ANALYTICAL LETTERS, vol.51, pp.83-95, 2018 (SCI-Expanded)
High-performance liquid chromatography (HPLC) with refractive index detection was used for the rapid direct determination of inulin with adequate sensitivity, quantitative recoveries, no matrix interferences, and good precision without acidic or enzymatic pretreatment. This method was shown to be reliable by good correlation with acidic hydrolysis of inulin. The new method includes extraction of inulin with hot water in an ultrasonic bath at 70 degrees C for 1 h, followed by direct determination of inulin, fructose, glucose, and sucrose and comparison with acidic hydrolysis of inulin to fructose and glucose by 0.2 mol L-1 hydrochloric acid at 80 degrees C for 1 h. The released total fructose and glucose were also determined by HPLC. The concentration ranges of inulin from 20 samples were from 89.78 to 143.95 g kg(-1). For fructose, glucose, and sucrose, the linear ranges were from 1.52 to 5.86, 0.09 to 1.95, and 3.52 to 8.59 g kg(-1), respectively. The recoveries were from 80.75 to 110.90%. An internal standard of L-rhamnose was used to quantify free saccharides and total fructose and glucose. The limits of detection for fructose, glucose, sucrose, and inulin were 0.14, 0.20, 0.09, and 0.23 g kg(-1), respectively, with average relative standard deviations of 1.05% for repeatability and 3.82% for reproducibility. Chicory root cakes contain many elements, 62.9 to 141.4 g kg(-1) crude protein, and 37.6 to 61.2 g kg(-1) ash, and are a suitable livestock feed.