Abstract
Indigenous and non-commercial fruits can be an important source of antioxidant polyphenols; however, the identity and content of polyphenols from non-commercial fruits are often poorly described. The study aimed to extract, identify, and quantify polyphenols from the skin of the indigenous Africa fruit Ximenia caffra, using solvent extraction. Three solvents (hexane, acetone, and 70% v/v ethanol) over three extraction times (30, 60 and 120 min) were used in a 32 full factorial experimental design to determine effects on polyphenol recovery, and individual polyphenolics were characterised using liquid chromatography high-resolution mass spectrometry (LC-HRMS). Ethanol was the most effective extraction solvent, and extracts had high levels of total phenolics and flavonoids (65 mg gallic and 40 mg catechin equivalents per gram dry sample respectively), and high antioxidant activity (18.2 mg mL−1 ascorbic acid equivalents). LC-HRMS positively identified 16 compounds, of which 14 were flavonoids including flavonoid glycosides, and indicated that concentrations of some flavonoids decreased for extraction times beyond 60 min. It was concluded that the fruit of Ximenia caffra is rich in natural polyphenolic antioxidants; the present work identified and quantified a number of these, while also establishing suitable solvent extraction conditions for the recovery of these potentially high-value compounds.
Highlights
Fruits of the indigenous African tree Ximenia caffra (Sonder) have been shown to contain high amounts of polyphenolic compounds in both the pulp and skins [1]
All extraction samples were assayed for total phenolics and total flavonoids, and the ethanol extracts were further assayed for antioxidant activityaccording to the N,N-Dimethyl-p-phenylenediamine dihydrochloride (DMPD) assay
The current study reports findings on solvent extraction of polyphenols displaying high antioxidant activity from the fruits of X. caffra, and reports the identity of the individual compounds obtained in the ethanol extracts
Summary
Fruits of the indigenous African tree Ximenia caffra (Sonder) have been shown to contain high amounts of polyphenolic compounds in both the pulp and skins [1]. The plant produces edible fruits which are utilised as food by humans and animals, while different parts of the plant including the leaves, bark, and roots are used in traditional medicine to treat a range of diseases and disorders [6,8,9,10], with reports of antibacterial and antifungal activity of X. caffra extracts providing support for the ethnomedicinal uses of the plant [9,11]. The fruit pulp and skins of X. caffra are a potential source from which natural antioxidants could be extracted, especially the skins, which contain higher amounts of polyphenols than the pulp, and which are regularly not consumed due to poor palatability [1,6,13]. Polyphenols can find applications as food colourants, and as the raw materials for industrial applications e.g., for the production of paints, cosmetics, and paper [16,19]
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