Evaluation Of The O/W Emulsion Oxidation Stability With AC Impedance Spectroscopy

This dissertation is based on the relationship of the variation of both EIS and POV with time during the process of O/W emulsion oxidation, the oxidation stability of emulsion could be evaluated by the oxidation induction time and the oxidation reaction rate constant. In addition, the shelf life of emulsion in different temperature also be predicted with Arrhenius Equation.The main research contents and results were as follows.The effect of solvent, the supporting electrolyte, and the frequencies of measurement on the detection of the impedances were thoroughly investigated. The POV-t and Rct-t curves were concluded by simultaneously measuring the oil’s POV and EIS. At the first period of time,both POV and Rct were slowly changed as hydrogen peroxide began to produce in the oil. The variation trends of POV and Rct were accelerated with the progress of oxidation. It was found that there was a relationship between Rct-t curves and POVs-t curves.The induction times of the four studied oils were got from POV-time curves and impedance-time curves. The longer the induction time was, the better stability of the oil would be. The order of oxidation stability of four kinds of oil was: soybean oil >blend oil>olive oil>almond oil. The t-test and F-test results revealed that the induction times obtained from two different methods had no significant differences. According to POV-t curves and Rct-t curves of the oils, the oxidation rate constants of those oils were obtained. The oxidation rate constants of the oils at different temperatures were: almond oil > olive oil> blend oil >soybean oil. The shelf lives of oils were predicted by POV-t curves and Rct-t curves with Arrhenius equation.The results showed that the prediction shelf lives by two different methods were almost the same.The effect of the amounts of emulsion, equivalent circuit,and the frequencies of measurement on the detection of the impedances were investigated. The POV-t and Rct-t curves were obtained by simultaneously measuring POV and EIS of the emulsions. It was showed that there was a certain relationship between Rct and POVs.The O/W emulsions were prepared by almond oil,olive oil, blend oil, soybean oil. The induction times of the four studied emulsions were got from POV-t curves and Rct-t curves. The longer the induction time was, the better stability of the emulsion would be. The order of oxidation stability of four kinds of emulsions was: soybean oil emulsion>blend oil emulsion>olive oil emulsion>almond oil emulsion. And the t-test and F-test results revealed that the induction times obtained from two different methods had no significant differences. According to POV-t curves and Rct-t curves of the emulsions,the oxidation rate constants of those emulsions were obtained. The oxidation rate constants of the emulsions at different temperatures were: almond oil emulsion> olive oil emulsion> blend oil emulsion >soybean oil emulsion. Experimental results showed that there were certain relations between the oxidation stability of O/W emulsion and the rate constant. The shelf lives of emulsions were predicted by POV-t curves and Rct-t curves with Arrhenius equation.The results showed that the prediction shelf lives by two different methods were almost the same.