Water properties in food: classical and Knudsen thermogravimetry approach

Thermo-Gravimetric Analysis (TGA) investigations suggest that in many foods water is partitioned in various states related to the different disperse phases of the system. Dough samples of various cereal and pseudo-cereal flours were investigated. Classical TGA results indicated the gross water partition at the macroscopic level, while Knudsen TGA investigations, that allow evaluation of the relative humidity of the dough at room temperature, suggested the involvement of water in the structure of the dough at a supra-molecular level. The overall moisture content, the mechanical stresses and the presence of extra non-starch polysaccharides and/or soluble proteins, were found to affect this partition, either promoting water displacements across the inter-phases, or modifying the supra-molecular structure of the system. The investigations, extended to bread crumb during ageing, indicate that water undergoes displacements and forms stronger links with the components of the aged crumb with a kinetic law that can be influenced by the presence of extra non-starch carbohydrates.