Apurinic/apyrimidinic (AP) sites are frequently observed DNA lesions when cells are exposed to hydroxyl radicals. We developed a new method for measurement of the antioxidative activity of foods using the occurrence frequency of AP sites on DNA. Combined with the electron spin resonance (ESR) method as a standard method, we examined whether fish and soy sauces including puffer fish [Takifugu rubripes (Temminck et Schlegel)] sauce could protect DNA from damage caused by hydroxyl radicals. The results showed that the ratios of DNA protection by puffer fish sauce, salmon fish sauce, sandfish fish sauce (Shottsuru), colorless soy sauce, squid fish sauce (Ishiru), dark color soy sauce and light color soy sauce were 68.9, 67.0, 60.1, 49.7, 34.1, 28.2 and -4.4%, respectively. Puffer, salmon, and sandfish fish sauces showed high ratios of DNA protection against hydroxyl radicals. On the other hand, IC50 values of hydroxyl radical scavenging of the puffer, salmon, sandfish, squid fish sauces and colorless, dark and light color soy sauces were 0.20, 0.09, 4.16, 0.26% and 0.28, 0.14 and 0.18%, respectively. Though the puffer fish sauce exhibited the highest level of DNA protection among the examined samples and a high hydroxyl radical scavenging capability, a correlation between the radical scavenging capability and DNA protection against hydroxyl radicals among the examined fish and soy sauces was not found.

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