Incorporation in pasta of either of two soluble fibres, carboxymethylcellulose sodium salt (CMC) and guar
gum (GG), was found to significantly reduce the rate of in vitro starch digestion. The amount of reducing
sugars produced over 300 min was reduced by 18% at 1.5% CMC incorporation and 24% at 20% GG incorporation.
Negative effects on sensory and technological properties were seen at the high levels of GG
needed to reduce the rate of in vitro digestion, and a ‘matty’ layer covering the surfaces of starch granules
was observed by scanning electron microscopy and confocal scanning laser microscopy. By contrast, levels
of CMC incorporation giving large reductions in in vitro digestion had no negative effects on pasta
properties. No significant alteration in pasta structure on CMC incorporation was observed by microscopy.
The large difference in the amounts of soluble fibre required to bring about equivalent reductions
in digestion rate suggests that different mechanisms may be involved in the two cases.