A simplified spectrophotometric method for the determination of inulin in Jerusalem artichoke (Helianthus tuberosus L.) tubers

A simple spectrophotometric method was developed for the analysis of inulin in Jerusalem artichoke tubers. The inulin was extracted from the artichoke tuber samples using accelerated solvent extraction method, before subsequent hydrolysis in acid condition. The hydrolysates were then analyzed for fructose using spectrophotometry. The spectrophotometric method is based on oxidation of fructose by periodate and evaluation of the remaining periodate by measuring the absorbance at 350 nm of the triiodide complex formed, upon addition of potassium iodide. The optimum conditions for the detection of fructose were 0.1 mmol L(-1) periodate and 1.5 mmol L(-1) potassium iodide at pH 6.0. The proposed method was validated for its analytical performance parameters including accuracy, precision, and recovery. The method was applied to the determination of inulin in ten varieties of Jerusalem artichoke grown in the northeastern part of Thailand. The inulin content in the samples was found to be in the range of 63-75.5% dry weight, and the degree of polymerization was in the range of 14-20. The inulin contents obtained from the proposed spectrophotometry were not significantly different (p = 0.05) from those obtained from high-performance anion-exchange chromatography coupled with pulsed amperometric detection. The results indicated that the present spectrophotometric method can be used as an alternative to chromatographic analysis for the determination of inulin in plant samples.