Characterization of anthocyanins from selected plant species in Uganda

Abstract

Different plant species were collected from different parts of the country in the period 2003 to 2007. Extraction of the plant material collected was done using methanol acidified with various amounts of trifluoroacetic acid depending on the anthocyanins present in each particular plant species. Purification of the crude methanol extracts was done by partition (several times) against solvents, ethyl acetate and petroleum spirit of boiling range 40-600C. Further purification and separation was performed using ion exchange resins (amberliteXAD-7 and sephadex LH-20) and toyopearl LW- 40, packed in chromatographic columns. Final separations of the anthocyanins were achieved by preparative High Performance Liquid Chromatography.

The anthocyanins were identified by a combination of Thin Layer, High Performance Liquid Chromatography (HPLC), online UV spectroscopy, one Dimensional and two Dimensional (1H &13C) Nuclear Magnetic Resonance spectroscopy (NMR) techniques and Liquid Chromatography-Mass spectrometry (LC-MS). The quantitative determination of anthocyanins was accomplished with Analytical HPLC using reference samples isolated under the same conditions. The colors of the Hippeastrum cultivars were described by the CIELab coordinates L* (lightness), C* (chroma) and hab (hue angles).

Twelve plant species, which included; Rubus pinnatus, Rubus rigidus, Carissa edulis, seven Hippeastrum cultivars, Acalypha hispida and Ricinus communis, were analysed. Ten structures of anthocyanins including four novel ones were characterised in this study and five papers (Paper I –V) (attached in Part II) have been published.