Spectrophotometric Determination of Total Anthocyanin Content (TAC) in Costus afer Flower Extract and its Application as pH Indicator in Acid/Base Titrations

Abstract

This paper reports for the first time, the spectrophotometric determination of the total anthocyanin pigments in the extract of the flowers of the wild plant, costus afer Ker Gawl (called bush cane) growing abundantly in the lowland rainforests of the Niger Delta Region of Nigeria. The anthocyanin-rich extract was obtained by subjecting the dried flowers to extraction using absolute ethanol acidified with 0.1% HCl. The total anthocyanin content (TAC) was spectrophotometrically determined using the pH differential method. The total anthocyanin content was 268.58 µg/g cyanidin-3-glucoside equivalent. This parent extract was subsequently concentrated and employed as indicator in acid/base titrations of varying concentrations: 0.1 M, 0.5 M and 1.0 M. The acid/base pairs employed in this study were hydrochloric acid sodium hydroxide, hydrochloric acid/ammonia, acetic acid/sodium hydroxide and acetic acid/ammonia. The mean titre values at equivalence points of the titrations were compared with corresponding values obtained using standard synthetic indicators: phenolphthalein and methyl red. The results revealed that the equivalence points for the various titrations using the flower extract as indicator showed no significant difference (P > 0.05) when compared to the values obtained when standard synthetic indicators were employed. These results, thus; indicate that the under-utilized flowers of this wild plant is a rich source of anthocyanin pigments which could be explored as cost- effective eco-friendly pH indicators as well as other potential industrial applications.