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AACC International Approved Methods - AACC Method 32-31.01. Fructans in Foods and Food Products—Ion Exchange Chromatographic Method

AACC International Approved Methods

Fiber

AACCI Method 32-31.01
Fructans in Foods and Food Products—Ion Exchange Chromatographic Method

VIEW METHOD

Objective
Fructans are polydisperse mixtures of molecules that consist of fructose moieties linked to each other by beta(2-1) bonds. A glucose moiety may be linked to the end of the chain by an alpha(1-2) bond, as in sucrose. The degree of polymerization (DP) may vary from 2 to several hundreds. The main components of fructans are inulin (mainly DP 2–60) and oligofructose (DP 2–10). This method allows the quantitative determination of fructans in processed foods and raw materials, such as cereal products, fruits, and vegetables.

The method relies on the enzymatic treatment of the sample with an inulinase enzyme, followed by determination of the released sugars. The fructans are extracted from the sample with boiling water. An aliquot of the extract is hydrolyzed using a lyophilized amyloglucosidase enzyme. Subsequently, a part of that hydrolysate is treated with Fructozym.

The first and the second hydrolysate and the initial sample are analyzed using high-performance anion-exchange chromatography (HPAEC)-pulsed amperometric detection. In sugar analysis 1, free fructose (Ff) and sucrose (S) are determined in the initial sample. In sugar analysis 2, the sum of the amount of free glucose (Gf) and glucose from maltodextrins and starch (Gm) are determined in the first hydrolysate. In sugar analysis 3, the total amount of glucose (Gt) and the total amount of fructose (Ft) are determined in the second hydrolysate. The concentration of glucose and fructose released from fructan is calculated by difference from these determinations.

Glucose released from fructan (Gi) = GtS/1.9 – (Gf + Gm)

Fructose released from fructan (Fi) = FtS/1.9 – Ff

The fructan content (i) is the sum of Gi and Fi, corrected for the water loss during hydrolysis: i = k (Gi + Fi). For inulin from chicory, k = 0.91, and for oligofructose, k = 0.925.