AOAC 2018 Methods

(e) Inulin and levan control powders . —Extract and analyse 100 mg of these control powders as per G(a)( 2 ).

G. Assay Procedure

(a) Extraction of fructan .—( 1 ) Products containing 0-10% w/w fructan .— Run D-fructose working standard solution (in quadruplicate), reagent blank (in duplicate), fructan control flour, and sucrose control flour with each set of tests. Use reagent blank to zero the spectrophotometer. ( i ) Accurately weigh approximately 400 mg test portion of sample into a dry pyrex screw cap culture tube (25 x 150 mm) and add 25 mL of distilled water. Loosely cap the tube. Place the tube into a boiling water bath and heat for a total of 10 min. After 5 min, tighten the tube cap and vigorously mix the contents on a vortex mixer. Return the tube to the boiling water bath. After a further 5 min, remove the tube from the boiling water and mix the contents by inversion and shaking. ( iii ) Centrifuge the solution at 13,000 rpm for 5 min in a microfuge C ( b ), and analyze within 1 h after centrifugation. The supernatant may be slightly turbid. This is not a problem. (If the solution is stored for several hours at low temperature before analysis, the fructan may precipitate from solution. In such cases, reheat solution to ~80°C and let cool to room temperature before removing solutions for analysis.) Use this solution for determination of fructan as per G(b)( 1 ). ( 2 ) Products containing 10-40% w/w fructan . — Run D-fructose working standard solution (in quadruplicate), reagent blank (in duplicate), fructan control flour, and sucrose control flour with each set of tests. Use reagent blank to zero the spectrophotometer. (i) Accurately weigh approximately 100 mg of the sample into a dry pyrex screw cap culture tube (25 x 150 mm) and add 25 mL of distilled water. Loosely cap the tube. Place the tube into a boiling water bath and heat for a total of 10 min. After 5 min, tighten the tube cap and vigorously mix the contents on a vortex mixer. Return the tube to the boiling water bath. After a further 5 min, remove the tube from the boiling water bath and mix the contents by inversion and shaking. ( ii ) Cool the solution to room temperature and mix thoroughly. Transfer 2.0 mL into a disposable 2.0 mL polypropylene microfuge tube C ( c ).

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