Sorption properties of selected dietary fibers

The aim of this study was to characterize and compare the water-binding and water -holding capacities of fibre preparations based on an evaluation of their adsorption properties. The scope of the work included the determination of the water content and activity in the tested material, the determination of adsorption isotherms at 20ºC, a mathematical description of sorption isotherms using the theoretical GAB sorption model as well as an estimation of the microstructural parameters of the tested fibre samples. The following commercial fibre preparations were examined: wheat – WF 200, WF 400, WF 600, potato – KF 200, apple – BJ, oats – BO and carrot – BM. The water content in the analysed fibre preparations covered the range from 6.604 g 100 g–1 for BO fibre to 10.81 g 100 g–1 for BM fibre while their water activity ranged between 0.495 for KF200 fibre and 0.564 for WF200 fibre. The fraction of free water present in carrot (BM) and potato (KF200) fibres was significantly more tightly bound to the product matrix than the fraction of free water in oats fibre (BO). Based on the studies conducted it was established that both the genetic variety and the technological process of micronization had an impact on the water-binding and holding capacities. This was proven on the basis of the evaluation of the adsorption properties and the differences in the surface microstructure of the preparations under examination. Not only the components present in the complex fraction of fibres, but also their physical state are of the utmost importance.