Possible occurrence of new mutagens with the DNA breaking activity in coffee.

Brewed and instant coffee emitted strong chemiluminescence due to singlet oxygen and excited carbonyls, which may be originated by the Maillard reaction of sugars and amino acids but not by the reaction of polyphenolics. Instant coffee cleaved DNA giving single-strand breaks only after it was purified by high performance liquid chromatography (HPLC) or by gel filtration. Retention times of component(s) with strong DNA breaking activity in HPLC were different from those of chemiluminescence emitters, although they were coeluted on a gel filtration. The major DNA breaking component(s) must be different from chemiluminescence emitters. Active oxygen radicals participated little in DNA breaking because active oxygen radical scavengers had only a marginal effect on DNA breaking of the active gel fraction. DNA breaking by the active gel fraction was inhibited by high concentrations of inorganic salts probably because the salts stabilized the DNA double strands. The active gel fraction was mutagenic to Salmonella typhimurium TA98 without metabolic activation. The number of His+ revertant colonies/g of instant coffee powder was estimated to be 4000.