Table of Contents
International Journal of Carbohydrate Chemistry
Volume 2009 (2009), Article ID 493737, 9 pages
http://dx.doi.org/10.1155/2009/493737
Research Article

Isolation and Structural Analysis In Vivo of Newly Synthesized Fructooligosaccharides in Onion Bulbs Tissues (Allium cepa L.) during Storage

1Department of Food Science, Graduate School of Dairy Science Research, Rakuno Gakuen University, Ebetsu 069-8501, Japan
2Graduate School of Agriculture, Hokkaido University, Sapporo 060-8589, Japan
3Department of Life Sciences, The University of the West Indies, Mona Campus, Kingston 7, Jamaica

Received 2 February 2009; Accepted 20 April 2009

Academic Editor: Thomas Heinze

Copyright © 2009 Masaki Fujishima et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Fructooligosaccharides are involved in physiological activities and quality attributes of onion bulbs. This work describes structures of newly synthesized oligosaccharides formed by fructose moieties in onion bulb tissues during storage. Onion bulbs were stored for four weeks at 10 C . HPAEC-PAD analysis showed that saccharide 1 was eluted after 1-kestose while saccharide 2 was eluted after nystose ( 𝟒 a ) . Saccharides 1 and 2 have R-sucrose values of 1.55 and 2.15 by HPAEC, a reducing terminal, a reducing sugar-to-fructose ratio of 0.5 and 0.3, and a degree of polymerization of 2 and 3 by TOF-MS, respectively. GLC analysis of the methyl derivatives and NMR measurement of the saccharides confirmed the presence of two different structures: the structure of saccharide 1 is composed by two fructose moieties and linked by 𝛽 ( 2 1 ) linkage and was identified as inulobiose [ 𝛽 -D-fructofuranosyl- ( 2 1 ) - 𝛽 -D-fructopyranose]. The structure of saccharide 2 consists of three units of fructose linked by 𝛽 ( 2 1 ) linkage and was identified as inulotriose [ 𝛽 -D-fructofuranosyl- ( 2 1 ) - 𝛽 -D-fructofuranosyl- ( 2 1 ) - 𝛽 -D-fructopyranose]. The spectra also showed that 70 to 80% of the terminal fructose residue of the two saccharides is of pyranosyl form, while 20 to 30% is of furanosyl form. This finding demonstrated that these newly produced saccharides, catalyzed by onion-purified 6G-FFT, were synthesized by the action of 1-FFT fructosyltransfer from 1-kestose to free fructopyranose yielding inulobiose and sucrose, while elongation of fructofuranosyl units occurs at this transferred fructofuranosyl residue to produce inulooligosaccharide having an additional unit of fructofuranose.