Assessing the potential of coffee pericarp extract for use as an acid base indicator

Abstract

Synthetic acid base indicators are commonly used to determine the pH (acidity or basicity) of a solution. They have a variety of applications which include titration to determine the endpoint of an acid-base reaction, gauging pH values of different solutions and to carry out interesting color change demonstrations. However, synthetic acid-base indicators are generally expensive, cause environmental pollution and have toxic effects on human health. This research highlights the potential of using red coffee pericarp extract as a cheaper and less toxic pH indicator in Chemistry Laboratories. In this study, two coffee types commonly grown in Uganda were used i.e. robusta coffee and arabica coffee. The varieties used in this experiment included two varieties of robusta coffee i.e. the traditional robusta (Nganda) coffee and the high yielding clonal robusta coffee (Kolono), and one variety of the arabica coffee (Nyasaland). The anthocyanins in the red coffee pericarps were extracted from the three varieties by soaking the plant materials in 97% ethanol for 48 hours. After filtration, the resulting ethanolic extracts were tested for their acid base indicator properties and found to cause different color changes in acidic and basic media. The extracts were then tested for their potential use as an acid-base indicator by noting the color change obtained after adding the indicators to acidic and basic solutions. Furthermore, the titre values obtained using the natural coffee extracts were compared to those obtained using the commercially available synthetic indicators. (Phenolphthalein and methyl orange indicators). The mean titre values obtained from using the three bioindicators and the synthetic indicators were analysed using Analysis of Variance and results showed no significant statistical difference between the titre values of the different coffee extracts and the two synthetic indicators. This result suggests that coffee pericarp extract can be used as potential pH indicator in substituting synthetic pH indicators such as methyl orange and phenolphthalein for titration experiments.