Research On Preparation Of Soy Protein Isolated Edible Film

The edible film of soy protein isolate (SPI) is a kind of green packaging of food, which is the important direction of modern packing materials of food research. The effects of physical treatment (thermal, ultrasonic and microwave treatment), material proportion (tannin, sodium polyphosphate, soluble starch and sodium carboxymethyl cellulose) and chemical modification (phosphorylation of SPI) on properties of SPI films were explored. The parameters of filming technology of SPI were studied through orthogonal assay. Finally, practical application of SPI edible film in coating of bread was investigated.The results showed that thermal treatment decreased (P<0.01) tensile strength (TS) and the oxygen permeability. Thermal treatment increased (P<0.01) transparency at60℃and water vapor permeability (WVP) at80℃. The ultrasonic or microwave treatment decreased water-solubility (WS) and the oxygen permeability (P<0.01), while increased transparency (P<0.01). The ultrasonic treatment increased TS significantly, and the microwave treatment decreased TS (P<0.05) and WVP (P<0.01) greatly. Microwave treatment on SPI film decreased (P<0.01) WS and increased (P<0.01) TS significantly, while microwave treating for1min at50W decreased (P<0.05) WVP.The additional of tannin or soluble starch in the film decreased (P<0.01) WS, WVP and the oxygen permeability significantly, and additional of soluble starch increased (P<0.01) TS greatly, while tannin decreased (P<0.01) transparency significantly. The addition of sodium polyphosphate in the film increased WS (P<0.01) and TS (P<0.05) significantly, and decreased the oxygen permeability (P<0.01) and WVP (P<0.05) greatly. CMC-Na improved TS (P<0.01) and oxygen permeability (P<0.05) greatly, while decreased (P<0.05) WS, transparency and WVP significantly. And P-SPI decreased the oxygen permeability (P<0.05), transparency and TS (P<0.01).The optimum film-forming parameters were as follows:keeping SPI at60℃for6h,0.15g of tannin.0.1g of soluble starch,2.5g of GLY, microwave treating for5min at100W and ultrasonic treating for15min at80W.Eight percent and11%of SPI edible coating film could extend the storage life and maintain the freshness of bread.