Abstract

An alkaline starch suspension was charged with citric acid and incubated for different durations (0, 8.5 or 17 h). The suspension was then supplemented with caffeine and gelatinized to fabricate hydrogels which were subsequently stored for varying periods (0, 24 or 48 h). Charging of the well-dissolved alkaline starch suspension with citric acid decreased at first both the flow index and consistency coefficient (K); however, starch cross-linking over time by the generated trisodium citrate increased the K value. The latter also inhibited gel syneresis and increased its water-holding capacity. Trisodium citrate did not nonetheless influence the gel hardness except for the sample incubated for maximum duration and stored for the longest period. The amount of the caffeine released from hydrogel decreased by citrate cross-linking and was higher at neutral pH than pH 2.0. Fourier-transform infra-red spectroscopy suggested that caffeine was enclosed within the gel network via non-covalent interactions. (C) 2016 Elsevier Ltd. All rights reserved.