HPLC/DAD/MS characterisation and analysis of flavonoids and cynnamoil derivatives in four Nigerian green-leafy vegetables

The present study sought to carry out a screening of the phenolic fraction of four Nigerian plants, Ocimum gratissimum L. (Og), Vernonia amygdalina L. (Va), Corchorus olitorius L., (Co) and Manihot utilissima Pohl. (Mu) consumed as food at least once daily by people in southwestern Nigeria and also used for medicinal purposes by local populations. HPLC/DAD and HPLC/ESI/MS analyses were applied as the most suitable techniques to investigate the phenolic content of the dried leaves. This screening allowed detection of up to 17 constituents in Va, five phenols in Mu, eight and 11 different metabolites in Co and Og, respectively. Some compounds have been detected for the first time in these vegetables: cichoric acid in Og, amentoflavone in Mu and several dicaffeoyl compounds in Va and Co. The study of the decoction demonstrated that almost all the phenolic constituents are stable even after a strong heating process such as boiling, as usually applied by Nigerian people prior to the consumption of these vegetables.