Rapid analysis of fructans and comparison of fructan profiles in several different types of asparagus storage roots using MALDI-TOF MS

Appropriate conditions for analysing fructans in the storage roots of field-grown asparagus using matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF MS) were investigated. High resolution and ionisation were achieved when lyophilised and ground storage root powders were extracted twice with 1.0 ml distilled and deionised hot water (90 degrees C), supplemented with 1.0 ml of 100% (v/v) ethanol, concentrated to approx. 1.0 ml, and mixed with 10 g l(-1) 2,5-dihydroxybenzoic acid (DHB) at 1:1 (v/v) before loading on a sample slide for MALDI-TOF MS, which was performed in the linear positive ion mode at a laser intensity of 15 kV. The mass spectral profiles showed that the degree of polymerisation (DP) of fructans ranged from three-to-21 in storage roots collected in the Winter. When different amounts of gamma-cyclodextrin were added to each sample, a linear positive relationship was observed between the amount of gamma-cyclodextrin and the relative positive ion intensity. With gamma-cyclodextrin as an internal standard, fructan profiles were compared between Summer- and Winter-collected asparagus storage root samples. Furthermore, the fructan profiles of three different types of storage root of different colours (i.e., milky-white, yellow, or dark-brown) were also examined. Fructan contents were always higher in the Winter-collected samples than in those collected in the Summer, regardless of the DP. However, samples from the different coloured roots showed variable fructan profiles, depending on the DP. These results indicate that fructan analysis using MALDI-TOF MS would be useful for examining the dynamics of carbohydrate metabolism in asparagus storage roots because of its high degree of accuracy and its simplicity.