Determination of the Geographic Origin of Onions between Three Main Production Areas in Japan and Other Countries by Mineral Composition

Onions (Allium cepa L.) are produced in many countries and are one of the most popular vegetables
in the world, thus leading to an enormous amount of international trade. It is currently important that
a scientific technique be developed for determining geographic origin as a means to detect fraudulent
labeling. We have therefore developed a technique based on mineral analysis and linear discriminant
analysis (LDA). The onion samples used in this study were from Hokkaido, Hyogo, and Saga, which
are the primary onion-growing areas in Japan, and those from countries that export onions to Japan
(China, the United States, New Zealand, Thailand, Australia, and Chile). Of 309 samples, 108 were
from Hokkaido, 52 were from Saga, 77 were from Hyogo, and 72 were from abroad. Fourteen elements
(Na, Mg, P, Mn, Co, Ni, Cu, Zn, Rb, Sr, Mo, Cd, Cs, and Ba) in the samples were determined by
frame atomic adsorption spectrometry, inductively coupled plasma optical emission spectrometry,
and inductively coupled plasma mass spectrometry. The models established by LDA were used to
discriminate the geographic origin between Hokkaido and abroad, Hyogo and abroad, and Saga and
abroad. Ten-fold cross-validations were conducted using these models. The discrimination accuracies
obtained by cross-validation between Hokkaido and abroad were 100 and 86%, respectively. Those
between Hyogo and abroad were 100 and 90%, respectively. Those between Saga and abroad were
98 and 90%, respectively. In addition, it was demonstrated that the fingerprint of an element pattern
from a specific production area, which a crop receives, did not easily change by the variations of
fertilization, crop year, variety, soil type, and production year if appropriate elements were chosen.
Keywords: Onion; geographic origin; mineral; element; composition; liner discriminant analysis; ICP