If you cannot beat them, join them: Exploring the fruits of the invasive species Carpobrotus edulis (L.) N.E. Br as a source of bioactive products

Abstract

The halophyte species Carpobrotus edulis (L.) N.E. Br, also known as Hottentot-fig, is one of the 20 most aggressive invasive species of coastal areas worldwide. It is native to South Africa, where it is used in traditional medicine for the treatment of several diseases, including tuberculosis and acquired immunodeficiency syndrome (AIDS) caused by the human immunodeficiency virus (HIV). Aiming at a sustainable use of its biomass as a value-added product, this work reports for the first time the in vitro antioxidant, anti-microbial, enzymatic inhibitory properties and toxicity of peel and flesh extracts of Hottentot-fig mature fruits. The extracts’ chemical composition was also determined by spectrophotometric methods (total contents of phenolics: TPC; flavonoids: TFC and tannins: TTC), and by high-performance liquid chromatography coupled with electrospray ionization mass spectrometry (HPLC-ESI-MS/MS). The peels’ extracts had generally the highest TPC, TFC and TTC, especially the ethanol ones (TPC: 272.82 mg gallic acid equivalents (GAE)/g dry weight (DW), TFC: 1.58 mg quercetin equivalents (QE)/g DW and TTC: 20.3 mg catechin equivalents (CE)/g DW). The peels’ extracts also had the highest diversity of compounds, mostly phenolic acids, flavonoids, and coumarins, as identified by HPLC-ESI-MS/MS. Some molecules were specific to a particular fruit part, for example, coumaric acid and uvaol in the peel, and vanillin and kaempferol-O-(rhamnosyl)hexosylhexoside in the flesh. Some compounds are here described for the first time in Hottentot-fig, s uch as azelaic acid and emodin. The peel´s extracts had the highest anti radical activity, especially the ethanol and acetone towards 2,2-diphenyl-1-picrylhydrazyl (DPPH) (half maximal inhibitory concentration (IC50) values of 0.59 and 0.88 mg/mL, respectively), and the acetone extract against 2,2′-Azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) (IC50 = 0.56 mg/mL). Samples had nil capacity to chelate iron, a low copper chelation potential, but a significant capacity to reduce iron, especially the ethanol (IC50 = 0.09 mg/mL) and the acetone extracts of peels (IC50 = 0.10 mg/mL) and flesh (IC50 = 0.11 mg/mL) and also the water peel’s extracts (IC50 = 0.18 mg/mL). Samples had nil to low activity towards the enzymes acetylcholinesterase (AChE), butyrylcholinesterase (BuChE), α-amylase and α-glucosidase, but displayed a strong inhibition of tyrosinase, especially the ethanol peel’s extracts (29.55 mg kojic acid equivalents (KAE)/g). Samples had nil to low in vitro toxicity towards human keratinocytes. All together our results suggests possible novel biotechnological applications of Hottentot-fig fruits as sources of innovative bioactive ingredients for the food, cosmetic, agriculture and/or pharmaceutical industries.