Browsing by Author "Tuomi, Ilona"

The aim of this thesis was to validate the AOAC integrated total dietary fibre method (2011.25) for tomato. Additional purpose of this study was to update dietary fibre values in Finnish food composition database Fineli. The literature review focused on the background of dietary fibre analysis, method development and dietary fibre composition of vegetables. The method measures separately insoluble dietary fibre (IDF), dietary fibre soluble in water but precipitated in ethanol (SDFP) and dietary fibre soluble in water and not precipitated in ethanol (SDFS; oligosaccharides). The method includes a 16 hour starch hydrolyzing incubation that was presumed to stimulate enzyme activity in tomato. The effect of endogenous enzyme activity was examined with preliminary experiments, which included keeping the sample at room temperature before analysis, inactivation of enzymes with heat treatment and performing the analysis without incubation. Repeatability and reproducibility of the method were determined by analysing a pooled sample consisting of Finnish tomatoes. The amount of IDF was highest in samples prepared without incubation. In incubated and heat treated samples, and in samples kept at room temperature the amount of IDF was lower and the amount of SDFP was higher compared to the samples prepared without incubation. This was propably due to pectin depolymerisation and solubilisation by enzymes. Validation sample was prepared without heat treatment. Validation was performed with incubated samples, because standard deviation for non-incubated samples was markedly higher. The amount of TDF (total dietary fibre) in digested samples was 1.3 % (1.1 % IDF and 0.2 % SDFP). Oligosaccharides were found only in trace amounts. Repeatability of the method was 11 % (TDF), 13 % (IDF) and 23 % (SDFP). Reproducibility was 11 % (TDF), 12 % (IDF) and 17 % (SDFP). Repeatability and reproducibility were propably impaired by the inhomogeneity of the sample matrix. Uncertainty of the method was 26 %. The method was validated and proven to be fit for purpose.