2.5. Analytical quality control
Two commercial products, namely, a mixture of inulin and oligofructose (Orafti® P95, Beneo, Belgium) and granulated inulin powder (Orafti® GR, Beneo Belgium), were used as reference materials for checking accuracy, while inulin fortified milk powder (Protection 1+, Nestle®) was used as a laboratory quality control sample for checking precision in inulin analysis. These materials were analysed in each run along with the unknown samples. Results obtained were evaluated using the values of inulin in the reference materials and the assigned value of inulin in the quality control sample.
3. Results and discussion
3.1. Quality control system for inulin and sugar analysis
Inulin analysis using reference materials, a quality control sample and the unknown food samples was performed in triplicate. Table 1 shows accuracy and precision performance for inulin analysis. Recovery of inulin in the reference materials (Orafti® P95 and Orafti® GR) was 98–102% which fell within the accepted range (AOAC, 2012) indicating good accuracy performance. Results obtained from analysis of the quality control sample fell within the mean ± 2SD of the assigned value (Table 1). This indicated good performance of laboratory precision. The obtained relative standard deviation from intralaboratory reproducibility (%RSDr = 7.1), triplicate analysis, was in the range of 0.3–1.3 of the relative standard deviation between laboratories (pRSDR) at inulin level of 4.6 g/100 g (%RSDR = 11.1) as derived from interlaboratory study using AOAC method No. 997.08 (AOAC, 2005). This evidence indicated good intermediate precision performance for the analyst.