Multiple Stable Isotope Analyses for Verifying Geographical Origin and Agricultural Practice of Japanese Rice Samples

Abstract

We determined the differences in carbon, nitrogen and oxygen isotopic compositions (δ13C, δ15N, and δ18O) between short grain rice samples from 9 locations (Hokkaido, Yamagata, Niigata, Nagano, Ibaraki, Tokyo, Mie, Hiroshima and Okinawa) in Japan to discriminate their geographical origin. Oxygen isotopic composition of brown rice is well correlation with that of ambient water (R2 = 0.69). The δ18O values of rice samples are correlated with an increase in the latitude (R2 = 0.82). The δ13C values of upland rice are higher than those of paddy rice, depending on the water stress. These results suggest that δ18O and δ13C values of Japanese rice samples are reflected the difference in growth condition. The δ15N values of rice depend on the soil nutrition, where the rice is cultivated. Organic rice is characterized by higher nitrogen isotopic compositions (+ 3.0 to + 8.9‰) than conventional rice (−0.4 to + 3.2‰). Thus, δ15N would become a strong tool to discriminate between organic and conventional rice samples. Thus, the δ18O and δ13C values will be potentially useful for the discrimination of organic rice, and the geographical origin of rice within Japan.