Optimization and Analysis of Physicochemical Properties of Protein Extraction from Flax Seed by Nitrogen-Assisted Positive Pressure Cavitation

Using hulled hemp seed powder as raw material, nitrogen was introduced to produce positive pressure cavitation, which realized the effect of accelerating the protein extraction rate. Taking the yield of protein as the evaluation index, the effects of pH, temperature, time, material-liquid ratio and aeration on protein extraction rate were explored by combining univariate test and response surface test. Results showed that, the optimal process conditions for nitrogen-assisted positive pressure cavitation extraction of hemp seed protein were as follows: The material-liquid ratio was 1:50 (g/mL), the pH was 12, the extraction temperature was 52 °C, the extraction time was 50 min, and the nitrogen ventilation was 1.6 L/min, under these conditions, the protein yield was 76.03%±1.64%. It was significantly higher than the magnetic stirring method under the same conditions by 56.32%. The physicochemical properties of hemp seed protein extracted by four methods (positive pressure alkaline solubility, magnetic alkaline solubility, positive pressure enzymatic hydrolysis, and magnetic enzymatic hydrolysis) were compared, and the results showed that the foaming and oil-holding properties of the proteins by magnetic alkalinity solution method were the strongest, 145% and 246%, respectively. There was little difference between water holding capacity and emulsification of the four methods. The protein denaturation temperature of the four extraction methods was compared, and the termination temperature of protein denaturation of the positive pressure alkaline solution method was 105.5 ℃, which was 4~13 ℃ higher than the other three methods. Hemp seed protein treated by positive pressure enzymatic hydrolysis contains 17 amino acids and an EAA/TAA score of nearly 40%, which was very in line with the FAO/WHO recommendation for high-quality protein. Experiments showed that nitrogen-assisted positive pressure cavitation could increase the extraction rate of hemp seed protein and had good physicochemical properties.