STUDIES ON NATTO .5. DETERMINATION OF GAM MA-POLYGLUTAMIC ACID IN NATTO USING CETYLTRIMETHYLAMMONIUM BROMIDE

A simple and rapid spectrophotometric method has been established for determination of gamma-polyglutamic acid (gamma-PGA) which is the stic ky material in fermentated soybean food ''natto''. The method is based on the complex formation between gamma-PGA and cetyltrimethylammonium bromide (GET). The complex could be determined by the measurement of absorbance at 400 nm. The linear relationship was obtained between abs orbance and gamma-PGA. concentration in the range from 0 to 54.85 mu g per 6 mi of a reaction mixture. The complex formation with CET was no t observed on glutamic acid, glutamylglutamic acid, levan and pectin. When gamma-PGA prepared from ''natto'' was decomposed by gamma-glutamy ldepolymerase induced by Bacillus natto bacteriophage infection, visco sity of the reaction mixture decreased rapidly, while the absorbance o f the complex with CET was not decreased. Therefore, it was confirmed that values obtained by the method was not affected by the molecular w eight of gamma-PGA. We demonstrated the formation of gamma-PGA during manufacturing process of ''natto'' and its content of the commercial p roducts by the method. gamma-PGA was detected at 10h from the beginnin g of the fermentation and then increased. The mean value of the gamma- PGA content and standard deviation in 34 commercial ''natto'' were 328 mg+/-120.99 per 100 g on wet basis.