Hydrogen peroxide is responsible for certain bactericidal effects observed in biological systems, such as growth inhibition of one bacterial species by another and killing of invading microorganisms by activated phagocytic cells. H2O2 might be generated in bacteriological media by their exposure to light and/or oxygen and become an important mediator of toxic effects. H2O2 cytotoxicity is apparently due to its capacity—generally mediated by transition metal ions—to generate more reactive and cytotoxic oxygen species such as the hydroxyl radical, which is a powerful oxidant, and which can initiate oxidation of biomolecules. The conversion of H2O2 into more cytotoxic compounds may be potentiated by reducing agents and by peroxidases. Cells may protect themselves against H2O2 toxicity either by the action of catalases or, in the case of DNA damage, by repairing the damage after it has taken place. Assays for the detection and quantitation of H2O2 in cell cultures include those based on (i) catalase-dependent oxidation of formate to CO2, (ii) generation of fluorescent products due to a H2O2- mediated oxidative reaction, (iii) the loss of fluorescence upon the oxidation of scopoletin, (iv) change in absorbance upon oxidation of phenol red, or (v) formation of complexes with peroxidases. Some possible antimicrobial uses of H2O2 in the food industry are presented.

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