI film and SPI/MCS/nano-TiO₂ composite film in cherry tomatoes preservation was studied.The results showed that the SPI/MCS/nano-TiO₂ composite film played an important role in preserving the cherry tomatoes during storage.Compared with pure SPI film packaging samples,the sensory score,weight loss rate,hardness,soluble solid content and VC content of the samples packaged in SPI/MCS/Nano-TiO₂ composite film were better than those of pure SPI film after 18 days of storage and the preservation effect was better.