| Walnut(Juglans mandshunca), a famous woody oil plant, is one of the important economic trees in China. Because of its unique flavor, high nutrition and healthy function, walnut is honoured as the functional food. Walnut oil contains more than 90% unsaturated fatty acid. Among them, linoleic acid is up to 63%. Consquently, walnut oil is the best source of unsaturated fatty acids needed by human body. To further develop walnut resource, and enhance the application of walnut oil into the food, cosmetic, pharmaceutical industry, the oil-in-water emulsion system was established by employing walnut oil as the material. The effects of different type surfactants on the physical and oxidative stability of walnut oil-in-water emulsions were also investigated; the influence of displacement between protein and surfactants on the physical and oxidation stability of oil in water emulsion was further studied. The main results were as follows:To explore the application of whey protein isolate(WPI) in the emulsion, the physical properties of WPI in comparison with soybean protein isolate(SPI), Casein(Casein) were first researched. The results showed that compared with SPI and Casein, the influence of p H on the solubility of WPI was weaker. And WPI was highly dissolved near the isoelectric point. The influence of calcium ion on the WPI solubility was stronger than sodium ions. Moreover, the tolerance of WPI to sodium and calcium ions was higher than SPI and Casein. The viscosity and emulsification of WPI were lower than SPI and Casein However, the emulsion stability of WPI was better than the other two proteins. It indicated that WPI had stable physical properties, and was suitable for the application in oil-in-water emulsion. Based on the above results, the present work further explored the influence of the WPI displacement by SDS, DTAB and Tween20, respectively, on the physical stability of emulsions. The results showed that the displacement of protein interfacial film by DTAB and Tween20 was influenced by aqueous phase p H. At p H 7.0, WPI interacted with DTAB, resulting in the unstabliziton of emulsions. Similarly, the emulsion was not stable when SDS was added into the emulsion containing WPI at p H 3.0. The displacement between WPI and Tween20 was not influenced by p H. And the emulsions are very stable after displacement. Finally, the influence of four kinds of emulsifiers on the emulsion oxidation stability was investigated. At the same time, the small molecular surfactants, such as SDS, DTAB, and Tween20 were incorporated into the emulsions stabilized by WPI. And the effects of the protein interfacial displacement by these different kinds of emulsifiers, respectively, on the oxidative stability of the emulsions were further studied. The results showed that the order of oxidation stability of four types emulsions was: DTAB≥WPI>Tween20>SDS. Adding SDS leaded to the reducting of oxidative stability of the emulsions., As the protein was completely replaced by SDS at the interface, the oxidation stability of the emulsions was similar to that of the SDS emulsion; The oxidative stability of the WPI emulsions was affected by adding Tween20 with the increase of Tween20 concentration resulting in the reduction of the oxidative stability. On the contrary, the oxidation stability of the emulsions containing WPI increased with the increasing DTAB. And it was close to that of the DTAB emulsions. |
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