Effects Of Alkylperoxyl Radical Oxidation-modification On Structure And Properties Of Soy Protein

Soybean protein is the most abundant and the cheapest protein in the world. Because of its high nutrition, especially its various functionalities, soybean protein is widely used in the food industry. However, when soybean is processed, there always exists oxidative stress environment. And oxidation-modification will influence both structure and properties of soybean protein. Accordingly, study on the influence of oxidation-modification on the structure of soybean protein and the mechanism which oxidation-modification changes the properties of soybean protein on molecular level is extremely important for soybean industry.In this study, according to the inadequate research about oxidation modified soybean protein, the oxidative stress environment of soybean protein was studied. Using the chemical characteristics of AAPH which can be decomposed under oxygen condition, ROO·, the product of pyrogenic decomposition, is capable of inducing the oxidation of soybean protein. Through a series of analytical methods, the influence of alkylperoxyl radical oxidation-modification on the structure of soybean protein was investigated. From the angle of aggregation behavior, the effect of alkylperoxyl radical oxidation-modification on the properties of soybean protein was analyzed. The main conclusions were obtained as follows:1. Alkylperoxyl radical modified soybean protein is prepared using SPI as reaction material, AAPH as inductive agent. The effect of alkylperoxyl radical oxidation-modification on the structure of soybean protein was characterized by FTIR, CD, intrinsic fluorescence and DSC. The test results showed that:peroxyl radical oxidation-modification did not change the basic structure of soybean protein. Under the excitation wavelength (295nm), blue shift of Xmax, occurred and the intensity of intrinsic fluorescence decreased when the degree of oxidation increased. In the meantime, oxidation aggregates formed. Besides, the second structure of soybean protein was also influenced by oxidation-modification. The increasing concentration of AAPH results in the loss of a-helix structure. Trough DSC analysis, it was shown that the exothermic peak of samples moved towards high-temperature direction with the increasing degree of oxidation, which revealed that thermal properties of soybean protein was effected.2. By the way of size distribution analysis, studied the effect of alkylperoxyl radical oxidation-modification on aggregation behavior of heating and cooled soybean protein. The results as follows:With the increase of heating temperature, the average size of native soybean protein and alkylperoxyl radical modified soybean protein which were in the process of heating increased. When the heating temperature was90℃, the average size of soybean protein decreased as extent of protein oxidation improved. Moreover, after cooling, the size-distribution of soybean protein shifted to the lower nanometer direction because of alkylperoxyl radical oxidation-modification.3. In the matter of properties, alkylperoxyl radical oxidation-modification, at large extent, effected the texture of soybean protein gel. The influence mainly shows on two sides: hardness and springiness. Both the two kinds of texture properties dramatically declined with the enhancement of level of alkylperoxyl radical oxidation. The decrease of the former one resulted from the decrease of average size of soybean protein in the process of heating. With the help of chroma meter, investigated the differences between chromaticity of gel prepared from native soy protein and chromaticity of gel prepared from alkylperoxyl radical modified soybean protein. Results showed that the color of gel deepened to yellow as the degree of alkylperoxyl radical oxidation-modification increased. Also, alkylperoxyl radical oxidation-modification leaded to the reduction of water-holding capacity of soybean protein gel.