Preparation And Properties Of Enzyme Modified Soy Protein Isolate Antimicrobial Films

Soy protein isolate is a commonly used material to prepare edible films. However, large isolated soy protein molecules, complex structure, mechanical properties of environmentally sensitive, easy to breed bacteria and mold, and the shorter shelf-life limits its wider application. By enzymatic modification of soy protein to increase its intra-molecular or intermolecular cross-linking, it can improve the protein film properties. Adding the natural antibacterial agent to the soy protein isolate films, which can not affect eating, but it can inhibit microorganism growth and reproduction of the food and films membrane surface, or directly kill microorganism. It can reach the purpose of inhibiting the micro-organisms and extending the shelf life of food.In this paper, soy protein isolate as the membrane substrate, by enzyme modified soy protein isolate and adding natural antibacterial agent, developed with excellent mechanical properties and antibacterial effects of the composite film, the main research work and the results are as follows:(1) We used papain, alkaline protease and trypsin to modify soy protein isolate to study the enzymatic modification effect of the film thickness, tensile strength, elongation, water vapor permeability and other properties. Research indicates that with increasing concentration of enzyme, the thickness of modified films first increases and then decreases; tensile strength of papain and alkaline protease modified films increases with increased enzyme concentration, but the trypsin modified films first increases and then decreases; Elongation decreases with increasing enzyme concentration; transmission rate with increased enzyme concentration first increases and then decreases; when protease concentration is 5.0U/g, the water vapor transmission of the films is the minimum amount, and the trypsin modified films have lower water vapor permeability; microscope research indicates that enzyme modified film surface is protruding strip, and the film surface is more uniform and compact, especially trypsin modified film.(2) Inhibition zone method is used to research antibacterial properties of chitosan, lysozyme and oregano oil. Against E.coli and S.aureus, minimum inhibitory concentration was measured by the double dilution. With the same concentration of chitosan, the S.aureus inhibition zone diameter is slightly larger than E.coli. The inhibitory effect of oregano oil and lysozyme against E.coli and S.aureus gradually increased with increasing concentration. With the same concentration of lysozyme and oregano oil, the S.aureus inhibition zone diameter is large than E.coli.(3) Inhibition zone method is used to research antibacterial properties of soy protein isolate films added chitosan, lysozyme and oregano oil against E.coli and S.aureus. Soy protein isolate film added chitosan, lysozyme and oregano oil has antibacterial properties against E.coli and S.aureus, and antimicrobial activity enhance with increase quantity. Compare inhibitory effect, the inhibitory effect on E.coli: oregano oil> chitosan> lysozyme; the inhibitory effect on S.aureus: oregano oil> chitosan> lysozyme. The ability to inhibit S.aureus of regano oil, chitosan and lysozyme were stronger than the inhibition of E.coli.(4) Inhibition zone method is used to research antibacterial properties of soy protein isolate films added chitosan, lysozyme and oregano oil against S.cerevisiae and A.niger. Soy protein isolate film added chitosan, lysozyme and oregano oil has antibacterial properties against S.cerevisiae and A.niger, and antimicrobial activity enhance with increase quantity. Compare inhibitory effect of antibacterial film, the inhibitory effect on S.cerevisiae: chitosan> oregano oil> lysozyme; the inhibitory effect on A.niger: oregano oil> chitosan> lysozyme. The ability to inhibit S.cerevisiae of oregano oil, chitosan and lysozyme were stronger than the inhibition of A.niger.(5) We determine the film preparation conditions by single factor test. The suitable concentration of soy protein isolate is 4%. The suitable concentration of glycerol is 1%. The appropriate concentration of trypsin is 4U/g. The suitable concentration of oregano oil is 0.4%, and the best drying Temperature is 55℃.(6) We did the orthogonal experiment to obtain the best process condition. For tensile strength optimum conditions were: isolated soy protein of 4%, glycerol of 1%, trypsin of 5U/g, oregano oil of 0.4%, drying temperature of 55℃. For the elongation the best conditions were: isolated soy protein of 4%, glycerol of 1%, trypsin concentration of 4U/g, oregano oil of 0.4%, drying temperature of 55℃.