Impact of dietary fibre on in vitro digestibility of modified tapioca starch: viscosity effect

In the current work, amylolysis of modified tapioca starch in simulated small intestinal conditions was studied in the presence of each of four dietary fibre types including yellow mustard mucilage, soluble flaxseed gum, fenugreek gum or oat gum. Each fibre was used at concentrations that were matched across the four fibre types for post-digestion viscosity. Due to molecular heterogeneity these concentrations were different for each fibre. The progress of amylolysis was studied by measuring the decline of digesta apparent viscosity over time at constant shear rate 60 s−1. Expressing these data as a percentage of initial viscosity, and plotting it as a natural logarithm against time transformed the data to a linear form with a slope denoted as a viscosity decay constant (kv). Additionally, for some of the digesta samples progress of amylolysis was assessed by evaluating increases in reducing sugar concentration. Based on the kv values, the progress of amylolysis was reduced as the concentration of each fibre and therefore viscosity of digesta increased. However, the influence to hinder amylolysis was diminishing with increase of digesta viscosity. The progress of amylolysis was similar when each fibre was present at a concentration to match for post-digestion viscosity. Measurements of changes in reducing sugar content also confirmed these findings. Therefore, it was concluded that to alter amylolysis to a similar extent fibres have to be present at amounts to result in similar post-digestion viscosity even though their concentrations may not match.