Molecular structures of fructans from agave tequilana

J. Agric. Food Chem. 2003, 51, 7835−7840

7835

Molecular Structures of Fructans from Agave tequilana Weber var. azul
MERCEDES G. LOPEZ,*,† NORMA A. MANCILLA-MARGALLI,† GUILLERMO MENDOZA-DIAZ‡
AND

Departamento de Biotecnologıa y Bioquımica, Centro de Investigacion y de Estudios Avanzados del ´ ´ ´ IPN, Unidad Irapuato, Apartado Postal 629, Irapuato, Gto., 36500 Mexico, and Facultad deQuımica, ´ ´ Universidad de Guanajuato, Noria Alta s/n, Guanajuato, Gto., 36050 Mexico ´

Agave plants utilize crassulacean acid metabolism (CAM) for CO2 fixation. Fructans are the principal photosynthetic products generated by agave plants. These carbohydrates are fructose-bound polymers frequently with a single glucose moiety. Agave tequilana Weber var. azul is an economically important CAMspecies not only because it is the sole plant allowed for tequila production but because it is a potential source of prebiotics. Because of the large amounts of carbohydrates in A. tequilana, in this study the molecular structures of its fructans were determined by fructan derivatization for linkage analysis coupled with gas chromatography-mass spectrometry (GC-MS), nuclear magnetic resonance (NMR),and matrix-assisted laser desorption time-of-flight mass spectrometry (MALDITOF-MS). Fructans were extracted from 8-year-old A. tequilana plants. The linkage types present in fructans from A. tequilana were determined by permethylation followed by reductive cleavage, acetylation, and finally GC-MS analysis. Analysis of the degree of polymerization (DP) estimated by 1H NMR integration and 13C NMR andconfirmed by MALDI-TOF-MS showed a wide DP ranging from 3 to 29 units. All of the analyses performed demonstrated that fructans from A. tequilana consist of a complex mixture of fructooligosaccharides containing principally (2 f 1) linkages, but also (2 f 6) and branch moieties were observed. Finally, it can be stated that fructans from A. tequilana Weber var. azul are not an inulin type aspreviously thought.
KEYWORDS: Agave tequilana; fructans; linkage; permethylated alditol acetates; degree of polymerization (DP); matrix-assisted laser desorption time-of-flight mass spectrometry (MALDI-TOF-MS)

INTRODUCTION

Mexico has been considered the center of origin and biodiversity of the AgaVe genus due to the taxonomic diversity within its territory. Of the 310 species reported, about 272can be found in this country (1). Members of the Agavaceae family are distributed within and well adapted to arid and semiarid regions. They have undergone some morphological and physiological adaptations to survive in these adverse conditions. A physiological plant adaptation is the use of crassulacean acid metabolism (CAM), which involves reduced transpirational water loss (2) by opening thestomata at night when the temperature is cooler and, hence, the evaporative demand decreases (3). The principal photosynthetic product of CAM in Agave plants has been reported to be fructan, a soluble fructose polymer with generally one glucose moiety per molecule (4, 5). Fructans in AgaVe species are synthesized and stored in the stems, and their main function in such CAM plants is as storage. Theymay also act as osmoprotectants during drought (6),
* Corresponding author [telephone +52 (462) 623 9644; fax +52 (462) 624 5996; e-mail mlopez@ira.cinvestav.mx]. † Unidad Irapuato. ‡ Universidad de Guanajuato.

constituting another possible physiological adaptation to arid environments. Fructan structures seem to be species dependent; in fact, Bonnett et al. (7) proposed the elucidation offructan structures as a potential taxonomic marker in Poaceae. More recently, Sims et al. (8) reported the presence of a similar fructan structure in members of the Asparagales order, in which the Agavaceae family is included. However, in AgaVe species more than one fructan structure has been reported. Sanchez-Marroquın and ´ ´ Hope (4) and Bathia and Nandra (9) reported inulin, a fructan type...