A Study Of The Extraction And Antibacterial Properties Of SGBP From Soybean Meal

In this study, theisoelectric point precipitation method was used to extractsoybean globulin from defatted soybean meal.After that, the soybean globulin waspurified through glucan gel chromatography. Then the soybean globulin basicpolypeptide (SGBP) was extracted from purifiedsoybean globulin. The optimalextracting conditions of SGBP were determined by single factor experiment andorthogonal experiment. Then the antibacterial activity and antibacterial mechanismofSGBP were investigated using Staphylococcus aureus. The main experimentalresults are as follows:(1) According to the principle of isoelectric precipitation, soybean globulin wasextracted from defatted soybean meal. The pH of solution of soybean globulin wasadjusted to6.0,6.2,6.4,6.6,6.8, respectively, then cooling precipitation. SephadexG150was used to purify soybean globulin. It is concluded that the optimal pH valueof soybean globulinextraction was6.4.(2) SGBP was extracted from the purified soybean globulin. Disulfide bendsbetween acidic and basic peptide was cut off using β-mercaptoethanol before twokinds of peptides were isolated according to the difference of isoelectric point of thepeptide. Search for the impact of material liquid ratio, water bath temperature, bathtime and pH on the extraction conditions of SGBP. Analyze on the optimal extractionconditions of SGBP by orthogonal experiment. The results of single factor experimentare as follow: the optimal ratio of material to liquid was1:25, the optimal extractiontemperature was70°C, the optimal extraction time was45min and the optimalextraction pH was8.25.(3) Antimicrobial activity and minimal inhibitory concentration (MIC) against S.aureus was determined by Oxford cup method and spectrophotometric method,respectively. The dynamics study of SGBP against S. aureus wasinvestigated by thecolony counting method. The results showed that the MIC of SGBP was50μɡ/mLand the optimal concentration of SGBP was200μɡ/ml. The antibacterial activityagainst S. aureus increased with the increase of SGBP concentration.(4) Changes in the cell walls of S. aureus treated with SGBPwere determined byspectrophotometric method. There was no significant difference of OD630betweenexperiment group (treated with SGBP) and negative control (treated with phosphatebuffer), showing that SGBP has no effect on cell wall of S. aureus. Crystal violet experiments, conductivityanalysis and ion leakage analysis were performed onS.aureus treated with SGBP to reveal the effect on membrane permeability. The value ofOD590increased with the increase of SGBP concentration. And the value ofconductivity and ion leakage increased with the increase of time, showing SGBP canchange cell membrane permeability. DNA of S. aureus treated with SGBP wasextracted and compared with blank control group, the DNA banding of experimentgroup emerged dimmed and trailing, these results indicated that SGBP can act onDNA of S. aureus.