Preparation And Slow Release Behavior Of The Modified Soy Protein Isolate Active Film

Biodegradable polymers are considered to be an ideal alternative to petroleum based materials because of their abundant sources,low cost and biodegradability.Soybean protein isolate(SPI)has the characteristics of low cost,sustainability,richness and functionality.The development of environment-friendly protein materials with excellent properties such as regeneration,biocompatibility and biodegradability has attracted extensive attention.In this study,after proper modification of SPI by sodium sulfite(Na₂SO₃)and transglutaminase(TG),different modified SPI films were prepared by casting method.The performance of modified SPI was studied by characterization methods such as water sensitivity,hydrophobicity,mechanical properties,optical properties and microstructure.Then add tea polyphenols and quercetin two active substances.Then tea polyphenols and quercetin were added to study the effects of tea polyphenols and quercetin on the properties of different modified SPI films and the release law in the film,so that SPI can be more effectively applied in various fields.(1)Na₂SO₃ reduced the moisture content and total soluble matter(TSM)of the SPI film,which indicated that the hydrophilicity of the film was reduced.Moreover,the water vapor permeability of the film decreased from 3.56×e^-10(g cm/(cm² s Pa))to 2.73×e^-10(g cm/(cm² s Pa)),and the contact angle decreased from 41.3°increased to 81.9°.It showed that the modification of Na₂SO₃ improved the water blocking performance and surface hydrophobicity of the SPI film.When the amount of Na₂SO₃ added was 2%,the tensile strength of the film was 4.11 MPa,which was significantly higher than that of the unmodified SPI film(2.29 MPa).However,the Na₂SO₃ modification reduced the elongation at break of the SPI film and increased the opacity of the film.(2)The tensile strength of the SPI film increased when the TG content was 0 U/g?4 U/g.When the addition amount of TG was 4 U/g,tensile strength reached the maximum value of 4.24 MPa.The TG concentration further increased and the tensile strength of the film decreased.Due to the cross-linking effect of TG,the elongation at break of the SPI film decreased from 202.2%to 100.4%.When the amount of TG added was 4 U/g,the WVP of the SPI film was the smallest and has better water blocking performance.When the concentration was greater than 4 U/g,the tensile strength of the SPI film decreased and the water vapor permeability increased.Surface of the film modified by TG was not uniform and a rough surface can be observed.(3)The mechanical properties of Na₂SO₃ modified SPI films were improved by the addition of tea polyphenols.The content of tea polyphenols increased from 0%to 5%,and the tensile strength of the film increased from 3.11 MPa to 5.11 MPa.But the elongation at break decreased from 101.7%to 50.8%.Tea polyphenol reduced the water vapor permeability of the Na₂SO₃ modified SPI film and increased the contact angle of the SPI film.There are pigments in tea polyphenols.After adding tea polyphenols,the total color difference of the Na₂SO₃ modified SPI film increased from 11.62 to 72.52,and the opacity also increased.The release rate of tea polyphenols in the TG modified SPI film was faster than that in the Na₂SO₃ modified SPI film.(4)Quercetin improved the contact angle and tensile strength of the Na₂SO₃modified SPI film,and reduced the water vapor permeability of the film.However,quercetin had a weak effect on TG,when the amount of quercetin added was 2.5%.The mechanical properties of the film decreased,and the total soluble matter of the film increased.Quercetin improved the b*value(yellowness value)and opacity of the two modified films.The release of the two modified SPI films with quercetin added was lower in the 10%ethanol simulant solution.However,quercetin had a high dissolution rate in95%ethanol simulant solution,and the dissolution rate was fast.The dissolution rate and the amount of quercetin in the TG modified SPI film were higher than those in the Na₂SO₃modified SPI film.