Betalains and Phenolic Compounds of Leaves and Stems of <i>Alternanthera brasiliana</i> and <i>Alternanthera tenella</i>

Abstract

Betacyanins and phenolic compounds from acetonitrile:acidified water extracts of <i>Alternanthera brasiliana</i> and <i>Alternanthera tenella</i> were characterized and quantified using a high-performance liquid chromatography system coupled with diode array and electrospray mass spectrometry detection. Four betacyanins (amaranthine, isoamaranthine, betanin and isobetanin) were tentatively identified and quantified. Twenty eight phenolic compounds of four different families (hydroxybenzoic and hydroxycinnamic acids, flavones and flavonols) were separated and characterized on the basis of their accurate MS and MS/MS information out of which ten compounds were confirmed by authentic standards. These plant species could be considered as an especially rich source of natural bioactive compounds and potential food colorants. <i>A. brasiliana</i> showed the highest betacyanin and polyphenols content (89 μg/g and 35243 μg/g, respectively). Among polyphenols, flavonols were the more abundant (kaempferol-glucoside, kaempferol-rutinoside and kaempferol-rhamnosyl-rhamnosylglycoside). Meanwhile, <i>A. tenella</i> showed a different polyphenols profile with flavones as major compounds (glucopyranosil-vitexin and vitexin). As a novelty, pentosylvitexin and pentosyl-isovitexin were detected for the first time in <i>Alternanthera</i> plants. Both <i>A. brasiliana</i> and <i>A. tenella</i> leaves showed high total polyphenol content and in vitro antioxidant activity (FRAP). These results provide an analytical base concerning the phenolic and betalains composition and the antioxidant properties of two members of the promising <i>Alternanthera</i> gender, for subsequent applications, such as functional food ingredients.