Seed oil content, fatty acids composition and antioxidant properties as affected by genotype in Allium cepa L. and perennial onion species

The antioxidant content in plant seeds is deemed to affect seed oil protection against auto-oxidation to a large extent, whereas the relationship between a strong antioxidant element such as selenium (Se) and either seed oil accumulation or fatty acids composition has not been investigated so far. The aim of the present work was to assess Se concentrations in seeds and their relationships with oil content and fatty acids composition in: a) ten Allium cepa cultivars, i. e. eight Russian and two Italian; and b) six perennial onion species (A. schoenoprasum, A. obliquum, A. altaicum, A. fistulosum, A. nutans, A. ramnósum). Fatty acids composition of Allium seed oil was determined by gas chromatography method, whereas total and water soluble Se concentration was assessed by microfluorimetric method. The oil content of Allium cepa seeds was 1.7 fold higher (10.7-16.5%) than that recorded in perennial onions (4.0-10.8%) and it was positively correlated with the total Se concentration. Within A. cepa, the seeds of the two Italian cultivars Ramata di Montoro and Rossa di Tropea were characterized by the highest oil content (16.5-16.6%) and oleic acid (25-27%). Linoleic (C18:2) acid was the main fatty acid, followed by oleic (C18:1) and palmitic acids (C16:0) in all cultivars. Among the perennial onion seeds, the highest oil percentage was detected in A. schoenoprasum (10.8%) and the lowest in A. ramnósum (4.0%). Compared to A. cepa cultivars, the perennial onion species showed a similar oil fatty acid composition, with the main acids being C18:2, C18:1 and C16:0 in decreasing order, a lower level of C16:0, and enhanced levels of minor SFA, such as C20:0, C22:0 and C24:0. Further differences also included decreased levels of C16:1, 11-trance C18:1 and a higher concentration of C22:1. The concentration of water soluble forms of Se in seeds was positively correlated with linoleic acid and with total phenolics. Conversely, oleic acid was negatively correlated with water soluble forms of Se.