Study On Preparation And Solubility Of Peanut Protein Concentrate

Peanut protein, which could provide a substantial amount of protein for human consumption, has been used in a variety of food products as a replacement for animal source proteins. Peanut protein concentrate, extracted from the defatted peanut flour, was used to prepare high solubility product by several modification methods, including physical modifications and limited enzymatic hydrolysis.Peanut protein concentrate was extracted by ethanol precipitation and the extraction time was determined as twice. The effects of liquid-to-solid ratio, ethanol concentration and reaction temperature on the solubility of peanut protein concentrate, were studied for the primary extraction and the later two factors were studied for the secondary extraction by response surface methodology. The results showed that a liquid-to-solid ratio of 11.79: 1 (v/w), an ethanol concentration of 85%, an extract temperature of 36.35℃for the primary extraction and a corresponding list of variables of 8:1 (v/w), 97.50% and 38.40℃for the secondary extraction were found to be optimal for the protein extraction from the defatted peanut flour. In this way, the peanut protein concentrate with the optimum nitrogen solubility index (NSI) of 65.30% extracted from defatted peanut protein was obtained.The solubility of the extracted peanut protein concentrate was enhanced by four physical modification methods including water bath heating, microwave heating, high speed stirring and ultrasonic wave modification, and the later two methods were found to be more effective. Moreover, a stirring rate of 22000r/min, an operation time of 1.1min, a liquid-to-solid ratio of 7: 1 (v/w) for high speed stirring and a water bath temperature of 75℃, an ultrasonic power of 210W, an ultrasonic frequency of 28KHz, a modification time of 7min, a liquid-to-solid ratio of 10: 1 (v/w) for the ultrasonic wave modification were defined as the optimum conditions. By additional experiment, these two methods applied in turn were confirmed to increase the NSI of peanut protein concentrate to 78.18%, and it could be used as the pretreatment of the limited enzymatic hydrolysis.According to the evaluation and analysis of solubilization of limited enzymatic hydrolysis, papain was selected as the optimal enzyme among several commercially available neutral proteases. Response surface methodology was used to optimize the limited enzymatic hydrolysis conditions of the physical modified peanut protein concentrate. The optimum hydrolysis conditions were defined as follows: the liquid-to-solid ratio was 10: 1 (v/w), the E: S was 0.291%, the enzymolysis time was 18.95min, the reaction temperature was 49.70℃. Under these conditions, the NSI of peanut protein concentrate after limited enzymatic modification could be increased up to 86.34%.Furthermore, the peanut protein concentrate after enzymatic modification was solubilized by high pressure homogenization. The study confirmed that a liquid-to-solid ratio of 13: 1 (v/w), a homogenization pressure of 50MPa, a reaction time of 2 min were found to be the optimal conditions for the homogeneous modification. The final NSI of peanut protein concentrate has been improved to 96.57% after high pressure homogenization.The observation by scanning electron microscope showed that the sizes and shapes of those protein molecules had been gradually changed by those processes of ethanol extraction, combined physical modification, limited enzymatic hydrolyzation and high pressure homogenization. The sodium dodecyl sulfate polyacrylamide gel electrophoresis pattern indicated that the electrophoretic patterns of the defatted peanut flour and the peanut protein concentrate after ethanol extraction and after combined physical modification were similar, while peanut protein concentrates after limited enzymatic hydrolyzation and after high pressure homogenization were significantly different from the former three and slightly different from each other. Furthermore, the secondary structure of each sample was detected by mid-infrared lasers. In addition to the functional properties of peanut protein samples, those progresses all showed the effects on the improvement of emulsifying and oil binding properties, meanwhile, the water binding properties was improved by the ethanol precipitation, the combined physical and the enzymatic modifications but decreased by homogenization. The foaming properties of the protein samples after each treatment increased while the foam stability decreased as compared with the former. The viscosities after each treatment were also changed significantly.The critical control points had been confirmed as raw material check, enzyme passivation and sterilization. The general quality control system was designed and constructed for the factories making peanut protein concentrate with high solubility, which made from ethanol extraction and solubilization processing.