Effects of Processing on Stable Isotope Compositions (δ13C, δ15N, and δ18O) of Rice (Oryza sativa) and Stable Isotope Analysis of Asian Rice Samples for Tracing Their Geographical Origins

We evaluated the effects of processing (i.e., polishing, washing, boiling, and rice cake preparation) on the stable carbon (δ13C), nitrogen (δ15N), and oxygen (δ18O) isotopic compositions of rice (Oryza sativa) to assess its geographical origin. There were no significant differences in their δ13C, δ15N, and δ18O values before and after boiling and rice cake preparation, indicating that the database of the δ13C, δ15N, and δ18O values of rice samples could be adapted and used to trace the geographical origin of rice used for cooking and rice cake preparation. Conversely, the δ13C and δ18O values were significantly altered after polishing. After the brown rice samples were polished at a polishing rate of 90%-92%, we determined the δ13C, δ15N, and δ18O values of the polished rice samples from nine countries—Australia, Bangladesh, China, Japan, Malaysia, Myanmar, Philippines, Sri Lanka, and Thailand. The rice samples from Bangladesh, Malaysia, Philippines, and Sri Lanka had significantly lower δ13C values than those from the other five countries. The Chinese, Japanese, and Philippine rice samples had lower δ18O values than those from the other countries. The δ13C and δ18O values could be potential tools for tracing the geographical origin of Asian rice.