Antimicrobial activity of some natural extracts encapsulated within silica matrices

Natural extracts (anthocyanins, tannin, anatto, curcuma and olive leaf extracts) were encapsulated within a silica network by acid or base-catalyzed sol-gel methods. The nominal encapsulated contents were between 2.5 and 50wt.-%. The resulting materials were characterized by Fourier transform infrared spectroscopy, diffuse reflectance in the UV region, nitrogen adsorption/desorption porosimetry and small angle X-ray scattering. Encapsulated anthocyanin and tannin afforded inhibition zones between 9-21mm towards Staphylococcus aureus, Escherichia coli, Bacillus cereus, Candida sp. and Aspergillus niger, which was comparable to the free bioactive material in which the inhibition zones were between 10 and 22mm. Anthocyanin exhibited high antioxidant activity in the free state, while tannin showed good antioxidant activity both in its free state and in its encapsulated form. Antimicrobial and antioxidant activities were shown to be dependent on the textural characteristics of the encapsulated materials.