Stability Factors Of Soy Protein Isolate Films During Storage

Soy protein isolate(SPI) films can be used as edible packaging materials. Its eating and packing values depend on the quality variation in storage. External factors and internal factors both can influence its quality. This paper firstly studied the optimum conditions to make SPI films. Secondly studied the effects of environment humidity, storage mode, avoid light and not on the quality of SPI films. Thirdly studied the component changes of SPI films in storage. Finally studied the protection of oil which packed by SPI films in storage, and the impact of oils on the SPI films.The research results show that: the protein concentration is 0.06 g/mL, glycerol amount is 0.3~0.6 g/g can form the most suitable SPI films.The relative humidity of storage environment, storage mode have obvious effects on the SPI films quality, avoid light or not does not affect the SPI film quality changes. When relative humidity between 43% and 63%, the relative humidity is higher, the flexibility and oil resistance of films is better, strength of films is weaker; however, when relative humidity achieve 75%, films is easy to spoilage; If SPI films were stored in chilled conditions, flexibility and oil resistance is best, strength slightly weaker, frozen storage conditions will make the films quality worst. Considering the films appearance, mechanical and oil resistance, chilled is the best storage conditions.Composition of SPI films will change significantly during storage. Moisture and glycerol will move out to surface, protein thiol reduce gradually, and β-turn mostly turn into beta β-sheet. During storage, the biggest change is the middle water, free water and water with little change, and their degree of freedom will deduce. With the migration of moisture and reducing of sulfhydryl, SPI films will more hardens, flexibility and oil resistance variation. The migration of water and glycerol were positively correlated.SPI films as packing materials, has a significant protective effect on linseed oil. The time of POV arrived at 10 meq/Kg will increase by 32 h to 76 h if packed by SPI films. At the same time, the study also found that films will more flexible if contacted with oils. Combined with the analysis of scanning electron microscope, the SPI films will leak oil. And the oil will residual in the films.