Cultivar and regional differences in the metabolite composition of onion (Allium cepa)

• We grew 2 onion cultivars in different regions in Japan for 2 consecutive years.
• We comprehensively analyzed the metabolite compositions of onion bulbs using GC–MS.
• Metabolite compositions were affected by difference in cultivars and regions.
• The effect of cultivar or region for onion metabolites was similar among 2 years.
• The most influential factor for onion metabolites was different between 2 years.

Onion (Allium cepa) is a globally famous vegetable and is used in a variety of ways, including eaten fresh, added as a spice or prepared as a main ingredient in cooking. Pungent taste, sweet taste, texture, and several other qualities are required for onions to be suitable as processing ingredients. These qualities are influenced by the metabolite composition. In this study, we comprehensively analyzed the metabolite compositions of onion bulbs using gas chromatography mass spectrometry (GC–MS) in order to characterize onions produced from different cultivars and regions. We compared the metabolite composition of two onion cultivars, ‘Kitako-1’ and “Kitamomiji 2000” (‘Kitamomiji’), from two consecutive seasons (2011/2012) using bulbs cultivated in different regions in Hokkaido, the most dominant production region for onions in Japan. Principal component analysis (PCA) was applied to 48 or 55 compound peaks identified from bulbs in 2011 and 2012, respectively, by GC–MS analysis. In 2011, the first and second principal components (PC1 and PC2) accounted for 34% and 21% of the total variance, respectively, and were associated with both cultivar and cultivated region. By contrast, in 2012, PC1 which accounted for 35% of the total variance was influenced only by onion cultivar, and PC2 which accounted for 17% of total variance was influenced only by cultivated region. Many amino acids tended to be present at a higher concentration in ‘Kitamomiji’ than in ‘Kitako-1’, whereas some sugars and organic acids tended to be present at a higher concentration in ‘Kitako-1’ in both years. The concentration of some amino acids was significantly higher in bulbs cultivated in Sapporo and Memuro (2011), and in Sapporo (2012). These results suggest that the optimal usage of onions as processing ingredients varied with cultivar and cultivated region.

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