Analytical Sciences

Development of a Method to Isolate Glutamic Acid from Foodstuffs for a Precise Determination of Their Stable Carbon Isotope Ratio

Kazuhiro KOBAYASHI,* Masaharu TANAKA,* Yoichi YATSUKAWA,* Soichi TANABE,** Mitsuru TANAKA,*,** and Naohiko OHKOUCHI***

*Global Food Safety Institute, Nissin Foods Holdings Co., Ltd., 2100 Tobuki-machi, Hachioji, Tokyo 192-0001, Japan
**Global Innovation Research Center, Nissin Foods Holdings Co., Ltd., 2100 Tobuki-machi, Hachioji, Tokyo 192-0001, Japan
***Department of Biogeochemistry, Japan Agency for Marine-Earth Science and Technology, 2-15 Natsushima-cho, Yokosuka, Kanagawa 237-0061, Japan

Recent growing health awareness is leading to increasingly conscious decisions by consumers regarding the production and traceability of food. Stable isotopic compositions provide useful information for tracing the origin of foodstuffs and processes of food production. Plants exhibit different ratios of stable carbon isotopes (δ¹³C) because they utilized different photosynthetic (carbon fixation) pathways and grow in various environments. The origins of glutamic acid in foodstuffs can be differentiated on the basis of these photosynthetic characteristics. Here, we have developed a method to isolate glutamic acid in foodstuffs for determining the δ¹³C value by elemental analyzer-isotope-ratio mass spectrometry (EA/IRMS) without unintended isotopic fractionation. Briefly, following acid-hydrolysis, samples were defatted and passed through activated carbon and a cation-exchange column. Then, glutamic acid was isolated using preparative HPLC. This method is applicable to measuring, with a low standard deviation, the δ¹³C values of glutamic acid from foodstuffs derived from C3 and C4 plants and marine algae.

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