Peroxidase enzyme is one of the most important enzymes in plant tissue which can bind to hydrogen peroxide and produce an activated complex that can react with a wide range of donor molecules. Therefore inactivation of the enzyme may increase the shelf life of raw and unblanched frozen vegetables. In order to inactivate of the enzyme several physical and chemical treatments among them heating (blanching), lowering pH or aw or adding chemical additives can be used, however each of the above mentioned methods has a kind of shortcoming. Nowadays consumer's trend has been oriented to use fresh products or foods prepared by little process, therefore producers are interested the ways to increase the shelf life by use of alternative methods. In this study the effect of natural essential oils (cumin, fennel and clove oils) on peroxidase enzyme activity were investigated. Optimization of peroxidase enzyme inactivation under different variable (essential oils concentration and the time of enzyme activity) was performed using response surface methodology. Results indicated that red cabbage and cabbage has the highest and potato and lettuce has the lowest peroxidase activity respectively (p<0.05). Although peroxidase resistance to essential oils varied among different vegetables but clove, in all concentration had the best effects in decrease of peroxidase activity (p<0.05) whereas cumin and fennel were partially able to reduce the enzyme activity (p<0.05). Optimum conditions for non thermal inactivation of peroxidase enzyme of cabbage for different used oils were as: cumin concentration 50 ppm, the time of enzyme activity 60 second and enzyme activity (absorption) 0.186055, fennel concentration 50 ppm, the time of enzyme activity 60 second and enzyme activity (absorption) 0.179738 and clove oil concentration 50 ppm, the time of enzyme activity 60 second and enzyme activity (absorption) 0.154761 [1-2].
