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AACC Approved Methods of Analysis, 11th Edition - AACC Method 32-33.01. Determination of trans-Galactooligosaccharides in Selected Food Products by Ion-Exchange Chromatographic Method

AACC Approved Methods of Analysis, 11th Edition


AACC Method 32-33.01
Determination of trans-Galactooligosaccharides in Selected Food Products by Ion-Exchange Chromatographic Method


trans-Galactooligosaccharides (TGOS) are fully soluble glycosides produced from lactose by enzymatic transgalactosylation and are used by the food and feed industry as prebiotic ingredients in numerous applications. TGOS are di- to octasaccharides composed of one to seven galactose units linked to a glucose molecule at the reducing end. The bond type is strongly dependent on the enzyme and the conditions used in the reaction. In healthy humans, TGOS are barely digested in the small intestine but are fermented in the colon by the bacterial flora and can thus be classified as dietary fiber (2). Even transgalactosylated disaccharides consisting of galactose and glucose with different beta-glycoside bonds from lactose are considered dietary fiber since they have physiological characteristics similar to those of longer TGOS (5). The prebiotic TGOS affect the host beneficially by selectively stimulating the growth of one or a limited number of health-promoting intracolonic bacteria, such as bifidobacteria.

Having a generally applicable and reliable method for the analysis of TGOS in different types of foods is very important. Classical methods such as HPLC lack the desired sensitivity and selectivity, so a new procedure has been developed, based on the method published by Quemener et al (4). This method relies on the enzymatic treatment of a test solution with a beta-galactosidase enzyme, followed by the quantitative determination of galactose by high-performance anion-exchange chromatography with pulsed amperometric detection (HPAEC-PAD).

TGOS and lactose are extracted from a test portion with hot phosphate buffer. The extract is treated with beta-galactosidase to hydrolyze TGOS and lactose. Both the initial and the treated solutions are analyzed using HPAEC-PAD. In the first assay, free galactose and lactose are determined in the initial test solution. In the second assay, the total amount of galactose released from TGOS and lactose is determined in the treated solution. TGOS are calculated from the concentrations of lactose and galactose.