Characterization of fructan oligomers from species of the genus Allium L.

Abstract

Storage tissue of leaf bases from several species of the genus Allium [A. cepa L. var. cepa (onion, 6 cvs.), A. cepa L. var. ascalonicum (shallot, 7 cvs.), A. ampeloprasum L. var. porrum (leek, 3 cvs.), A. schoenoprasum L. (chives), A. sativum L. (garlic), A. fistulosum L. (Japanese bunching onion/Welsh onion), A. tuberosum Rottl. ex. spr. (Chinese chives/Nira), and other species] were analyzed to determine their water soluble carbohydrate composition. The Allium species analyzed can be divided into three groups according to their fructan profiles: Those with relatively high amounts of larger fructan polymers, Those with relatively high amounts of small fructan polymers up to a degree of polymerization of about 15, and Those with both large and small fructan polymers. Four major fructan series with exclusively (2→1) fructosyl-fructose linkages have been characterized that are typical of those Allium species containing small fructan polymers. They are: an inulin series with the general formula: G-1,2-F-1,(2-F-1)n,2-F(G-1,2-F=sucrose), a neokestose-based series with chain elongation only at the glucose end of the original sucrose molecule: F-2,(1-F-2)m,1-F-2,6-G-1,2-F, a neokestose-based series with elongation from both sides of the sucrose: F-2,(1-F-2)m,1-F-2,6-G-1,2-F-1,(2-F-1)n,2-F,and an inulo-n-ose series without a terminal glucose F-1,(2-F-1)n,2-F. While the first three fructan series were present in relatively high concentrations in all samples with high amounts of small fructans, the inulo-n-ose series was detectable in most samples, but in varying concentrations.