Performance Optimization And Mass Transfer Of Protein Based Controlled-release Antibacterial Films

Protein based edible packaging films have good biocompatibility and degradability, safe non-toxic, which can partly replace plastic packaging products and reduce the pollution of the environment. Adding antibacterial agent to the protein based flilms can improve the performance of edible films. Edible films as the good carrier of antibacterial agent have slow release effect for the release of antibacterial agent, which can affect the shelf life of food. According to the characteristics of protein based controlled-release antibacterial films, they mainly apply in low water activity of food such as instant coffee, instant relish, etc., so they have a broad market value. In this thesis, controlled-release antibacterial films were prepared using whey protein isolate(WPI) and sodium caseinate(NaCas) as base materials, glycerin(Gly) as plasticizer and potassium sorbate(PS) as an antibacterial agent. And the mass transfer behaviours of antibacterial agent in films were discussed. Main work and results are as follows:Firstly, four factors with three level Box-Behnken response surface design was employed to investigate the influence of whey protein isolate, sodium caseinate, glycerol and potassium sorbate concentrations in antibacterial protein films on tensile strength, enlongation, light transparency, haze, water solubility and water vapor permeability. Functional relationships between film-forming component concentrations and packaging performance were created and the optimal formula were found. Analysis of variance and regression coefficients of models for responses showed that quadratic models were significant to predict tensile strength, light transparency, haze, water solubility of the films, whereas enlongation and water vapor permeability could be fitted by liner model and interactive model, respectively. Among all the film-forming components, with the addition of whey protein isolate, light transparency and water solubility of the films markedly decreased. Tensile strength and enlongation of films were improved with the increase of NaCas. When Gly increased, tensile strength decreased dramatically, whereas enlongation, light transparency and water vapor permeability increased. In addition, the interaction effects of film-forming components on packaging properties were significant observiously.By prediction of regressive models, when WPI=6.84g/100 ml, NaCas=5.11g/100 ml, Gly=35.00% and PS=0.50g/200 ml, the packaging properties of films could be optimized.Secondly, the effect of food simulation system on mass transfer of protein based controlled-release antibacterial films was studied. Adding 0.150%, 0.375% and 0.750%(w/v) potassium sorbate to film-forming solutions to prepare the antibacterial films, and then the effect of pH(3.8, 5.2 and 7.0) and temperature(15, 25 and 35℃) of food simulation system on diffusion of potassium sorbate of composite films were investigated by the measured value and calculated value with Fickian diffusion model. The kinetics of potassium sorbate release followed non-Fickian diffusion(when pH is 3.8) and Fick’s first law of diffusion as shown by diffusional exponent of power function model. Diffusion coefficient was found to be increased with increased concentration of potassium sorbate and temperature in the range of values tested, but decreased with pH due to swelling behavior in low pH condition. When p H value was 3.8 and at 35℃, diffusion coefficient of antibacterial films was up to 5.722E-12. According to activation energy(Ea) of the Arrhenius activation energy model, when pH value was 3.8, the diffusivity to temperature changes was more sensitive. Sustained release effects of antibacterial films were different when in different food simulation system.Thirdly, the effect of various proportions of WPI/Nacas, Gly and initial PS content in film formula on mass transfer of potassium sorbate from protein based antibacterial films to food simulant liquid was discussed by establishing migration model and determining the diffusion coefficient of potassium sorbate. Results demonstrated that: when Mt/M∞<2/3, anomalous(non-Fickian) transport or Super Case II transport were found by using the power law model(Mt /M∞= kt n) to describe the early process of mass transfer behavior of potassium sorbate in antibacterial films-food simulation system, in which complex mass transfer process were closely related to the swelling behavior of films. And the negative exponential growth model(Mt /M∞=yo-a? e-b? t)fitting well to experimental data had more advantages than the power law model in describing the whole process of mass transfer of protein based slow-release antibacterial films. On the whole mass transfer process, films showed a better sustained release effect of potassium sorbate with higher ratio of whey protein isolate to sodium caseinateand lower glycerol and initial content of potassium sorbate content. By modifying the film-forming formula, controlled release of antibacterial agent in protein-based antibacterial films could be realized to a certain extent.