Yaeko Suzuki

Geographical origin of polished rice based on multiple element and stable isotope analyses

We determined carbon and nitrogen contents (C and N contents) and stable carbon, nitrogen, and oxygen isotopic compositions (δ(13)C, δ(15)N, and δ(18)O) of polished rice in order to develop a simple method to discriminate its geographical origin. As a first attempt, we examined a single cultivar, Koshihikari rice, from 14 different cultivation areas including Australia (n=1), Japan (n=12), and USA (n=1). For all rice samples, C and N contents and the isotopic compositions are consistent with those of general plant materials, being 37.2-40.0% (C content), 0.8-1.4% (N content), -27.1 to -25.4% (δ(13)C), +0.4 to +9.0% (δ(15)N), and +18.8 to +22.9% (δ(18)O). However, its cultivated area is clearly distinguished by a pentagonal radar plot based on the elemental and isotopic compositions. Thus, the comparison of C and N contents and δ(13)C, δ(15)N, and δ(18)O values would potentially be useful for rapid and routine discrimination of geographical origin of the polished rice.

Stable carbon, nitrogen, and oxygen isotope analysis as a potential tool for verifying geographical origin of beef.

Stable isotope analysis of organic elements such as carbon and nitrogen has been employed as a powerful tool for provenance determination of food materials, because isotopic compositions of the materials reflect many factors in natural environment. In this study, we examined carbon, nitrogen, and oxygen isotope signatures of beef from Australia, Japan, and USA, in order to confirm the method as a potential tool for verifying geographical origin of beef commercially distributed in Japan. Defatted dry matter of beef from USA was characterized by higher carbon isotopic composition (-13.6 per thousand to -11.1 per thousand) than that from Japan (-19.6 per thousand to -17.0 per thousand) and Australia (-23.6 per thousand to -18.7 per thousand). That from Australia was characterized by higher oxygen isotopic composition (+15.0 per thousand to +19.4 per thousand) than that from Japan (+7.3 per thousand to +13.6 per thousand) and USA (+9.5 per thousand to +11.7 per thousand). The oxygen isotopic composition in Japanese beef showed a positive correlation with the isotopic composition of cattle drinking water, the difference in which is clearly latitude dependent. These results suggest that a comparison of carbon, nitrogen, and oxygen isotopic compositions is applicable as a potential tool to discriminate the provenance of beef not only between different countries (i.e. Australia, Japan, and USA) but also among different regions within Japan.

A comparison of freeze-drying and oven-drying preparation methods for bulk and compound-specific carbon stable isotope analyses: examples using the benthic macroinvertebrates Stenopsyche marmorata and Epeorus latifolium.

RATIONALE Carbon stable isotope analysis of bulk samples and fatty acids is an established method for tracing carbon flow pathways and reconstructing trophic interactions, but there is no consensus on which sample drying method should be used for sample preparation. The aim of this study was to determine if freeze-drying and oven-drying treatments used to prepare samples of the benthic macroinvertebrates Stenopsyche marmorata and Epeorus latifolium for bulk and fatty-acid-specific carbon stable isotope analysis yield different isotopic ratio values. METHODS Five individuals each from two species were split in half; one half was freeze-dried and the other half was oven-dried. The samples were ground and the δ(13)C values of the bulk samples and eight fatty acids were measured following combustion using an isotope ratio mass spectrometer coupled to an elemental analyzer or gas chromatography system. RESULTS The mean difference in the bulk and fatty acid δ(13)C values between freeze-dried and oven-dried samples was small (≤0.1‰ in both cases), although relatively large variations were observed in individual fatty-acid-specific δ(13)C values (maximum of ≤0.9 ‰). There were no significant differences in either bulk sample or fatty-acid-specific δ(13)C values between freeze-dried or oven-dried samples of the same species. CONCLUSIONS Freeze-drying and oven-drying are equally acceptable methods for preparing freshly caught S. marmorata and E. latifolium samples for bulk and fatty-acid-specific carbon stable isotope analyses.