Chemical Profiles of Methylpyrazines Contained in Commercially Available Natto
Structures and amounts of methylpyrazines contained in commercial natto, a fermented soybean food in Japan, were determined using HPLC equipped with an acid resistant reversed phase column, Capcell Pak C18 ACR (Shiseido). Mobile phase solvent mixtures consisted of acidic phosphate buŠer solution (pH 2.0) containing 2% acetonitrile gave satisfactory results with baseline separation of the authentic specimens, such as naked pyrazine, monomethylpyrazine, 2,3-, 2,5-, and 2,6-dimethylpyrazine,
... ethylpyrazine, trimethylpyrazine, and tetramethylpyrazine. We used the mobile-phase solvent with a ‰ow rate of 1 ml/min at 15.0°C. Before HPLC, commercial natto samples were treated with water to prepare diluted suspensions of surface mucous materials. The suspensions were treated on Sep Pac C18 Cartridges (Waters) with phosphate buŠer solutions containing 2-7% acetonitrile. The extracts were then injected into the analytical column to obtain chromatograms that were used to determine the structures and amounts of methylpyrazines. The results showed that a commercialiy packed natto contains a considerable amount of 2,5-dimethylpyrazine instead of the tetrametyl-and trimethylpyrazines in the traditional products. This may be a result of recent eŠorts of natto makers whose interests have been focused on new methods for preparing odorless products.