Background and Objectives: Proxidase enzyme is one of the most important enzymes in plant tissues, 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 un-blanched frozen vegetables. In order to inactivate the enzyme methods such as heating, lowering pH or aw or adding chemical additives (SO₂) 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 in using alternative methods in order that increase the product’s shelf life.

Materials and Methods: In this study the effect of natural essential oils (Golpar, Thyme and Clove oils) on peroxidase enzyme activity was investigated. Optimization of peroxidase enzyme inactivation under different variables (essential oils concentration, the time of enzyme activity, blanching time and temperature) was performed using response surface methodology.

Results: The results showed that peroxidase activity of celery extracts was affected by all the studied oils and its activity was reduced. Optimum conditions for non-thermal inactivation of peroxidase enzyme of celery for different used oils were as: Golpar concentration 50 ppm, the time of enzyme activity 60 seconds, and enzyme activity (absorption) 0.467599; Thyme concentration 50 ppm, the time of enzyme activity 60 seconds and enzyme activity (absorption) 0.0523847; and clove oil concentration 50 ppm, the time of enzyme activity 60 seconds and enzyme activity (absorption) 0.120615.

Conclusion: This study showed that essential oils have the ability to inhibit and inactivate peroxidase enzyme activity.

Key­words: Essential oils, Anti oxidant, Peroxidase enzyme activity, Optimization, Response surface methodology