Preparation And Properties Of Films From Soy Protein Isolate And Potato Starch Crosslinked With Oxidized Sucrose

As two kinds of natural polymers, the hydroxyl groups on soy protein and starch molecules lead to a high hydrophilicity of films, which present lower strain values and poor mechanical properties. The poor mechanical properties and lack of hydrolysis of starch and soy protein have limited their applications in various fields.In this paper, oxidized sucrose was selected to crosslink the soy protein isolate and potato starch films to improve the water-resistance and the sensitivity of its mechanical properties to the humidity of environment. The structure of the crosslinker was characterized by NMR. The effects of reaction temperature, reaction time and glycerol weight added were investigated. The optimal conditions on the crosslinking soy protein isolate were obtained as follows:crosslinking temperature180℃, crosslinking time5min,plasticizer glycerol weight20%; the optimal conditions on the crosslinking potato starch were obtained as follows:crosslinking temperature170℃,crosslinking time10min, plasticizer glycerol weight15%.The uncrosslinked soy protein isolate films and crosslinked soy protein films were immersed in acidic, alkaline and neutral water for at25℃for24h. Soy protein isolate films dissolved to a greater extent in alkali. The percent soluble matter values were lower in the acidic medium than in water. This indicated that crosslinking improved the acidic, alkaline and water resistance of the films.Potato starch films crosslinked with1%of crosslinker remained intact in boiling water for24h. However, uncrosslinked potato starch films turned into small pieces in boiling water for24h. This indicated that hydrolysis of potato starch was improved after crosslinked with oxidized sucrose.Changes in the molecular weight of the soy protein isolate were studied using SDS-PAGE. The molecular weight of soy protein isolate crosslinked with5%oxidized sucrose is obviously higher than the control cured with no crosslinker. The observed increase in molecular weight supported the effective crosslinking of soy protein isolate by oxidized sucrose under the curing conditions. The thermal stability of the soy protein isolate and potato starch was studied using DSC and TGA. The soy protein isolate crosslinked with5%oxidized sucrose had a shifting of melting peak from148℃to174℃than the control. The potato starch crosslinked with1%oxidized sucrose had a shifting of melting peak from160℃to182℃than the control. The observed increase in the melting peak supported the thermal stability of the soy protein isolate and the potato starch by oxidized sucrose was improved.