The Studies On Preparation And Functionality Of Peanut Protein Concentrate

Peanut is rich in oil and protein. When it is pressed under low temperature, oil and undenatured protein can be prepared at the same time. Because of low protein content and high oil remained, the low tempreture pressed peanut cake is limited in food industry. In the paper, peanut protein concentrate was extracted from the low temperature pressed peanut cake by ethanol and mixed-solvent (hexane-ethanol-water) respectively. For the preparation of peanut protein concentrate with better functionality, the peanut protein concentrate extracted by mixed-solvent was used to heat by microwave and water bath respectively. At last the structure of each sample was analyzed.During the research of ethanol extraction, the effects of ethanol concentration, reaction temperature, time, solid-to-liquid ratio and extraction times on the protein content and residual oil of peanut protein concentrate, were studied by response surface methodology to get the optimum conditions. The results showed that an ethanol concentration of 56%, an extraction temperature of 54℃, an extraction time of 70min, a liquid-to-solid ratio of 1:6(w/v) and extracted 3 times, then the peanut protein concentrate acquired 69.01%(dry material) protein content and 2.43% oil remaining. In the research of mixed-solvent extraction, most effect factors were the same as the former, but one more factor was solvent ratio (hexane: ethanol-water solution). The results by orthogonal tests showed that an ethanol concentration of 75%, an extraction temperature of 50℃, an extraction time of 60min, a liquid-to-solid ratio of 1:11(w/v), extraction times of 4 and a solvent ratio of 3.5:6.5. In this way, the peanut protein concentrate obtained 70.50% (dry material) protein content and 0.52% oil remaining.The solubility of the extracted peanut protein concentrate was enhanced by two modification methods including microwave heating and water bath heating. The results showed that the later method was more effective. The optimum microwave modification conditions obtained by orthogonal tests were microwave heating time of 60s, microwave power of 480W, solid-to-liquid ratio of 1:12(w/v) and pH 9.0. By means of it, the NSI (nitrogen soluble index) of modification protein concentrate could be 54.26%. Meanwhile, the optimum conditions of water bath heating were defined as follows: pH9.0, modification time of 7 min, the temperature of 75℃and solid-to-liquid ratio of 1:11(w/v). Under these conditions, the prepared peanut protein concentrate had an NSI of 72.33%, which was even higher than the raw material.Functionalities of peanut protein concentrate were compared both raw materials and samples. Compared the alcohol extracted peanut protein concentrate with mixed-solvent extracted protein, there were improvement of emulsifying ability, emulsifying stability, water binding capability and foaming capacity, but declining on oil binding capacity and the foaming stability. The microwave modification peanut protein concentrate was weak on emulsifying ability, water binding capability and foaming capacity compared with water bath modification protein. But emulsifying stability and foaming stability were stronger. They were equal on oil binding capacity.The observation by scanning electron microscope showed that the sizes and shapes of those protein molecules had been changed by those processes of ethanol extraction, mixed-solvent extraction, microwave heating modification, and water bath heating modification. The sodium dodecyl sulfate polyacrylamide gel electrophoresis pattern indicated that the electrophoresis patterns of the defatted peanut cake, the peanut protein concentrate extracted by ethanol and mixed-solvent extracted peanut protein concentrate were similar, while peanut protein concentrate after microwave modification and after water bath heating were slightly different from each other. Furthermore, the secondary structures of each sample were detected by infrared lasers.