from cell membrane and by destroying cell membrane. And also it oxidises the SH groups of enzymes of bacteria and since the reaction is not reversible, this process destroys the micro organism (Block and Febiger, 1991). Fresh vegetables and fruits can be decontaminated by using chlorine in suitable concentrations without decreasing product quality. By applying suitable chlorine to the food, micro organism population can be decreased and the product safety can be provided without decreasing food value(BIock and Febiger, 1991). Sensitivity degree of some micro organisms against chlorine shown in table 2.4 (Gardner, 1991) Table 2.4: Sensitivity degree of some micro organisms against chlorine: Gram-negative bacteria Very sensitive Bacteria spore Sensitive (PH 7.6 optimum) ‘Amoebic cysts’, algaes Sensitive Prion Low sensitive (in high Effectiveness of chlorine based disinfectants depend on some factors such as PH and concentration, organic material existence, robustness and heat of the water used (Gardner, 1991). The effect of concentration and PH can be evaluated together. NaOCI which has a PH 7.6 and 100 ppm or PH 9 and 1000 ppm can easily inactivate Bacillus subtilis (Gardner, 1991