Effect of Active Acidity of a Colloidal Solution of Titanium Dioxide in the Form of Anatase on the Aggregate Stability of Nanofraction

Depending on the active acidity of an aqueous solution, the colloidal stability of a titanium dioxide suspension in the form of anatase (food additive E171), containing nanoparticle with average sizes of ~10 and ~200 nm is studied. It is shown that the nanoparticle stability is reached in an alkali medium at pH > 9.6. A decrease in pH from 9.6 to 6.2 (neutral) results in an increase in the zeta-potential from –30 to –20 mV and is accompanied by the formation of nanoagglomerates ~20 nm in size involving small particles. In an acidic medium with pH ~2.6 (human stomach), the zeta-potential increases to +10 mV and is accompanied by small agglomerate coarsening to 50–60 nm. In this case, an increase in the average size to ~40 nm is observed even for ~2 min. The found rapid agglomeration should reduce the probability of E171 nanofraction penetration through cellular membranes in the human stomach. However, the Е171 nanofraction penetrability significantly increases in the small intestine where food intake mostly occurs, and a medium is close to neutral, pH ~ 8.