Formation and characterization of tannic acid/beta-glucan complexes: Influence of pH, ionic strength, and temperature

Oat beta-glucan (BG) is a natural non-ionic polysaccharide that can be used as a functional ingredient in food, cosmetic, and pharmaceutical applications. Tannic acid (TA) is a natural polyphenol with demonstrated biological activity and a long history of industrial application. In the present work, colloidal complexes were formed by mixing TA and BG solutions together. Turbidity, particle diameter, and zeta-potential measurements were used to provide information about the formation of TA/BG complexes. Insights into the nature of the TA-BG interactions were obtained using isothermal titration calorimetry (ITC) and by incorporation of additives known to interfere with particular interactions (urea, sodium dodecyl sulfonate, and NaCl). The impact of environmental factors, including pH, ionic strength and temperature, on TA-BG complexation was also investigated. As the TA-to-BG mass ratio increased from 0.4 to 1.0 (pH 5.0), the solution turbidity and mean particle diameter (from 380 to 818 nm) increased, which is indicative of increasing complex formation. ITC analysis and addition of specific additives suggested the TA-BG interaction was mainly due to hydrogen bonding and hydrophobic interactions. The turbidity of the TA/BG complexes decreased when the pH was increased from 2 to 9, as well as when the temperature was raised from 20 to 90 degrees C. Conversely, the turbidity increased when the ionic strength was raised from 0 to 0.25 M. In summary, the TA/BG complexes formed in this study are environmentally sensitive colloidal particles that have potential for application as triggered-release delivery systems.