Optimization of inulin extraction from Inula helenium L. using response surface methodology followed by its MALDI-TOF and TLC-FLD based characterization

Inulin, a prebiotic, is a mixture of linear chains β-2,1 fructans with a degree of polymerization (DP) of 2 to 60. Different DPs have various applications in the cosmetics, pharmaceutical, and food industries.

This study aims to find the best method for DP determination.

RSM was applied to optimize the extraction of inulin from Inula helenium. Four factors, including time, temperature, solvent-to-sample ratio, and pH and yield as response were selected. Inulin was purified using a hot water extraction followed by a slurry of calcium hydroxide and phosphoric acid. TLC-FLD, MALDI-TOF, and spectrophotometric methods were used to characterize and compare the DP of inulin.

RSM proposed a maximum yield (10.1 %) at a temperature of 79.6 °C, time of 31.9 min, the solvent-to-sample ratio of 39.9: 1, and pH of 7.7. The quality of extracted inulin was evaluated as follow: FT-IR spectra indicated typical bands at 820, 864, and 932 cm-1 that assigned the presence of 2-ketose, β-(2→1) fructofuranosyl unit, and α-D-glucopyranose residue. Inulin with DP (16) and molecular weight 2633 Da was determined in MALDI-TOF. Furthermore, TLC-FLD confirmed the approximate fructose and DP from (1-15). Also, the spectrophotometric method showed an approximate number of 22.3 ± 0.04 as the DP.

In conclusion, the optimized isolation factors for inulin from the Inula helenium were proposed. In comparison with the spectrophotometric result, TLC-FLD quantitative result is much more confirmable to MALDI-TOF. TLC-FLD technique offered a simple and more precise than the spectrophotometric method for the quality of inulin.