Binding of Water, Oil, and Bile Acids to Dietary Fibers of the Cellan Type

Dietary fibers (DF) of the "cellan" type (consisting mainly or exclusively of undestroyed cells) were prepared as ethanol-dried materials from apple, cabbage, sugar-beet, soybean hulls, wheat bran, and suspension cultures of Chenopodium album L. and investigated with respect to their interactions with water, water oil dispersions, bile acids, and oil. Water binding and retention capacities were found to be especially high in cellans obtained from thin-walled raw material. Water damp sorption by dry cellans, when analyzed according to the GAB and BET equations, shows a considerable fraction of monolayer water. At a water activity of 0.98, the cell and capillary spaces outside the walls remained in the air-filled state but the cell wall pores are filled with water. When the water content of a concentrated aqueous cellan suspension was equal to or below the water binding capacity, its rheological behavior was found to be of pseudoplastic nature. At a given dry weight concentration, yield stress and viscosity of such concentrated suspensions were highest for cellans with the highest water binding capacity. Dry cellan particles absorbed fatty oils without swelling but swell in a detergent-stabilized oil/water emulsion with a similar liquid absorption capacity as in water. In contrast to the dry or alkane-saturated cell wall, the hydrated wall is not permeable to oils in the absence of a detergent. Oil droplets may be entrapped within the cells, yielding a stable dispersion of oil in water. As DF of the cellan type absorb bile acids, preferentially glycoconjugates, from diluted solutions, they may have a potential to decrease the serum cholesterol level.