The partitioning of water in aggregates of undigested and digested dietary particles.

The hydration of fibre particles derived from wheat and wood was quantified, before and after in vitro digestion, and compared with fibre particles from the colonic digesta of pigs and from human faeces. Total water and the extra- and intra-particulate water components were determined using a combination of centrifugation, drying, gas pycnometry and image analysis. The water of saturation (WS) of wood particles and AllBran® measured after in vitro digestion was up to double that of wheat fibres after in vitro digestion, and increased with particle size and loss of soluble material, but was not associated with the chemical composition of the fibres. Fibre that had undergone in vitro gastric digestion and that had been recovered from the colon or faeces, sequestered about 3% of the Ws into intra-particulate spaces, the remainder occupying extra-particulate spaces. The authors speculate that large quantities of fibre must be eaten to sequester toxins that locate into the intra-particulate space.