Evaluation of resistant starch from teff (Eragrostis tef) grain as a film coating material for colon-targeted drug delivery

Teff (Eragrostis tef, family Poaceae) is a native cereal crop widely grown in Ethiopia, containing approximately 73% carbohydrates, of which about 30% is resistant starch. This study evaluates resistant starch extracted from teff grain as a film coating material for colon-targeted delivery of metronidazole, used as a model drug. Starch was extracted from teff and resistant starch was isolated from the total starch. Metronidazole core tablets were prepared by wet granulation, compressed, and coated with a resistant starch-based film. The physicochemical properties of the tablets were evaluated in vitro. To prevent premature film disruption caused by the swelling of amylose, a dominant component of resistant starch, a water-insoluble polymer, ethylcellulose, was added. Various proportions of amylose and ethylcellulose were used as film coating materials and evaluated in simulated conditions to determine the optimal combination for drug release in the colon, but not in the upper gastrointestinal tract. The results of the dissolution and fermentation studies indicated the best film coating proportions of amylose to ethylcellulose and the corresponding thicknesses in percentage of total weight gain were: 1:1 ratio at 6% thickness, 1:2 ratio at 4% and 6% thickness, and 1:3 ratio at 2% and 4% thickness. The targeted drug release of the film material is attributed to bacterial enzyme digestion of the resistant starch component in the colon. The digestion of resistant starch creates pores in the ethylcellulose film scaffold, leading to the disruption of the film and release of the drug exclusively in the colon, where the bacterial microflora reside. Based on these results, resistant starch from teff grain shows potential as a colon-targeting excipient.