The Effect of In Vitro Gastrointestinal Condition on Aggregation of Nano Silica Particles

Abstract: The presence of Nano particles in food is a topic that have gain much attention lately. The aim of this study is to investigate the aggregation behavior of nano silica under in vitro gastrointestinal conditions using asymmetric flow field flow fractionation (AF4) coupled with several detectors. Major part of this work is to find a suitable condition for the experiments. With measurements of Z-potential and utilizing the DLVO theory a suitable condition for the experiment is developed. To avoid membrane interaction a relatively high surface energy membrane (Regenerated cellulose) is most suitable. The carrier liquid should have a low ionic strength and a pH away from the iso electric point to contribute to a greater electrostatic repulsion. These actions lead to less membrane interaction as well as ensuring the carrier liquid does not interfere with the aggregation. Parameters in the gastrointestinal environment like the ionic strength, pH, presence of proteins and Bile salts are altered individually during experiments, to examine the effect of each parameter. Under gastric conditions the high ionic strength and low pH gives the silica particles a poor electrostatic repulsion causing the particles to aggregate. The enzymes present in the gastric conditions is insufficient to cover the particles and might causes bridging. The ionic strength and pH conditions of the intestinal fluids cause a small electrostatic repulsion but not enough to entirely prevent aggregation, instead the large number of mixed enzymes will initiate aggregation by protein-protein interaction. The aggregation of silica particles is greatly reduced when bile salt is introduced to the fluid. Bile salt will act as a surfactant stabilizing the suspension.