Modification of physicochemical properties of dietary fibre in carrots by mono- and divalent cations

Physicochemical changes of dietary fibre in the presence of NaCl or CaCl2 (0, 100 or 400 mM) during boiling (4 or 25 min) of blanched/frozen carrots were investigated. Addition of NaCl (100 mM) to the boiling water reduced total dietary fibre (TDF) content, due to a reduction of insoluble polymers. Higher concentrations had no further effects. NaCl showed minor effects on molecular weight distribution as well as on viscosity of water-soluble polysaccharides (WSP) isolated. The low concentration of CaCl2 did not affect TDF content, but there was a redistribution of soluble (SDF) to insoluble dietary fibre (IDF), mainly uronic acids but to some extent also arabinose and galactose. The higher concentration of CaCl2 caused a significant loss of TDF (∼18%), both soluble (uronic acids ∼9%, galactose ∼2% and arabinose ∼2%) and insoluble polymers (glucose ∼4%). Reduced amounts of the various WSP fractions were isolated (60–70%) in the presence of CaCl2. The viscosities of these fractions were comparatively lower, which may be explained by the proportionally lower amounts of arabinose and galactose in the high molecular weight fraction. All low molecular weight fractions isolated (not quantified in the dietary fibre analyses) contained high proportions of non-starch glucose. It is concluded that CaCl2 and NaCl modify physicochemical properties of dietary fibre to a great extent and, as a consequence, also nutritional effects.