Study On The Preparation And Modification Of Peanut Protein Films

Peanut protein has excellent film-forming property because of which has a large amount of hydrogen bond, hydrophobic bond, van der waals force, ionic bond and coordination bond. In this paper, the preparation, modification technology and application of peanut protein films which making use of peanut protein were studied.The preparation technology of peaut protein films which making use of peanut protein isolate was optimized. On the base of single factors experiments, the effects of peanut protein concentration, glycerol dosage, pH and reaction temperature on the properties of peanut protein films were studied by response surface methodology. The results showed that peanut protein concentration 6% (w/w), glycerol dosage 25% (g/g peanut protein), pH 9 and reaction temperature 70℃were optimal for the preparation of peanut protein films. In this way, the mechanical properties and water vapor permeability of peanut protein films were up to 14.87±3.00MPa, 12.06±2.56% and 2.67±0.021×10^-11g·mm/h·kPa·m² respectively.Physical methods (including microwave heating, ultrasonic wave and ultraviolet irradiation), chemical methods (including reducing agent, cross linking agent and surfactant) and enzymatic methods (transglutaminase) were utilized to modify peanut protein films's properties, and the optimal condition of 7 modification methods were obtained finally. Furthermore, the transglutaminase modification which dosage was 1.5U/g (peanut protein) was found to be more effective for tensible strength and the sodium dodecyl sulfate modification which dosage was 10% (g/g peanut protein) was found to be more effective for elongation at break at the same time. And the effect of the two optimal methods on tensible strength and elongation at break were 54.62% and 168.30% respectively.The physical-chemical and physical-enzymatic modification methods were researched, and the best compound modification method was defined, that was transglutaminase dosage of 1.5U/g (peanut protein) for enzyme modification and a radiating time of 4h for ultraviolet irradiation modification by additional experiment. These two methods which were applied in turn were confirmed to increase the mechanical properties of peanut protein films to 3.22±0.070MPa and 98.61±6.31% for tensible strength and elongation at break respectively. The observation by scanning electron microscope showed that the sizes and shapes of those protein molecules had not been changed significantly by these processes methods. But peanut protein's structure had been destroyed completely. The granularity and structure of peanut protein became to be smaller and more compact by compound modification.The application of peanut protein films in food packaging was preliminary studied. The results indicated that the water sorption isotherm of peanut protein films was showed "S" type. By using the GAB model, the monolayer moisture content of the peanut protein films were calculated, and was 0.070(g/g peanut protein film). Futhermore, the thermal stability of peanut protein when was made to films was improved. Moreover, associated the effect of relative humidity on the thermal property of films, the films could be applied in environment which relative humidity was 50%⁷0%, but with a view of hydrophilic group of films, it could be appied in inner packing.