Study On Preparation And Antimicrobial Activity Of Sesamin And Its Ferrous Chelate

Sesame oilseed meal is rich in protein,but the by-products of sesame oilseed extraction are treated as animal feed,fertilizer or waste,resulting in the waste of protein resources.Protease enzymatic hydrolysis of protein is an effective method to improve the function of food protein and to prepare bioactive peptides,which broadens the application field of protein.Therefore,sesame oilseed meal rich in protein can be a potential source of more valuable bioactive peptides.This topic through the enzyme solution was prepared sesame protein peptide,bacteriostatic activity of sesame with multistage high antibacterial activity of purified oligopeptides,and oligopeptide and ferrous ion chelating,develop a broader antibacterial peptide chelate-ferrous ions,in order to improve the economic value of sesame protein and development of new antibacterial agent provides a new way.The hydrolysates of sesame protein neutral protease had no antibacterial effect on Staphylococcus aureus and Salmonella.The hydrolysate of sesame protein alkaline protease had no antibacterial effect on Salmonella,but showed obvious antibacterial effect on Staphylococcus aureus.Therefore,Staphylococcus aureus was selected as indicator bacteria.Response surface optimization was used to determine the optimal enzymatic hydrolysis conditions for preparation of sesame bacteriostatic peptide by alkaline protease:pH 10,enzyme dosage 16040 U,temperature 51?,and enzymatic hydrolysis time 3.5 h.With these conditions,the measured bacteriostatic circle diameter was 15.09 mm.Three components,Q₁,Q₂ and Q₃,were finally obtained by separating and purifying the enzymatic hydrolysates with a variety of separation techniques.Q₂ had the highest antibacterial activity with a diameter of17.93 mm.Compared with positive control,the antibacterial effect of Q₂ was significantly stronger than that of potassium sorbate,but lower than that of streptococcus lactate.Staphylococcus aureus treated with sesame peptide was observed by transmission electron microscopy.The surface of the bacteria appeared rupture and bulge.In addition,the leakage of alkaline phosphatase,?-galactosidase,nucleic acid and protein in the bacteria were detected,which indicated that sesame peptide could damage the cell wall of S.aureus,change the permeability of cell membrane,and finally inhibit the growth of bacteria.In order to expand the antibacterial spectrum of sesame peptide,the peptide was modified by chelating with ferrous ion.Although the antimicrobial activity of sesame peptide against Staphylococcus aureus was not improved after modification,the antimicrobial activity of sesame peptide against Salmonella was enhanced.The optimal chelating conditions of sesame peptide and ferrous chloride were determined by response surface optimization:p H 6 mass ratio 3:1,temperature 41?,enzymatic hydrolysis time 15 min.With these conditions,the measured bacteriostatic circle diameter and chelating rate were 14.63 mm and 74.81%,respectively.Two components,S₂₂ and S₂₃,were obtained by separation and purification of ferrous iron chelate of sesame peptide.Among them,S₂₃ had the highest chelation rate(90.69%)and antibacterial activity(antibacterial zone diameter 15.96 mm).The properties and structures of the chelates were characterized by ultraviolet spectroscopy,infrared spectroscopy,scanning electron microscopy and amino acid composition analysis.The results showed that sesame peptide and ferrous chelates were two kinds of substances with different morphology.Sesame peptides chelate with ferrous iron to form-COO-Fe²⁺and-C-O-Fe²⁺structures.It is speculated that the new substance may be formed by the interaction of coordination bond and ionic bond between sesame peptide and ferrous ion.The main binding sites of chelating reaction are amino group,carboxyl group and peptide bond.Glu,Asp and Cys are involved in the chelating reaction.The stability test results showed that the ferrous chelate of sesame peptide had good stability in the p H range of 5-7,but its thermal stability was not as good as that of sesame peptide.In summary,the antibacterial peptides of sesame protein which can inhibit Staphylococcus aureus were prepared by alkaline protease.The antimicrobial activity of sesame peptides against Salmonella was improved by chelating sesame peptides with ferrous ions.These results provide a new idea for expanding the application of sesame protein and developing new natural preservatives.