1 Introduction Starch, an α-D-glucan biopolymer, is composed of two molecular entities, a linear fraction, amylose, and its branched counterpart, amylopectin. Physicochemical prop- erties of isolated starches differ widely due to plant origin, and the information on properties is vital in choosing starch- es for various food and non-food (paper, textiles, mining, pharmaceutical, etc.) industrial applications. These proper- ties depend on the starch molecular structure, composition and morphology of the starch granule itself. The structure refers to both fine structure (molecular size, degree of branching, chain length, etc.) of the component molecules (amylose and amylopectin) and the supra-molecular order, i.e. the manner in which amylose and amylopectin are arranged within the granule and the degree of intermolecular interaction among them. Amylopectin is a highly branched starch molecule com- posed of many linear chains (α-1,4-D-glucan) with about 4–6 % of the total glucosidic bonds branching from the linear polymers via α-1,6-D-glucan linkages. The presence of these branching points gives rise to a number of possible arrange- ments of the linear chains. Because of its general dominance in the composition of a starch granule (usually > 75 %), the structure and properties of amylopectin have been the sub- ject of many investigations on molecular size, branching, in- ner/outer chain lengths, etc. [1–5]. These studies suggest that the molecular structural features of amylopectin highly in- fluence starch physicochemical properties and functionality. Structural investigation of amylopectin has relied upon the progress in methodological development, both enzymat- ic and instrumental. Enzymatic debranching of amylopectin using pullulanase or isoamylase, followed by the separation of linear chains using liquid chromatography, has been the most commonly used technique in the analysis and interpre- tation of the amylopectin fine structure. Various types of columns packed with size exclusion and anion exchange gels have been used for the separations. The analysis generally gives a bi- or trimodal elution profile, indicating the pres- ence of chains with different chain length or molecular weight [3, 4]. The use of high performance anion exchange (HPAE) liq- uid chromatography connected to a pulsed amperometric de- tector (PAD) has shown the highest resolution of molecular weights of the debranched chains. Usually in the application of this technique, after elution from the HPAE column but prior to detection with PAD, the linear starch chain is con- verted to glucose using an enzyme pad. This conversion is carried out with the assumption that the conversion of linear debranched starch chains to glucose is quantitative. This is a requirement since different saccharides, such as glucose and maltose for example, can have different responses with PAD detection. The efficiency of enzymatic conversion is usually established using low molecular weight maltooligosaccha- rides as standard (with degree of polymerization, or DP, of 1–7) and then extrapolated to higher molecular weight debranched starch polysaccharides. Matrix-assisted laser desorption/ionization mass spec- trometry (MALDI-MS) was originally developed for deter- mining the mass of large molecules such as proteins. MALDI-MS has also been applied to carbohydrate molec- ular sizing and quantification [6–8]. The measurement is quick and the technique often requires little sample purifica- tion. The objective of this study was to develop a methodol- ogy to determine the chain length profile of debranched amylopectin using MALDI-MS. 2 Experimental 2.1 Materials A small sample of waxy corn starch was obtained from Prof. Jay-Lin Jane, Department of Food Science and Human Nutrition, Iowa State University, IA, 50011. Waxy barley grains (Candle) were obtained from Agricore, Calgary, Al- berta. Regular barley grains were obtained from Dr. Jim Helm, Alberta Agriculture, Food and Rural Development, Lacombe, Alberta. Isoamylase (E.C 3.2.1.68) and Sepharose CL-6B were obtained from Sigma Co. (St. Louis, MO); Sep-pak C18 cartridges, from Waters Corp. (Milford, MA); Macro-sep centrifuge concentrators (30 K), from Filtron Tech. Corp. (Northborough, MA); and the Sephadex G10 Starch/Stärke 51 (1999) Nr. 7, S. 243–248 © WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1999 0038-9056/99/0707-0243$17.50+.50/0 243 Forschungsbeiträge/Research Papers A protocol was developed for molecular characterization of debranched starch amylopectin using Matrix-assisted laser desorption/ionization- mass spectrometry (MALDI-MS). Starch from waxy corn was used in the protocol development. Various factors influencing the protocol were investigated and discussed. Using the developed protocols, starch MALDI-MS Characterization of Maltooligo/polysaccharides From Debranched Starch Amylopectin of Corn and Barley Jian Wang, Gaosong Jiang, Thava Vasanthan, and Peter Sporns, Edmonton, Alberta (Canada) amylopectin from barley grains (waxy-type Candle and regular-type Phoenix) were also characterized. The study suggested that MALDI- MS is suitable to determine the molecular size profile of debranched starch (maltooligo- and polysaccharides) faster and with greater accu- racy than any present analytical methodology.