Characterisation of phenolic acids, flavonoids, proanthocyanidins and antioxidant activity of water extracts from seed coats of marama bean [Tylosema esculentum] - an underutilised food legume

Abstract

Freeze-dried aqueous phenolic extracts with possible application as natural antioxidant functional food ingredients were prepared from marama bean seed coats by extracting with water. Phenolic acids, flavonoids and proanthocyanidins in the extracts were characterised by HPLC/MS. The major flavonoids were the flavanols methyl (epi)afzelechin-3-O-gallate (40%) and methyl (epi)catechin-3-O-gallate (28%), and the major phenolic acid was gallic acid (10%). Proanthocyanidins in the extracts were predominantly prodelphinidins composed of epicatechin-3-O-gallate and epigallocatechin present as major terminal and extension units and epigallocatechin-3-O-gallate and epicatechin present as minor extension unit constituents. The polymer structure was found to be unique compared with other legumes because of the high percentage of galloylated units. Extracts showed a high DPPH free radical scavenging activity (707 μmol TE g−1), protective effect against AAPH-induced human red blood cell haemolysis and copper-catalysed human LDL oxidation suggesting that the extracts may have potential health benefits.