Within the standard method for determination of nitrite in processed foods, sample solutions containing nitrite extracted from the foods are treated with sodium hydroxide and zinc acetate, as deproteinizing agents, before colorimetry is conducted by diazotizationcoupling. However, in the case of pollack roe, analysis is very di$cult or often impossible to carry out due to the turbidity, decrease in filtration rate, and foaming of the sample solution. It is suspected that these conditions are caused by the high concentration of soluble proteins originating from pollack roe. With this in mind, improvement of the procedure for preparing sample solution from pollack roe and its products was investigated. Results showed that decreases in filtration rate were resolved by the use of half the volume of deproteinizing agents in addition to twice the concentration as that of the standard method. The addition of silicone-type antifoaming agent SI suppressed the sample solution foaming and increased the filtration rate. Adding sodium chloride was not e#ective in avoiding turbidity or decreasing filtration rate and foaming. Using our modified method for preparing sample solutions, concentration of nitrite in pollack roe was determined to be *.*2*.*, ppm and the recovery ratio of / ppm of nitrite added to pollack roe was 23.2,./ῌ, respectively.

Increases in nitrite ions in tarako, ikura and sujiko during manufacture or cold storage have been observed. We isolated 30 bacterial strains from tarako and examined their nitrite-producing abilities. Eleven strains among the isolates reduced nitrate to nitrite at 0-5 % NaCl and 5-30℃ in a succinate-nitrate liquid medium. 16S rRNA gene sequence analysis indicated that these nitrate-reducing bacteria belonged to Vibrio, Halomonas or Cobetia. Two strains (strains No. 6 and No. 19) that showed the highest nitrite production among the isolates, and one strain (strain No. 17) that showed the lowest nitrite production, were inoculated in tarako and mentaiko. Then, they were tested for nitrite production after storage at 5, 10 and 20℃. Results showed that strain No. 19 produced nitrite ions at every tested temperature. We also found that frozen Alaska pollack roe imported from the USA and Russia were contaminated with nitrite-producing bacteria from 8 to 340 CFU/g. These results suggest that the increase in nitrite ions in tarako and mentaiko is due to the reduction of ingredient-derived nitrate to nitrite by nitrate-reducing bacteria that contaminate Alaska pollack roe.