The solution properties of galactomannan after simulated digestion of guar fortified bread predict the extent of postprandial insulin reduction in healthy adult overweight subjects

Summary

Coil overlap occurs when random coil polysaccharides such as cereal beta-glucan or galactomannan in
solution are abundant enough and large enough to entangle with one another to form networks. It was
recently shown that this concept applied to in vitro digested cereal-based foods could predict the
efficacy of the food to reduce postprandial glycaemia. In the current study we further investigate the role
of coil overlap for prediction of glycaemic and insulinaemic responses using four guar fortified breads
(10–15% wheat flour replacement level) with galactomannans of different weight-average molecular
weight (Mw). The breads, including a wheat flour control, were tested in a randomised crossover study in
12 overweight adults. Addition of guar reduced postprandial serum insulin, but not glucose responses.
The extent of postprandial insulin reduction correlated with the solution properties of galactomannan
after in vitro digestion. A significantly greater reduction in insulin response was observed for two of the
breads where the galactomannan Mw and concentration in solution after in vitro digestion was above coil
overlap, in contrast to two other breads, which resulted in digests containing galactomannan below coil
overlap and a significantly lower reduction of postprandial insulin. Further in vitro digestion experiments
focusing on amylolysis of starch with kinetic modelling showed a greater proportion of slowly digested
starch in breads with galactomannan above coil overlap than below. A combination of the molecular
weight of dietary fibre in a food and its soluble concentration are key parameters explaining its physiological
efficiency in the upper gastrointestinal tract.

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DOI : doi.org/10.1039/d2fo01762h
NVA : hdl.handle.net/11250/3022852