Preliminary study of the influence of dietary fiber on the properties of oil-in-water emulsions passing through an in vitro human digestion model

The objective of this preliminary study was to obtain a better understanding of the influence of dietary fiber on the digestibility of emulsified lipids. The influence of fiber type (pectin and chitosan), fiber concentration (0-0.5 wt%), and fiber molecular weight (15 and 2500 kDa chitosan) was examined on the zeta-potential, particle size and creaming stability of 5 wt% corn oil-in-water emulsions (1 wt% Tween 80) subjected to an in vitro digestion model (pH similar to 7, 1 h; pH similar to 2, 1 h; pH similar to 5.3, + bile salts, 2 h; pH similar to 7.5, 2 h: 37 degrees C). In the absence of dietary fiber, the emulsion droplets were anionic and remained stable to aggregation throughout the digestion model. Anionic pectin did not adsorb to the anionic droplet surfaces at any pH, but it promoted extensive droplet flocculation through a depletion mechanism. Cationic chitosan adsorbed to the droplet surfaces at some pH values and promoted droplet flocculation through a bridging mechanism. For example, at pH 5.3, the electrical charge for the emulsion containing 0.5 wt% chitosan (MW =2500 kDa) was highly cationic (zeta = + 19 mV), whereas it was anionic (zeta = -12 mV) for the emulsion containing no chitosan, which indicated that chitosan bound to the droplet surfaces. On the other hand, low molecular weight chitosan (15 kDa) did not absorb to the droplet surfaces under the same conditions. These results may have important implications for understanding the influence of dietary fibers on lipid digestion, since they show that chitosan is able to bind to the droplet surfaces and pectin is able to promote droplet aggregation, which may decrease the access of digestive enzymes to the lipids, and therefore, decrease lipid digestion. This study could therefore be used to create food emulsions with low caloric level, or to optimize diets for individuals with lipid digestion problems. (c) 2005 Elsevier Ltd. All rights reserved.